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Disaster recovery plan
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A disaster recovery plan (DRP) is a documented process or set of procedures to recover and protect a business IT infrastructure in the event of a disaster.[1] Such a plan, ordinarily documented in written form, specifies procedures an organization is to follow in the event of a disaster. It is "a comprehensive statement of consistent actions to be taken before, during and after a disaster".[2] The disaster could be natural, environmental or man-made. Man-made disasters could be intentional (for example, an act of a terrorist) or unintentional (that is, accidental, such as the breakage of a man-made dam).
Given organizations' increasing dependency on information technology to run their operations, a disaster recovery plan, sometimes erroneously called a Continuity of Operations Plan (COOP), is increasingly associated with the recovery of information technology data, assets, and facilities.
Contents
[hide]
1 Objectives
2 Relationship to the Business Continuity Plan
3 Benefits
4 Types of plans
5 Types of disasters
5.1 Natural disaster
5.2 Man-made disasters
6 Planning methodology
6.1 Obtaining top management commitment
6.2 Establishing a planning committee
6.3 Performing a risk assessment
6.4 Establishing priorities for processing and operations
6.5 Determining recovery strategies
6.6 Collecting data
6.7 Organizing and documenting a written plan
6.8 Developing testing criteria and procedures
6.9 Testing the plan
6.10 Obtaining plan approval
7 Caveats/controversies
7.1 Lack of buy-in
7.2 Incomplete RTOs and RPOs
7.3 Systems myopia
7.4 Lax security
7.5 Outdated plans
8 See also
9 References
Objectives[edit]
Organizations cannot always avoid disasters, but with careful planning the effects of a disaster can be minimized. The objective of a disaster recovery plan is to minimize downtime and data loss.[3] The primary objective is to protect the organization in the event that all or part of its operations and/or computer services are rendered unusable. The plan minimizes the disruption of operations and ensures that some level of organizational stability and an orderly recovery after a disaster will prevail.[2] Minimizing downtime and data loss is measured in terms of two concepts: the recovery time objective (RTO) and the recovery point objective (RPO).
The recovery time objective is the time within which a business process must be restored, after a major incident (MI) has occurred, in order to avoid unacceptable consequences associated with a break in business continuity. The recovery point objective (RPO) is the age of files that must be recovered from backup storage for normal operations to resume if a computer, system, or network goes down as a result of a MI. The RPO is expressed backwards in time (that is, into the past) starting from the instant at which the MI occurs, and can be specified in seconds, minutes, hours, or days.[4] The recovery point objective (RPO) is thus the maximum acceptable amount of data loss measured in time. It is the age of the files or data in backup storage required to resume normal operations after the MI.[5]
A DR plan illustrating the chronology of the RPO and the RTO with respect to the MI.
Relationship to the Business Continuity Plan[edit]
According to the SANS institute, the Business Continuity Plan (BCP) is a comprehensive organizational plan that includes the disaster recovery plan. The Institute further states that a Business Continuity Plan (BCP) consists of the five component plans:[6]
Business Resumption Plan
Occupant Emergency Plan
Continuity of Operations Plan
Incident Management Plan
Disaster Recovery Plan
The Institute states that the first three plans (Business Resumption, Occupant Emergency, and Continuity of Operations Plans) do not deal with the IT infrastructure. They further state that the Incident Management Plan (IMP) does deal with the IT infrastructure, but since it establishes structure and procedures to address cyber attacks against an organization’s IT systems, it generally does not represent an agent for activating the Disaster Recovery Plan, leaving The Disaster Recovery Plan as the only BCP component of interest to IT.[6]
Disaster Recovery Institute International states that disaster recovery is the area of business continuity that deals with technology recovery as opposed to the recovery of business operations.[7]
Benefits[edit]
Like every insurance plan, there are benefits that can be obtained from the drafting of a disaster recovery plan. Some of these benefits are:[2]
Providing a sense of security
Minimizing risk of delays
Guaranteeing the reliability of standby systems
Providing a standard for testing the plan
Minimizing decision-making during a disaster
Reducing potential legal liabilities
Lowering unnecessarily stressful work environment
Types of plans[edit]
There is no one right type of disaster recovery plan,[8] nor is there a one-size-fits-all disaster recovery plan.[1][8] However, there are three basic strategies that feature in all disaster recovery plans: (1) preventive measures, (2) detective measures, and (3) corrective measures.[9] Preventive measures will try to prevent a disaster from occurring. These measures seek to identify and reduce risks. They are designed to mitigate or prevent an event from happening. These measures may include keeping data backed up and off site, using surge protectors, installing generators and conducting routine inspections. Detective measures are taken to discover the presence of any unwanted events within the IT infrastructure. Their aim is to uncover new potential threats. They may detect or uncover unwanted events. These measures include installing fire alarms, using up-to-date antivirus software, holding employee training sessions, and installing server and network monitoring software. Corrective measures are aimed to restore a system after a disaster or otherwise unwanted event takes place. These measures focus on fixing or restoring the systems after a disaster. Corrective measures may include keeping critical documents in the Disaster Recovery Plan or securing proper insurance policies, after a "lessons learned" brainstorming session.[1][10]
A disaster recovery plan must answer at least three basic questions: (1) what is its objective and purpose, (2) who will be the people or teams who will be responsible in case any disruptions happen, and (3) what will these people do (the procedures to be followed) when the disaster strikes.[11]
Types of disasters[edit]
The tsunami that affected Japan in 2011, a type of natural disaster
September 11, 2001, in New York City, a type of man-made disaster: it caused pollution, loss of lives, property damage, and considerable data loss
Disasters can be natural or man-made. Man-made disasters could be intentional (for example, sabotage or an act of terrorism) or unintentional (that is, accidental, such as the breakage of a man-made dam). Disasters may encompass more than weather. They may involve Internet threats or take on other man-made manifestations such as theft.[1]
Natural disaster[edit]
Main article: Natural disaster
A natural disaster is a major adverse event resulting from the earth's natural hazards. Examples of natural disasters are floods, tsunamis, tornadoes, hurricanes/cyclones, volcanic eruptions, earthquakes, heat waves, and landslides. Other types of disasters include the more cosmic scenario of an asteroid hitting the Earth.
Man-made disasters[edit]
Main article: Man-made disasters
Man-made disasters are the consequence of technological or human hazards. Examples include stampedes, urban fires, industrial accidents, oil spills, nuclear explosions/nuclear radiation and acts of war. Other types of man-made disasters include the more cosmic scenarios of catastrophic global warming, nuclear war, and bioterrorism.
