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Example Questions
Example Question #1171 : Biochemistry
Which of the following enzymes relieves the tension that is created due to DNA coiling?
Topoisomerase
RNA polymerase
DNA polymerase
Helicase
Primase
Topoisomerase
A double helix DNA structure can be coiled or even supercoiled. In order to relieve the tension that is inevitably formed by this coiling, topoisomerase acts upon the DNA to relieve the stress that has been created. Helicase unwinds DNA before replication. DNA polymerase elongates the DNA during replication. RNA polymerase makes RNA from a template strand of DNA. Primase creates a temporary primer to begin DNA synthesis/replication.
Example Question #33 : Anabolic Pathways And Synthesis
DNA replication is an important process that allows hereditary information to be passed to new cells. As such, there are a variety of enzymes that are crucial to this process. Helicase is one such enzyme. What is the function of helicase in DNA replication.
Holds the parent DNA strands in place during replication to prevent them from associating with one another
Stitches together the various daughter DNA fragments into a single strand
Lays down an RNA primer so that the synthesis of complementary daughter DNA can occur
Separates the two parental strands of DNA by breaking hydrogen bonds
Separates the two parental strands of DNA by breaking hydrogen bonds
In DNA replication, the role of helicase is to unwind the strand by breaking the hydrogen bonds that hold that two strands together.
All of the other answer choices describe a role performed by a different DNA replication enzyme. Let's go ahead and review these.
- Lays down an RNA primer so that the synthesis of complementary daughter DNA can occur
This enzyme is called Primase.
- Stitches together the various daughter DNA fragments into a single strand
This enzyme is called DNA Ligase. It is able to join the okazaki fragments formed on the lagging strand, as well as any other areas where there is a break in the strand.
- Holds the parent DNA strands in place during replication to prevent them from associating with one another
This enzyme is known as single-strand binding protein.
Example Question #11 : Nucleic Acid Synthesis
Which DNA polymerase excises RNA primer with a exonuclease?
DNA polymerase I
DNA polymerase II
DNA polymerase is not associated with the exonuclease
DNA polymerase III
DNA polymerase I
DNA polymerase I is in prokaryotes only. It degrades the RNA primer and fills in the gap with DNA. DNA polymerase III has synthesis and proofreads with exonuclease. This is also in prokaryotes only. It elongates the leading strand by adding deoxynucleotides to the 3’ end. It elongates the lagging strand until it reaches primer of preceding fragment. exonuclease activity “proofreads” each added nucleotide. The function of DNA polymerase II is unknown.
Example Question #13 : Dna Replication
Given the DNA sequence, what is the correct synthesis?
DNA sequence: TCGGTCAAG
5' CTTGACCGA
3' GATTGACCT
5' TCCAGTTAG
5' AGCCAGTTC
5' CTTGACCGA
Remember, it’s complementary and antiparallel. Therefore, when writing the complement of the DNA sequence, it’s 3’ to 5’, so you must change answer to be 5’ to 3’.
Example Question #11 : Nucleic Acid Synthesis
In DNA replication, which is true regarding ribonucleotide reductase?
Ribonucleotide reductase is inhibited by hydroxyurea
Ribonucleotide reductase converts ribonucleotide diphosphate to deoxyribonucleotide diphosphate
Deoxythymidine diphosphate is not a substrate for ribonucleotide reductase
All of these
Ribonucleotide reductase regulates the rate of DNA synthesis
All of these
Ribonucleotide reductase regulates the rate of DNA synthesis and the total DNA to cell mass ratio. The enzyme converts adenosine diphosphate (ADP), guanosine diphosphate (GDP), cytidine diphosphate (CDP), uridine diphosphate (UDP). The ribonucleotide thymidine diphosphate is not a substrate for this enzyme. Thymidine nucleotides are products of another enzyme: thymidylate kinase.
Example Question #12 : Nucleic Acid Synthesis
Which amino acids are required for the the synthesis of adenine and guanine (purines) from ribose?
I. Lysine
II. Aspartate
III. Glutamine
IV. Glycine
II and IV
I, II, III, and IV
II, III, and IV
II and III
I, II, and III
II, III, and IV
Purines can be synthesized de novo from ribose phosphate. 5-phosphoribosylamine is converted to inosine monophosphate, which is an intermediary for adenine monophosphate and guanine monophosphate production. The reaction requires the presence of glycine, aspartate and glutamine, but not lysine.
Example Question #12 : Nucleic Acid Synthesis
Which of the following regarding phosphoribosyl pyrophosphate (PRPP) in nucleotide synthesis necessary for DNA replication is true?
All of these
PRPP is formed from ribose-5-phosphate by PRPP synthase
Increased levels of PRPP can cause an increase in uric acid and produce gout
PRPP is the precursor of purines
PRPP is the precursor of pyrimidines
All of these
Phosphoribosyl pyrophosphate (PRPP) is a precursor of both purines (adenine and guanine), as well as pyrimidines (cytosine, uracil, and thymine) in nucleotide synthesis. In certain enzyme deficiencies, levels of PRPP can increase leading indirectly to uric acid production and gout.
Example Question #13 : Nucleic Acid Synthesis
In DNA replication and repair what is the role of nucleases?
Nucleases can be exonucleases or endonucleases
Nucleases can remove mispaired nucleotides
All of these
Nucleases may remove nucleotides from the ends of DNA or from within the molecule of DNA
Nucleases hydrolyze phosphodiester bonds in DNA
All of these
Nucleases are important in excision of nucleotides from the DNA chain. Phosphodiester bonds between two nucleotides are broken and the DNA chain becomes fragmented. Site-specific nucleases can function as restriction enzymes cutting phosphodiester bonds at specific locations inside the DNA molecule. In DNA repair they remove nucleotides incorrectly placed during DNA synthesis.
Example Question #14 : Nucleic Acid Synthesis
In DNA replication, in bacteria, what is the role of the DnaA protein?
In bacteria, DnaA replaces DNA with RNA
In bacteria, DnaA recognizes the base sequence at the origin of replication
In bacteria, DnaA protein synthesizes RNA primers
In bacteria, DnaA protein stabilizes unwound template strands
In bacteria, DnaA unwinds the DNA double helix
In bacteria, DnaA recognizes the base sequence at the origin of replication
DnaA protein in bacteria binds to a base pair sequence at the origin of replication serving as an initiation factor for DNA synthesis. All the other answers are wrong as: helicase, not DnaA protein unwinds DNA; single-stranded DNA binding protein stabilizes separated DNA strands; primase synthesizes RNA primers; and DNA polymerase I replaces RNA with DNA.
Example Question #15 : Nucleic Acid Synthesis
Which of the following enzymes joins together the Okazaki fragments in the lagging strand during DNA replication?
DNA ligase
DNA topoisomerase
DNA polymerase
DNA primase
DNA gyrase
DNA ligase
Because the lagging strand is created in various separate segments during DNA replication, after polymerization they must be joined together by an enzyme. The enzyme that is responsible for these connections is DNA ligase.