GRE Subject Test: Biochemistry, Cell, and Molecular Biology : Help with DNA Replication Proteins

Study concepts, example questions & explanations for GRE Subject Test: Biochemistry, Cell, and Molecular Biology

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Example Questions

Example Question #1 : Dna Replication And Repair

Which of the following is NOT a DNA repair mechanism?

Possible Answers:

Mismatch repair

Nucleotide excision repair

Binding-protein excision repair

Base excision repair

Correct answer:

Binding-protein excision repair

Explanation:

There are three main single-stranded DNA repair mechanisms.

The first is nucleotide excision repair. In this mechanism, specific endonuclease enzymes remove nucleotides containing damaged bases. DNA polymerase then replaces the region with undamaged bases, and ligase seals the addition with phosphodiester bonds.

The second mechanism is base excision repair. In this mechanism, glycosylase enzymes detect and excise damaged bases. DNA polymerase then replaces the region with undamaged bases, and ligase seals the addition with phosphodiester bonds.

Finally, there is mismatch repair. In this mechanism a new strand of DNA is tested for pairing with the template strand, prior to methylation. Any mismatched nucleotides are removed, replaced, and joined into the complete strand.

Example Question #2 : Dna Replication And Repair

Which of the following enzymes adds DNA to the ends of chromosomes to avoid loss of genetic material with duplication?

Possible Answers:

Primase

Telomerase

Helicase

Polymerase

Correct answer:

Telomerase

Explanation:

Telomeres are regions of non-coding DNA at the ends of the DNA strands. The telomeres function as regions of acquired damage and mutation, protecting the actual genome. Telomerase is the enzyme responsible for adding additional nucleotides to the 3' end of the chromosome to maintain the telomere.

Helicase unwinds the DNA helix and separates the strands to form the replication fork. Primase synthesizes short RNA primers on the DNA template to help recruit DNA polymerase, which then adds nucleotides to build the new DNA strand.

Example Question #3 : Dna Replication And Repair

What is the role of helicase?

Possible Answers:

Facilitates formation of phosphodiester bonds

Unwinds DNA template at the replication fork

Prevents DNA strands from reannealing

Nicks the DNA backbone to relieve supercoils

Correct answer:

Unwinds DNA template at the replication fork

Explanation:

Helicase is one of the first proteins necessary for initiating DNA replication. It is responsible for unwinding the DNA double-helix and separating the hydrogen bonds that hold the two strands together. This allows DNA polymerase to enter the replication fork and recruit nucleotides to build daughter DNA molecules.

Single-strand binding proteins attach to the DNA in the replication fork to prevent it from reannealing. Topoisomerase breaks phosphodiester bonds in the DNA backbone to relieve tension, while DNA ligase reestablishes these bonds after replication is complete and fuses Okazaki fragments on the lagging strand.

Example Question #4 : Dna Replication And Repair

Which of the following structures indicates where DNA replication begins?

Possible Answers:

Helicase

Replication fork

Origin of replication

DNA polymerase III

Correct answer:

Origin of replication

Explanation:

The origin of replication is the particular sequence in the genome where DNA replication begins. In prokaryotes, there is a single origin of replication, whereas there are multiple origins of replication in eukaryotes. At the origin of replication in eukaryotes, certain proteins bind to form the origin recognition complex. This complex is then used to recruit replication proteins and initiate the process of DNA replication.

Example Question #1 : Help With Dna Replication Proteins

__________ is the primary prokaryotic replicatory polymerase that can proofread DNA and fix incorrect base pairs due to its __________

Possible Answers:

DNA polymerase I . . . 3'-5' exonuclease function

DNA polymerase III . . . 3'-5' exonuclease function

DNA polymerase III . . . 3'-5' endonuclease function

DNA polymerase I . . . 3'-5' endonuclease function

Correct answer:

DNA polymerase III . . . 3'-5' exonuclease function

Explanation:

DNA polymerase III is the main replicatory polymerase in prokaryotic cells, responsible for synthesizing daughter DNA strands during replication. DNA polymerase I performs more specialized functions, such as synthesizing DNA during DNA repair pathways.

The difference between an endonuclease and an exonuclease is whether or not the cleavage takes place in the middle or at the end of a strand, respectively. DNA polymerase III is cleaving bases at the end of the strand, meaning it has exonuclease function.

Example Question #6 : Dna Replication And Repair

During DNA replication, single-stranded DNA is kept from reannealing due to the function of __________

Possible Answers:

single-strand binding proteins

helicase

DNA topoisomerase 

histones

Correct answer:

single-strand binding proteins

Explanation:

Single-strand binding proteins, as the name suggests, bind single-stranded DNA. This is important because it helps prevent the strands from reannealing prematurely. These proteins are essential for maintaining the replication fork.

Helicase is responsible for separating the strands at the replication fork, but is not directly responsible for preventing single-stranded DNA from reannealing. It creates the replication fork, but is incapable of maintaining it. DNA topoisomerase cuts the DNA backbone ahead of the replication fork to avoid topological problems. Histone proteins are removed during DNA replication, and are not involved in this process. 

Example Question #7 : Dna Replication And Repair

A select mutation is causing a cell lineage to be unable to replicate DNA successfully. When observed under a microscope, researchers observe that the DNA is able to be separated, but the template strands keep coming back together before the new strands can be replicated.

Based on this observation, which protein involved in DNA replication is most likely mutated?

Possible Answers:

DNA helicase

DNA primase

Single-stranded binding protein

DNA polymerase

Correct answer:

Single-stranded binding protein

Explanation:

Since the strands can be successfully "unzipped" from one another, this suggests that DNA helicase is working just fine. There is also nothing in the prompt that states the synthesis of new strands is not working, so DNA polymerase is fine as well. The problem involves keeping the strands separated for a long enough time. This is the job of single-stranded binding proteins. Because of this, we can argue that this protein is mutated in the cell.

All GRE Subject Test: Biochemistry, Cell, and Molecular Biology Resources

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