Biology MCQ – MCQ on DNA Replication
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.
2. DNA replicates by which of the following models?
- none of the above
3. What is the initial mechanism for repairing nucleotide errors in DNA?
- mismatch repair
- thymine dimers
- DNA polymerase proofreading
- nucleotide excision repair
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.
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
6. Which of the following is not involved in the initiation of replication?
- DNA gyrase
- single-stranded binding protein
7. Which of the following enzymes involved in DNA replication is unique to eukaryotes?
- DNA polymerase
8. Which of the following would be synthesized using 5′-CAGTTCGGA-3′ as a template?
9. The enzyme responsible for relaxing supercoiled DNA to allow for the initiation of replication is called __.
11. More primers are used in lagging strand synthesis than in leading strand synthesis.
12. When cell has stalled DNA replication fork, which checkpoint should be predominantly activated?
- Both G2/M and M
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
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….
15. how many cycles of dna replication in meiosis?
- No Replication Occurs
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.
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
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 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
- DNA polymerase
- Peptidyl transferase.
20. definite region in dna where replication starts is called
- Promoter region
- Origin of replication
- Replication fork
- Template strand