Molecular Biology: Error-Correcting Mechanisms in DNA Replication

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Questions and Answers

What is the primary mechanism that ensures the high fidelity of DNA replication?

The initial base-pairing

The proofreading step by DNA polymerase (correct)

DNA topoisomerases

Several mismatch repair mechanisms

What is the role of DNA polymerase in proofreading during DNA replication?

It corrects any initial mispairings that might have occurred

It removes replication errors that remain in the wake of the replication machine

It performs the first proofreading step just before a new nucleotide is covalently added (correct)

It performs the final proofreading step after the nucleotide is covalently added

What is the name of the system that removes replication errors that remain in the wake of the replication machine?

Strand-directed mismatch repair system (correct)

Proofreading mechanism

Mismatch repair system

DNA repair system

What is the characteristic of the DNA replication fork?

It is asymmetrical Signup and view all the answers

What is the purpose of the conformational change in DNA polymerase during proofreading?

To allow the polymerase to double-check the exact base pair geometry Signup and view all the answers

What is a characteristic of DNA polymerase that enables it to correct its own errors during DNA synthesis?

Its ability to function as a 'self-correcting' enzyme Signup and view all the answers

What is the direction of DNA synthesis during replication?

5'-to-3' Signup and view all the answers

What is the purpose of the 3'-to-5' proofreading exonuclease activity of DNA polymerase?

To remove mismatched nucleotides at the primer terminus Signup and view all the answers

Why is it necessary for DNA polymerase to have an existing primer to initiate DNA synthesis?

Because DNA polymerase lacks the ability to initiate DNA synthesis de novo Signup and view all the answers

What is the result of the stability of the DNA double helix under physiological conditions?

It requires high temperatures to separate the two strands Signup and view all the answers

What is the primary function of DNA helicases in DNA replication?

To unwind the DNA double helix in front of the replication fork Signup and view all the answers

What is the role of single-strand DNA-binding proteins in DNA replication?

To remove hairpin helices from single-stranded DNA Signup and view all the answers

In which direction can a DNA helicase move along a single DNA strand to unwind the DNA double helix?

Either in the 5′-to-3′ or 3′-to-5′ direction Signup and view all the answers

Why do DNA polymerase molecules synthesize only short strings of nucleotides before falling off the DNA template?

Because they are not processive enzymes Signup and view all the answers

What is the consequence of not removing hairpin helices from single-stranded DNA during replication?

Impaired DNA synthesis Signup and view all the answers

What is the approximate mutation rate during DNA replication?

One nucleotide change per 10^10 nucleotides Signup and view all the answers

Why is it essential to maintain low mutation rates in germ cells?

To maintain the species and prevent genetic changes Signup and view all the answers

What is the significance of maintaining accurate DNA sequences in somatic cells?

To prevent changes that lead to cancer Signup and view all the answers

What is the estimated number of nucleotide pairs in the human genome?

approximately 3.1 X 10^9 nucleotide pairs Signup and view all the answers

What is the result of the remarkable accuracy of DNA replication in human cells?

The passing of accurate genetic instructions from one generation to the next Signup and view all the answers

Study Notes

DNA Replication Mechanisms

DNA replication involves a sliding ring that holds DNA polymerase onto the DNA strand, creating a collaborative replication machine.
Eukaryotic and bacterial DNA replication mechanisms share fundamental similarities despite distinct cellular structures.

Mismatch Repair and Fidelity

Strand-directed mismatch repair systems eliminate replication errors that remain post-replication.
Ribonucleotide incorporation during replication is accidental but can be corrected by specific repair mechanisms.

Role of DNA Topoisomerases

DNA topoisomerases prevent tangling of DNA, maintaining appropriate supercoiling during replication.

Proofreading Mechanisms

High fidelity of DNA replication is critical, relying on initial base-pairing and several proofreading mechanisms to correct errors.
DNA polymerase performs an initial proofreading step before adding new nucleotides, enhancing accuracy through conformational changes that favor correct base pairing.

Error Correction

Exonucleolytic proofreading occurs immediately after incorrect nucleotide incorporation, removing mispaired nucleotides using a separate catalytic site on the polymerase.
DNA polymerase is a self-correcting enzyme that removes its own errors while synthesizing the DNA strand.

Directionality of DNA Replication

DNA synthesis occurs in a 5'-to-3' direction, facilitating efficient error correction.
RNA primer synthesis is initiated by specialized nucleotide-polymerizing enzymes.

Role of Helicases and SSB Proteins

DNA helicases open the DNA double helix at the replication fork, hydrolyzing ATP to power their movement along the DNA.
Single-strand DNA-binding (SSB) proteins stabilize and protect single-stranded DNA from forming hairpin structures, which can inhibit polymerase activity.

Sliding Ring Nature of DNA Polymerase

DNA polymerase synthesizes only short segments before detaching from the DNA template; a sliding ring structure helps retain it on the DNA during replication.

Mutation Rates and Maintenance of DNA Sequences

DNA sequences are maintained with high fidelity, with mutation rates around one nucleotide change per 10 billion replicated nucleotides.
Accurate replication is essential for transmitting genetic information, ensuring minimal changes in the human genome across cell divisions.

Importance of Mutation Rate Control

Low mutation rates are vital for survival, protecting germ cells from mutations to maintain species integrity and somatic cells from changes that could lead to cancer.

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Description

Learn about the mechanisms that correct errors in DNA replication, including the role of exonucleolytic proofreading and 3'-5' proofreading exonuclease in ensuring the accuracy of DNA synthesis. Test your knowledge of molecular biology and DNA replication processes.