Yacoubb's Bio 3+4 Questions

[Yacoubb]

Does transcription start when RNA polymerase binds to the promotor in the upstream (flanking region) of a gene? I mean, is it that once RNA polymerase forms a complex with the promotor, transcription of the DNA template strand occurs?

[vox nihili]

Does transcription start when RNA polymerase binds to the promotor in the upstream (flanking region) of a gene? I mean, is it that once RNA polymerase forms a complex with the promotor, transcription of the DNA template strand occurs?

In the traditional sense, yes. Though it's outside of the course.

[Yacoubb]

I've taken a look at the 2012 assessment report on what they listed as the steps for PCR (Polymerase Chain Reaction). I've added a few things of my own to my explanation. Could someone please check if it is good enough? I've ensured I've covered the points mentioned by VCAA but added a few of my own for a bit more detail. Thanks!

1. The DNA is heated to approximately 95^oC; the DNA molecule denatures, and the two complementary polynucleotide strands separate as the hydrogen bonds between the two strands are broken.
2. The DNA is cooled to approximately 50^oC; the primer (short, single stranded DNA or RNA molecule made up of 10-20 nucleotides) anneals to the 3' end of the target DNA sequence.
3. The DNA is heated to approximately 72^oC; TAQ/DNA polymerase begins to construct the complementary DNA strands indicated by the primer in a 3' to 5' direction.
4. The cycle is repeated to further amplify the quantity of DNA.

Thank you!

[vox nihili]

I've taken a look at the 2012 assessment report on what they listed as the steps for PCR (Polymerase Chain Reaction). I've added a few things of my own to my explanation. Could someone please check if it is good enough? I've ensured I've covered the points mentioned by VCAA but added a few of my own for a bit more detail. Thanks!

1. The DNA is heated to approximately 95^oC; the DNA molecule denatures, and the two complementary polynucleotide strands separate as the hydrogen bonds between the two strands are broken.
2. The DNA is cooled to approximately 50^oC; the primer (short, single stranded DNA or RNA molecule made up of 10-20 nucleotides) anneals to the 3' end of the target DNA sequence.
3. The DNA is heated to approximately 72^oC; TAQ/DNA polymerase begins to construct the complementary DNA strands indicated by the primer in a 3' to 5' direction.
4. The cycle is repeated to further amplify the quantity of DNA.

Thank you!

Nothing wrong with it. Remember that PCR does it to both strands. Yours seems to suggest that there's one target strand, but really, that's not particularly important!

[Yacoubb]

Is it accurate to say that male mammals are hemizygous for the X chromosome? Would it be accurate to state that only females can be carriers for autosomal recessive traits because a carrier must be heterozygous (thus have two X chromosomes), and males only have one X chromosomes (hence hemizygous for the X chromosome), rendering them unable to be carriers and instead either affected or not affected by the trait under investigation.

Also, would we need to ever state the genotypic ratio for a dihybrid cross involving two heterozygote parents (for each of the traits - e.g. TtBb). Because there are literally 9 different possible genotypes. The phenotypic ratio for such a cross is much simpler to write.

[psyxwar]

Is it accurate to say that male mammals are hemizygous for the X chromosome? Would it be accurate to state that only females can be carriers for autosomal recessive traits because a carrier must be heterozygous (thus have two X chromosomes), and males only have one X chromosomes (hence hemizygous for the X chromosome), rendering them unable to be carriers and instead either affected or not affected by the trait under investigation.

Also, would we need to ever state the genotypic ratio for a dihybrid cross involving two heterozygote parents (for each of the traits - e.g. TtBb). Because there are literally 9 different possible genotypes. The phenotypic ratio for such a cross is much simpler to write.

Hemizygous refers to genotype when it's an X-linked gene and you're talking about a male afaik (rather than homo or hetero as you only have one chromosome actually carrying the gene). I don't think you use it to reference chromosomes, eg. You don't say that females are homozygous for the X

[simpak]

Also, would we need to ever state the genotypic ratio for a dihybrid cross involving two heterozygote parents (for each of the traits - e.g. TtBb). Because there are literally 9 different possible genotypes. The phenotypic ratio for such a cross is much simpler to write.

Potentially, but it would probably come as a part of drawing a cross.  So they would be right in front of them and you would just reiterate them at the bottom.  If you mean 'am I expected to know there are x number of this genotype and x number of that genotype off by heart without doing a cross' the answer is no.  Just the kind of phenotypic ratio you would have off by heart, if they ask you for the genotypic ratio I'm sure drawing the cross would also be worth some kind of marks and there would be space for that on the page.

[Yacoubb]

Hemizygous refers to genotype when it's an X-linked gene and you're talking about a male afaik (rather than homo or hetero as you only have one chromosome actually carrying the gene). I don't think you use it to reference chromosomes, eg. You don't say that females are homozygous for the X

Okay I forgot to mention that the trait under investigation was X-linked. So what other way could I say that males are unable to be carriers because in this case, the trait is autosomal recessive, and so females whom are heterozgous (e.g. X^HX^h) can be carriers, but because males have only one X chromosome, they can either be affected with the trait (X^hY) or unaffected (X^HY).

Note: h is the allele for the recessive trait and H is the allele for the dominant trait.

[psyxwar]

Okay I forgot to mention that the trait under investigation was X-linked. So what other way could I say that males are unable to be carriers because in this case, the trait is autosomal recessive, and so females whom are heterozgous (e.g. X^HX^h) can be carriers, but because males have only one X chromosome, they can either be affected with the trait (X^hY) or unaffected (X^HY).

Note: h is the allele for the recessive trait and H is the allele for the dominant trait.

I'm not sure why a male couldn't be a carrier for an autosomal recessive trait? Autosomes are your non-sex chromosomes and both males and females have a homologous pair.

[Yacoubb]

I'm not sure why a male couldn't be a carrier for an autosomal recessive trait? Autosomes are your non-sex chromosomes and both males and females have a homologous pair.

Edit: X-linked recessive! Sorry I'm so out of it today LOL!

[Yacoubb]

Does progeny mean offspring?

[Scooby]

Does progeny mean offspring?

yup

[Smiley_]

That all looks fine. Though you don't need to say the last bit about RNA polymerase. Just that it synthesises pre-mRNA from DNA

The remarks about pre-mRNA and mRNA are completely correct too, and I think your definitions of the different RNAs are sufficient as well!

ok this is going to sound really stupid but i keep getting confused on transcription and translation and dna replication because i keep seeing different notes on it

does anyone have any clear notes pleases

[Yacoubb]

ok this is going to sound really stupid but i keep getting confused on transcription and translation and dna replication because i keep seeing different notes on it

does anyone have any clear notes pleases

Remember DNA replication as being part of the cell cycle (S-phase of Interphase), and then remember Transcription and Translation as gene expression!

[Smiley_]

Remember DNA replication as being part of the cell cycle (S-phase of Interphase), and then remember Transcription and Translation as gene expression!

whats gene expresssion?

and does dna replication come first?

where do all the enzymes come in ?