MCQs on DNA

1. The accepted hypothesis for DNA replication is

A. Conservative theory
B. Dispersive theory
C. Semi-conservative theory
D. Evolutionary theory

Answer: C

2. When DNA polymerase is in contact with guanine in the parental strand, what does it add to the growing daughter strand?

A. Phosphate
B. Cytosine
C. Uracil
D. Guanine

Answer: B

3. Telomeres are usually rich in which nucleotide?

A. Adenine
B. Guanine
C. Thymine
D. Cytosine

Answer: B

4. Which is the largest among the followings?

A. Nucleotide
B. Nitrogenous base
C. Phosphate
D. Carbon

Answer: A

5. The chromosomal DNA complexes with

A. Three types of histone as H1, H2A and H4
B. Five types of histone as H1, H2A, H2B, H3 and H4
C. Four types of histone as H1, H2A, H3 and H4
D. Two types of histone as H1 and H4

Answer: B

6. Taylor, Woods and Hughes labeled Vicia DNA by allowing new DNA synthesis in the presence of radioactive thymine. After DNA replication (S phase of the cell cycle), it was observed that

A. Only one chromatid of a chromosome was labeled
B. Both chromatids of a chromosome were labeled
C. Both (a) and (b)
D. Neither chromatid was labeled

Answer: B

7. In DNA double helix, the two DNA chains are held together by

A. Covalent bonds between the pair of bases
B. Hydrogen bonds between the pair of bases
C. Ionic bonds between the pair of bases
D. None of the above

Answer: B

8. The 5′ and 3′ numbers are related to the

A. Length of the DNA strand
B. Carbon number in sugar
C. The number of phosphates
D. The base pair rule

Answer: B

9. Messelsen and Stahl model of replication was called

A. Conservative replication
B. Semi-conservative replication
C. Dispersive replication
D. Cri du Chat

Answer: B

10. The most common liquid volumes in molecular biology are measured in

A. ml
B. μl
C. nl
D. 1

Answer: B

11. DNA replication takes place in which direction?

A. 3′ to 5′
B. 5′ to 3′
C. Randomly
D. Vary from organism to organism

Answer: B

12. DNA gyrase in E. coli

A. Adds positive supercoils to chromosomal DNA
B. Can be inhibited with antibiotics
C. Is required only at the oriC site
D. Performs the same function as helicase in eukaryotes

Answer: B

13. In DNA, there are

A. Five bases known as adenine, guanine, thymine, tryptophan and cytosine
B. Four bases known as adenine, guanine, thymine and cytosine
C. Three bases known as adenine, guanine and cytosine
D. Only two bases known as adenine and cytosine

Answer: B

14. In DNA, guanine pairs with

A. Adenine
B. Cytosine
C. Thymine
D. Uracil

Answer: B

15. Which of the following is incorrect?

A. In DNA double helix, two strands of the DNA are bound with each other with the bases
B. Adenine always pairs with thymine
C. Guanine always pairs with the cytosine
D. None of the above

Answer: D

16. What is the only common methylation in the DNA of eukaryotes?

A. Adenosine in GpA dinucleotides
B. Guanosine in ApGpA trinucleotides
C. Cytosine in CpG dinucleotides
D. None of the above

Answer: C

17. DNAs when charged, migrate in a gel towards the

A. Positive pole
B. Negative pole
C. Will not migrate
D. None of these

Answer: A

18. What is the approximate size (in kb) of the E. coli genome?

A. 3000 kilobase
B. 4500 kilobase
C. 5500 kilobase
D. 6500 kilobase

Answer: B

19. In the study of one experiment it was found that the value of Tm for DNA is = 40° C. If the cell has 20% GC at the above Tm, then what will be value of ‘Tm’ if the GC% increases to 60%?

A. Remains same
B. Increases
C. Decreases
D. Can not be compared

Answer: B

20. What is the range of melting point temperatures (Tm) for most DNA molecules?

A. 50 to 60°C
B. 60 to 80°C
C. 70 to 90°C
D. 80 to l00°C

Answer: D

21. The overall conclusion of the Hershey-Chase experiment was that

A. DNA was responsible for heredity
B. Proteins and DNA were responsible for heredity
C. The ratio of Adenine to thymine was always the same
D. Phage DNA was similar to bacterial DNA

