CLEP Biology DNA Structure and Replication 4 — Questions and Answers
Question 1: Which of the following correctly pairs a base with its complementary base in DNA?
- Adenine — Guanine
- Cytosine — Thymine
- Guanine — Cytosine (Correct answer)
- Adenine — Uracil
Correct answer: Guanine — Cytosine
In DNA, guanine pairs with cytosine (3 H-bonds) and adenine pairs with thymine (2 H-bonds); uracil is found only in RNA.
Question 2: The 3' to 5' exonuclease activity of DNA polymerase I serves which function?
- Synthesizing the new DNA strand
- Proofreading to remove incorrectly incorporated nucleotides (Correct answer)
- Removing correctly paired nucleotides ahead of the fork
- Joining Okazaki fragments
Correct answer: Proofreading to remove incorrectly incorporated nucleotides
The 3'→5' exonuclease activity of DNA polymerase removes mismatched nucleotides just added during synthesis, providing proofreading ability.
Question 3: In eukaryotes, DNA replication begins at:
- A single origin of replication per chromosome
- Multiple origins of replication along each chromosome (Correct answer)
- The centromere of each chromosome
- The telomere of each chromosome
Correct answer: Multiple origins of replication along each chromosome
Eukaryotic chromosomes are large, so they have multiple origins of replication that fire simultaneously to complete replication in a reasonable time.
Question 4: Which of the following bonds holds the two strands of the DNA double helix together?
- Covalent bonds between bases
- Ionic bonds between sugar molecules
- Hydrogen bonds between complementary bases (Correct answer)
- Peptide bonds between nucleotides
Correct answer: Hydrogen bonds between complementary bases
The two strands are held together by hydrogen bonds between complementary base pairs (A-T: 2 bonds; G-C: 3 bonds).
Question 5: What type of bond connects adjacent nucleotides within a single DNA strand?
- Hydrogen bond
- Peptide bond
- Phosphodiester bond (Correct answer)
- Disulfide bond
Correct answer: Phosphodiester bond
Phosphodiester bonds form between the 3'-OH of one nucleotide and the 5'-phosphate of the next, creating the sugar-phosphate backbone.
Question 6: Telomerase is particularly important in which type of cell?
- Muscle cells, because they contract repeatedly
- Neurons, because they must survive for decades
- Germ cells and stem cells, because they divide continuously (Correct answer)
- Red blood cells, because they lack a nucleus
Correct answer: Germ cells and stem cells, because they divide continuously
Telomerase extends telomeres using an RNA template, which is especially important in continuously dividing cells like germ cells and stem cells to prevent chromosomal shortening.
Question 7: During DNA replication, which enzyme synthesizes the RNA primer on the lagging strand template?
- DNA polymerase III
- DNA ligase
- Primase (Correct answer)
- Helicase
Correct answer: Primase
Primase, a type of RNA polymerase, synthesizes short RNA primers complementary to the DNA template, giving DNA polymerase a 3'-OH to extend.
CLEP Biology DNA Structure and Replication 4
Which of the following correctly pairs a base with its complementary base in DNA?