The following table categorizes some disasters and notes first response initiatives. Note that whereas the sources of a disaster may be natural (for example, heavy rains) or man-made (for example, a broken dam), the results may be similar (flooding).[12]
Natural
Disaster
Example
Profile
First Response
Avalanche The sudden, drastic flow of snow down a slope, occurring when either natural triggers, such as loading from new snow or rain, or artificial triggers, such as explosives or backcountry skiers, overload the snowpack Shut off utilities; Evacuate building if necessary; Determine impact on the equipment and facilities and any disruption
Blizzard A severe snowstorm characterized by very strong winds and low temperatures Power off all equipment; listen to blizzard advisories; Evacuate area, if unsafe; Assess damage
Earthquake The shaking of the earth’s crust, caused by underground volcanic forces of breaking and shifting rock beneath the earth’s surface Shut off utilities; Evacuate building if necessary; Determine impact on the equipment and facilities and any disruption
Fire (wild) Fires that originate in uninhabited areas and which pose the risk to spread to inhabited areas Attempt to suppress fire in early stages; Evacuate personnel on alarm, as necessary; Notify fire department; Shut off utilities; Monitor weather advisories
Flood Flash flooding: Small creeks, gullies, dry streambeds, ravines, culverts or even low-lying areas flood quickly Monitor flood advisories; Determine flood potential to facilities; Pre-stage emergency power generating equipment; Assess damage
Freezing Rain Rain occurring when outside surface temperature is below freezing Monitor weather advisories; Notify employees of business closure; home; Arrange for snow and ice removal
Heat wave A prolonged period of excessively hot weather relative to the usual weather pattern of an area and relative to normal temperatures for the season Listen to weather advisories; Power-off all servers after a graceful shutdown if there is imminent potential of power failure; Shut down main electric circuit usually located in the basement or the first floor
Hurricane Heavy rains and high winds Power off all equipment; listen to hurricane advisories; Evacuate area, if flooding is possible; Check gas, water and electrical lines for damage; Do not use telephones, in the event of severe lightning; Assess damage
Landslide Geological phenomenon which includes a range of ground movement, such as rock falls, deep failure of slopes and shallow debris flows Shut off utilities; Evacuate building if necessary; Determine impact on the equipment and facilities and any disruption
Lightning strike An electrical discharge caused by lightning, typically during thunderstorms Power off all equipment; listen to hurricane advisories; Evacuate area, if flooding is possible; Check gas, water and electrical lines for damage; Do not use telephones, in the event of severe lightning; Assess damage
Limnic eruption The sudden eruption of carbon dioxide from deep lake water Shut off utilities; Evacuate building if necessary; Determine impact on the equipment and facilities and any disruption
Tornado Violent rotating columns of air which descent from severe thunderstorm cloud systems Monitor tornado advisories; Power off equipment; Shut off utilities (power and gas); Assess damage once storm passes
Tsunami A series of water waves caused by the displacement of a large volume of a body of water, typically an ocean or a large lake, usually caused by earthquakes, volcanic eruptions, underwater explosions, landslides, glacier calvings, meteorite impacts and other disturbances above or below water Power off all equipment; listen to tsunami advisories; Evacuate area, if flooding is possible; Check gas, water and electrical lines for damage; Assess damage
Volcanic eruption The release of hot magma, volcanic ash and/or gases from a volcano Shut off utilities; Evacuate building if necessary; Determine impact on the equipment and facilities and any disruption
Man-made
Bioterrorism The intentional release or dissemination of biological agents as a means of coercion Get information immediately from your Public Health officials via the news media as to the right course of action; If you think you have been exposed, quickly remove your clothing and wash off your skin; Also put on a HEPA to help prevent inhalation of the agent[13]
Civil unrest A disturbance caused by a group of people that may include sit-ins and other forms of obstructions, riots, sabotage and other forms of crime, and which is intended to be a demonstration to the public and the government, but can escalate into general chaos Contact local police or law enforcement[14][15]
Fire (urban) Even with strict building fire codes, people still perish needlessly in fires Attempt to suppress fire in early stages; Evacuate personnel on alarm, as necessary; Notify fire department; Shut off utilities; Monitor weather advisories
Hazardous material spills The escape of solids, liquids, or gases that can harm people, other living organisms, property or the environment, from their intended controlled environment such as a container. Leave the area and call the local fire department for help.[16] If anyone was affected by the spill, call the your local Emergency Medical Services line[17]
Nuclear and Radiation Accidents An event involving significant release of radioactivity to the environment or a reactor core meltdown and which leads to major undesirable consequences to people, the environment, or the facility Recognize that a CBRN incident has or may occur. Gather, assess and disseminate all available information to first responders. Establish an overview of the affected area. Provide and obtain regular updates to and from first responders.[18]
Power Failure Caused by summer or winter storms, lightning or construction equipment digging in the wrong location Wait 5–10 minutes; Power-off all Servers after a graceful shutdown; Do not use telephones, in the event of severe lightning; Shut down main electric circuit usually located in the basement or the first floor
In the realm of information technology per se, disasters may also be the result of a computer security exploit. Some of these are: computer viruses, cyberattacks, denial-of-service attacks, hacking, and malware exploits. These are ordinarily attended to by information security experts.
Planning methodology[edit]
According to Geoffrey H. Wold of the Disaster Recovery Journal, the entire process involved in developing a Disaster Recovery Plan consists of 10 steps:[2]
Obtaining top management commitment[edit]
For a disaster recovery plan to be successful, the central responsibility for the plan must reside on top management. Management is responsible for coordinating the disaster recovery plan and ensuring its effectiveness within the organization. It is also responsible for allocating adequate time and resources required in the development of an effective plan. Resources that management must allocate include both financial considerations and the effort of all personnel involved.
Establishing a planning committee[edit]
A planning committee is appointed to oversee the development and implementation of the plan. The planning committee includes representatives from all functional areas of the organization. Key committee members customarily include the operations manager and the data processing manager. The committee also defines the scope of the plan.
Performing a risk assessment[edit]
The planning committee prepares a risk analysis and a business impact analysis (BIA) that includes a range of possible disasters, including natural, technical and human threats. Each functional area of the organization is analyzed to determine the potential consequence and impact associated with several disaster scenarios. The risk assessment process also evaluates the safety of critical documents and vital records. Traditionally, fire has posed the greatest threat to an organization. Intentional human destruction, however, should also be considered. A thorough plan provides for the “worst case” situation: destruction of the main building. It is important to assess the impacts and consequences resulting from loss of information and services. The planning committee also analyzes the costs related to minimizing the potential exposures.
Establishing priorities for processing and operations[edit]
At this point, the critical needs of each department within the organization are evaluated in order to prioritize them. Establishing priorities is important because no organization possesses infinite resources and criteria must be set as to where to allocate resources first. Some of the areas often reviewed during the prioritization process are functional operations, key personnel and their functions, information flow, processing systems used, services provided, existing documentation, historical records, and the department's policies and procedures.
Processing and operations are analyzed to determine the maximum amount of time that the department and organization can operate without each critical system. This will later get mapped into the Recovery Time Objective. A critical system is defined as that which is part of a system or procedure necessary to continue operations should a department, computer center, main facility or a combination of these be destroyed or become inaccessible. A method used to determine the critical needs of a department is to document all the functions performed by each department. Once the primary functions have been identified, the operations and processes are then ranked in order of priority: essential, important and non-essential.
