Biological Sciences - DNA Replication

What happens in S phase of cell division of eukaryotic cells?

DNA Replication

In prokaryotic cells, what phase of cell division does the DNA replicate?

Binary Fission

The doubled stranded molecule of DNA is referred to as…

A DNA Double Helix

What makes up the backbone of DNA?

The backbone of a DNA Double Helix consist of sugar and phosphate groups.

What bonds form between the nitrogenous bases of the DNA?

Hydrogen bonds form between the nitrogenous bases of the DNA.

What is a Purine?

A type of nitrogenous base in DNA and RNA, specifically adenine and guanine, characterized by a two-ring structure.

What is pyrimidine?

A type of nitrogenous base in DNA and RNA, specifically cytosine, thymine, and uracil, characterized by a single-ring structure.

Uracil is found specifically in?

RNA and not DNA.

Which one of the pyrimidine bases are found in both DNA and RNA?

Cytosine, is found in both DNA and RNA.

What is the rule of base pairing?

The rule of base pairing states that in DNA, adenine pairs with thymine, and cytosine pairs with guanine, while in RNA, adenine pairs with uracil.

How many hydrogen bonds form between thymine and adenine?

Two hydrogen bonds form between thymine and adenine.

How many hydrogen bonds form between Guanine and Cytosine?

Three hydrogen bonds form between guanine and cytosine.

Purines always bond with pyrimidines because?

They maintain a uniform width in the DNA double helix.

A always pair with T, and G always pairs with C

This pairing is due to the specific hydrogen bonding patterns, which ensure the stability and uniformity of the DNA structure.

What does it mean when we say a DNA double helix is antiparallel?

It means that the two strands of DNA run in opposite directions, with one strand oriented 5' to 3' and the other 3' to 5'. This orientation is crucial for replication and function.

What does semiconservative mean when referring to DNA replication?

It refers to the method of DNA replication where each new double helix consists of one old strand and one newly synthesized strand, preserving half of the original DNA.

What is the function of DNA Helicase?

DNA Helicase unwinds the double helix, separating the two strands to allow for replication and transcription.

What is a replication fork?

A structure that forms during DNA replication, where the double helix is unwound and the two strands are separated, allowing replication to occur.

What is the role of SSBP?

Single-stranded binding proteins (SSBPs) stabilize the unwound DNA strands during replication, preventing them from re-annealing or forming secondary structures.

What is the name for the enzyme that seperate’s two strands of DNA?

DNA Helicase

What is the name for a protein that keeps the DNA double helix broken and separated during DNA replication?

Single-stranded binding protein (SSBP)

DNA Polymerase synthesizes new DNA strands in what direction?

5' to 3' direction.

Why can’t DNA polymerase build a new strand?

Because it requires a primer with a free 3' hydroxyl group to initiate synthesis.

What is the name for an enzyme that synthesizes new strands of DNA by connecting nucleotides together?

DNA Polymerase

What are two important aspects of DNA Polymerase?

It synthesizes DNA in the 5' to 3' direction and requires a primer to initiate synthesis.

What is DNA Primase responsible for?

Synthesizing RNA primers for DNA replication.

What is an Okazaki Fragment?

Short segments of DNA synthesized on the lagging strand during DNA replication.

What is the difference between the lagging and leading strand of DNA synthesis?

The leading strand is synthesized continuously in the 5' to 3' direction, while the lagging strand is synthesized discontinuously in short segments called Okazaki fragments.

What is a DNA Primase primer made of?

RNA nucleotides that initiate DNA synthesis.

Why will the primers need to be removed?

Primers must be removed to allow DNA synthesis to proceed without RNA nucleotides and ensure the final DNA molecule is composed solely of nucleotides.

What is the enzyme DNA Ligase responsible for?

Joining Okazaki fragments and sealing nicks in the sugar-phosphate backbone of DNA during replication.

DNA is replicated in what manner?

DNA is replicated in a semi-conservative manner. In this type of replication, the DNA stands are separated from each other and each strand (parental strands) are used as templates for the daughter strand. At the end of DNA replication, there should be two DNA double helices composed of one parental strand and one daughter strand.

What provides the energy for making new strands of DNA?

Nucleotides

What end does DNA Polymerase add nucleotides to the strand?

DNA Polymerase adds nucleotides to the 3’ end of the new strand, thus it synthesizes in a 5’ to 3’ direction.

When a new nucleotide is added into a strand of DNA that is being synthesized, what is released as a result?

Pyrophosphate is released

Where does DNA replication take place?

The Origin of Replication

How many Origin of Replications do prokaryotic organisms have?

Single, One

In eukaryotes, how many Origin of Replication are found, is it singular or multiple?

Multiple

Which organism has a circular chromosome?

Prokaryotes

Which organisms have linear chromosomes?

Eukaryotes

DNA replication is considered…

Bidirectional

Why is DNA replication bidirectional?

There are two DNA Helicases and they are moving in opposite directions of each other from the origin or replication. DNA replication will proceed in both directions away from the origin of replication.

How does the DNA Polymerase proofreading function work?

By allowing it to recognize and correct incorrect nucleotides during DNA synthesis. The enzyme can detect mismatches due to improper base pairing. It will utilize the 3’ to 5’ exonuclease.

What does high fidelity mean when referring to DNA replication?

High fidelity in DNA replication refers to the accuracy of the replication process, ensuring that new DNA strands are synthesized with minimal error rate, preserving the correct sequence of nucleotides.

What happens every time a linear chromosome is replicated?

The chromosome becomes shorter and it loses some DNA.

Define a Telomere

A repetitive nucleotide sequence at the ends of linear chromosomes that protects the genetic information during cell division and prevents the chromosome from deterioration or fusion with neighboring chromosomes.

Do Telomeres contain genes?

NO

What is the enzyme Telomerase?

This enzyme adds repetitive nucleotide sequences to the ends of telomeres, extending them and helping to maintain the length and integrity of chromosomes during cell division.

What type of cell is telomerase active in?

Germ cells

Why do germ cells use telomerase?

To ensure that the chromosomes inherited by the offspring will not be shortned.

Is Telomerase active in somatic cells?

NO