DNA Replication - Lecture 3

Question 1

How many polymerases does DNA polymerase have and what are their general functions?

Answer 1

5; Polymerase I and III -> involved in DNA replication

Polymerase II, IV, and V -> repair mechanisms

Question 2

What are the features and functions of polymerase I?

Answer 2

has both 3’ to 5’ and 5’ to 3’ exonuclease activity, aids in removal of RNA primer

Question 3

What are the features and functions of DNA polymerase III?

Answer 3

only has 3’ to 5’ exonuclease activity, is the main replicative polymerase and has a beta sliding clamp

Question 4

How is the lagging strand replicated with polymerase in prokaryotes?

Answer 4

The okazaki fragments loop to allow the polymerase to go in the right direction
When poly III reaches the 5’ of the RNA primer, poly III is swapped for poly I
Poly I removes RNA primer and synthesises a short tract of DNA
After the RNA primer is replaces a nick remains in the strand
DNA ligase seals the nick with a phosphodiester bond between the 5’ P group and 3’OH group of the two nucleotides

Question 5

What are the unique aspects of eukaryotic DNA replication?

Answer 5

• Occurs during S phase
• short RNA primer and Okazaki fragments
• Multiple polymerases (at least 15): Pol ε ~ performs leading strand replication, Pol 𝛿 ~ performs lagging strand replication and Pol ⍺ ~ synthesizes primase activity
• Bidirectional with multiple origins of replication
• Nucleosomes are removed and reassembled
• Telomeres shorten

Question 6

How is the problem of chromosomes being shortened after every round of replication being solved?

Answer 6

telomerase extends eukaryotic chromosomes by adding repeating sequences to the ends