Determining recovery strategies[edit]
During this phase, the most practical alternatives for processing in case of a disaster are researched and evaluated. All aspects of the organization are considered, including physical facilities, computer hardware and software, communications links, data files and databases, customer services provided, user operations, the overall management information systems (MIS) structure, end-user systems, and any other processing operations.
Alternatives, dependent upon the evaluation of the computer function, may include: hot sites, warm sites, cold sites, reciprocal agreements, the provision of more than one data center, the installation and deployment of multiple computer system, duplication of service center, consortium arrangements, lease of equipment, and any combinations of the above.
Written agreements for the specific recovery alternatives selected are prepared, specifying contract duration, termination conditions, system testing, cost, any special security procedures, procedure for the notification of system changes, hours of operation, the specific hardware and other equipment required for processing, personnel requirements, definition of the circumstances constituting an emergency, process to negotiate service extensions, guarantee of compatibility, availability, non-mainframe resource requirements, priorities, and other contractual issues.
Collecting data[edit]
In this phase, data collection takes place. Among the recommended data gathering materials and documentation often included are various lists (employee backup position listing, critical telephone numbers list, master call list, master vendor list, notification checklist), inventories (communications equipment, documentation, office equipment, forms, insurance policies, workgroup and data center computer hardware, microcomputer hardware and software, office supply, off-site storage location equipment, telephones, etc.), distribution register, software and data files backup/retention schedules, temporary location specifications, any other such other lists, materials, inventories and documentation. Pre-formatted forms are often used to facilitate the data gathering process.
Organizing and documenting a written plan[edit]
Next, an outline of the plan’s contents is prepared to guide the development of the detailed procedures. Top management reviews and approves the proposed plan. The outline can ultimately be used for the table of contents after final revision. Other four benefits of this approach are that (1) it helps to organize the detailed procedures, (2) identifies all major steps before the actual writing process begins, (3) identifies redundant procedures that only need to be written once, and (4) provides a road map for developing the procedures.
It is often considered best practice to develop a standard format for the disaster recovery plan so as to facilitate the writing of detailed procedures and the documentation of other information to be included in the plan later. This helps ensure that the disaster plan follows a consistent format and allows for its ongoing future maintenance. Standardization is also important if more than one person is involved in writing the procedures.
It is during this phase that the actual written plan is developed in its entirety, including all detailed procedures to be used before, during, and after a disaster. The procedures include methods for maintaining and updating the plan to reflect any significant internal, external or systems changes. The procedures allow for a regular review of the plan by key personnel within the organization. The disaster recovery plan is structured using a team approach. Specific responsibilities are assigned to the appropriate team for each functional area of the organization. Teams responsible for administrative functions, facilities, logistics, user support, computer backup, restoration and other important areas in the organization are identified.
The structure of the contingency organization may not be the same as the existing organization chart. The contingency organization is usually structured with teams responsible for major functional areas such as administrative functions, facilities, logistics, user support, computer backup, restoration, and any other important area.
The management team is especially important because it coordinates the recovery process. The team assesses the disaster, activates the recovery plan, and contacts team managers. The management team also oversees, documents and monitors the recovery process. It is helpful when management team members are the final decision-makers in setting priorities, policies and procedures. Each team has specific responsibilities that are completed to ensure successful execution of the plan. The teams have an assigned manager and an alternate in case the team manager is not available. Other team members may also have specific assignments where possible.
Developing testing criteria and procedures[edit]
Best practices dictate that DR plans be thoroughly tested and evaluated on a regular basis (at least annually). Thorough DR plans include documentation with the procedures for testing the plan. The tests will provide the organization with the assurance that all necessary steps are included in the plan. Other reasons for testing include:
Determining the feasibility and compatibility of backup facilities and procedures.
Identifying areas in the plan that need modification.
Providing training to the team managers and team members.
Demonstrating the ability of the organization to recover.
Providing motivation for maintaining and updating the disaster recovery plan.
Testing the plan[edit]
After testing procedures have been completed, an initial "dry run" of the plan is performed by conducting a structured walk-through test. The test will provide additional information regarding any further steps that may need to be included, changes in procedures that are not effective, and other appropriate adjustments. These may not become evident unless an actual dry-run test is performed. The plan is subsequently updated to correct any problems identified during the test. Initially, testing of the plan is done in sections and after normal business hours to minimize disruptions to the overall operations of the organization. As the plan is further polished, future tests occur during normal business hours.
Types of tests include: checklist tests, simulation tests, parallel tests, and full interruption tests.
Obtaining plan approval[edit]
Once the disaster recovery plan has been written and tested, the plan is then submitted to management for approval. It is top management’s ultimate responsibility that the organization has a documented and tested plan. Management is responsible for (1) establishing the policies, procedures and responsibilities for comprehensive contingency planning, and (2) reviewing and approving the contingency plan annually, documenting such reviews in writing.
Organizations that receive information processing from service bureaus will, in addition, also need to (1) evaluate the adequacy of contingency plans for its service bureau, and (2)ensure that its contingency plan is compatible with its service bureau’s plan.
Caveats/controversies[edit]
Due to its high cost, disaster recovery plans are not without critics. Cormac Foster has identified five "common mistakes" organizations often make related to disaster recovery planning:[19]
Lack of buy-in[edit]
One factor is the perception by executive management that DR planning is "just another fake earthquake drill" or CEOs that fail to make DR planning and preparation a priority, are often significant contributors to the failure of a DR plan.
Incomplete RTOs and RPOs[edit]
Another critical point is failure to include each and every important business process or a block of data. "Every item in your DR plan requires a Recovery Time Objective (RTO) defining maximum process downtime or a Recovery Point Objective (RPO) noting an acceptable restore point. Anything less creates ripples that can extend the disaster's impact." As an example, "payroll, accounting and the weekly customer newsletter may not be mission-critical in the first 24 hours, but left alone for several days, they can become more important than any of your initial problems."
Systems myopia[edit]
A third point of failure involves focusing only on DR without considering the larger business continuity needs: "Data and systems restoration after a disaster are essential, but every business process in your organization will need IT support, and that support requires planning and resources." As an example, corporate office space lost to a disaster can result in an instant pool of teleworkers which, in turn, can overload a company's VPN overnight, overwork the IT support staff at the blink of an eye and cause serious bottlenecks and monopolies with the dial-in PBX system.
Lax security[edit]
When there is a disaster, an organization's data and business processes become vulnerable. As such, security can be more important than the raw speed involved in a disaster recovery plan's RTO. The most critical consideration then becomes securing the new data pipelines: from new VPNs to the connection from offsite backup services. Another security concern includes documenting every step of the recovery process—something that is especially important in highly regulated industries, government agencies, or in disasters requiring post-mortem forensics. Locking down or remotely wiping lost handheld devices is also an area that may require addressing.
Outdated plans[edit]
Another important aspect that is often overlooked involves the frequency with which DR Plans are updated. Yearly updates are recommended but some industries or organizations require more frequent updates because business processes evolve or because of quicker data growth. To stay relevant, disaster recovery plans should be an integral part of all business analysis processes, and should be revisited at every major corporate acquisition, at every new product launch and at every new system development milestone.
