AP Biology: Transcription and Translation Practice Questions
Test yourself on AP Biology: Transcription and Translation with 12 original AP Exams practice questions. Pick an answer to see instant feedback and a full explanation.
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1. A protein-coding gene is expressed in a cell. Which sequence correctly identifies the information transfers in transcription and translation?
Explanation. Transcription uses a DNA template to produce RNA. For a protein-coding gene, ribosomes then read the mRNA sequence during translation to assemble amino acids into a polypeptide. The DNA itself is not translated by a ribosome.
2. RNA polymerase transcribes the short DNA template segment 3'-TACCTG-5'. What RNA sequence is produced from this segment?
Explanation. The RNA is complementary and antiparallel to the template. Reading the template 3'-to-5' gives RNA 5'-AUGGAC-3'. RNA uses uracil instead of thymine, so the product contains U where a DNA complement would contain T.
3. During transcription elongation, which statement correctly describes the direction of RNA synthesis?
Explanation. RNA polymerase adds ribonucleotides to the free 3' end of the growing RNA. The product therefore extends 5'-to-3', while the complementary DNA template is read in the opposite direction. Codon boundaries do not change this chemistry.
4. In a typical eukaryotic protein-coding gene, which event removes introns from the primary RNA transcript?
Explanation. Splicing removes intron sequences from the primary transcript and joins retained exons to form the mature RNA sequence. This is RNA processing, distinct from DNA replication and from the reactions that build a polypeptide during translation.
5. For a typical nuclear protein-coding gene in a eukaryotic cell, where do transcription and translation occur?
Explanation. A nuclear gene is transcribed in the nucleus, where its RNA is processed before export. Cytoplasmic ribosomes, either free or associated with rough endoplasmic reticulum, translate the mature mRNA. The question concerns nuclear genes rather than organelle genes.
6. A ribosome translates 5'-AUG GCU UUU UGA-3', starting at AUG. Given AUG = methionine, GCU = alanine, UUU = phenylalanine, and UGA = stop, what polypeptide is initially produced?
Explanation. The ribosome reads mRNA codons 5'-to-3' beginning at the stated start codon. The first three codons specify methionine, alanine, and phenylalanine. UGA signals termination rather than adding a fourth amino acid to the chain.
7. Using ordinary complementary base pairing, which tRNA anticodon pairs antiparallel with the mRNA codon 5'-GAA-3'?
Explanation. Complementary pairing requires G with C and A with U, with the two RNA strands antiparallel. Thus 5'-GAA-3' pairs with 3'-CUU-5'. Written in the opposite orientation, the same anticodon would be 5'-UUC-3'.
8. Which molecule forms the catalytic core responsible for peptide-bond formation in the ribosome?
Explanation. The large ribosomal subunit contains a peptidyl-transferase center whose catalytic core is ribosomal RNA. The ribosome is therefore a ribozyme. mRNA supplies the codon sequence, while tRNAs bring amino acids to the translating ribosome.
9. A substitution changes an internal mRNA codon from GAA to GAG. Both codons specify glutamate. What is the direct effect on the amino acid specified at this position?
Explanation. The genetic code is redundant: more than one codon can specify the same amino acid. Since GAA and GAG both encode glutamate, the amino acid at this position is unchanged. This does not establish that every possible effect on RNA behavior is absent.
10. A mutation changes the second codon of an mRNA from UAU, which encodes tyrosine, to UAA, a stop codon. Assuming normal initiation and termination, what is the most direct outcome?
Explanation. Changing a sense codon to a stop codon is a nonsense mutation. A ribosome encountering UAA terminates translation, releasing a much shorter product in this example. A single-base substitution does not itself shift the reading frame.
11. One nucleotide is inserted into the coding region after the start codon of an mRNA. No later insertion or deletion restores the original frame. What happens to how downstream bases are grouped?
Explanation. Ribosomes read consecutive groups of three bases from the established start position. Adding one base changes the grouping of later bases because one is not a multiple of three. A new stop codon may appear in the shifted frame, shortening translation.
12. Two matched cell samples begin with equal amounts of a stable mRNA. A drug-treated sample makes much less new protein from that mRNA than a vehicle control during a short interval, while mRNA abundance remains equal. Which conclusion is best supported?
Explanation. Reduced new protein production despite unchanged mRNA abundance is consistent with an effect on translation. The matched vehicle control supports comparison, but these measurements alone cannot distinguish effects on initiation, elongation, tRNA charging, or other contributing processes.
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FAQ
How can I distinguish a DNA template strand from a coding strand?
The RNA is complementary and antiparallel to the template strand. When written 5'-to-3', a coding DNA strand matches the corresponding primary RNA sequence except that DNA uses T and RNA uses U. Splicing can remove sequences before a mature mRNA is translated.
Are codons and anticodons read in the same direction?
Codons are conventionally written as mRNA sequences 5'-to-3'. A paired anticodon runs antiparallel, so always check its labeled ends. The anticodon paired with 5'-GAA-3' can be written 3'-CUU-5' or, in reverse orientation, 5'-UUC-3'.
How do synonymous, nonsense, and frameshift mutations differ?
A synonymous change preserves the encoded amino acid at a position. A nonsense change creates a stop codon. An insertion or deletion within a translated region shifts the downstream reading frame when its size is not a multiple of three.