Indicate whether each of the following statements about the

Indicate whether each of the following statements about the structure of DNA is true or false. (Each is used to refer to the concentration of that base in DNA.) (a) A + T = G + C (b) A = G; C = T (c) A/T = C/G (d) T/A = C/G (e) A + G = C + T (g) A = T within each single strand. (h) Hydrogen bonding provides stability to the double helix in aqueous cytoplasms. (i) Hydrophobic bonding provides stability to the double helix in aqueous cytoplasms. (j) When separated, the two strands of a double helix are identical. (k) Once the base sequence of one strand of a DNA double helix is known, the base sequence of the second strand can be deduced. (l) The structure of a DNA double helix is invariant. (m) Each nucleotide pair contains two phosphate groups, two deoxyribose molecules and two bases. The nucleic acids from various viruses were extracted and examined to determine their base composition. Given the following results, what can you hypothesize about the physical nature of the nucleic acids from these viruses? (a) 35% A, 35% T, 15% G, and 15% C (b) 35% A, 15% T, 25% G, and 25% C (c) 35% A, 30% U, 30% G, and 5% C

Solution

Answer:

a) A+T=G+C - False, total concentration of purines = total concentration of pyrimidines i.e. A+G = T+C

b) A=G; C=T - False (explanation A=T, G=C)

c) A/T = C/G - True, (explanation, A/T =1 and C/G =1)

d) T/A = C/G - True, (explanation T/A =1 and C/G =1)

e) A+G = C+T, True (explanation  total concentration of purines = total concentration of pyrimidines i.e. A+G = T+C)

f) G/C = 1, True (total concentration of Guanine = total concentration of cytosine)

g) A=T within each strand, false, (explanation A=T in complementary strands)

h) hydrogen bonding provides stability to double helix in aqueous cytoplasms - true

i) Hydrophobic bonding provides stability to double helix in aqueous cytoplasms - true

j) When separated the two strands of double helix are identical - false (two strands are complementary to each other)

k) Once the base sequence of strand of a DNA double helix is known, the base sequence of the second strand can be deduced - true, the sequence of the second strand is complementary to the first strand and can be deduced from it)

l) The structure of a DNA double helix is invariant - false

m) Each nucleotide pair contains two phosphate groups, two deoxyribose molecules and two bases - true (explanation, each nucleotide pair contains 2 phosphate groups, two deoxyribose molecules and two bases)

15)

a) 35% A, 35% T, 15% G and 15% C - in this case since A = T, G=C and A+G = T+C, therefore this viral DNA is double helix

b) 35% A, 15% T, 25% G and 25% C - In this case since concentration of A (35%) is not equal to T (15%), therefore the viral DNA is single helix

c) 35% A, 30% U, 30% G and 5% C - In this case since A (35%) is not equal to U (30%) and G (30%) is not equal to C (5%) and since it contains Uracil instead of Thymine, therefore this virus contains single strand of RNA.