Replication DNA

Question 1

Name and describe the enzymes at the replication fork

Answer 1

DNA polymerase: catalyzes the addition of nucleotides to the growing strands at the 3’ end
DNA helicase: unwraps the double helix using the energy from ATP hydrolysis.
Replication protein A: binds to ssDNA and prevents ds from forming
Sliding clamp: binds to the polymerase and keeps it attached to the strand. The clamp loader locks the sliding clamp on the polymerase
Primase: creates the primers necessary for the initiation of the DNA synthesis.
DNA ligase: joins the Okazaki fragments together using ATP energy.

Question 2

In eukaryotes which DNA polymerases exist and what are their responsibilities

Answer 2

pol epsilon: works on leading strand
pol delta: works on lagging strand (and leading strand)
pol alpha/primase: primase creates a primer and pol alpha starts elongating the primer with ~20 nucleoides
pol gamma: replicates mtDNA

Question 3

Explain Leading strand and lagging strand/Okazaki fragment

Answer 3

The leading strand needs only one primer and has a polymerase that works continuous as the replication fork moves. Since elongation can only occur in 5´-3´ direction the other strand will lag. The lagging strand will be compromised of Okazaki fragment and will need the constant production of primers. Ligase will connect all the fragments.

Question 4

*Describe the replication (3 phases)

Answer 4

Initiation
Elongation
Termination

Question 5

*How is the termination a “problem” in eukaryotic cells ?

Answer 5

Telomerase