Question 1

Which enzyme seals nicks and joins Okazaki fragments?&#10;a.DNA polymerase I&#10;b.DNA gyrase&#10;c.DNA primase&#10;d.DNA ligase&#10;e.DNA helicase

Accepted Answer

DNA ligase is responsible for sealing nicks and joining Okazaki fragments during DNA replication. It catalyzes the formation of a phosphodiester bond between adjacent nucleotides in the DNA strand, thereby completing the formation of the new strand. The other enzymes listed do not have this specific function.

Question 2

Mismatch repair requires the ability to distinguish between template and newly synthesized DNA strands.How can E.coli distinguish between these two strands?
a.Template DNA is methylated.
b.New DNA is methylated.
c.Template DNA is phosphorylated.
d.New DNA is phosphorylated.
e.New DNA contains single-stranded binding proteins.

Template DNA is methylated.

Accepted Answer

In E.coli, template DNA is methylated, while new DNA is not methylated. The mismatch repair system uses this difference to distinguish between the two strands and remove any mismatches in the new DNA strand to ensure proper replication fidelity.

Question 3

Okazaki fragments are found associated with&#10;a.the leading strand.&#10;b.the lagging strand.&#10;c.both the leading and the lagging strands.&#10;d.the base of the replication fork.

Accepted Answer

Okazaki fragments are short, discontinuous segments of DNA that are synthesized on the lagging strand during DNA replication. Therefore, they are only found associated with the lagging strand.

Question 4

You identify a mutant whose chromosomes shorten after each round of replication.A mutation in which gene would explain this observation?
a.DNA polymerase
b.telomerase
c.DNA ligase
d.DNA gyrase

Accepted Answer

Telomerase is responsible for maintaining the length of telomeres (the ends of chromosomes) during DNA replication. Without telomerase activity, the telomeres shorten with each round of replication, eventually leading to cellular senescence or death. Therefore, a mutation in the telomerase gene would explain the observed shortening of chromosomes. Mutations in DNA polymerase, DNA ligase, or DNA gyrase would not directly affect telomere length.

Question 5

DNA polymerase requires a 3' OH group provided by a primer before it can begin DNA synthesis.How is it that the primer can be synthesized on the DNA without a 3' OH group?
a.The primer is RNA-synthesized by RNA polymerase,which does not require a 3' OH group.
b.These primers require an even shorter primer sequence.
c.The primer uses an artificial 3' OH group provided by a unique enzyme.
d. Primers use a 5' OH group.

Accepted Answer

The primer is synthesized by RNA polymerase, which can add nucleotides to the 3' end of the RNA molecule without the need for a 3' OH group. The RNA primer is then later converted to DNA by DNA polymerase, which can add nucleotides to the 3' end of the DNA molecule using the RNA primer as a starting point.

Question 6

During replication,what is the role of helicase?
a.It joins Okazaki fragments on the lagging strand.
b.It stabilizes the single-stranded DNA.
c.It reduces torsional strain by making double-stranded DNA breaks.
d.It replicates the DNA.
e.It breaks hydrogen bonds between the two DNA strands.

Accepted Answer

Helicase breaks the hydrogen bonds between the two DNA strands, separating them and allowing the unwinding of the double helix for DNA replication to occur.

Question 7

Eukaryotic DNA replication is similar to prokaryotic DNA replication.However,eukaryotes require unique replication strategies because of unique features of eukaryotic DNA.Which is NOT a unique feature linked to replication strategies?
a.Eukaryotic chromosomes are linear.
b.Eukaryotic chromosomes contain histone proteins.
c.Eukaryotic DNA contains introns.
d.Because of its size,eukaryotic DNA requires several replication forks.

Accepted Answer

The presence of introns in eukaryotic DNA is not directly linked to replication strategies. It is a unique feature of eukaryotic genes and their expression, but does not affect the replication process itself.

Deck 9: DNA Replication