See also[edit]
Disaster recovery
Business continuity planning
Federal Emergency Management Agency
Backup rotation scheme
Seven tiers of disaster recovery
References[edit]
^ Jump up to: a b c d Abram, Bill (14 June 2012). "5 Tips to Build an Effective Disaster Recovery Plan". Small Business Computing. Retrieved 9 August 2012.
^ Jump up to: a b c d Wold, Geoffrey H. (1997). "Disaster Recovery Planning Process". Disaster Recovery Journal. Adapted from Volume 5 #1. Disaster Recovery World. Archived from the original on 15 August 2012. Retrieved 8 August 2012.
Jump up ^ An Overview of the Disaster Recovery Planning Process - From Start to Finish. Comprehensive Consulting Solutions Inc.( "Disaster Recovey Planning, An Overview: White Paper." )March 1999. Retrieved 8 August 2012.
Jump up ^ Definition: Recovery point objective (RPO). Retrieved 10 August 2012.
Jump up ^ "Recovery Point Objective (RPO): Definition - What does Recovery Point Objective (RPO) mean?". Techopedia. Janalta Interactive Inc. 2012. Retrieved 10 August 2012.
^ Jump up to: a b The Disaster Recovery Plan. Chad Bahan. GSEC Practical Assignment version 1.4b. SANS Institute InfoSec Reading Room. June 2003. Retrieved 24 August 2012.
Jump up ^ https://www.drii.org/glossary.php
^ Jump up to: a b "Disaster Recovery Planning - Step by Step Guide". Michigan State University. Archived from the original on 8 March 2014. Retrieved 9 May 2014.
Jump up ^ "Backup Disaster Recovery". Email Archiving and Remote Backup. 2010. Retrieved 9 May 2014.
Jump up ^ "Disaster Recovery & Business Continuity Plans". Stone Crossing Solutions. 2012. Archived from the original on 23 August 2012. Retrieved 9 August 2012.
Jump up ^ "Disaster Recovery – Benefits of Getting Disaster Planning Software and Template and Contracting with Companies Offering Data Disaster Recovery Plans, Solutions and Services: Why Would You Need a Disaster Recovery Plan?". Continuity Compliance. 7 June 2011. Archived from the original on 8 May 2014. Retrieved 14 August 2012.
Jump up ^ Business Continuity Planning (BCP): Sample Plan For Nonprofit Organizations. Archived June 2, 2010, at the Wayback Machine. Pages 11-12. Retrieved 8 August 2012.
Jump up ^ What should I do if there has been a bioterrorism attack?. Edmond A. Hooker. WebMD. 9 October 2007. Retrieved 18 September 2012.
Jump up ^ Report of the Joint Fire/Police Task Force on Civil Unrest (FA-142): Recommendations for Organization and Operations During Civil Disturbance. Page 55. FEMA. Retrieved 21 October 2012.
Jump up ^ Business Continuity Planning: Developing a Strategy to Minimize Risk and Maintain Operations. Archived March 27, 2014, at the Wayback Machine. Adam Booher. Retrieved 19 September 2012.
Jump up ^ Hazardous Materials. Archived October 11, 2012, at the Wayback Machine. Tennessee Emergency Management Office. Retrieved 7 September 2012.
Jump up ^ Managing Hazardous Materials Incidents (MHMIs). Center for Disease Control. Retrieved 7 September 2012.
Jump up ^ Guidelines for First Response to a CBRN Incident. Project on Minimum Standards and Non-Binding Guidelines for First Responders Regarding Planning, Training, Procedure and Equipment for Chemical, Biological, Radiological and Nuclear (CBRN) Incidents.] NATO. Emergency Management. Retrieved 21 October 2012.
Jump up ^ Five Mistakes That Can Kill a Disaster Recovery Plan. In archive.org Cormac Foster. Dell Corporation. 25 October 2010. Retrieved 8 August 2012.
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DNA replication
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DNA replication: The double helix is un'zipped' and unwound, then each separated strand (turquoise) acts as a template for replicating a new partner strand (green). Nucleotides (bases) are matched to synthesize the new partner strands into two new double helices.
In molecular biology, DNA replication is the biological process of producing two identical replicas of DNA from one original DNA molecule. This process occurs in all living organisms and is the basis for biological inheritance. The cell possesses the distinctive property of division, which makes replication of DNA essential.
DNA is made up of a double helix of two complementary strands. During replication, these strands are separated. Each strand of the original DNA molecule then serves as a template for the production of its counterpart, a process referred to as semiconservative replication. Cellular proofreading and error-checking mechanisms ensure near perfect fidelity for DNA replication.[1][2]
In a cell, DNA replication begins at specific locations, or origins of replication, in the genome.[3] Unwinding of DNA at the origin and synthesis of new strands, accommodated by an enzyme known as ligase, results in replication forks growing bi-directionally from the origin. A number of proteins are associated with the replication fork to help in the initiation and continuation of DNA synthesis. Most prominently, DNA polymerase synthesizes the new strands by adding nucleotides that complement each (template) strand. DNA replication occurs during the S-stage of interphase.
DNA replication can also be performed in vitro (artificially, outside a cell). DNA polymerases isolated from cells and artificial DNA primers can be used to initiate DNA synthesis at known sequences in a template DNA molecule. The polymerase chain reaction (PCR), a common laboratory technique, cyclically applies such artificial synthesis to amplify a specific target DNA fragment from a pool of DNA.
Contents
[hide]
1 DNA structure
2 DNA polymerase
3 Replication process
3.1 Initiation
3.2 Elongation
3.3 Replication fork
3.3.1 Leading strand
3.3.2 Lagging strand
3.3.3 Dynamics at the replication fork
3.4 DNA replication proteins
3.5 Replication machinery
3.6 Termination
4 Regulation
4.1 Eukaryotes
4.1.1 Replication focus
4.2 Bacteria
5 Polymerase chain reaction
6 See also
7 Notes
8 References
DNA structure[edit]
DNA exists as a double-stranded structure, with both strands coiled together to form the characteristic double-helix. Each single strand of DNA is a chain of four types of nucleotides. Nucleotides in DNA contain a deoxyribose sugar, a phosphate, and a nucleobase. The four types of nucleotide correspond to the four nucleobases adenine, cytosine, guanine, and thymine, commonly abbreviated as A, C, G and T. Adenine and guanine are purine bases, while cytosine and thymine are pyrimidines. These nucleotides form phosphodiester bonds, creating the phosphate-deoxyribose backbone of the DNA double helix with the nucleobases pointing inward (i.e., toward the opposing strand). Nucleobases are matched between strands through hydrogen bonds to form base pairs. Adenine pairs with thymine (two hydrogen bonds), and guanine pairs with cytosine (three hydrogen bonds).
