Edexcel AS Biology help

Hi,
Could someone please explain transcription and translation to me, I just can't wrap my head around it

thanks :smile:

Reply 1

strawberrypocky

Transcription:
-occurs in the nucleus
-the H bonds between the bases in the DNA strand break revealing the bases
- RNA polymerase attaches to the template DNA strand
- Free RNA nucleotides line up against the DNA strand via complementary base pairing
- RNA polymerase forms phosphodiester bonds between the RNA nucleotides (via a condensation reaction)
- Forms a strand of mRNA which then detaches from the DNA template strand and exits the nucleus through the nuclear pores

Translation
- Occurs at the ribosomes; mRNA attaches to a ribosomes binding site
- a tRNA molecule carring the anti triplet codon (to the triplet code on the mRNA strand) and a specific amino acid comes and attaches to the binding site of the ribosome
- Another tRNA molecule comes and attaches to the binding site
- A peptide bond forms between the two amino acids carried by the tRNA molecules
- The first tRNA molecule leaves and a new tRNA molecule comes along
- Process repeats itself and the ribosome moves along the mRNA strand until it reaches a stop codon.
- Results in the formation of a polypeptide chain

Hope this helps :smile:

Reply 2

lw010499

hi could anyone do a brief explanation of sexual reproduction in both plants and mammals

Reply 3

username2624347

thankyou so much :smile:

Reply 4

Dinaa

Original post by lw010499

hi could anyone do a brief explanation of sexual reproduction in both plants and mammals

Are you retaking because I don't think you need to know that? Or are you not retaking otherwise ignore me.

Reply 5

Dinaa

Can someone explain the Meselson and Stahl experiment? I know the experiment but haven't seen it crop up in an exam as a 5marker so idk how to word it all.

Thanks

Reply 6

Sunethra

Original post by Dinaa

Can someone explain the Meselson and Stahl experiment? I know the experiment but haven't seen it crop up in an exam as a 5marker so idk how to word it all.

Thanks

These scientists took a sample of E.coli bacteria and left it in a dish containing N15 which is know as the heavy nitrogen. The after cell divsison is was weighed and they realized that It was very heavy. they then put it in a medium of normal nitrogen N14 and it was allowed to divide only once and after that the first generation is obtained and when they weighed they realized that the DNA was intermediate btw the N15 and N14