DNA Replication and Synthesis Overview

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Questions and Answers

What is the primary role of telomerase in relation to the chromosome ends?

To initiate DNA replication at the leading strand

To digest mismatched nucleotides from the newly synthesized DNA

To extend the 3’ end of the chromosome by adding telomeric repeats (correct)

To synthesize RNA primers for DNA polymerase

Which of the following statements about telomere function is correct?

Telomeres are synthesized exclusively by RNA polymerase.

Single-stranded DNA overhangs at telomeres are unnecessary for their function.

All somatic cells have active telomerase throughout their lifespan.

Telomeres are protected from progressive shortening by telomerase activity. (correct)

Which proteins are specifically involved in inhibiting telomerase activity in yeast?

Cdc13 and Rap1

Cdc13 and TRF2

Rap1, Rif1, and Rif2 (correct)

TRF1 and Rif2

What mechanism allows the lagging-strand DNA replication machinery to extend the 5’ end after telomerase has acted?

DNA polymerase synthesizing complementary DNA toward the 5’ end Signup and view all the answers

What is the Hayflick limit?

The maximum number of times a somatic cell can divide due to telomere shortening Signup and view all the answers

Which process is primarily responsible for the formation of Okazaki fragments during DNA replication?

Discontinuous replication on the lagging strand Signup and view all the answers

Which enzyme is involved in synthesizing the complementary DNA strand toward the 5’ end?

DNA polymerase Signup and view all the answers

What is the significance of the remaining 3’ ssDNA overhang at the chromosome end?

It is essential for recruiting telomerase. Signup and view all the answers

Which of the following accurately describes the function of telomerase?

It extends telomeres by using an RNA template for DNA synthesis. Signup and view all the answers

What is the primary role of the RNA component in telomerase?

To act as a physical template for the DNA polymerase activity. Signup and view all the answers

During DNA replication, which strand is synthesized continuously?

Leading strand Signup and view all the answers

How does telomerase function in regard to the RNA template?

It uses the RNA template to create a complementary strand and then displaces the RNA. Signup and view all the answers

What is a major characteristic of the Okazaki fragments during DNA replication?

They require multiple primers for synthesis. Signup and view all the answers

Which of the following statements about DNA polymerase is true?

DNA polymerase has both proofreading and synthesis capabilities. Signup and view all the answers

Which statement correctly differentiates leading and lagging strands in DNA replication?

The lagging strand is synthesized in the direction opposite to the replication fork movement. Signup and view all the answers

What occurs during the exonuclease proofreading activity of DNA polymerase?

Incorrect nucleotides are excised from the growing DNA strand. Signup and view all the answers

What role does the shelterin complex serve in relation to telomeres?

It helps protect telomeres from being recognized as DNA damage. Signup and view all the answers

How do telomere-binding proteins affect telomerase activity when telomeres are short?

They allow more telomerase access by reducing their own binding. Signup and view all the answers

What happens when telomeres are elongated and double-stranded?

More telomere-binding proteins associate, increasing the inhibition of telomerase. Signup and view all the answers

What is the function of POT1 within the telomere-binding proteins?

It binds to single-stranded telomere repeat DNA and inhibits telomerase activity. Signup and view all the answers

How does the negative feedback mechanism work in maintaining telomere length?

It increases binding of telomere-associated proteins, inhibiting further extension. Signup and view all the answers

Why is it important that telomeres are not recognized as DNA breaks?

To ensure chromosomal instability does not occur due to recombination. Signup and view all the answers

Which of the following accurately describes the effect of short telomeres on protein binding?

Short telomeres have fewer telomere-binding proteins attached. Signup and view all the answers

What role does TIN2 play within the shelterin complex?

It helps stabilize telomere-binding protein interactions. Signup and view all the answers

Study Notes

DNA Replication General Features

DNA strands are complementary, each acting as a template for its partner
Replication is semi-conservative
Replication is often bidirectional
Replication requires RNA primers

DNA Synthesis Chemistry

DNA synthesis uses deoxynucleoside triphosphates (dNTPs)
dNTPs have three phosphate groups
The primer provides a 3'-OH group
DNA synthesis extends the 3' end, releasing pyrophosphate
Pyrophosphate is quickly hydrolyzed into phosphate molecules by pyrophosphatase
DNA strand orientation (template strand is opposite the growing strand)
The reaction is favored thermodynamically

DNA Polymerase Mechanism

DNA polymerases use a single active site to catalyze DNA synthesis
Correct base pairing is essential for catalysis
Steric constraints prevent use of rNTPs
DNA polymerase has a three-domain structure: palm, fingers, and thumb
Metal ions in the active site are essential for catalysis.
There are multiple DNA polymerases; Pol ε and Pol δ are prominent in eukaryotic replication

DNA Polymerase Function and Activity

DNA polymerase monitors ability of incoming nucleotides to form correct base pairs (A-T or G-C)
Incorrect base pairing is quickly corrected by exonuclease activity
DNA polymerase activity is measured by nucleotide incorporation assay
Two metal ions bound to the enzyme catalyze nucleotide addition.

DNA Replication Processes

DNA polymerase I is responsible for removing RNA primers
Klenow Fragment polymerase is responsible for proofreading and removal of errors during DNA replication
DNA Replication is semi-discontinuous
The leading strand replicates continuously in the direction of the replication fork
The lagging strand replicates discontinuously in fragments called Okazaki Fragments
DNA pol III and accessory proteins like the sliding clamp ensure high processivity

DNA Polymerase Processivity

Sliding clamp proteins dramatically increase DNA polymerase processivity
The sliding clamp is a ring-shaped structure that enhances DNA polymerase processivity by preventing it from dissociating from the template strand
Clamp loaders are essential for loading sliding clamps onto DNA

DNA Replication Initiation

The replicon model describes initiation of replication
E. coli contains the origin of replication (oriC) where DNA replication initiates
Initiation requires proteins to unwind the DNA double helix which includes DnaA proteins.
Initiation is tightly regulated by the cell cycle, to ensure duplication only occurs once per cycle.
Proteins that load helicases onto the origin of replication, including Cdc6/Cdt1 and Mcm2-7, have roles in coordinating this initiation step

Eukaryotic DNA Replication

Eukaryotic DNA synthesis is similar but more complex than prokaryotic replication because of larger genome size and linear chromosomes
Replicators are specific regions where initiation begins; Origin Recognition Complexes (ORCs)
There are multiple origins of replication in eukaryotic chromosomes

Telomerase

Telomeres are repetitive sequences at the ends of linear chromosomes and shorten during replication
Telomerase is an enzyme that extends telomeres, preventing further shortening
Telomerase contains an RNA component guiding DNA synthesis
Shelterin proteins protect telomeres from the cell's DNA repair machinery by binding to the telomere region, thus preventing it from being recognized as a break

DNA Replication Errors and Proofreading

DNA polymerase has proofreading capability to reduce replication errors
DNA is scanned for errors after base pairing
Base-pairing mismatches and incorrect nucleotides are removed before replication proceeds further
This ensures high fidelity of replication, minimizing mutations in the genome

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Description

This quiz explores the general features, chemistry, and mechanisms involved in DNA replication and synthesis. It covers topics such as the semi-conservative nature of replication, the role of RNA primers, and the action of DNA polymerase. Test your knowledge about these essential biological processes!