CBSE Class 12 Biology Molecular Basis of Inheritance MCQs Set A

Question: In a DNA strand the nucleotides are linked together by

a) phosphodiester bonds

b) glycosidic bonds

c) peptide bonds

d) hydrogen bonds

Answer :  phosphodiester bonds

Question: A nucleoside differs from a nucleotide. It lacks the:

a) phosphate group

b) hydroxyl group

c) sugar

d) base

Answer :  phosphate group

Question: Both deoxyribose and ribose belong to a class of sugars called

a) pentoses

b) polysaccharides

c) hexoses

d) trioses

Answer :  pentoses

Question: The fact that a purine base always paired through hydrogen bonds with a pyrimidine base leads to, in the DNA double helix

a) uniform width throughout DNA

b) uniform length in all DNA

c) the semiconservative nature

d) the antiparallel nature

Answer :  uniform width throughout DNA

Question: The net electric charge on DNA and histones is

a) negative and positive, respectively

b) both negative

c) both positive

d) zero

Answer :  negative and positive, respectively

Question: The promoter site and the terminator site for transcription are located at

a) 5' (upstream) end and 3' (downstream) end, respectively of thetranscription unit

b) the 5' (upstream) end

c) the 3' (downstream) end

d) 3' (downstream) end and 5' (upstream) end, respectively of the transcription unit

Answer :  5' (upstream) end and 3' (downstream) end, respectively of thetranscription unit

Question: Which of the following statements is the most appropriate for sickle cell anaemia?

a) All of the above

b) It confers resistance to acquiring malaria

c) It is a molecular disease

d) It cannot be treated with iron supplements

Answer :  All of the above

Question: One of the following is true with respect to AUG

a) All of the above

b) It codes for methionine in both prokaryotes and eukaryotes

c) It is also an initiation codon

d) It codes for methionine only

Answer :  All of the above

Question: The first genetic material could be

a) RNA

b) DNA

c) carbohydrates

d) protein

Answer :  RNA

Question: With regard to mature mRNA in eukaryotes

a) exons appear but introns do not appear in the mature RNA

b) exons and 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 :  exons appear but introns do not appear in the mature RNA

Question: The human chromosome with the highest and least number of genes in them are respectively

a) Chromosome 1 and Y

b) Chromosome 1 and X

c) Chromosome X and Y

d) Chromosome 21 and Y

Answer :  Chromosome 1 and Y

Question: Who amongst the following scientists had no contribution in the development of the double helix model for the structure of DNA?

a) Meselson and Stahl

b) Erwin Chargaff

c) Maurice Wilkins

d) Rosalind Franklin

Answer :  Meselson and Stahl

Question: 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) Remove/Replace 3' OH group in deoxy ribose

b) Remove/Replace 2' OH group with some other group in deoxy ribose

c) Both ‘B’ and ‘C’

d) Replace purine with pyrimidines

Answer :  Remove/Replace 3' OH group in deoxy ribose

Question: Discontinuous synthesis of DNA occurs in one strand, because

a)

b) DNA molecule being synthesised is very long

c) it is a more efficient process

d) DNA ligase has to have a role

Answer :

Question: Which of the following steps in transcription is catalysed by RNA polymerse?

a) Elongation

b) Initiation

c) Termination

d) All of the above

Answer :  Elongation

Question:  Control of gene expression takes place at the level of

a) Transcription

b) Translation

c) None of the above

d) DNA-replication

Answer :  Transcription

Question: Regulatory proteins are the accessory proteins that interact with RNA polymerase and affect its role in transcription. Which of the following statements is correct about regulatory protein?

a) They can act both as activators and as repressors

b) They interact with RNA polymerase but do not affect the expression

c) They only decrease expression

d) They only increase expression

Answer :  They can act both as activators and as repressors

Question: Which was the last human chromosome to be completely sequenced:

a) Chromosome 1

b) Chromosome 11

c) Chromosome 21

d) Chromosome x

Answer :  Chromosome 1

Question: Which of the following are the functions of RNA?

a) All of the above

b) It is a constituent component of ribosomes

c) It carries amino acids to ribosomes

d) It is a carrier of genetic information from DNA to ribosomes synthesising polypeptides

Answer :  All of the above

Question: 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 single stranded DNA

b) it is a double stranded circular DNA

c) It is a double stranded linear DNA

d) No conclusion can be drawn

Answer :  It is single stranded DNA 

Question: In some viruses, DNA is synthesised by using RNA as template. Such a DNA is called:

a) c DNA

b) r DNA

c) B-DNA

d) A-DNA

Answer: c DNA

Question:

a) 0:1:7

b) 0:1:3

c) 1:4:0

d) 1:1:0

Answer: 0:1:7

Question:

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: 5' - A U G A A U G - 3'

Question: The RNA polymerase holoenzyme transcribes:

a) the structural gene and the terminator regions

b) the structural gene only

c) the promoter, and the

d) the promoter, structural gene and the terminator region

Answer: the structural gene and the terminator regions

Question: If the base sequence of a codon in mRNA is 5'-AUG-3', the sequence of tRNA pairing with it must be

a) 5' - CAU - 3'

b) 5' - AUG - 3'

c) 5' - GUA - 3'

d) 5' - UAC - 3'

Answer: 5' - CAU - 3'

Question: The amino acid attaches to the tRNA at its:

a) 3' - end

b) 5' - end

c) Anti codon site

d) DHU loop

Answer: 3' - end

Question: To initiate translation, the mRNA first binds to

a) The smaller ribosomal sub-unit

b) The larger ribosomal sub-unit

c) The whole ribosome

d) No such specificity exists

Answer: The smaller ribosomal sub-unit

Question: 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: lactose is present and it binds to the repressor

Question: The nucleic acid synthesis takes place in

a) 5’-3’ direction

b) 3’-5’ direction

c) Both ways

d) Any direction

Answer: 5’-3’ direction

Question: What is the nature of the strands of the DNA duplex?

a) Anti-parallel and complementary

b) Identical and complementary

c) Anti=parallel and non-complementary

d) Dissimilar and non-complementary

Answer: Anti-parallel and complementary