DNA strands have a directionality, and the different ends of a single strand are called the "3' (three-prime) end" and the "5' (five-prime) end". By convention, if the base sequence of a single strand of DNA is given, the left end of the sequence is the 5' end, while the right end of the sequence is the 3' end. The strands of the double helix are anti-parallel with one being 5' to 3', and the opposite strand 3' to 5'. These terms refer to the carbon atom in deoxyribose to which the next phosphate in the chain attaches. Directionality has consequences in DNA synthesis, because DNA polymerase can synthesize DNA in only one direction by adding nucleotides to the 3' end of a DNA strand.
The pairing of complementary bases in DNA (through hydrogen bonding) means that the information contained within each strand is useless. phosphoodiester (intra-strand) bonds are stronger than hydrogen (inter-strand) bonds. This allows the strands to be separated from one another. The nucleotides on a single strand can therefore be used to reconstruct nucleotides on a newly synthesized partner strand.[4]
DNA polymerase[edit]
Main article: DNA polymerase
DNA polymerases adds nucleotides to the 3' end of a strand of DNA.[5] If a mismatch is accidentally incorporated, the polymerase is inhibited from further extension. Proofreading removes the mismatched nucleotide and extension continues.
DNA polymerases are a family of enzymes that carry out all forms of DNA replication.[6] DNA polymerases in general cannot initiate synthesis of new strands, but can only extend an existing DNA or RNA strand paired with a template strand. To begin synthesis, a short fragment of RNA, called a primer, must be created and paired with the template DNA strand.
DNA polymerase adds a new strand of DNA by extending the 3' end of an existing nucleotide chain, adding new nucleotides matched to the template strand one at a time via the creation of phosphodiester bonds. The energy for this process of DNA polymerization comes from hydrolysis of the high-energy phosphate (phosphoanhydride) bonds between the three phosphates attached to each unincorporated base. Free bases with their attached phosphate groups are called nucleotides; in particular, bases with three attached phosphate groups are called nucleoside triphosphates. When a nucleotide is being added to a growing DNA strand, the formation of a phosphodiester bond between the proximal phosphate of the nucleotide to the growing chain is accompanied by hydrolysis of a high-energy phosphate bond with release of the two distal phosphates as a pyrophosphate. Enzymatic hydrolysis of the resulting pyrophosphate into inorganic phosphate consumes a second high-energy phosphate bond and renders the reaction effectively irreversible.[Note 1]
In general, DNA polymerases are highly accurate, with an intrinsic error rate of less than one mistake for every 107 nucleotides added.[7] In addition, some DNA polymerases also have proofreading ability; they can remove nucleotides from the end of a growing strand in order to correct mismatched bases. Finally, post-replication mismatch repair mechanisms monitor the DNA for errors, being capable of distinguishing mismatches in the newly synthesized DNA strand from the original strand sequence. Together, these three discrimination steps enable replication fidelity of less than one mistake for every 109 nucleotides added.[7]
The rate of DNA replication in a living cell was first measured as the rate of phage T4 DNA elongation in phage-infected E. coli.[8] During the period of exponential DNA increase at 37 °C, the rate was 749 nucleotides per second. The mutation rate per base pair per replication during phage T4 DNA synthesis is 1.7 per 108.[9]
Replication process[edit]
Main articles: Prokaryotic DNA replication and Eukaryotic DNA replication
DNA replication, like all biological polymerization processes, proceeds in three enzymatically catalyzed and coordinated steps: initiation, elongation and termination.
Initiation[edit]
Role of initiators for initiation of DNA replication.
Formation of pre-replication complex.
For a cell to divide, it must first replicate its DNA.[10] This process is initiated at particular points in the DNA, known as "origins", which are targeted by initiator proteins.[3] In E. coli this protein is DnaA; in yeast, this is the origin recognition complex.[11] Sequences used by initiator proteins tend to be "AT-rich" (rich in adenine and thymine bases), because A-T base pairs have two hydrogen bonds (rather than the three formed in a C-G pair) and thus are easier to strand-separate.[12] Once the origin has been located, these initiators recruit other proteins and form the pre-replication complex, which unwinds the double-stranded DNA.
Elongation[edit]
DNA polymerase has 5′–3′ activity. All known DNA replication systems require a free 3' hydroxyl group before synthesis can be initiated (note: the DNA template is read in 3′ to 5′ direction whereas a new strand is synthesized in the 5′ to 3′ direction—this is often confused). Four distinct mechanisms for DNA synthesis are recognized:
All cellular life forms and many DNA viruses, phages and plasmids use a primase to synthesize a short RNA primer with a free 3′ OH group which is subsequently elongated by a DNA polymerase.
The retroelements (including retroviruses) employ a transfer RNA that primes DNA replication by providing a free 3′ OH that is used for elongation by the reverse transcriptase.
In the adenoviruses and the φ29 family of bacteriophages, the 3' OH group is provided by the side chain of an amino acid of the genome attached protein (the terminal protein) to which nucleotides are added by the DNA polymerase to form a new strand.
In the single stranded DNA viruses—a group that includes the circoviruses, the geminiviruses, the parvoviruses and others—and also the many phages and plasmids that use the rolling circle replication (RCR) mechanism, the RCR endonuclease creates a nick in the genome strand (single stranded viruses) or one of the DNA strands (plasmids). The 5′ end of the nicked strand is transferred to a tyrosine residue on the nuclease and the free 3′ OH group is then used by the DNA polymerase to synthesize the new strand.
The first is the best known of these mechanisms and is used by the cellular organisms. In this mechanism, once the two strands are separated, primase adds RNA primers to the template strands. The leading strand receives one RNA primer while the lagging strand receives several. The leading strand is continuously extended from the primer by a DNA polymerase with high processivity, while the lagging strand is extended discontinuously from each primer forming Okazaki fragments. RNase removes the primer RNA fragments, and a low processivity DNA polymerase distinct from the replicative polymerase enters to fill the gaps. When this is complete, a single nick on the leading strand and several nicks on the lagging strand can be found. Ligase works to fill these nicks in, thus completing the newly replicated DNA molecule.
The primase used in this process differs significantly between bacteria and archaea/eukaryotes. Bacteria use a primase belonging to the DnaG protein superfamily which contains a catalytic domain of the TOPRIM fold type.[13] The TOPRIM fold contains an α/β core with four conserved strands in a Rossmann-like topology. This structure is also found in the catalytic domains of topoisomerase Ia, topoisomerase II, the OLD-family nucleases and DNA repair proteins related to the RecR protein.
The primase used by archaea and eukaryotes, in contrast, contains a highly derived version of the RNA recognition motif (RRM). This primase is structurally similar to many viral RNA-dependent RNA polymerases, reverse transcriptases, cyclic nucleotide generating cyclases and DNA polymerases of the A/B/Y families that are involved in DNA replication and repair. In eukaryotic replication, the primase forms a complex with Pol α.[14]
Multiple DNA polymerases take on different roles in the DNA replication process. In E. coli, DNA Pol III is the polymerase enzyme primarily responsible for DNA replication. It assembles into a replication complex at the replication fork that exhibits extremely high processivity, remaining intact for the entire replication cycle. In contrast, DNA Pol I is the enzyme responsible for replacing RNA primers with DNA. DNA Pol I has a 5′ to 3′ exonuclease activity in addition to its polymerase activity, and uses its exonuclease activity to degrade the RNA primers ahead of it as it extends the DNA strand behind it, in a process called nick translation. Pol I is much less processive than Pol III because its primary function in DNA replication is to create many short DNA regions rather than a few very long regions.
