PLEASE EXPLAIN YOUR CHOICES FOR ANSWERS IN ALL 3 QUESTIONS T

PLEASE EXPLAIN YOUR CHOICES FOR ANSWERS IN ALL 3 QUESTIONS. THANK YOU :)

The mutation in the CYP1A-1 allele:
(check all that apply)

Select one or more:

a. Prevents export of the RNA from the nucleus

b. Suppresses transcription of the CYP71A1 gene

c. Invokes nonsense mediated RNA decay

d. The pioneer ribosome pauses at the mutation site during translation

e. Translation of the mutant RNA is prevented due to pausing of the ribosome small subunit at the 5\' cap.

f. Causes defect in RNA splicing at splice donor site

g. Causes defect in RNA splicing at splice acceptor site

h. Does not invoke nonsense mediate decay

i. Mutant RNA is translated into a truncated polypeptide

j. Mutant RNA causes frameshift which results in altered amino acid sequence downstream from the mutation site and a truncated polypeptide due to out of frame stop codon.

k. Mutant RNA causes translation of an intron sequence which in turn generates a polypeptide longer than normal.

l. None of the above apply.

The mutation in the CYP1A-2 allele:
(check all that apply)

Select one or more:

a. Prevents export of the RNA from the nucleus

b. Suppresses transcription of the CYP71A1 gene

c. Invokes nonsense mediated RNA decay

d. Ribosome release factors allow continued translation past the stop codon.

e. Translation of the mutant RNA is prevented due to pausing of the ribosome small subunit at the 5\' cap.

f. Causes defect in RNA splicing at splice donor site

g. Causes defect in RNA splicing at splice acceptor site

h. Does not invoke nonsense mediate decay

i. Mutant RNA is translated into a truncated polypeptide

j. Mutant RNA causes frameshift which results in altered amino acid sequence downstream from the mutation site and a truncated polypeptide due to out of frame stop codon.

k. Mutant RNA causes translation of an intron sequence which in turn generates a polypeptide longer than normal.

l. None of the above apply.

The mutation in the CYP1A-3 allele:
(check all that apply)

Select one or more:

a. Prevents export of the RNA from the nucleus

b. Suppresses transcription of the CYP71A1 gene

c. Invokes nonsense mediated RNA decay

d. The pioneer ribosome pauses at the mutation site during translation

e. Translation of the mutant RNA is prevented due to pausing of the ribosome small subunit at the 5\' cap.

f. Causes defect in RNA splicing at splice donor site

g. Causes defect in RNA splicing at splice acceptor site

h. Does not invoke nonsense mediate decay

i. Mutant RNA is translated into a truncated polypeptide

j. Mutant RNA causes frameshift which results in altered amino acid sequence downstream from the mutation site and a truncated polypeptide due to out of frame stop codon.

k. Mutant RNA causes translation of an intron sequence which in turn generates a polypeptide longer than normal.

l. None of the above apply.

Solution

For CYP1A-1 mutant we do not see a band either in the northern blot analysis or western blot analysis. This means that neither the mRNA nor the protein is made. Consequently option a and any other option involving the export or translation of mRNA is wrong. The possible reasons for absence of mRNA are:

b. suppresses transcription of CYP1-A1 gene: Without transcription no mRNA are formed.

c. invokes non sense mediated RNA decay: Any RNA that is made is decayed and thus present below the detection limit if any.

The other reasons would involve atleast the mRNA species to be detected.

The mutation in CYP1A-2 allele shows both mRNA and protein. The mRNA size is equal to that of wild type but the protein is smaller indicating problems after translation has occured.

h. does not invoke non sense mediated decay because mRNA is present in considerable amounrt.

i. Mutant RNA is translated into a truncated peptide: Due to presence of Stop codon and a smaller protein observed in western blot analysis.

The mutation in CYP1A-3 allele resulted in a larger mRNA and larger polypeptide than wild type. This may happen due to following reasons:

f. Causes defect in RNA splicing at splice donor site

g. Causes defect in RNA splicing at splice acceptor site.

k. Mutant RNA causes translation of an intron sequence which in turn generates a polypeptide longer than normal.

The first 2 cases lead to the third case resulting in larger mRNA and polypeptide. However, if we read the question carefully, the mutation was 2bp downstream of exon 2 in CYP1A-3 mutant. So, the defect is at the donor site not the acceptor site.

So only f. and k. will be applicable.