Q1: Gene X has a point mutation resulting in a premature stop codon in the mRNA.
ID: 142819 • Letter: Q
Question
Q1: Gene X has a point mutation resulting in a premature stop codon in the mRNA. Imagine one cell line with this mutant was wild type (for all non Gene X genes) while another had a mutation in the nonsense mediated decay (NMD) pathway in addition to the Gene X mutation. If proteins were extracted from each cell line and a western blot probing for Gene X was performed, what would we expect to see on the western blot?
1) The Gene X band from both cell lines will be the same size and intensity.
2) The Gene X band in the wild type cell will be darker but the same size as the NMD mutant cell line band
3) The Gene X band in the wild type cell will be lighter but the same size as the NMD mutant cell line band
4) The Gene X band in the wild type cell will be lighter but a larger size compared to the NMD mutant cell line.
Q2: Which of the following would support the idea that an RNA molecule and not a protein is responsible for peptide bond formation by the ribosome? More than one answer is possible
1) Addition of a nuclease blocks peptide bond formation
2) Addition of a protease blocks peptide bond formation
3) Addition of a low amount of heat (incapable of breaking hydrogen bonds) blocks peptide bond formation
4) Expression of a specific protein coding gene is inhibited leading to a block in peptide bond formation
Explanation / Answer
ans.1 Nonsense-mediated decay (NMD) is an evolutionarily conserved mRNA quality control system in all eukaryotes that degrades transcripts containing premature termination codons. This system prevents the formation of truncated proteins.
Now in first X gene, there is a point mutation resulting in a premature stop codon in the mRNA.Thus this mutation will not result in the truncated protein as here NMD pathway is active which will prevent the formation of truncated proteins. Hence normal length protein will be formed here. The other gene had a mutation in NMD pathway along with Gene X mutation. Hence in these lines, there will be truncated proteins produced. This would be the correct answer.
4) The Gene X band in the wild-type cell will be lighter but a larger size compared to the NMD mutant cell line.
ans.2
Addition of a nuclease blocks peptide bond formation- As nuclease acts on RNAs only and not on proteins which would mean that RNA helps in the formation of a peptide bond.
Addition of a low amount of heat (incapable of breaking hydrogen bonds) blocks peptide bond formation- hydrogen bonds are present in RNA and if they are not broken this means that RNA is intact and is capable of forming peptide bonds.
Addition of a protease blocks peptide bond formation-protease only acts on proteins and not on RNA-
This would mean that proteins are responsible for peptide bond formation.
Expression of a specific protein-coding gene is inhibited leading to a block in peptide bond formation-This would mean that proteins are responsible for peptide bond formation.
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.