NEET Biology Molecular Basis of Inheritance MCQs Set 18

Answer: (b) mitochondria

Explanation:
1. Mitochondria (and chloroplasts) carry circular double-stranded DNA, like prokaryotes.
2. So the correct choice is option (b).

Teacher's Note:
1. Organelle DNA is bacteria-like.
2. Nuclear DNA is linear.

Answer: (b) B-DNA

Explanation:
1. B-DNA is the commonest right-handed form, with 10 base pairs per turn.
2. So the correct choice is option (b).

Teacher's Note:
1. B-DNA: 3.4 nm per turn.
2. Z-DNA is left-handed.

Answer: (c) 20,000

Explanation:
1. Each base pair has two nucleotides, one on each strand.
2. So the correct choice is option (c).

Teacher's Note:
1. 1 bp = 2 nucleotides.
2. Do not forget both strands.

Answer: (d) phosphate groups

Explanation:
1. Both have phosphate groups. Their sugars are pentoses (deoxyribose or ribose), and thymine occurs only in DNA.
2. So the correct choice is option (d).

Teacher's Note:
1. Phosphate forms the backbone.
2. Adenine, guanine and cytosine are common.

Answer: (a) nitrogenous base, pentose sugar and phosphoric acid

Explanation:
1. Base + pentose + phosphate = nucleotide; base + sugar alone is a nucleoside.
2. So the correct choice is option (a).

Teacher's Note:
1. Nucleoside + phosphate = nucleotide.
2. Pentose has five carbons.

Answer: (d) phosphorus

Explanation:
1. Bases contain C, H, N and O. Phosphorus is in the phosphate group.
2. So the correct choice is option (d).

Teacher's Note:
1. Phosphate is a separate part.
2. Bases are purines or pyrimidines.

Answer: (a) Miescher

Explanation:
1. Friedrich Miescher isolated 'nuclein' from pus cell nuclei in 1869.
2. So the correct choice is option (a).

Teacher's Note:
1. Nuclein = DNA with protein.
2. Watson and Crick gave the structure.

Answer: (a) DNA

Explanation:
1. Thymine is present in DNA; RNA has uracil instead.
2. So the correct choice is option (a).

Teacher's Note:
1. T in DNA, U in RNA.
2. Thymine = 5-methyl uracil.

Answer: (d) DNA but no histones

Explanation:
1. Prokaryotes have a naked circular DNA without histones (though some basic proteins are associated).
2. So the correct choice is option (d).

Teacher's Note:
1. Histones are eukaryotic.
2. Bacterial DNA forms the nucleoid.

Answer: (c) guanine

Explanation:
1. Guanine and adenine are purines; thymine, cytosine and uracil are pyrimidines.
2. So the correct choice is option (c).

Teacher's Note:
1. Purines have two rings.
2. Pyrimidines have one ring.

Answer: (c) three

Explanation:
1. G pairs with C by three hydrogen bonds; A pairs with T by two.
2. So the correct choice is option (c).

Teacher's Note:
1. A=T, G≡C.
2. GC-rich DNA is more stable.

Answer: (b) antiparallel and complementary

Explanation:
1. One strand runs 5' to 3' and the other 3' to 5', and their bases pair by specific complementarity.
2. So the correct choice is option (b).

Teacher's Note:
1. Complementary, not identical.
2. Polarity is opposite.

Answer: (a) 0.34 nm

Explanation:
1. Base pairs are stacked 0.34 nm apart, and one turn of 10 bp is 3.4 nm.
2. So the correct choice is option (a).

Teacher's Note:
1. 0.34 nm x 10 = 3.4 nm.
2. 3.4 Å is not correct.

Answer: (d) 35%

Explanation:
1. By Chargaff's rule G = C, so C is also 35 percent.
2. So the correct choice is option (d).

Teacher's Note:
1. G pairs with C.
2. A + T = 30.

Answer: (b) A + G = T + C

Explanation:
1. In double-stranded DNA A = T and G = C, so purines equal pyrimidines (A + G = T + C).
2. So the correct choice is option (b).

Teacher's Note:
1. The ratio A+T / G+C varies with species.
2. Purine = pyrimidine.

Answer: (b) phosphodiester bonds

Explanation:
1. The 3' carbon of one nucleotide links to the 5' phosphate of the next by a phosphodiester bond.
2. So the correct choice is option (b).

Teacher's Note:
1. Same in DNA.
2. H-bonds hold base pairs.

Answer: (a) phosphate

Explanation:
1. A nucleoside is base + sugar; adding phosphate makes a nucleotide.
2. So the correct choice is option (a).

Teacher's Note:
1. Nucleo-side = base + sugar.
2. Nucleo-tide = plus phosphate.

Answer: (a) 3.4 nm

Explanation:
1. One turn has 10 base pairs at 0.34 nm each, i.e. 3.4 nm.
2. So the correct choice is option (a).

Teacher's Note:
1. Pitch = 3.4 nm.
2. Diameter about 2 nm.

Answer: (b) 12

Explanation:
1. A-T gives 2 bonds each (three such pairs: 6) and C-G gives 3 each (two such pairs: 6), so the total is 12.
2. So the correct choice is option (b).

Teacher's Note:
1. A=T: 2.
2. C≡G: 3.

Answer: (b) guanine and adenine

Explanation:
1. Adenine and guanine are purines.
2. So the correct choice is option (b).

Teacher's Note:
1. Pure As Gold: A and G.
2. Pyrimidines: C, T, U.

Answer: (d) phosphodiester bond

Explanation:
1. Nucleotides join through phosphodiester bonds between 3' OH and 5' phosphate.
2. So the correct choice is option (d).

Teacher's Note:
1. Peptide bonds join amino acids.
2. Disulphide links cysteine.

Answer: (d) 340

Explanation:
1. T = A = 80 and G = C = 90, so the total is 80 + 80 + 90 + 90 = 340.
2. So the correct choice is option (d).

Teacher's Note:
1. Pairing doubles each count.
2. Use Chargaff's rule.

Answer: (a) double-stranded circular

Explanation:
1. Bacterial chromosomes are double-stranded closed circles.
2. So the correct choice is option (a).

Teacher's Note:
1. Some viruses have ssDNA.
2. Eukaryotic DNA is linear.

Answer: (d) sugar + base

Explanation:
1. Sugar plus nitrogen base makes a nucleoside, e.g. adenosine.
2. So the correct choice is option (d).

Teacher's Note:
1. No phosphate.
2. Add phosphate to make a nucleotide.

Answer: (b) ribose

Explanation:
1. RNA has ribose, which has a 2' hydroxyl group; DNA has deoxyribose.
2. So the correct choice is option (b).

Teacher's Note:
1. Ribose has one extra OH.
2. This makes RNA more reactive.