Lecture 23 - DNA replication

Question 1

Know the basic structure of DNA

Answer 1

• 5 carbon sugar
• phosphate group
• nitrogenous base

Question 2

Describe and compare the Conservative and Semi-Conservative models of replication

Answer 2

• Semiconservative model:
after DNA replication, the new DNA duplex consists of one parental
strand and one new daughter strand.

• Conservative model:
after DNA replication, the new DNA duplex consists of two newly
synthesized daughter strands.

Question 3

• Know the function and properties of DNA Polymerase, including its proofreading ability

Answer 3

• synthesizes a new DNA strand from
  existing strands, can only synthesize in the 5’ to 3’ direction. needs primase to synthesize the lagging strand in Okazaki fragments.
  • corrects mistakes in replication

Question 4

Describe and compare continuous (leading strand) and discontinuous (lagging strand)
replication

Answer 4

Leading strand:

• 3’ end pointed towards from the replication fork
• is synthesized continuously towards the replication fork.

Lagging strand:

• 3’ end pointed away from the replication fork
• is synthesized discontinuously away from the replication fork, in short fragments called Okazaki fragments.

Question 5

Know the function of RNA primers and Primase in DNA replication

Answer 5

• DNA polymerase cannot begin a
new strand on its own: it can only
elongate the end of an existing
piece of DNA or RNA
• Each new DNA strand begins with a
short stretch of RNA that serves as
a primer for DNA synthesis
• The primer is made by an RNA
polymerase called RNA Primase

Question 6

• Know the function of Helicase, Topoisomerase II, and Single-stranded binding proteins during DNA replication

Answer 6

• Helicase unwinds the DNA double helix.
• Topoisomerase II manage DNA tangles and super coils.
• SSB’s stabilize single strands of DNA.

Question 7

Define the Origin of Replication

Answer 7

The region of DNA where replication begins.

Question 8

• Compare replication of circular DNA (prokaryotic) and linear DNA (eukaryotic)

Answer 8

• In circular (prokaryotic) DNA their is only one origin of replication.
• In linear (eukaryotic) DNA there are mulitple origins of replication.

Question 9

• Illustrate the process of DNA synthesis at a Replication Bubble, including all proteins
involved (Primase, DNA Polymerase, Helicase, Topoisomerase II, Single-stranded binding
proteins)

Answer 9

?

Question 10

Describe the end problem of DNA and the use of Telomerase and telomeres to combat
this problem

Answer 10

• at the end of replication a section of DNA remains unreplicated, as the last RNA primer is removed.
• This shortened template results in a shortened chromosome.
• The end of a linear (eukaryotic) chromosome is capped by a repeating sequence called a telomere..
• In humans the telomere is 5’-TTAGGG-3’