Question

biol 210
chapter 8 quiz 2

1. all of the following pertain to nitrogenous bases except

a) form pairs by hydrogen bonding
b) guanine pairs with uracil
c) adenine pairs with thymine
d) cytosine and thymine are pyrimidines
e) adenine and guanine are purines

1. each nucleotide is composed of

a) one phosphate, one nitrogenous base, and one sugar
b) one phosphate, one nitrogenous base, and two sugars
c) two phosphates, one nitrogenous base, and one sugar
d) two phosphates, one nitrogenous base, and two sugars
e) one phosphate, two nitrogenous bases, and one sugar

1. base pairs in dna are held together by bonds.

a) peptide
b) nonpolar covalent
c) polar covalent
d) hydrogen
e) sulfhydryl

1. semiconservative replication refers to

a) each base bonding at the 1 position of the sugar
b) a purine always bonding to a pyrimidine
c) one helix strand that runs from the 5 to 3 direction and the other strand run direction
d) an original parent dna strand and one newly synthesized dna strand cor dna molecule
e) none of the choices are correct.

1. okazaki fragments are attached to the growing end of the lagging strand by

a) dna ligases
b) dna polymerases
c) dna helicases
d) dna gyrases
e) primases

Explanation:

• Question 6: In DNA, guanine pairs with cytosine, not uracil (which pairs with adenine in RNA). Adenine pairs with thymine (C is correct), cytosine and thymine are pyrimidines (D is correct), adenine and guanine are purines (E is correct). So the incorrect one is B.
• Question 7: A nucleotide is composed of one phosphate, one nitrogenous base, and one sugar. So B is correct.
• Question 8: Base pairs in DNA (A - T, G - C) are held together by hydrogen bonds. Peptide bonds are in proteins, non - polar and polar covalent bonds are within molecules (not between base pairs in DNA), sulfhydryl groups are - SH groups. So D is correct.
• Question 9: Semiconservative replication means that each new DNA molecule consists of an original parent DNA strand and one newly synthesized DNA strand. Option D describes this. A is about base - sugar bonding, B is about base - pairing rules (not replication), C is about strand direction (not replication concept). So D is correct.
• Question 10: Okazaki fragments on the lagging strand are joined together by DNA ligases. DNA polymerases synthesize DNA, DNA helicases unwind DNA, DNA gyrases relieve supercoiling, primases synthesize RNA primers. So A is correct.

Answer:

1. B. guanine pairs with uracil
2. B. one phosphate, one nitrogenous base, and one sugar
3. D. hydrogen
4. D. an original parent DNA strand and one newly synthesized DNA strand in a DNA molecule
5. A. DNA ligases