CLEP Biology DNA Structure and Replication 5 — Questions and Answers
Question 1: The end-replication problem refers to the inability of DNA polymerase to fully replicate:
- The lagging strand at the 3' end of linear chromosomes, causing telomere shortening (Correct answer)
- The leading strand at origins of replication
- Circular chromosomes in prokaryotes
- The repetitive sequences within centromeres
Correct answer: The lagging strand at the 3' end of linear chromosomes, causing telomere shortening
After the final RNA primer on the lagging strand is removed from the 5' end, there is no upstream 3'-OH to fill in the gap, causing progressive shortening of linear chromosome ends.
Question 2: Which of the following nucleotides is found in DNA but NOT in RNA?
- Adenosine monophosphate (AMP)
- Guanosine monophosphate (GMP)
- Deoxythymidine monophosphate (dTMP) (Correct answer)
- Cytidine monophosphate (CMP)
Correct answer: Deoxythymidine monophosphate (dTMP)
Thymine (as deoxythymidine) is found only in DNA; RNA uses uracil instead of thymine and contains ribose instead of deoxyribose.
Question 3: A DNA molecule is described as B-form. This means it is:
- A left-handed double helix with 10 base pairs per turn
- The standard right-handed double helix with approximately 10.5 base pairs per turn (Correct answer)
- A triple-stranded structure found in chromatin
- A single-stranded loop found in telomeres
Correct answer: The standard right-handed double helix with approximately 10.5 base pairs per turn
B-form DNA is the most common form under physiological conditions: a right-handed double helix with about 10.5 base pairs per helical turn.
Question 4: If one strand of a DNA molecule has the sequence 5'-ATCGGC-3', what is the sequence of the complementary strand?
- 5'-ATCGGC-3'
- 5'-GCGGAT-3'
- 5'-GCCGAT-3' (Correct answer)
- 3'-ATCGGC-5'
Correct answer: 5'-GCCGAT-3'
The complement of 5'-ATCGGC-3' is written antiparallel as 3'-TAGCCG-5', which is the same as 5'-GCCGAT-3'.
Question 5: Which of the following correctly describes semi-conservative replication?
- Each daughter DNA molecule consists of two entirely new strands
- Each daughter molecule contains one original parental strand and one newly synthesized strand (Correct answer)
- The parental DNA is broken into fragments and reassembled randomly
- Only one daughter cell receives the original DNA strands
Correct answer: Each daughter molecule contains one original parental strand and one newly synthesized strand
In semi-conservative replication, the double helix unwinds and each original strand serves as a template for a new complementary strand, so each daughter molecule is a hybrid.
Question 6: What would happen if a cell lacked functional DNA ligase during replication?
- The replication fork would not open
- RNA primers could not be synthesized
- Okazaki fragments on the lagging strand would remain unjoined (Correct answer)
- The leading strand could not be synthesized continuously
Correct answer: Okazaki fragments on the lagging strand would remain unjoined
Without ligase, the nicks between Okazaki fragments on the lagging strand after primer replacement could not be sealed, leaving a broken lagging strand.
Question 7: The major and minor grooves of the DNA double helix are important because they:
- Determine the directionality of strand synthesis
- Allow proteins to access and read the base sequence without fully unwinding DNA (Correct answer)
- Provide sites where phosphodiester bonds form
- Store the energy needed for replication
Correct answer: Allow proteins to access and read the base sequence without fully unwinding DNA
Proteins such as transcription factors and restriction enzymes can insert into the grooves and make contact with specific base pairs to read the genetic sequence.
CLEP Biology DNA Structure and Replication 5
The end-replication problem refers to the inability of DNA polymerase to fully replicate: