MOL 114: DNA Replication and Repair

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the outcome when replication errors escape the proofreading function during DNA synthesis?

The activation of DNA ligase

The removal of an exonuclease

A correct base pairing

A mismatch of one to several bases (correct)

What is the disease associated with mutations in the proteins involved in mismatch repair?

Hereditary breast cancer

Hereditary nonpolyposis colorectal cancer (correct)

Xeroderma Pigmentosum

Sickle cell anemia

Which enzyme is responsible for removing the mismatched nucleotide during mismatch repair?

DNA ligase

Helicase

Exonuclease (correct)

Primase

What is the purpose of the mismatch repair machinery?

To proofread DNA during replication Signup and view all the answers

What is the consequence of a mutation in the proteins involved in mismatch repair?

An increase in genetic mutations Signup and view all the answers

What is the term for the process of correcting errors during DNA replication?

Mismatch repair Signup and view all the answers

What is the role of primase enzyme in DNA replication?

To synthesize the RNA primer Signup and view all the answers

What is the main difference between the leading strand and the lagging strand?

The leading strand is synthesized continuously, while the lagging strand is synthesized in short segments Signup and view all the answers

What is the role of DNA ligase in DNA replication?

To join Okazaki fragments together Signup and view all the answers

What is the consequence of telomere shortening in most normal cells?

The cells die due to shortened telomeres Signup and view all the answers

What is the relationship between telomere length and human health?

There is a correlation between telomere length and human aging, disease progression, and developmental delay Signup and view all the answers

What is the characteristic of Okazaki fragments?

They are short, discontinuous segments of DNA Signup and view all the answers

What happens to the telomeres during DNA replication?

They are shortened Signup and view all the answers

What is the purpose of the RNA primer in DNA replication?

To provide a starting point for DNA synthesis Signup and view all the answers

What is the purpose of origins of replication in DNA replication?

To provide a site for DNA replication to begin Signup and view all the answers

What is the role of DNA helicase in DNA replication?

To separate the DNA strands Signup and view all the answers

What is the result of supercoiling during DNA replication?

The formation of supercoils ahead of the replication fork Signup and view all the answers

What is the function of DNA topoisomerase in DNA replication?

To relax the supercoils Signup and view all the answers

What is the direction of DNA synthesis by DNA polymerase?

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

What is the function of proofreading in DNA replication?

To correct mistakes during DNA synthesis Signup and view all the answers

What is the role of RNA primer in DNA replication?

To initiate DNA synthesis Signup and view all the answers

What is the purpose of DNA ligase in DNA replication?

To ligate the Okazaki fragments Signup and view all the answers

What is the result of DNA strand separation during DNA replication?

The formation of replication bubbles Signup and view all the answers

What is the direction of DNA synthesis on the lagging strand?

Discontinuous synthesis Signup and view all the answers

Study Notes

DNA Replication and Repair

DNA replication is the process of duplicating chromosomes before cell division, ensuring each daughter cell receives an accurate copy of genetic information.
The primary structure of DNA is a polymer of nucleotides linked by 3'→5' phosphodiester bonds.

Eukaryotic DNA Replication

Replication begins at special sites called origins of replication, where the two DNA strands are separated, opening up a replication "bubble".
A eukaryotic chromosome may have hundreds or thousands of origins of replication.
Replication proceeds in both directions from each origin, until the entire molecule is copied.

Formation of the Replication Fork

Proteins required for DNA strand separation: DNA helicase and single-stranded DNA-binding protein.
Unwinding at the replication fork causes supercoiling, which is relieved by DNA topoisomerases.

Action of DNA Topoisomerases

They have strand-cutting and strand-resealing activities.
Type I DNA topoisomerases and Type II DNA topoisomerases (DNA gyrase in prokaryotes) are used to relieve supercoiling.

DNA Polymerase

The enzyme responsible for copying DNA templates, reading parental nucleotide sequences in the 3'→5' direction, and synthesizing new DNA strands only in the 5'→3' direction.
DNA polymerases catalyze the elongation of new DNA at a replication fork and have proofreading capabilities, correcting mistakes through 3'→5' exonuclease activity.

RNA Primer and Primase

DNA polymerases require an RNA primer, which is a short, double-stranded region consisting of RNA base-paired to the DNA template.
The primer is short (5–10 nucleotides long), and the 3'end serves as the starting point for the new DNA strand.
RNA primer is synthesized using primase enzyme.

Leading and Lagging Strands

Along one template strand of DNA, the DNA polymerase synthesizes a leading strand continuously, moving toward the replication fork.
The lagging strand is synthesized as a series of segments called Okazaki fragments, which are joined together by DNA ligase.

Telomeres

Telomeres are non-coding and repetitive sequences at the ends of linear DNA molecules in eukaryotic chromosomes.
With each round of replication, telomeres are shortened because DNA polymerase cannot complete synthesis of the 5' end of each strand.
This contributes to the aging of cells, as eventually the telomeres become so short that the chromosomes cannot function properly and the cells die.

Mismatch Repair

Replication errors can cause a mismatch of one to several bases, which can be corrected by identifying the strand containing the mismatch and removing the mismatched nucleotide by an exonuclease.
Mutation to the proteins involved in mismatch repair in humans is associated with hereditary nonpolyposis colorectal cancer (HNPCC), also known as Lynch syndrome.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

This quiz covers the process of DNA replication, causes of DNA damage, and repair mechanisms. It also explores the effects of DNA repair failure and its connection to antivirals and cancer treatments.