Ch.11: DNA Replication

Question 1

Describe the Structural overview of DNA replication

Answer 1

-two newly-made DNA strands = daughter strands
The two original DNA strands = parental strands
-One replicated strand, the leading strand, occurs in the
direction towards the replication fork
-One replicated strand, the lagging strand, occurs in the
direction away from the replication for

Question 2

Initiation of replication only occurs efficiently on…?

Answer 2

fully methylated DNA

Question 3

DNA synthesis requires…?

Answer 3

either a RNA or a DNA primer;
In the cell both the lagging and leading replicated DNA strands are synthesized by DNA Pol III using RNA primers
synthesized by the primase protein

Question 4

DNA polymerase catalyzes the formation of a covalent ester bond between the…?

Answer 4

innermost phosphate group of the incoming
deoxyribonucleoside triphosphate
AND
3’-OH of the sugar of the previous
deoxynucleotide
(last two phosphates of the
incoming nucleotide are released in the form of
pyrophosphate (PPi))

Question 5

What is the only polymerase to associate with the primase protein? Why?

Answer 5

DNA polymerase alpha (DNA pol a) to synthesize the leading strand and DNA polymerase delta (DNA pol δ) to
synthesize the lagging strand
(polymerase switch)

Question 6

What 2 key features are DNA polymerase defined by?

Answer 6

-They synthesize DNA only in the 5’ to 3’ direction; They cannot initiate DNA synthesis on a bare (unprimed) DNA strand; At the 3’ ends of linear chromosomes - the end of the strand cannot be replicated
-The telomerase protein binds to telomeric repeat sequences in the telomeres at the ends of the; chromosome using an RNA primer known as telomeric RNA and replicates the ends of the chromosome.

Question 7

Where does DNA synthesis begin?

Answer 7

Two replication forks form at the origin of replication and eventually meet at the opposite side of the bacterial chromosome and replication is terminated

Question 8

What 3 types of DNA sequences in oriC are functionally important?

Answer 8

DnaA boxes: sites for the binding of DnaA protein

AT-rich regions: sites where the DNA strands separate

GATC methylation sites: sites that help to regulate DNA replication

Question 9

Describe the action of the DnaA and DnaB proteins

Answer 9

DNA-binding domains binds to DnaA boxes in the origin; after DnaA starts the process DnaB (helicase) starts to unwind the DNA

Question 10

What do DNA pol I and DNA pol III do?

Answer 10

DNA pol I: Composed of a single polypeptide

DNA pol III: Responsible for most of the DNA replication

Question 11

Primosome

Answer 11

DNA helicase and primase bind to each other to form a complex

Question 12

Replisome

Answer 12

The primosome is associated with two DNA polymerase holoenzymes to form this

Question 13

How does one terminate the replication of the chromosome?

Answer 13

the tus (termination utilization substance) protein binds to the ter sequences, which stops
the movement of the replication forks; NA replication ends when oppositely advancing
forks meet (usually at T1 or T2) and then DNA
ligase covalently links the two daughter strands

Question 14

DNA polymerase III can….

Answer 14

identify a mismatched nucleotide and remove it from the daughter strand; uses a 3’ to 5’ exonuclease activity to digest the newly made strand until the mismatched nucleotide is removed

Question 15

Name 3 ways DNA replication in eukaryotes is more complicated

Answer 15

• A number of large linear chromosomes must be replicated
• The chromatin is tightly packed within nucleosomes
• The cell cycle is more complicated

Question 16

Bacteria can have…as well

Answer 16

translesion-replicating (replicating across mutated DNA) DNA polymerases

Question 17

How does the cell solve telomeric repeat sequences?

Answer 17

by adding DNA sequences to the ends of telomeres that are recognized by the enzyme
telomerase