module 6 dna replication

Describe the general function of DNA

DNA contains instructions for making proteins and copying itself to make new cells. 

Name the parts of a nucleotide

Phosphate group, five carbon sugar, and nitrogenous base

Which parts of a nucleotide are involved in phosphodiester bonds?

The phosphate group of one nucleotide (5’ carbon) and the hydroxyl group (3’ carbon)

Use the sequence of one DNA strand to predict the sequence of its complementary strand.

A=T, C=G

Name the functional groups found at the 5’ and 3’ ends of a DNA strand.

A phosphate group is at the 5’ end and a hydroxyl group is at the 3’ end.

Explain the importance of the 3’ end of a DNA strand in the process of DNA replication.

Nucleotides can only be added to the 3’ end 

Explain what is meant by “semiconservative replication”

Both strands of the DNA can be used as templates for a new strand and new helixes are made of half parent DNA and half daughter DNA

Describe the role of origins of replication in the process of DNA replication

Origins of replication are where DNA replication begins. Bacterial chromosomes usually have one ORI. Human chromosomes have several ORI.

What are the major enzymes involved in DNA replication?

DNA helicase, topoisomerase, primase, DNA polymerase III, DNA polymerase I, DNA ligase,

Explain why the leading strand of DNA is made continuously while the lagging strand is not.

The leading strand of DNA is made continuously because the 3’ is oriented towards the fork and the 5’ is oriented towards the ORI, allowing nucleotides to be added to the 3’ end. It is also made continuously because the DNA polymerase is moving in the same direction as the replication fork. 

Describe the roles of DNA Polymerase III and nucleotide excision enzymes in ensuring the quality of copied DNA.

DNA polymerase III checks the work as it builds new DNA strands. If it adds an incorrect base, it removes and replaces it.

Nucleotide excision enzymes remove large chunks of DNA that were incorrectly copied and polymerase III tries to copy the template strand again.

Which parts of a nucleotide are involved in hydrogen bonds?

The hydroxyl group of a nucleotide is involved in hydrogen bonds. 

Describe the role of replication bubbles in the process of DNA replication

A replication bubble is a gap between two complementary DNA strands. They are created when double helixes open at origin of replication. Allows for DNA replication at multiple simultaneous points. The bubbles formed during replication fuse and separate from the original DNA strands, making new DNA.

Describe the role of replication forks in the process of DNA replication

Replication forks are the edges at each replication bubble. Forks allow enzymes to use single strands as templates to synthesize new DNA.

What is the leading strand in the replication fork?

The leading strand is oriented with the 3’ towards the fork and the 5’ towards the ORI. This strand will be made continuously in one piece.

What is the lagging strand in the replication fork?

The lagging strand is oriented with the 3’ towards the ORI, and the 5’ towards the replication fork. This strand will be made in small Okazaki fragment pieces.

What is the function of DNA helicase?

Unwinds parental double helix at replication forks. Moves down the DNA strand and breaks hydrogen bonds between DNA strands.

What is the function of topoisomerase?

Relieves the strain ahead of replication forks/ helicase by breaking (cutting) into the DNA and rejoining DNA strands

What is the function of Primase?

Synthesizes an RNA primer at the 5’ end of a leading strand and at the 5’ end of each fragment of the lagging strand. 

What is the function of DNA polymerase III

Using parental DNA as a template, synthesizes new DNA strands by adding nucleotides to an RNA primer or a pre-existing DNA strand. Attaches complementary nucleotides to a template strand.

What is the function of DNA polymerase I?

Removes RNA nucleotides of primer from 5’ end and replaces them with DNA nucleotides.

What is the function of ligase?

Joins small Okazaki fragments of the lagging strand. On the leading strand, it joins the 3’ end of DNA that replaces primer to the rest of the leading strand of DNA. 

What nitrogenous bases are purines?

Guanine and Adenine

What nitrogenous bases are pyrimidines?

Uracil, Thymine, and Cytosine