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Molecular Basis of Inheritance Class 12 Biology MCQs Pdf
1. The DNA site where DNA-dependent RNA- polymerase binds for transcription, is called
(a) operator
(b) promotor
(c) regulator
(d) receptor
Answer
Answer: b
2. Operon model for regulation of transcription was proposed by
(а) Meselson and Stahl
(b) Jacob and Monod
(c) Watson and Crick
(d) Hershey and Chase
Answer
Answer: b
3. Eukaryotic RNA polymerase III catalyses the synthesis of
(a) mRNA
(b) rRNA
(c) hnRNA
(d) tRNA
Answer
Answer: d
4. The sequence of nitrogen bases in a # segment of a coding strand of DNA is ’ AATGCTTAGGCA. What will be the
sequence of nitrogen bases in the wRNA transcribed by it?
(a) UUA CGA AUC CGU
(b) AAU GCU AAC CGA
(c) AAU GCA AUC CGU
(d) AAU GCU UAG GCA
Answer
Answer: d
5. In the lac operon of E.coli, the i gene codes for
(a) inducer
(b) repressor
(c) lactase
(d) β-galactosidase
Answer
Answer: b
6. Which of the following sets of codons contains only termination codons?
(a) UAA, UGA, UAG
(b) UAA, UUU, UGG
(c) UAA, UAG, UAC
(d) UUU, UCC, UGG
Answer
Answer: a
7. The central dogma of molecular biology (genetic information flow) was modified by the discovery of
(a) RNA polymerase
(b) DNA ligase
(c) Reverse transcriptase
(d) DNA polymerase
Answer
Answer: c
8. The fact that a purine base always paired through hydrogen bonds with a pyrimidine base leads to, in the DNA double helix [NCERT Exemplar]
(a) the antiparallel nature
(b) the semiconservative nature
(c) uniform width throughout DNA
(d) uniform length in all DNA.
Answer
Answer: bc
9. The promoter site and the terminator site for transcription are located at [NCERT Exemplar]
(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
10. The human chromosome with the highest and least number of genes in them are respectively [NCERT Exemplar]
(a) Chromosome 21 and Y
(b) Chromosome 1 and X
(c) Chromosome 1 and Y
(d) Chromosome X and Y
Answer
Answer: c
11. Discontinuous synthesis of DNA occurs in one strand, because [NCERT Exemplar]
(a) DNA molecule being synthesised is very long.
(b) DNA dependent DNA polymearse catalyses polymerisation only in one direction (5′ → 3′).
(c) it is a more efficient process.
(d) DNA ligase has to have a role.
Answer
Answer: b
12. Which of the following are the functions of RNA? [NCERT Exemplar]
(a) It is a carrier of genetic information from DNA to ribosomes synthesising polypeptides.
(b) It carries amino acids to ribosomes
(c) It is a constituent component of ribosomes
(d) All of the above.
Answer
Answer: d
13. In E.coli, the lac operon gets switched on when [NCERT Exemplar]
(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: a
14. The net electric charge on DNA and histone, is
(a) positive, negative
(b) negative, positive
(c) negative, negative
(d) positive, positive.
Answer
Answer: b
15. If the sequence of the nitrogen bases in the coding strand of DNA is 5’- ATGAATT-3’, the sequence of bases in the RNA transcribed by it will be ______ .
Answer/Explanation
Answer:
Explaination: 3’ AUGAAUU 5’
16. _____ step in transcription is catalysed by the enzyme DNA-dependent RNA polymerase.
Answer/Explanation
Answer:
Explaination: Elongation.
17. Lac operon shows the control of gene expression at the _____ level, in E.coli.
Answer/Explanation
Answer:
Explaination: Transcription.
18. The enzyme DNA polymerase catalyses the polymerisation of nucleotides in the ______ direction, for the lagging strand.