In eukaryotes, the low-processivity enzyme, Pol α, helps to initiate replication because it forms a complex with primase.[15] In eukaryotes, leading strand synthesis is thought to be conducted by Pol ε; however, this view has recently been challenged, suggesting a role for Pol δ.[16] Primer removal is completed Pol δ[17] while repair of DNA during replication is completed by Pol ε.
As DNA synthesis continues, the original DNA strands continue to unwind on each side of the bubble, forming a replication fork with two prongs. In bacteria, which have a single origin of replication on their circular chromosome, this process creates a "theta structure" (resembling the Greek letter theta: θ). In contrast, eukaryotes have longer linear chromosomes and initiate replication at multiple origins within these.[18]
Replication fork[edit]
Scheme of the replication fork.
a: template, b: leading strand, c: lagging strand, d: replication fork, e: primer, f: Okazaki fragments
Many enzymes are involved in the DNA replication fork.
The replication fork is a structure that forms within the nucleus during DNA replication. It is created by helicases, which break the hydrogen bonds holding the two DNA strands together. The resulting structure has two branching "prongs", each one made up of a single strand of DNA. These two strands serve as the template for the leading and lagging strands, which will be created as DNA polymerase matches complementary nucleotides to the templates; the templates may be properly referred to as the leading strand template and the lagging strand template.
DNA is always synthesized in the 5' to 3' direction. Since the leading and lagging strand templates are oriented in opposite directions at the replication fork, a major issue is how to achieve synthesis of nascent (new) lagging strand DNA, whose direction of synthesis is opposite to the direction of the growing replication fork.
Leading strand[edit]
The leading strand is the strand of nascent DNA which is being synthesized in the same direction as the growing replication fork. A polymerase "reads" the leading strand template and adds complementary nucleotides to the nascent leading strand on a continuous basis.
Lagging strand[edit]
The lagging strand is the strand of nascent DNA whose direction of synthesis is opposite to the direction of the growing replication fork. Because of its orientation, replication of the lagging strand is more complicated as compared to that of the leading strand. As a consequence, the DNA polymerase on this strand is seen to "lag behind" the other strand.
The lagging strand is synthesized in short, separated segments. On the lagging strand template, a primase "reads" the template DNA and initiates synthesis of a short complementary RNA primer. A DNA polymerase extends the primed segments, forming Okazaki fragments. The RNA primers are then removed and replaced with DNA, and the fragments of DNA are joined together by DNA ligase.
Dynamics at the replication fork[edit]
The assembled human DNA clamp, a trimer of the protein PCNA.
As helicase unwinds DNA at the replication fork, the DNA ahead is forced to rotate. This process results in a build-up of twists in the DNA ahead.[19] This build-up forms a torsional resistance that would eventually halt the progress of the replication fork. Topoisomerases are enzymes that temporarily break the strands of DNA, relieving the tension caused by unwinding the two strands of the DNA helix; topoisomerases (including DNA gyrase) achieve this by adding negative supercoils to the DNA helix.[20]
Bare single-stranded DNA tends to fold back on itself forming secondary structures; these structures can interfere with the movement of DNA polymerase. To prevent this, single-strand binding proteins bind to the DNA until a second strand is synthesized, preventing secondary structure formation.[21]
Clamp proteins form a sliding clamp around DNA, helping the DNA polymerase maintain contact with its template, thereby assisting with processivity. The inner face of the clamp enables DNA to be threaded through it. Once the polymerase reaches the end of the template or detects double-stranded DNA, the sliding clamp undergoes a conformational change that releases the DNA polymerase. Clamp-loading proteins are used to initially load the clamp, recognizing the junction between template and RNA primers.[2]:274-5
DNA replication proteins[edit]
At the replication fork, many replication enzymes assemble on the DNA into a complex molecular machine called the replisome. The following is a list of major DNA replication enzymes that participate in the replisome:[22]
Enzyme
Function in DNA replication
DNA Helicase Also known as helix destabilizing enzyme. Helicase separates the two strands of DNA at the Replication Fork behind the topoisomerase.
DNA Polymerase The enzyme responsible for catalyzing the addition of nucleotide substrates to DNA in the 5' to 3' direction during DNA replication. Also performs proof-reading and error correction. There exist many different types of DNA Polymerase, each of which perform different functions in different types of cells.
DNA clamp A protein which prevents elongating DNA polymerases from dissociating from the DNA parent strand.
Single-Strand Binding (SSB) Proteins Bind to ssDNA and prevent the DNA double helix from re-annealing after DNA helicase unwinds it, thus maintaining the strand separation, and facilitating the synthesis of the nascent strand.
Topoisomerase Relaxes the DNA from its super-coiled nature.
DNA Gyrase Relieves strain of unwinding by DNA helicase; this is a specific type of topoisomerase
DNA Ligase Re-anneals the semi-conservative strands and joins Okazaki Fragments of the lagging strand.
Primase Provides a starting point of RNA (or DNA) for DNA polymerase to begin synthesis of the new DNA strand.
Telomerase Lengthens telomeric DNA by adding repetitive nucleotide sequences to the ends of eukaryotic chromosomes. This allows germ cells and stem cells to avoid the Hayflick limit on cell division.[23]
Replication machinery[edit]
Replication machineries consist of factors involved in DNA replication and appearing on template ssDNAs. Replication machineries include primosotors are replication enzymes; DNA polymerase, DNA helicases, DNA clamps and DNA topoisomerases, and replication proteins; e.g. single-stranded DNA binding proteins (SSB). In the replication machineries these components coordinate. In most of the bacteria, all of the factors involved in DNA replication are located on replication forks and the complexes stay on the forks during DNA replication. These replication machineries are called replisomes or DNA replicase systems. These terms are generic terms for proteins located on replication forks. In eukaryotic and some bacterial cells the replisomes are not formed.
