Review Questions
4. The AUC and AUA codons in mRNA both specify isoleucine. What feature of the genetic code explains this?
- complementarity
- nonsense codons
- universality
- degeneracy
5. How many nucleotides are in 12 mRNA codons?
- 12
- 24
- 36
- 48
6. Which event contradicts the central dogma of molecular biology?
- Poly-A polymerase enzymes process mRNA in the nucleus.
- Endonuclease enzymes splice out and repair damaged DNA.
- Scientists use reverse transcriptase enzymes to make DNA from RNA.
- Codons specifying amino acids are degenerate and universal.
7. Which subunit of the E. coli polymerase confers specificity to transcription?
- α
- β
- β‘
- σ
8. The -10 and -35 regions of prokaryotic promoters are called consensus sequences because ________.
- they are identical in all bacterial species
- they are similar in all bacterial species
- they exist in all organisms
- they have the same function in all organisms
9. Three different bacteria species have the following consensus sequences upstream of a conserved gene.
| Species A | Species B | Species C | |
| -10 | TAATAAT | TTTAAT | TATATT |
| -35 | TTGACA | TTGGCC | TTGAAA |
Order the bacteria from most to least efficient initiation of gene transcription.
- A > B > C
- B > C > A
- C > B > A
- A > C > B
10. Which feature of promoters can be found in both prokaryotes and eukaryotes?
- GC box
- TATA box
- octamer box
- -10 and -35 sequences
11. What transcripts will be most affected by low levels of α-amanitin?
- 18S and 28S rRNAs
- pre-mRNAs
- 5S rRNAs and tRNAs
- other small nuclear RNAs
12. How do enhancers and promoters differ?
- Enhancers bind transcription factors to silence gene expression, while promoters activate transcription.
- Enhancers increase the efficiency of gene expression, but are not essential for transcription. Promoter recognition is essential to transcription initiation.
- Promoters bind transcription factors to increase the efficiency of transcription. Enhancers bind RNA polymerases to initiate transcription.
- There is no difference. Both are transcription factor-binding sequences in DNA.
13. Which pre-mRNA processing step is important for initiating translation?
- poly-A tail
- RNA editing
- splicing
- 7-methylguanosine cap
14. What processing step enhances the stability of pre-tRNAs and pre-rRNAs?
- methylation
- nucleotide modification
- cleavage
- 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?
- 220bp
- 295bp
- 140bp
- 435bp
16. The RNA components of ribosomes are synthesized in the ________.
- cytoplasm
- nucleus
- nucleolus
- endoplasmic reticulum
17. In any given species, there are at least how many types of aminoacyl tRNA synthetases?
- 20
- 40
- 100
- 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?
- Translation stalls after the initiation AUG codon is identified.
- The ribosome cannot catalyze the formation of peptide bonds between the tRNAs in the A and P sites.
- The ribosome cannot interact with mRNAs.
- tRNAs cannot exit the E site of the ribosome.