151 Review Questions

4. The AUC and AUA codons in mRNA both specify isoleucine. What feature of the genetic code explains this?

1. complementarity
2. nonsense codons
3. universality
4. degeneracy

5. How many nucleotides are in 12 mRNA codons?

1. 12
2. 24
3. 36
4. 48

6. Which event contradicts the central dogma of molecular biology?

1. Poly-A polymerase enzymes process mRNA in the nucleus.
2. Endonuclease enzymes splice out and repair damaged DNA.
3. Scientists use reverse transcriptase enzymes to make DNA from RNA.
4. Codons specifying amino acids are degenerate and universal.

7. Which subunit of the E. coli polymerase confers specificity to transcription?

1. α
2. β
3. β’
4. σ

8. The -10 and -35 regions of prokaryotic promoters are called consensus sequences because ________.

1. they are identical in all bacterial species
2. they are similar in all bacterial species
3. they exist in all organisms
4. they have the same function in all organisms

9. Three different bacteria species have the following consensus sequences upstream of a conserved gene.

Order the bacteria from most to least efficient initiation of gene transcription.

1. A > B > C
2. B > C > A
3. C > B > A
4. A > C > B

10. Which feature of promoters can be found in both prokaryotes and eukaryotes?

1. GC box
2. TATA box
3. octamer box
4. -10 and -35 sequences

11. What transcripts will be most affected by low levels of α-amanitin?

1. 18S and 28S rRNAs
2. pre-mRNAs
3. 5S rRNAs and tRNAs
4. other small nuclear RNAs

12. How do enhancers and promoters differ?

1. Enhancers bind transcription factors to silence gene expression, while promoters activate transcription.
2. Enhancers increase the efficiency of gene expression, but are not essential for transcription. Promoter recognition is essential to transcription initiation.
3. Promoters bind transcription factors to increase the efficiency of transcription. Enhancers bind RNA polymerases to initiate transcription.
4. There is no difference. Both are transcription factor-binding sequences in DNA.

13. Which pre-mRNA processing step is important for initiating translation?

1. poly-A tail
2. RNA editing
3. splicing
4. 7-methylguanosine cap

14. What processing step enhances the stability of pre-tRNAs and pre-rRNAs?

1. methylation
2. nucleotide modification
3. cleavage
4. splicing

15. A scientist identifies a pre-mRNA with the following structure.

What is the predicted size of the corresponding mature mRNA in base pairs (bp), excluding the 5’ cap and 3’ poly-A tail?

1. 220bp
2. 295bp
3. 140bp
4. 435bp

16. The RNA components of ribosomes are synthesized in the ________.

1. cytoplasm
2. nucleus
3. nucleolus
4. endoplasmic reticulum

17. In any given species, there are at least how many types of aminoacyl tRNA synthetases?

1. 20
2. 40
3. 100
4. 200

18. A scientist introduces a mutation that makes the 60S ribosomal subunit nonfunctional in a human cell line. What would be the predicted effect on translation?

1. Translation stalls after the initiation AUG codon is identified.
2. The ribosome cannot catalyze the formation of peptide bonds between the tRNAs in the A and P sites.
3. The ribosome cannot interact with mRNAs.
4. tRNAs cannot exit the E site of the ribosome.