Answer/Explanation
Answer:
Explaination: 5′ → 3′
19. The last chromosome to be completely sequenced in the Human Genome Project (HGP) is ______ .
Answer/Explanation
Answer:
Explaination: Chromosome 1
20. RNA polymerase II in eukaryotes catalyses the transcription of ______ .
Answer/Explanation
Answer:
Explaination: hnRNA.
21. The presence of ______ group in every ribonucleotide makes RNA labile and reactive.
Answer/Explanation
Answer:
Explaination: 2′-OH.
22. Meselson and Stahl experimentally proved the _____ replication of DNA.
Answer/Explanation
Answer:
Explaination: Semiconservative.
23. During splicing in eukaryotes, the _____ are joined to from the RNA.
Answer/Explanation
Answer:
Explaination: Exons.
24. _____ factor functions as the initiation factor in the transcription of prokaryotes.
Answer/Explanation
Answer:
Explaination: Sigma (a)
25. Match the terms in Column I with those in Column II.
| Column I | Column II |
| A. Transcription | 1. A set of three bases on tRNA that is complementary to the bases of codon on mRNA. |
| B. Anticodon | 2. A unit of DNA that codes for a polypeptide. |
| C. Cistron | 3. Process of synthesis of polypeptide as dictated by mRNA. |
| D. Translation | 4. Process by which mRNA carries the information from nucleus to ribosomes. |
Answer/Explanation
Answer:
Explaination: A – 4, B – 1, C – 2, D – 3
26. Match the codons in Column I with the amino acids in Column II.
| Column I | Column II |
| A. UUU | 1. Termination |
| B. AUG | 2. Tyrosine |
| C. UAA | 3. Phenylalanine |
| D. AGU | 4. Methionine |
| E. UAC | 5. Serine |
Answer/Explanation
Answer:
Explaination: A – 3, B – 4, C – 1, D – 5, E – 2
27. Polycistronic mRNA is generally found in eukaryotes. [True/False]
Answer/Explanation
Answer:
Explaination: False.
28. The process of translation of mRNA begins, when the mRNA encounters the large subunit of ribosome [True/False]
Answer/Explanation
Answer:
Explaination: False.
29. VNTR belongs to a class of satellite DNA, called micro-satellite. [True/False]
Answer/Explanation
Answer:
Explaination: False.
30. If a double-stranded DNA contains 20% cytosine, it will have 20% guanine in it. [True/False]
Answer/Explanation
Answer:
Explaination: True.
31. Termination/Stop codons do not have any tRNAs [True/False]
Answer/Explanation
Answer:
Explaination: True.
Directions (Q32 to Q35): Mark the odd one in each of the following groups.
32. UAA, UGG, UAG, UGA
Answer/Explanation
Answer:
Explaination: UGG
33. 5S rRNA, snRNA, hnRNA, tRNA
Answer/Explanation
Answer:
Explaination: hnRNA
34. Har Gobind Khorana, Marshal Nirenberg, Severo Ochoa, Alec Jeffreys.
Answer/Explanation
Answer:
Explaination: Alec Jeffreys.
35. Promoter, Inducer, Operator, Terminator.
Answer/Explanation
Answer:
Explaination: Inducer.
36. Name the two types of nucleic acids in living systems.
Answer/Explanation
Answer:
Explaination: Deoxyribonucleic acid and ribonucleic acid.
37. How is the length of DNA usually defined?
Answer/Explanation
Answer:
Explaination:
Length of DNA is defined as the:
(i) number of nucleotides in single-stranded DNA, and
(ii) number of pairs of nucleotides (base pairs) in double-stranded DNA.
38. Name the specific components and the linkage between them that form deoxyadenosine. [Delhi 2013C]
Answer/Explanation
Answer:
Explaination: The nitrogenous base, adenine is linked to deoxyribose sugar through N-glycosidic linkage.
39. Name the specific components and the linkages between them that form deoxy- guanosine. [All India 2013C]
Answer/Explanation
Answer:
Explaination: The nitrogenous base guanine is linked to deoxyribose sugar by N-glycosidic linkage.
