DNA Replication Quiz

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Questions and Answers

What happens to the parental strands during semi-conservative replication?

The parental strands are randomly distributed in the daughter molecules.

The parental strands separate, and each serves as a template for a new strand. (correct)

Both parental strands are completely conserved.

One parental strand is conserved, and the other is entirely newly synthesized.

During DNA replication, what is the role of helicase?

To synthesize new DNA strands from the existing templates.

To break the hydrogen bonds between complementary bases and unzip the DNA. (correct)

To bind to the replication fork to stabilize it.

To add nucleotides to the growing DNA strand.

What distinguishes the origin of replication in prokaryotes from that in eukaryotes?

Prokaryotes have multiple origins of replication, while eukaryotes have a single origin.

Prokaryotes have a single origin of replication, while eukaryotes have multiple origins. (correct)

Eukaryotes have a unique Ori C, while prokaryotes do not.

Both prokaryotes and eukaryotes have only one origin of replication.

Which model of DNA replication involves one parental molecule directing the synthesis of a completely new double-stranded molecule?

Conservative model Signup and view all the answers

What is created where the DNA strands are separated during replication?

Replication fork Signup and view all the answers

What role do Single-Strand Binding Proteins (SSBs) play during DNA replication?

They stabilize the separated DNA strands and prevent them from re-annealing. Signup and view all the answers

Which enzyme catalyzes the addition of nucleotides to the growing DNA chain in prokaryotes?

DNA polymerase III Signup and view all the answers

What is the orientation of the leading strand during DNA replication?

5’ to 3’ towards the replication fork. Signup and view all the answers

Why are multiple primers needed along the lagging strand during replication?

Because primase can only synthesize one primer at a time. Signup and view all the answers

What is the primary function of the enzyme Topoisomerase during DNA replication?

To alleviate the strain of supercoiling ahead of the replication fork. Signup and view all the answers

How does base pairing differ when RNA is involved in DNA replication?

U replaces T, pairing with A in the RNA primer. Signup and view all the answers

What is the consequence of DNA polymerase only being able to add nucleotides to a growing polymer?

It necessitates the use of a primer for new strand synthesis. Signup and view all the answers

Which strand is known as the lagging strand during DNA replication?

The strand that requires multiple primers for its synthesis. Signup and view all the answers

During DNA replication, what is the role of primase?

To synthesize short RNA primers for DNA polymerase. Signup and view all the answers

Study Notes

Replication

The process by which DNA makes a copy of itself during cell division
DNA is copied during the "S" or synthesis phase of interphase
The new cells will require identical DNA strands

Models of Replication

There are three models of replication:
- Conservative: the parental molecule directs synthesis of an entirely new double-stranded molecule. After one round of replication there is one molecule that is conserved as two old strands
- Semi-Conservative: the two parental strands separate and each makes a copy of itself. After one round of replication, two daughter molecules each comprise one old strand and one new strand
- Dispersive: material in the two parental strands is distributed randomly between two daughter molecules.

Replication Fork

Daughter DNA is a double helix with 1 parent strand and 1 new strand
One strand serves as the template for the new strand
Each strand of the parent DNA is used as a template to make the new daughter strand
DNA replication makes 2 new complete double helices, each with 1 old and 1 new strand
The site where replication begins is called "ori"
- In E. coli, there is one called "Ori C"
- In humans, there are thousands called "ori"
Strands are separated to allow replication machinery to contact the DNA
Many A-T base pairs are found in the replication origin
Note anti-parallel chains
Prokaryotes (bacteria) have a single bubble
Eukaryotic chromosomes have many bubbles

Unzipping the Double Helix

DNA helicase separates the two strands of DNA by breaking the hydrogen bonds between complementary bases (A to T, C to G)
This separation creates a "Y" shape called a replication fork
The two separated strands will act as templates for making the new strands of DNA
Single Strand Binding Proteins (SSBs) attach to the DNA and keep the two strands separated and untwisted
DNA helicase and SSBs lead to DNA unwinding and active replication
The enzyme Topoisomerase attaches to the two forks of the bubble to relieve stress on the DNA molecule as it separates

Bidirectional Movement of DNA Replication Machinery

The DNA replication machinery moves bidirectionally

Leading and Lagging Strands

One strand is oriented in the 3’ to 5’ direction (towards the replication fork), this is the leading strand.
The other strand is oriented in the 5’ to 3’ direction (away from the replication fork), this is the lagging strand
The two strands are replicated differently because of their different orientations.

DNA Polymerase

In prokaryotes, there are three types of polymerase I, II and III
An enzyme (Pol III) catalyzes the addition of a nucleotide to the growing DNA chain
A nucleotide enters as a nucleotide tri-PO4
DNA polymerase can only ADD nucleotides to a growing primer
Another enzyme, primase, synthesizes a short RNA chain called a primer
- This is a DNA/RNA hybrid for this short stretch
- Base pairing rules are followed (BUT A-U)

Primer Removal

The primer is later removed and replaced by DNA and the backbone is sealed (ligated)
In eukaryotic cells, DNA polymerase alpha is responsible for the synthesis of primers.

Leading Strand Replication

A primer is added along the leading strand
DNA polymerase reads 3’ to 5’ from the RNA primer
Synthesis proceeds 5’ to 3’ with respect to the new daughter strand
The nucleotides are usually added 5’ to 3’

Lagging Strand Replication

The other daughter strand (lagging strand) is also synthesized 5’ to 3’ because that is the only way that DNA can be assembled; due to this, the opposing template is being read 5’ to 3’
The DNA strand is fed through the polymerase to compensate for the lagging strand direction
Many primers are used to make many short segments that are later joined (ligated) together (= Okazaki fragments)
This is called the lagging strand because it is a discontinuous process (the Okazaki fragments need to be joined up later)

Okazaki Fragments

Once all of the bases are matched up (A with T, C with G), an enzyme called Exonuclease strips away the primer(s).
The gaps were then filled by yet more complementary nucleotides.
Finally, an enzyme called DNA Ligase seals up the sequence of DNA into two continuous double strands.

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Description

Test your knowledge on DNA replication processes including the models of replication and the structure of the replication fork. This quiz will cover key concepts such as conservative, semi-conservative, and dispersive replication. Understand the significance of each model in the context of cell division.