MCQ Questions for Class 12 Biology Chapter 6 Molecular Basis of Inheritance
Q.1. Gene controls
(a) protein synthesis but not heredity
(b) protein synthesis and heredity
(c) heredity but not protein synthesis
(d) biochemical reaction of some enzymes
Answer
Answer: (b)Q.2. With regard to mature mRNA in eukaryotes
(a) exons and introns do not appear in the mature RNA
(b) exons appear but introns do not appear in the mature RNA
(c) introns appear but exons do not appear in the mature RNA
(d) both exons and introns appear in the mature RNA
Answer
Answer: (c)Q.3. DNA is a polymer of nucleotides which are linked to each other by 3′→ 5′ phosphodiester bond. To prevent polymerisation of nucleotides, which of the following modifications would you choose?
(a) Replace purine with pyrimidines
(b) Remove/replace 3′ OH group in deoxyribose
(c) Remove/replace 2′ OH group with some other group in deoxyribose
(d) Both ‘b’ and ‘c’
Answer
Answer: (b)Q.4. The human chromosome with the highest and least number of genes in them are respectively
(a) Chromosome 21 and Y
(b) Chromosome 1 and X
(c) Chromosome 1 and Y
(d) Chromosome X and Y
Answer
Answer: (d)Q.5. Who amongst the following scientists had no contribution in the development of the double helix model for the structure of DNA?
(a) Rosalind Franklin
(b) Maurice Wilkins
(c) Erwin Chargaff
(d) Meselson and Stahl
Answer
Answer: (d)Q.6. Discontinuous synthesis of DNA occurs in one strand, because
(a) DNA molecule being synthesised is very long
(b) DNA dependent DNA polymerase catalyses polymerisation only in one direction (5′ → 3′)
(c) it is a more efficient process
(d) DNA ligase joins the short stretches of DNA
Answer
Answer: (b)Q.7. Which of the following steps in transcription is catalysed by RNA polymerase?
(a) Initiation
(b) Elongation
(c) Termination
(d) All of the above
Answer
Answer: (b)Q.8. Which of the following statements is the most appropriate for sickle cell anaemia?
(a) It cannot be treated with iron supplements
(b) It is a molecular disease
(c) It confers resistance to acquiring malaria
(d) All of the above
Answer
Answer: (d)Q.9. Control of gene expression in prokaryotes take place at the level of
(a) DNA-replication
(b) Transcription
(c) Translation
(d) None of the above
Answer
Answer: (d)Q.10. Which of the following statements is correct about the role of regulatory proteins in transcription in prokaryotes?
(a) They only increase expression
(b) They only decrease expression
(c) They interact with RNA polymerase but do not affect the expression
(d) They can act both as activators and as repressors
Answer
Answer: (a)Q.11. Which was the last human chromosome to be completely sequenced?
(a) Chromosome 1
(b) Chromosome 11
(c) Chromosome 21
(d) Chromosome X
Answer
Answer: (d)Q.12. The promoter site and the terminator site for transcription are located at
(a) 3′ (downstream) end and 5′ (upstream) end, respectively of the transcription unit
(b) 5′ (upstream) end and 3′ (downstream) end, respectively of the transcription unit
(c) the 5′ (upstream) end
(d) the 3′ (downstream) end
Answer
Answer: (b)Q.13. If Meselson and Stahl’s experiment is continued for four generations in bacteria, the ratio of N15/N15: N15/N14: N14/N14 containing DNA in the fourth generation would be
(a) 1:1:0
(b) 1:4:0
(c) 0:1:3
(d) 0:1:7
Answer
Answer: (a)Q.14. Which of the following are the functions of RNA?
(a) It is a carrier of genetic information from DNA to ribosomes synthesizing polypeptides.
(b) It carries amino acids to ribosomes.
(c) It is a constituent component of ribosomes.
(d) All of the above.
Answer
Answer: (b)Q.15. While analysing the DNA of an organism a total number of 5386 nucleotides were found, out of which the proportion of different bases were: Adenine = 29%, Guanine = 17%, Cytosine = 32%, Thymine = 17%. Considering the Chargaff’s rule it can be concluded that
(a) it is a double stranded circular DNA
(b) it is single stranded DNA
(c) it is a double stranded linear DNA
(d) no conclusion can be drawn
Answer
Answer: (c)Q.16. In some viruses, DNA is synthesised by using RNA as template. Such a DNA is called
(a) A-DNA
(b) B-DNA
(c) cDNA
(d) rDNA
Answer
Answer: (d)Q.17. If the sequence of nitrogen bases of the coding strand of DNA in a transcription unit is:
5′ – A T G A A T G – 3′, the sequence of bases in its RNA transcript would be
(a) 5′ – A U G A A U G – 3′
(b) 5′ – U A C U U A C – 3′
(c) 5′ – C A U U C A U – 3′
(d) 5′ – G U A A G U A – 3′
Answer
Answer: (a)Q.18. Polysome is formed by
(a) a ribosome with several subunits
(b) ribosomes attached to each other in a linear arrangement
(c) several ribosomes attached to a single mRNA
(d) many ribosomes attached to a strand of endoplasmic reticulum.
Answer
Answer: (c)Q.19. In E.coli, the lac operon gets switched on when
(a) lactose is present and it binds to the repressor
(b) repressor binds to operator
(c) RNA polymerase binds to the operator
(d) lactose is present and it binds to RNA polymerase
Answer
Answer:Q.20. Amino acid sequence, in protein synthesis is decided by the sequence of
(a) rRNA
(b) tRNA
(c) mRNA
(d) cDNA
Answer
Answer: (c)Q.21. What is not true for genetic code?
(a) It is nearly universal.
(b) It is degenerate.
(c) It is unambiguous
(d) A codon in mRNAt is read in a non-contiguous fashion.
Answer
Answer: (d)Q.22. The net electric charge on DNA and histones is
(a) both positive
(b) both negative
(c) negative and positive, respectively
(d) zero
Answer
Answer: (c)Q.23. Antiparallel strands of a DNA molecule means that
(a) one strand turns clockwise
(b) one strand turns anti-clockwise
(c) the phosphate groups of two DNA strands, at their ends, share the same position
(d) the phosphate groups at the start of two DNA strands are in opposite position (pole).
Answer
Answer: (d)Q.24. In the DNA molecule
(a) the proportion of adenine in relation to thymine varies with the organism
(b) there are two strands which run antiparallel—one in 5l ” 3l direction and other in 3l ” 5l
(c) the total amount of purine nucleotides and pyrimidine nucleotides is not always equal
(d) there are two strands which run parallel in the 5l ” 3l direction.
Answer
Answer: (b)Q.25. Removal of introns and joining the exons in a defined order in a transcription unit is called
(a) tailing
(b) transformation
(c) capping
(d) splicing
