1. What is an exon ?
a) Non-coding sequences removed during splicing
b) Coding sequences for amino acids
c) Regulatory sequences that initiate transcription
d) Introns that remain in mature mRNA
Answer
b) Coding sequences for amino acids
2. DNA and RNA are both polynucleotide molecules. Give some ways in which DNA and RNA differ from each other.
Answer
DNA strand is double stranded, RNA is single stranded. DNA contains thymine, RNA contains uracil. DNA strand is much longer than RNA. DNA pentose sugar is deoxyribose, RNA pentose sugar is ribose.
3. After transcription, what must happen before the mRNA can code for proteins at the ribosome ?
a) mRNA needs to be spliced, where introns are removed
b) mRNA must be translated directly into amino acids
c) mRNA must bind to DNA to form a template
d) mRNA must be degraded before ribosomal binding
Answer
a) mRNA needs to be spliced, where introns are removed
4. Complete the table to indicate which properties the molecules have.
Answer
5. Rifamycin is an antibiotic that is used to treat bacterial infections. It is a non-competitive inhibitor of the enzyme that forms mRNA in bacteria. Use your knowledge of transcription to suggest how this drug works to kill bacteria.
Answer
Rifamycin attaches to RNA polymerase at a site other than the active site. This changes the shape of the active site, preventing the enzyme from functioning properly and stopping transcription.
6. Rifamycin moves freely across all cell membranes within the body. Use your understanding of enzyme structure to suggest why this drug does not affect transcription within cells of the human patient.
Answer
Prokaryotic (bacterial) RNA polymerase has a different tertiary structure from eukaryotic (human) RNA polymerase. The drug rifamycin is not complementary to human RNA polymerase. Therefore, it will not prevent the enzyme from attaching to DNA or initiating transcription.
7. One challenge faced by scientists is that strains of bacteria resistant to rifamycin can develop. Explain how.
Answer
A mutation in the base sequence of the gene coding for RNA polymerase changes the primary structure of the enzyme. This alters its tertiary structure, so RNA polymerase is no longer complementary to the drug rifamycin, and the drug has no effect.
8. Resistant bacteria are still able to carry out transcription. Suggest how a mutation in these bacteria would make bacteria resistant to this drug.
Answer
A mutation in the gene coding for RNA polymerase affects a region that is not the active site. As a result, rifamycin is unable to bind, or it binds differently, so transcription can still occur.
9. The figure below shows an image of a tRNA molecule that is involved in protein synthesis. Name the sections X and Y.
Answer
X = Anticodon,
10. Describe the role of X and Y in translation.
Answer
Anticodon is complementary to the codon. It brings the specific amino acid that corresponds to that code. So that a peptide bond can be formed with the adjacent amino acids.
11. Name the three bases that the tRNA shown above would bind to on the mRNA.
Answer
CUU.