DNA Replication II Flashcards
What is primase?
An enzyme that synthesizes short RNA sequences called primers
When does daughter strand synthesis begin?
It begins when primase adds the first 10-12 nucleotides of the new strand
What is the primer?
The first 10-12 nucleotides that is added by primase
What does primase do once the primer is produced?
Primase detaches from the template strand
DNA pol III takes over
What does DNA polymerase III do?
DNA pol III attaches to the 3’ end of the primer and adds more nucleotides to the new strand
What are the five different DNA pols in E. coli?
DNA pol I
II
III
IV
V
Which DNA pols are found in normal DNA replication?
DNA pol I and III
Which DNA pols are involved in the repair and replication of damaged DNA?
DNA pol II, IV, and V
What are DNA pols overall?
Enzymes that catalyze the formation of a phosphodiester bond between the 3’ end of a daughter strand and the phosphate group of a deoxyribonucleotide
What occurs at the catalytic site?
The reaction the DNA pols adding a phosphodiester bond between the 3’ end of a daughter strand and the phosphate group of a deoxyribonucleotide
Phosphodiester bond formation on DNA molecule (not rlly a question)
- DNA pol chooses a single d_TP (insert any base)
- DNA pol creates a phosphodiester bond between the nucleotide and the free 3’ hydroxyl group of the daughter strand
- Two phosphate groups are removed from the d_TP
- The nucleotide is now a d_MP once added to the new DNA strand
What are DNA pols limited to?
- DNA pol can only add nucleotides to the 3’ end of a DNA strand
- They cannot create a phosphodiester bond between two individual nucleotides
- They cannot add a nucleotide to the 5’ end of DNA
- They cannot link two DNA strands together
Why is primase necessary?
Primase must create the first part of the daughter strand because DNA pol III can only add nucleotides to the 3’ end of an existing strand
What is the role of DNA pol III?
To extend the daughter strand by adding nucleotides to the primer in a 5’ to 3’ direction
Why are DNA pols necessary?
How many DNA pol III enzymes are in a replication fork?
Two; one for each template strand
What direction does DNA pol III extend a primer?
5’ to 3’ direction
What direction does one DNA pol III synthesize a daughter strand?
Daughter strand synthesis will occur in the same direction as the movement of the replication fork: AWAY from the ori
What is the daughter strand synthesizing away from the ori called?
The leading strand
What direction does the other DNA pol III move?
In the opposite direction of the replication fork movement: AWAY from the ori
What is the daughter strand synthesizing toward the ori called?
The lagging strand
What is continuous synthesis?
When the leading strand is made as one long strand extended form a single primer; no breaks
What is discontinuous synthesis?
When the polymerase extends a primer in the 5’ to 3’ direction until it encounters a previous primer, detaches from the template strand, hops in the 3’ to 5’ direction along the template strand, and attaches to the next available primer. It will then extend that primer until it encounters the previous primer, at which time it will hop to the next primer.
How are Okazaki fragments formed?
When polymerase detaches from the template strand, changes direction by going to the other template strand, attaches to the next available primer, and extends that primer until it reaches the previous primer and goes to the next primer (damn what)
What is done before daughter strand synthesis is complete?
Primers must be removed from the daughter strands and replaced with deoxyribonucleotides
What is the function of DNA pol I?
The removal of the primer ribonucleotides and their replacement with deoxyribonucleotides
What is needed to be done once primers have been removed and replaced with DNA?
Okazaki fragments in the lagging strand must be linked together to create one complete daughter strand
What is needed to link Okazaki fragments together?
A phosphodiester bond between the 3’ end of one Okazaki fragment and the 5’ end of the next
What enzyme is used to connect Okazaki fragments?
DNA ligase
When does termination of DNA occur?
When the replication folks encounter base sequences called termination (ter) sequences
What are the two termination (ter) sequences?
T1 and T2
Where are T1 and T2 located?
On the side of the DNA molecule opposite to oriC
What will a protein called “termination utilization substance” (Tus) do with T1 or T2?
It will bind to either T1 or T2
What will ligase do once the replication fork stops?
It will link the daughter strand of each new DNA molecule
What enzyme separates the two new DNA molecules from one another?
Topoisomerase II
