AP Biology · Topic 6.1
DNA and RNA Structure Practice
Part of Gene Expression and Regulation.(IST-1.I)
Practice questions
4
Sample questions
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Sample 1difficulty 1/5
What does the antiparallel orientation of the DNA strands mean?
- A
The two strands run in the same direction.
- B
The strands separate completely with each replication.
- Ccheck_circle
One strand runs 5' to 3' while its complement runs 3' to 5'.
- D
Strands are joined by covalent bonds at their bases.
Why
DNA strands are antiparallel: their phosphodiester backbones run in opposite 5' to 3' directions, a structural requirement for complementary base-pairing and replication by DNA polymerase.
- A
Sample 2difficulty 2/5
The double helix shown has antiparallel sugar-phosphate backbones with base pairs (A=T, G≡C) connected by
- A
Disulfide bridges
- B
Ionic bonds
- Ccheck_circle
Hydrogen bonds
- D
Covalent bonds
Why
A=T (2 H-bonds), G≡C (3 H-bonds). The hydrogen bonding is what allows strands to separate easily during replication and transcription while remaining stable at body temperature.
- A
Sample 3difficulty 2/5
In any double-stranded DNA, the percentage of A equals the percent of _______, and percent G equals the percent of _______.
- A
C; T
- Bcheck_circle
T; C
- C
U; A
- D
G; A
Why
Base pairing: A=T, G=C → in dsDNA, %A = %T and %G = %C (Chargaff's rule).
- A
Sample 4difficulty 3/5
A double-stranded DNA sample has 30% A. The percent of G is
- A
30%
- Bcheck_circle
20%
- C
60%
- D
70%
Why
%T = 30 (Chargaff). A+T = 60% → G+C = 40% → %G = 20%.
- A