40. In which position is the phosphate group linked to a nucleoside? Name the linkage too.
Answer/Explanation
Answer:
Explaination:
– A phosphate group is linked to the 5′-OH of a nucleoside.
– Phosphoester linkage.
41. Name the components ‘a’ and ‘b’ in the nucleotide with a purine, given below:
Answer/Explanation
Answer:
Explaination:
a – Phosphate group,
b – Nitrogenous base
42. Mention the carbon positions to which the nitrogenous base and the phosphate molecule are respectively linked in the nucleotide given below:
Answer/Explanation
Answer:
Explaination:
– Nitrogenous base at the first carbon.
– Phosphate at the fifth carbon.
43. Mention the position of the ribonucleotide, where the OH group is present.
Answer/Explanation
Answer:
Explaination: The OH-group is present at the 2′-position.
44. Who discovered the nucleic acid DNA? What was it called then?
Answer/Explanation
Answer:
Explaination:
Frederich Meischer discovered DNA.
It was called nuclein.
45. The two strands of DNA have antiparallel polarity. What does it mean?
Answer/Explanation
Answer:
Explaination:
It means that one of the strands of DNA has
5′ → 3′ polarity and the other strand has
3′ → 5′ polarity.
46. If the base adenine constitutes 30 per cent of an isolated DNA fragment, then what is the expected percentage of the base cytosine in it? [Delhi 2011C; HOTS]
Answer/Explanation
Answer:
Explaination: 20 per cent.
47. How does the flow of genetic information in HIV7 deviate from the ‘central dogma’ proposed by Francis crick? [Foreign 2013]
Answer/Explanation
Answer:
Explaination: HIV shows reverse transcription, i.e. formation of DNA on RNA template.
48. How does HIV differ from a bacteriophage? [Delhi 201OC]
Answer/Explanation
Answer:
Explaination: HIV has RNA as its genome and shows reverse transcription, while bacteriophage has double-stranded DNA as its genome and no reverse transcription.
49. How is the length of DNA usually calculated?
Answer/Explanation
Answer:
Explaination: The length of DNA is calculated by multiplying the total number of base pairs with the distance between two consecutive base pairs, which is 0.34 nm or 0.34 × 10-9 m.
50. How may base pairs would a DNA segment of length 1.36 mm have? [Foreign 2017]
Answer/Explanation
Answer:
Explaination: It will have 1.36/0.34 × 10-9bp, i.e., 4.6 × 106bp.
51. What is a nucleoid?
Answer/Explanation
Answer:
Explaination: Nucleoid is the region in prokaryotic cells where DNA is organised as large loops held by some positively-charged proteins.
52. Name the positively charged protein around which the negatively charged DNA is wrapped. [AH India 2010C]
Answer/Explanation
Answer:
Explaination: Histone.
53. Name two basic amino acids that provide positive charge to histone proteins. [Delhi 2012C]
Answer/Explanation
Answer:
Explaination: Lysine and Arginine.
54. Write the role of histone proteins in packaging of DNA in eukaryotes. [Foreign 2017]
Answer/Explanation
Answer:
Explaination:
– Histone proteins are positively charged and are organized to from a unit of eight molecules, called a histone octamer,
– The negatively charged DNA molecule (of about 200 bp) wraps around the histone octamer to form a nucleosome, the repeating unit of chromatin.
55. Name the negatively charged and positively charged components of a nucleosome. [Delhi 2015C]
Answer/Explanation
Answer:
Explaination: Negatively charged component – DNA Positively charged component – histones.
56. Name the transcriptionally active region of chromatin in a nucleus. [Delhi 2015]
Answer/Explanation
Answer:
Explaination: Euchromatin.
57. Define transformation.
Answer/Explanation
Answer:
Explaination: Transformation is a phenomenon by which , the DNA isolated from one type of cell,
when introduced into another type, is able to bestow some of the properties of the former to the latter.
