DNA Replication and Fork Movement

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Questions and Answers

What is the rate of movement of the growing fork in E. coli?

1,000 bp/sec (correct)

2,000 bp/sec

100 bp/sec

500 bp/sec

What is the rate of fork movement in eukaryotic DNA?

100 bp/sec (correct)

1,000 bp/sec

2,000 bp/sec

500 bp/sec

What is the time taken to replicate the entire genomic DNA in E. coli?

1 hour

20 min

2 hours

42 min (correct)

Which enzyme is responsible for removing RNA primers during DNA replication?

FEN1 (Flap endonuclease 1) Signup and view all the answers

In which cells is telomerase activity extinguished during embryonic differentiation?

Most somatic cells Signup and view all the answers

What is the sequence of telomere tandem repeats in vertebrates?

TTAGGG Signup and view all the answers

What enables telomerase to extend the 3’ end of the DNA?

An internal RNA sequence Signup and view all the answers

How long does it take to replicate the entire genome in humans?

8 hrs Signup and view all the answers

What is the role of the 3' - 5' exonuclease activity in DNA replication?

To remove mispaired nucleotides at the 3' OH terminus of the newly synthesized DNA strand Signup and view all the answers

What is the function of DNA Primase in DNA replication?

To synthesize RNA primers for Okazaki fragments Signup and view all the answers

What is the main difference between prokaryotic and eukaryotic DNA replication?

The number of origin of replication sites Signup and view all the answers

What is the mechanism of RNA primer removal from Okazaki fragments?

Through the action of 5' - 3' exonuclease activity Signup and view all the answers

What is the rate of DNA replication in the presence of exonuclease activity?

20 nt/sec, which is not fast enough to be the main replicative enzyme Signup and view all the answers

What is the role of telomerase in DNA replication?

To elongate telomeres by adding nucleotides to the ends of chromosomes Signup and view all the answers

What is the characteristic of Okazaki fragments?

They are short, discontinuous strands of DNA synthesized in a 5' to 3' direction Signup and view all the answers

What is the direction of DNA synthesis in Okazaki fragments?

5' to 3' Signup and view all the answers

What is the role of telomerase in telomere replication?

To elongate telomeres by adding nucleotides Signup and view all the answers

What is the main difference between leading and lagging strands in DNA replication?

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

What is the function of RNA primers in DNA replication?

To provide a site for DNA polymerase to bind Signup and view all the answers

What is the role of DNA primase in DNA replication?

To synthesize RNA primers Signup and view all the answers

What is the result of telomere shortening after each cell division?

The cell stops dividing and dies Signup and view all the answers

How do telomeres normally get shorter after each cell division?

Because the DNA replication machinery is unable to replicate the ends of chromosomes Signup and view all the answers

What is the role of Okazaki fragments in DNA replication?

To synthesize the lagging strand in short fragments Signup and view all the answers

What is the enzyme responsible for removing RNA primers from the lagging strand?

RNAse H Signup and view all the answers

Study Notes

DNA Replication

DNA replication occurs at a speed of approximately 1,000 bp/sec in prokaryotes, taking around 42 minutes to duplicate the entire genomic DNA.
In eukaryotes, the fork movement is slower, around 100 bp/sec, possibly due to the association of DNA with histones.

RNA Primers

RNA primers are removed by DNA polymerase, with the help of RNase H and FEN1 (Flap endonuclease 1).

Telomere Elongation

Telomerase activity is extinguished during embryonic differentiation in most somatic cells, but remains active in some tissues, such as male germ cells, activated lymphocytes, and certain stem cell populations.
Telomeres have tandem repeats, such as TTAGGG in vertebrates, which differs in other organisms.
Telomerase carries an internal RNA sequence, enabling the extension of the 3’ end of the DNA, which then becomes a template for normal DNA synthesis.
Without telomerase, telomeres may get shorter after each cell division, leading to cell death.
Telomerase may have a role in aging and cancer.

DNA Structure

DNA is composed of purine and pyrimidine bases, 2’deoxyribose, and a phosphodiester backbone.
The structure of DNA requires an appreciation of its helical shape, external sugar-phosphate chains, and antiparallel sugar-phosphate chains.

DNA Replication Mechanism

DNA replication involves a mechanism of replication, differences between leading and lagging strands, and multiple enzymes involved.
Exonuclease 3’ – 5’ activity has an editing function to allow replication accuracy, removing mispaired nucleotides at the 3’ OH terminus of the newly synthesized DNA strand.
Exonuclease 5’ – 3’ activity removes ribonucleotide sequences, such as RNA primer sequences of Okazaki fragments.

DNA Replication Speed

DNA replication occurs at a speed of 20 nt/sec, which is not fast enough to be the main replicative enzyme, but is capable of "filling in" gaps.
Prokaryotic DNA replication is faster than eukaryotic DNA replication.

DNA Replication Initiation

Initiation of DNA replication occurs at the origin of replication (OriC), where DNA primase binds to create a replication fork.

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Description

This quiz covers the process of DNA replication, including the speed of fork movement in prokaryotic and eukaryotic DNA, and the role of RNA primers and enzymes in DNA replication.