Since replication machineries do not move relatively to template DNAs such as factories, they are called a replication factory.[24] In an alternative figure, DNA factories are similar to projectors and DNAs are like as cinematic films passing constantly into the projectors. In the replication factory model, after both DNA helicases for leading strands and lagging strands are loaded on the template DNAs, the helicases run along the DNAs into each other. The helicases remain associated for the remainder of replication process. Peter Meister et al. observed directly replication sites in budding yeast by monitoring green fluorescent protein(GFP)-tagged DNA polymerases α. They detected DNA replication of pairs of the tagged loci spaced apart symmetrically from a replication origin and found that the distance between the pairs decreased markedly by time.[25] This finding suggests that the mechanism of DNA replication goes with DNA factories. That is, couples of replication factories are loaded on replication origins and the factories associated with each other. Also, template DNAs move into the factories, which bring extrusion of the template ssDNAs and nascent DNAs. Meister’s finding is the first direct evidence of replication factory model. Subsequent research has shown that DNA helicases form dimers in many eukaryotic cells and bacterial replication machineries stay in single intranuclear location during DNA synthesis.[24]
The replication factories perform disentanglement of sister chromatids. The disentanglement is essential for distributing the chromatids into daughter cells after DNA replication. Because sister chromatids after DNA replication hold each other by Cohesin rings, there is the only chance for the disentanglement in DNA replication. Fixing of replication machineries as replication factories can improve the success rate of DNA replication. If replication forks move freely in chromosomes, catenation of nuclei is aggravated and impedes mitotic segregation.[25]
Termination[edit]
Eukaryotes initiate DNA replication at multiple points in the chromosome, so replication forks meet and terminate at many points in the chromosome. Because eukaryotes have linear chromosomes, DNA replication is unable to reach the very end of the chromosomes. Due to this problem, DNA is lost each replication cycle from the end of the chromosome. Telomeres are regions of repetitive DNA close to the ends and help prevent loss of genes due to this shortening. Shortening of the telomeres is a normal process in somatic cells. This shortens the telomeres of the daughter DNA chromosome. As a result, cells can only divide a certain number of times before the DNA loss prevents further division. (This is known as the Hayflick limit.) Within the germ cell line, which passes DNA to the next generation, telomerase extends the repetitive sequences of the telomere region to prevent degradation. Telomerase can become mistakenly active in somatic cells, sometimes leading to cancer formation. Increased telomerase activity is one of the hallmarks of cancer.
Termination requires that the progress of the DNA replication fork must stop or be blocked. Termination at a specific locus, when it occurs, involves the interaction between two components: (1) a termination site sequence in the DNA, and (2) a protein which binds to this sequence to physically stop DNA replication. In various bacterial species, this is named the DNA replication terminus site-binding protein, or Ter protein.
Because bacteria have circular chromosomes, termination of replication occurs when the two replication forks meet each other on the opposite end of the parental chromosome. E. coli regulates this process through the use of termination sequences that, when bound by the Tus protein, enable only one direction of replication fork to pass through. As a result, the replication forks are constrained to always meet within the termination region of the chromosome.[26]
Regulation[edit]
Main articles: Cell division and Cell cycle
The cell cycle of eukaryotic cells.
Eukaryotes[edit]
Within eukaryotes, DNA replication is controlled within the context of the cell cycle. As the cell grows and divides, it progresses through stages in the cell cycle; DNA replication takes place during the S phase (synthesis phase). The progress of the eukaryotic cell through the cycle is controlled by cell cycle checkpoints. Progression through checkpoints is controlled through complex interactions between various proteins, including cyclins and cyclin-dependent kinases.[27] Unlike bacteria, eukaryotic DNA replicates in the confines of the nucleus.[28]
The G1/S checkpoint (or restriction checkpoint) regulates whether eukaryotic cells enter the process of DNA replication and subsequent division. Cells that do not proceed through this checkpoint remain in the G0 stage and do not replicate their DNA.
Replication of chloroplast and mitochondrial genomes occurs independently of the cell cycle, through the process of D-loop replication.
Replication focus[edit]
In vertebrate cells, replication sites concentrate into positions called replication foci.[25] Replication sites can be detected by immunostaining daughter strands and replication enzymes and monitoring GFP-tagged replication factors. By these methods it is found that replication foci of varying size and positions appear in S phase of cell division and their number per nucleus is far smaller than the number of genomic replication forks.
P. Heun et al.(2001) tracked GFP-tagged replication foci in budding yeast cells and revealed that replication origins move constantly in G1 and S phase and the dynamics decreased significantly in S phase.[25] Traditionally, replication sites were fixed on spatial structure of chromosomes by nuclear matrix or lamins. The Heun’s results denied the traditional concepts, budding yeasts don't have lamins, and support that replication origins self-assemble and form replication foci.
By firing of replication origins, controlled spatially and temporally, the formation of replication foci is regulated. D. A. Jackson et al.(1998) revealed that neighboring origins fire simultaneously in mammalian cells.[25] Spatial juxtaposition of replication sites brings clustering of replication forks. The clustering do rescue of stalled replication forks and favors normal progress of replication forks. Progress of replication forks is inhibited by many factors; collision with proteins or with complexes binding strongly on DNA, deficiency of dNTPs, nicks on template DNAs and so on. If replication forks stall and the remaining sequences from the stalled forks are not replicated, the daughter strands have nick obtained un-replicated sites. The un-replicated sites on one parent's strand hold the other strand together but not daughter strands. Therefore, the resulting sister chromatids cannot separate from each other and cannot divide into 2 daughter cells. When neighboring origins fire and a fork from one origin is stalled, fork from other origin access on an opposite direction of the stalled fork and duplicate the un-replicated sites. As other mechanism of the rescue there is application of dormant replication origins that excess origins don't fire in normal DNA replication.
Bacteria[edit]
Dam methylates adenine of GATC sites after replication.
Most bacteria do not go through a well-defined cell cycle but instead continuously copy their DNA; during rapid growth, this can result in the concurrent occurrence of multiple rounds of replication.[29] In E. coli, the best-characterized bacteria, DNA replication is regulated through several mechanisms, including: the hemimethylation and sequestering of the origin sequence, the ratio of adenosine triphosphate (ATP) to adenosine diphosphate (ADP), and the levels of protein DnaA. All these control the binding of initiator proteins to the origin sequences.
Because E. coli methylates GATC DNA sequences, DNA synthesis results in hemimethylated sequences. This hemimethylated DNA is recognized by the protein SeqA, which binds and sequesters the origin sequence; in addition, DnaA (required for initiation of replication) binds less well to hemimethylated DNA. As a result, newly replicated origins are prevented from immediately initiating another round of DNA replication.[30]
ATP builds up when the cell is in a rich medium, triggering DNA replication once the cell has reached a specific size. ATP competes with ADP to bind to DnaA, and the DnaA-ATP complex is able to initiate replication. A certain number of DnaA proteins are also required for DNA replication — each time the origin is copied, the number of binding sites for DnaA doubles, requiring the synthesis of more DnaA to enable another initiation of replication.
See also: Plasmid, Plasmid copy number, and Plasmid partition system
Polymerase chain reaction[edit]
Main article: Polymerase chain reaction
Researchers commonly replicate DNA in vitro using the polymerase chain reaction (PCR). PCR uses a pair of primers to span a target region in template DNA, and then polymerizes partner strands in each direction from these primers using a thermostable DNA polymerase. Repeating this process through multiple cycles amplifies the targeted DNA region. At the start of each cycle, the mixture of template and primers is heated, separating the newly synthesized molecule and template. Then, as the mixture cools, both of these become templates for annealing of new primers, and the polymerase extends from these. As a result, the number of copies of the target region doubles each round, increasing exponentially.[31]
See also[edit]
Wikimedia Commons has media related to DNA replication.
