1. You isolate a cell strain in which the joining together of Okazaki fragments is impaired and suspect that a mutation has occurred in an enzyme found at the replication fork. The enzyme most likely to be mutated is__________, as this enzyme joins together Okazaki fragments.
Ligase/ligase
2. DNA replicates by which of the following models?
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conservative
semiconservative
dispersive
none of the above
semiconservative
3. What is the initial mechanism for repairing nucleotide errors in DNA?
mismatch repair
thymine dimers
DNA polymerase proofreading
nucleotide excision repair
DNA polymerase proofreading
4. The linear chromosomes in eukaryotes ensure that its ends are replicated completely because telomerase has an inbuilt RNA template that extends the 3′ end, so a primer is synthesized and extended, and the ends are protected.
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True
False
Ans: True
Correct. Telomerase has an inbuilt RNA template that extends the 3′ end, so a primer is synthesized and extended. Thus, the ends are protected.
5. Which of the following is the enzyme that replaces the RNA nucleotides in a primer with DNA nucleotides?
DNA polymerase III
DNA polymerase I
primase
helicase
Answer b. DNA polymerase I is the enzyme that replaces the RNA nucleotides in a primer with DNA nucleotides.
6. Which of the following is not involved in the initiation of replication?
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ligase
DNA gyrase
single-stranded binding protein
primase
Answer a. Ligase is not involved in the initiation of replication
7. Which of the following enzymes involved in DNA replication is unique to eukaryotes?
helicase
DNA polymerase
ligase
telomerase
Answer d. Telomerase is unique to eukaryotes
8. Which of the following would be synthesized using 5′-CAGTTCGGA-3′ as a template?
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3′-AGGCTTGAC-4′
3′-TCCGAACTG-5′
3′-GTCAAGCCT-5′
3′-CAGTTCGGA-5′
Answer c. 3′-GTCAAGCCT-5′
9. The enzyme responsible for relaxing supercoiled DNA to allow for the initiation of replication is called __.
DNA gyrase or topoisomerase II
10. Unidirectional replication of a circular DNA molecule like a plasmid that involves nicking one DNA strand and displacing it while synthesizing a new strand is called __.
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rolling circle replication
11. More primers are used in lagging strand synthesis than in leading strand synthesis.
True
False
True
12. When cell has stalled DNA replication fork, which checkpoint should be predominantly activated?
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M
Both G2/M and M
G1/S
G2/M
The correct option is C
Explanation of the correct answer:
Stalled forks activate checkpoint signaling and pause replication. Since, G1/S checkpoint checks DNA damage, cells size prior to S-phase (i.e. DNA replication phase). This checkpoint would be activated by stalled DNA replication fork.
13. Who proposed that dna replication is semiconservative?
Meselson and Stahl
Watson and Crick
The correct option is A
Explanation of the correct answer:
Meselson and Stahl Experiment was an experimental proof for semiconservative DNA replication. In 1958, Matthew Meselson and Franklin Stahl conducted an experiment on E.coli which divides in 20 minutes, to study the replication of DNA.
14. particular site at which dna replication starts….
single origin of replication
15. how many cycles of dna replication in meiosis?
One
Two
Three
No Replication Occurs
Correct option is A)
DNA replicates during the S phase of meiosis. During meiosis the cell passes only once through this phase and DNA synthesis by replication occurs only once during this phase. Hence, only one cycle of DNA replication occurs during meiosis.
So, the correct option is ‘one’.
16. When DNA replication starts
The leading strand produces Okazaki fragments.
The hydrogen bonds between the nucleotides of two strands break.
The phosphodiester bonds between the adjacent nucleotides break.
The bonds between the nitrogen base and deoxyribose sugar break.
Correct option is B)
Okazaki fragments are produced on lagging strand. DNA replication starts with unwinding of DNA duplexes which are held together by hydrogen bond. Helicases move along the double stranded DNA and separate the strands by breaking hydrogen bonds between base pairs. ATP hydrolysis provides the required energy for breaking of hydrogen bonds. DNA polymerase enzyme adds deoxyribonucleotides to primer by formation of phosphodiester bond betweenbetween the 3′ oxygen of a growing strand and alpha phosphate of a dNTP. Breaking of bond between nitrogen base and deoxyribose sugar is part of nucleotide catabolism; it does not occurs during DNA replication. Thus, the correct answer is option B.
17. the stage at which dna/chromosome replication occurs is
Prophase
Interphase
Metaphase
Previous telophase.
Correct option is B)
Interphase, a phase of the cell cycle, is the one in which a cell spends most of its life. During this phase, the cell copies its DNA in preparation for mitosis. The cell obtains nutrients, uses them to grow and conducts other “normal” cell functions. It was previously known as the resting phase although the cell is preparing for cell division at a later stage. It is divided into three phases:
1. G1 (first gap) – cell grows and functions normally. During G1, large amount of protein synthesis occurs and the cell grows (to approximately double its original size) – a number of organelles are produced and the volume of the cytoplasm increases. Also, certain intracellular components, such as the centrosomes undergo replication. It is an intermediate phase occupying the time between the end of cell division in mitosis and the beginning of DNA replication during S phase. During, G1, a review of the cellular environment occurs and only when the cell is ready, it enters the next phase. If not, cells enter G0 phase and can pause indefinitely at this phase.
2. S (synthesis) – the cell duplicates its DNA
3. G2 (second gap) – the cell resumes its growth in preparation for division
Hence, the correct answer is Option B.
18. enzyme which do not take part in dna replication is
DNA methyltransferase
DNA primase
DNA topoisomerase
DNA ligase
DNA polymerase helps in DNA dependent DNA synthesis i.e. replication. It is an enzyme that synthesis DNA molecules from deoxyribonucleotides, the building blocks of DNA.
DNA ligase helps in joining of Okazaki fragments together by catalyzing the formation of the phosphodiester bond. These fragments are formed in the lagging strand of DNA duplex.
DNA topoisomerase that helps in the overwinding or unwinding of DNA. It introduces negative and positive coils in the DNA during its replication process.
DNA primase is involved during replication to catalyze the synthesis of a short RNA segment complementary to a ssDNA template. It is a type of RNA polymerase.
DNA methyltransferase catalyzes the transfer of a methyl group to DNA.
So, the correct answer is ‘DNA methyltransferase’
19. which enzyme in dna replication has proofreading ability
Ligase
Helicase
Topoisomerase
DNA polymerase
Peptidyl transferase.
DNA polymerase
20. definite region in dna where replication starts is called
Promoter region
Origin of replication
Replication fork
Template strand
Origin of replication
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