VCE Biology Question Thread

[alchemy]

So during prophase, the chromatin condenses and there is a total of 46 chromosomes and 92 chromatids. Sister chromatids are joined at the centromere and are identical.
Do each of the 46 chromatids duplicate during the "S" phase of interphase, resulting in 92 chromatids?

The S phase of interphase is simply for the replication of DNA so that mitosis can occur. It comes before mitosis and there is no chromosome or chromatid duplication of the sort. Remember, interphase and mitosis are two distinct stages really.

[Reus]

DNA strands of

TAC GAT ACC CGA GCA (leading)
ATG CTA TGG GCT CGT

Identify the amino acid sequence? Quite straight forward yes, but which strand is the one that goes through transcription? The lagging or leading? I know it'd have to be a 3'-5', however in this case they don't provide the ends.

Would you translate TAC (leading), as its complementary codon is AUG (Met - Start)?

[alchemy]

DNA strands of

TAC GAT ACC CGA GCA (leading)
ATG CTA TGG GCT CGT

Identify the amino acid sequence? Quite straight forward yes, but which strand is the one that goes through transcription? The lagging or leading? I know it'd have to be a 3'-5', however in this case they don't provide the ends.

Would you translate TAC (leading), as its complementary codon is AUG (Met - Start)?

The leading strand is the one that goes through transcription into mRNA. So yes, the first codon in this case would be start codon AUG.

[Reus]

Thanks again alchemy!

[Reus]

Nonsense mutations occurs if the codon has been changed from a codon that codes for an amino acid to a stop codon which codes for a release factor.
Which means that an amino acid is shortened, hence the structure is not fully completed, effecting the function of the particular protein?

[katiesaliba]

Can someone please explain how the same strand of DNA can be both leading and lagging (as shown in the attached picture)?

[simpak]

The replication is occurring in two different directions.  So for one direction strand x is a leading strand, but in the other direction it is a lagging strand.

[Reus]

Gene X is 2500bp long. It normally has a restriction site for the restriction enzyme EcoRI at 400bp point.
This means that when the DNA is exposed to the enzyme two fragments will be produced, one 400bp long and one 2100bp long.

However, in a mutated one...

5' GAATTC ----> 5'GACTTC
3' CTTAAG ----> 5'CTGAAG
When the mutated gene is exposed to EcoRI there will be only one fragment; 2500bp

Explain why two fragments are produced when the normal gene is exposed to EcoRI and only one fragment is produced when the mutated gene is exposed to EcoRI.

I have a few ideas that might be correct
- The mutated gene is completely altered?
Or
- The mutation changes the restriction site hence, the enzyme produces only one fragment as there is no stop at 400bp.

Could someone please help me out 

[RazzMeTazz]

Is amino acyl synthetase a type of tRNA activating enzyme?

[Reus]

Is amino acyl synthetase a type of tRNA activating enzyme?

Yes. It's an enzyme that catalyses the esterification of specific amino acids. 

Could someone please help me out 

Bump! Someone pls 

[simpak]

Gene X is 2500bp long. It normally has a restriction site for the restriction enzyme EcoRI at 400bp point.
This means that when the DNA is exposed to the enzyme two fragments will be produced, one 400bp long and one 2100bp long.

However, in a mutated one...

5' GAATTC ----> 5'GACTTC
3' CTTAAG ----> 5'CTGAAG
When the mutated gene is exposed to EcoRI there will be only one fragment; 2500bp

Explain why two fragments are produced when the normal gene is exposed to EcoRI and only one fragment is produced when the mutated gene is exposed to EcoRI.

I have a few ideas that might be correct
- The mutated gene is completely altered?
Or
- The mutation changes the restriction site hence, the enzyme produces only one fragment as there is no stop at 400bp.

Could someone please help me out 

The second answer is correct - the enzyme no longer recognises the site so it cannot cut meaning the fragment remains as its original length - 2500 (or adding the two).

[Reus]

The second answer is correct - the enzyme no longer recognises the site so it cannot cut meaning the fragment remains as its original length - 2500 (or adding the two).

Thank you!!

[katiesaliba]

The replication is occurring in two different directions.  So for one direction strand x is a leading strand, but in the other direction it is a lagging strand.

I understand that, but can the same strand be leading and then turn into a lagging strand?

[ravi2]

when they ask for the products of fermentation, are you supposed to say: ethanol + carbon dioxide, or ethanol + carbon dioxide + 2 ATP
Thanks 

[nhmn0301]

 

I understand that, but can the same strand be leading and then turn into a lagging strand?

According to my knowledge, no.

when they ask for the products of fermentation, are you supposed to say: ethanol + carbon dioxide, or ethanol + carbon dioxide + 2 ATP
Thanks 

The product of fermentation itself in plants is just 2ethanol + 2CO2 and NAD+. Fermentation does not produce ATP, it just help to prevent the accumulation of NADH in glycolysis since NADH cannot be used in Krebs or ELC, the build up will slow down glycolysis. So, glycolysis produces the 2 ATP, not fermentation.