Wikiversity has learning resources about DNA#DNA_Replication
Autopoiesis
Data storage device
Self-replication
Notes[edit]
Jump up ^ The energetics of this process may also help explain the directionality of synthesis—if DNA were synthesized in the 3' to 5' direction, the energy for the process would come from the 5' end of the growing strand rather than from free nucleotides. The problem is that if the high energy triphosphates were on the growing strand and not on the free nucleotides, proof-reading by removing a mismatched terminal nucleotide would be problematic: Once a nucleotide is added, the triphosphate is lost and a single phosphate remains on the backbone between the new nucleotide and the rest of the strand. If the added nucleotide were mismatched, removal would result in a DNA strand terminated by a monophosphate at the end of the "growing strand" rather than a high energy triphosphate. So strand would be stuck and wouldn't be able to grow anymore. In actuality, the high energy triphosphates hydrolyzed at each step originate from the free nucleotides, not the polymerized strand, so this issue does not exist.
References[edit]
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^ Jump up to: a b Alberts B, Johnson A, Lewis J, Raff M, Roberts K, Walter P (2002). "5DNA Replication, Repair, and Recombination". Molecular Biology of the Cell. Garland Science. ISBN 0-8153-3218-1. External link in |chapter= (help)
^ Jump up to: a b Berg JM, Tymoczko JL, Stryer L, Clarke ND (2002). "Chapter 27, Section 4: DNA Replication of Both Strands Proceeds Rapidly from Specific Start Sites". Biochemistry. W.H. Freeman and Company. ISBN 0-7167-3051-0. External link in |chapter= (help)
Jump up ^ Alberts, B., et al., Molecular Biology of the Cell, Garland Science, 4th ed., 2002, pp. 238–240 ISBN 0-8153-3218-1
Jump up ^ Allison, Lizabeth A. Fundamental Molecular Biology. Blackwell Publishing. 2007. p.112 ISBN 978-1-4051-0379-4
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Jump up ^ Distinguishing the pathways of primer removal during Eukaryotic Okazaki fragment maturation Contributor Author Rossi, Marie Louise. Date Accessioned: 2009-02-23T17:05:09Z. Date Available: 2009-02-23T17:05:09Z. Date Issued: 2009-02-23T17:05:09Z. Identifier Uri: http://hdl.handle.net/1802/6537. Description: Dr. Robert A. Bambara, Faculty Advisor. Thesis (PhD) – School of Medicine and Dentistry, University of Rochester. UR only until January 2010. UR only until January 2010.
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Jump up ^ Alberts B, Johnson A, Lewis J, Raff M, Roberts K, Walter P (2002). Molecular Biology of the Cell. Garland Science. ISBN 0-8153-3218-1. DNA Replication Mechanisms: Special Proteins Help to Open Up the DNA Double Helix in Front of the Replication Fork
Jump up ^ Griffiths A.J.F.; Wessler S.R.; Lewontin R.C.; Carroll S.B. (2008). Introduction to Genetic Analysis. W. H. Freeman and Company. ISBN 0-7167-6887-9. [Chapter 7: DNA: Structure and Replication. pg 283–290]
Jump up ^ "Will the Hayflick limit keep us from living forever?". Howstuffworks. Retrieved January 20, 2015.
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^ Jump up to: a b c d e Peter Meister, Angela Taddei1, Susan M. Gasser(June 2006), "In and out of the Replication Factory", Cell 125 (7): 1233–1235
Jump up ^ TA Brown (2002). Genomes. BIOS Scientific Publishers. ISBN 1-85996-228-9. 13.2.3. Termination of replication
Jump up ^ Alberts B, Johnson A, Lewis J, Raff M, Roberts K, Walter P (2002). Molecular Biology of the Cell. Garland Science. ISBN 0-8153-3218-1. Intracellular Control of Cell-Cycle Events: S-Phase Cyclin-Cdk Complexes (S-Cdks) Initiate DNA Replication Once Per Cycle
Jump up ^ Brown, TA (2002). "13". Genomes (2nd ed.). Oxford: Wiley-Liss.
Jump up ^ Tobiason DM, Seifert HS (2006). "The Obligate Human Pathogen, Neisseria gonorrhoeae, Is Polyploid". PLoS Biology. 4 (6): e185. doi:10.1371/journal.pbio.0040185. PMC 1470461  . PMID 16719561.
Jump up ^ Slater, Steven; Wold, Sture; Lu, Min; Boye, Erik; Skarstad, Kirsten; Kleckner, Nancy (September 1995). "E. coli SeqA protein binds oriC in two different methyl-modulated reactions appropriate to its roles in DNA replication initiation and origin sequestration". Cell. 82 (6): 927–936. doi:10.1016/0092-8674(95)90272-4. PMID 7553853.
Jump up ^ Saiki, Randall; Gelfand, David H.; Stoffel, Susanne; Scharf, Stephen J.; Higuchi, Russell; Horn, Glenn T.; Mullis, Kary B.; Erlich, Henry A. (29 January 1988). "Primer-directed enzymatic amplification of DNA with a thermostable DNA polymerase". Science. 239 (4839): 487–491. Bibcode:1988Sci...239..487S. doi:10.1126/science.2448875. PMID 2448875. Retrieved 7 April 2016.
[hide]
v
t
e
DNA replication (comparing Prokaryotic to Eukaryotic)
Initiation
Prokaryotic
(initiation)
Pre-replication complex
dnaC
Cdc6
Helicase
dnaA
dnaB
T7
Primase
dnaG
Eukaryotic
(preparation in
G1 phase)
Pre-replication complex
Origin recognition complex
ORC1
ORC2
ORC3
ORC4
ORC5
ORC6
Cdc6
Cdt1
Minichromosome maintenance
MCM2
MCM3
MCM4
MCM5
MCM6
MCM7
Licensing factor
Autonomously replicating sequence
Single-strand binding protein
SSBP2
SSBP3
SSBP4
RNase H
RNASEH1
RNASEH2A
Helicase: HFM1
Primase: PRIM1
PRIM2
Both
Origin of replication/Ori/Replicon
Replication fork
Lagging and leading strands
Okazaki fragments
Primer
Replication
Prokaryotic
(elongation)
DNA polymerase III holoenzyme
dnaC
dnaE
dnaH
dnaN
dnaQ
dnaT
dnaX
holA
holB
holC
holD
holE
Replisome
DNA ligase
DNA clamp
Topoisomerase
DNA gyrase
Prokaryotic DNA polymerase: DNA polymerase I
Klenow fragment
Eukaryotic
(synthesis in
S phase)
Replication factor C
RFC1
Flap endonuclease
FEN1
Topoisomerase
Replication protein A
RPA1
Eukaryotic DNA polymerase:
alpha
POLA1
POLA2
PRIM1
PRIM2
delta
POLD1
POLD2
POLD3
POLD4
epsilon
POLE
POLE2
POLE3
POLE4
DNA clamp
PCNA
Control of chromosome duplication
Both
Movement: Processivity
DNA ligase
Termination
Telomere: Telomerase
TERT
TERC
DKC1
Molecular and cellular biology portal
Authority control
GND: 4153174-7
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