Answer: A

22. A cesium chloride will separate DNA molecules by

A. Absorption
B. Resorption
C. Density
D. Adhesion

Answer: C

23. If one cell has AT contents 40%, what will be the percentage of Guanine residue?

A. 60%
B. 15%
C. 30%
D. Guanine residue can not be calculated

Answer: C

24. Which of the following enzyme adds complementary bases during replication?

A. Helicase
B. Synthesase
C. Replicase
D. Polymerase

Answer: D

25. Which DNA polymerase removes RNA primers in DNA synthesis?

A. Polymerase I
B. Polymerase II
C. Polymerase III
D. None of these

Answer: A

26. Enzymes, responsible for unraveling short segments of DNA is

A. DNA polymerase
B. Helicase
C. DNA ligase
D. Primase

Answer: B

27.  Enzyme, responsible for proofreading base pairing is

A. DNA polymerase
B. Telomerase
C. Primase
D. DNA ligase

Answer: A

28. Which of the following would not contain DNA?

A. Yeast
B. Bacteria
C. Glass crystals
D. Mold

Answer: C

29. The nucleosome consists of histone

A. Octamer and 146 bp of DNA
B. Tetramer and 146 bp of DNA
C. Hexamer and 146 bp of DNA
D. None of the above

Answer: A

30. What bands will be observed in a cesium chloride gradient after two rounds of replication?

A. One light, one medium and one heavy band
B. One light and one medium band
C. One medium band
D. One medium and one heavy band

Answer: B

31. Proteins involved in opening a replication bubble are

A. DNA helicases
B. Single stranded binding proteins
C. Ligase
D. DNA topoisomerase

Answer: D

32. What is the main damaging effect of UV radiation on DNA?

A. Depurination
B. Formation of thymine dimers
C. Single strand break
D. Dehydration

Answer: B

33. The higher order structure of DNA shows symmetry, whereas the higher order structures of most proteins do not. Why isn’t protein shape more regular like DNA?

A. DNA has one main function in cells whereas proteins have many.
B. The many different amino acid R groups on proteins confer many different shapes.
C. Some S amino acids cause proteins to bend; others cause protein to flatten.
D. All of the above

Answer: D

34. DNA helicase is used to

A. Unwind the double helix
B. Interact the double helix closely
C. Break a phosphodiester bond in DNA strand
D. None of the above

Answer: A

35. Klenow fragment without free nucleotides exhibits

A. Exonuclease activity
B. Endonuclease activity
C. Nickase activity
D. No activity

Answer: A

36. E.coli DNA polymerases II and III lack

A. 5′ → 3′ exonuclease activity
B. 5′ → 3′ endonuclease activity
C. Partially 5′ → 3′ exonuclease activity
D. Partially 5′ → 3′ endonuclease activity

Answer: A

37.  In sperm heads, DNA is particularly highly condensed and the histones are replaced with small basic protein called

A. Protamines
B. Purines
C. Pyrimidines
D. All of the above

Answer: A

38. Okazaki fragments occur during

A. Transformation
B. Replication
C. Polymerase reaction
D. Synthesis

Answer: B

39. DNA can be sequenced by the

A. Chemical method
B. Chain termination procedure
C. Both (a) and (b)
D. Physical method

Answer: C

40. Which histone(s) are associated with the linker DNA of a nucleosome?

A. Histone H1
B. Histones H2A and H2B
C. Histone H3
D. Histone H4

Answer: A

41.  Each replication bubbles consists of

A. 3 replication forks
B. 2 replication forks
C. 4 replication forks
D. 1 replication forks

Answer: B

42. In DNA replication, one new strand is synthesized complementary to an old (parent) strand and is referred as

A. Mutational
B. Semiconservative
C. Discontinuous
D. Antiparallel

Answer: B

43.  In a cesium chloride gradient, DNA labeled with 15N and centrifuged will form a band

A. Above DNA containing 14N
B. Below DNA containing 14N
C. With 14N-containing DNA
D. All of these

Answer: B

44. The role of primase is to

A. Dismantle RNA primer
B. Cleave and unwinds short sections of DNA ahead of the replication fork
C. Proofread base pairing
D. Synthesize an RNA primer to begin the elongation process

Answer: D

45. Deoxyribonucleoside triphosphates, being need in the chain termination methods are

A. dATP
B. dGTP and dCTP
C. dTTP
D. All of these

Answer: D

46.  What is the approximate percentage of repetitive DNA sequences in human DNA?

A. 10 to 20%
B. 20 to 30%
C. 30 to 40%
D. 40 to 50%

Answer: B

47. The replication of a linear DNA molecule in a eukaryotic chromosome creates a problem which is reported to be sorted out by

A. Using enzyme called telomerase
B. Shortening of the double stranded replicated portion
C. Using RNA as a template
D. None of the above

Answer: A

48.  The rapid appearance of HIV-1 strains that are resistant to AIDS drugs is due in part to which of the following property of its reverse transcriptase?

A. AZT (zidovudine) is too expensive to be taken in effective doses
B. The RNase H domain of p66 causes error prone synthesis
C. It lacks a proofreading exonuclease
D. It has low affinity for the correct dNTP’s

Answer: C

49.  The packing ratio of nucleosomes is about

A. 6
B. 8
C. 7
D. 9

Answer: C

50. After one replication in 15N, how many bands should be observed in a cesium chloride gradient?

A. One
B. Two
C. Three
D. A smear

Answer: A