58. Write the conclusion Griffith arrived at, at the end of his experiments with Streptococcus pneumoniae. [All India 2017C]
Answer/Explanation
Answer:
Explaination:
– Griffith concluded that the R strain/non-virulent bacteria had been transformed y. into virulent form by the heat-killed S strain bacteria.
– It must be due to transfer of a transforming principle, i.e., genetic material from the heat-killed S strain bacteria.
59. What are bacteriophages?
Answer/Explanation
Answer:
Explaination: Bacteriophages are those viruses which infect the bacteria.
60. Why is RNA more reactive in comparison to DNA? [Delhi 2015CJ
Or
Why do RNA viruses undergo mutation and evolution faster than most of the DNA viruses? [HOTS]
Answer/Explanation
Answer:
Explaination: The 2′ OH-group in the nucleotides of RNA is a reactive group, that makes RNA labile 7- and easily degradable.
61. Write the scientific name of the plant on which Taylor et al performed their experiments.
Answer/Explanation
Answer:
Explaination: Vicia faba.
62. How long does the replication of human DNA take place?
Answer/Explanation
Answer:
Explaination: 38 minutes.
63. Name the enzyme and state its property that is responsible for continuous and discontinuous replication of the two strands of a DNA molecule. [Delhi 2013]
Answer/Explanation
Answer:
Explaination:
DNA-polymerase
– It polymerises the nucleotides only in 5′ → 3′ direction.
64. What is a replication fork?
Answer/Explanation
Answer:
Explaination: Replication fork is the Y-shaped structure formed when the double-stranded DNA is unwound up to a point during its replication.
65. Mention the direction in which:
(a) the leading strand is synthesised.
(b) discontinuous synthesis of DNA occurs.
Answer/Explanation
Answer:
Explaination:
(а) 5′ → 3′.
(b) 5′ → 3′.
66. Name the enzyme involved in the continuous replication of DNA strand. Mention the polarity of the template strand. [All India 2010]
Answer/Explanation
Answer:
Explaination:
DNA polymerase.
Template strand has 3′ → 5′ polarity.
67. Name the types of synthesis ‘a’ and ‘b’ occurring in the replication fork of DNA as shown below:
Answer/Explanation
Answer:
Explaination:
‘a’ – Continuous synthesis
‘b’ – Discontinuous synthesis.
68. Name the enzyme that joins the small fragments of DNA of a lagging strand during DNA replication. [Delhi 2013C]
Answer/Explanation
Answer:
Explaination: DNA – ligase.
69. Why are vectors needed for replication of DNA during rDNA technology? [HOTS]
Answer/Explanation
Answer:
Explaination: The vector provides the origin of replication.
70. What will happen if DNA replication is not followed by cell division in a eukaryotic cell? [All India 2014C]
Answer/Explanation
Answer:
Explaination: It will lead to polyploidy, a condition where the cell comes to possess more than two sets of chromosomes.
71. Define transcription.
Answer/Explanation
Answer:
Explaination: Transcription is the process of copying the genetic information from one of the strands of DNA into RNA.
72. Name the enzyme and the direction in which it catalyses the polymerisation of ribonucleotides.
Answer/Explanation
Answer:
Explaination:
– DNA-dependent RNA-polymerase.
– 5′ → 3′ direction.
73. Mention one difference to distinguish an exon from an intron. [Foreign 2016]
Answer/Explanation
Answer:
Explaination:
– An exon is a coding sequence that forms part of RNA.
– An intron is a non-coding sequence that is removed during splicing and does not forms a part of RNA.
74. When and at what end does the ‘tailing’ of hnRNA take place?
Answer/Explanation
Answer:
Explaination: Tailing occurs after splicing at the 3′ end.
75. At which ends do ‘capping’ and ‘tailing’ of hnRNA occur, respectively?
Answer/Explanation
Answer:
Explaination: Capping at the 5′ end and tailing at the 3′ end.
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