Practice quiz · by a Quizcard user

AP Biology: Gene Expression and Regulation — quiz

14 multiple-choice questions covering DNA & RNA Structure, DNA Replication, Transcription, RNA Processing, Translation. One answer each; you get a score at the end and the explanation for every question. No account needed.

Updated 2026-11-03. Keys 1–4 pick an answer, Enter moves on. Redo it any time, in order or shuffled.

The questions

Answers and explanations are shown after you finish.

1. DNA & RNA Structure

   A student isolates a single nucleotide from a sample of DNA and analyzes its components. Which three parts would be found?

   • A phosphate group, a deoxyribose sugar, and a nitrogenous base
   • A phosphate group, a ribose sugar, and an amino acid
   • Two sugar molecules and a phosphate group
   • A nitrogenous base, a ribose sugar, and a fatty acid
2. DNA & RNA Structure

   Which statement correctly compares the hydrogen bonding in DNA base pairs?

   • All base pairs form exactly 2 hydrogen bonds
   • G-C pairs form 3 hydrogen bonds, more than the 2 formed by A-T pairs, making GC-rich regions harder to separate
   • Purines pair with purines and pyrimidines pair with pyrimidines
   • A-T pairs form 3 hydrogen bonds, more than G-C pairs
3. DNA & RNA Structure

   A researcher analyzes an unlabeled single-stranded nucleic acid and finds it contains uracil instead of thymine. This molecule is most likely:

   • RNA, because it contains deoxyribose
   • DNA, because uracil is a DNA-specific base
   • DNA, because single strands only occur in DNA
   • RNA, because it uses ribose sugar and uracil in place of thymine
4. DNA Replication

   During DNA replication, which enzyme relieves the torsional strain that builds up ahead of the replication fork, and which enzyme actually separates the two DNA strands?

   • Topoisomerase relieves the strain; helicase unwinds the helix
   • DNA polymerase relieves the strain; ligase unwinds the helix
   • Helicase relieves the strain; primase unwinds the helix
   • Topoisomerase unwinds the helix; helicase relieves the strain
5. DNA Replication

   Why can't DNA polymerase begin synthesizing a new DNA strand entirely on its own?

   • It can only add nucleotides to an existing 3'-OH group, so primase must first lay down a short RNA primer
   • It only functions in the 3'→5' direction
   • It cannot bind directly to a DNA template strand
   • It requires ATP that only primase can supply
6. DNA Replication

   How does synthesis of the leading strand differ from synthesis of the lagging strand during replication?

   • The leading strand is made continuously toward the fork, while the lagging strand is made discontinuously as Okazaki fragments later joined by ligase
   • The leading strand is made in fragments while the lagging strand is continuous
   • The lagging strand is synthesized by ligase alone, with no DNA polymerase involved
   • Both strands are synthesized continuously in the same direction
7. DNA Replication

   After one round of DNA replication, a researcher examines a resulting double helix. What finding would support the semiconservative model of replication?

   • Each helix is a random patchwork of old and new segments on both strands
   • Both strands in the new helix are entirely newly synthesized
   • Both strands in the new helix are original parental strands
   • Each new helix contains one original parental strand and one newly synthesized strand
8. Transcription

   Which option correctly matches a stage of transcription to the event that occurs during it?

   • Termination: RNA polymerase unwinds the DNA helix for the first time
   • Initiation: RNA polymerase binds the promoter; Elongation: RNA is synthesized 5'→3'; Termination: polymerase reaches a terminator and releases the transcript
   • Elongation: RNA polymerase binds the promoter
   • Initiation: the ribosome binds the start codon
9. Transcription

   If the coding (sense) strand of a DNA gene reads 5'-ATGCGT-3', what will the corresponding mRNA sequence be after transcription?

   • 5'-UACGCA-3'
   • 5'-TACGCA-3'
   • 5'-AUGCGU-3'
   • 3'-AUGCGU-5'
10. RNA Processing

    Which combination of events correctly describes eukaryotic pre-mRNA processing before the transcript leaves the nucleus?

    • Addition of a 5' cap, addition of a poly-A tail, and removal of introns via splicing
    • Addition of a poly-A tail only, with no cap required
    • Removal of exons while introns are retained
    • Addition of a 5' cap and removal of exons, but no poly-A tail
11. RNA Processing

    A single gene produces several different protein products depending on the cell type, even though the DNA sequence is unchanged. This is best explained by:

    • Transcription of entirely different genes in each cell type
    • Use of different RNA polymerase enzymes in each tissue
    • Random mutation of the gene in different tissues
    • Alternative splicing, in which different combinations of exons are joined after introns are removed
12. Translation

    During the elongation phase of translation, a tRNA holding the growing polypeptide chain occupies one ribosomal site while a new charged tRNA enters another. Which sites are these, respectively?

    • The A site holds the growing polypeptide; the P site receives the incoming tRNA
    • The P site holds the growing polypeptide; the A site receives the incoming charged tRNA
    • The E site holds the growing polypeptide; the A site receives the incoming tRNA
    • The A site holds the growing polypeptide; the E site receives the incoming tRNA
13. Genetic Code

    A biologist observes that both human and bacterial cells translate the codon GGU into the same amino acid, glycine. This observation best illustrates that the genetic code is:

    • Ambiguous, meaning one codon can specify multiple amino acids
    • Degenerate, meaning multiple codons can specify the same amino acid
    • Overlapping, meaning adjacent codons share nucleotides
    • Universal, meaning nearly all organisms share the same codon-to-amino-acid assignments
14. Prokaryotic Gene Regulation

    Which statement correctly contrasts regulation of the lac operon with regulation of the trp operon?

    • Both operons are repressible and are turned off by their respective molecules
    • Both operons are inducible and are turned on by their respective molecules
    • The lac operon is inducible, normally off until lactose triggers transcription, while the trp operon is repressible, normally on until tryptophan shuts it off
    • The lac operon is repressible while the trp operon is inducible