Test 1 part 2 Flashcards
in transcription and translation: Why use rna, why not use DNA directly as a template?
Amplification of the signal. Using an intermediate we can amplify the process.
Transcription and translation
transcription using dna as a template to make a copy of mrna, and then translation - using the mrna as a template to make the protein.
Why use RNA? for transcription and translation
We can keep the dna protected in the nucleus. Rna lasts longer outside the cell - not as able to be broken down - lasts hours to days.
Transcription
When starting the process of transcription we need to know where to start - specific proteins called transcription factors - recognise a sequence of nucleotides called a promoter region.
They’re going to act as a signal to recruit the RNA polymerase so that it knows where to start.
The RNA polymerase comes a long and other proteins come along, and the RNA polymerase comes along and it separates the strands and then the hydrogen bonds are reforming at the back.
The rna polymerase produces RNA that comes out the otherside.
The monomers come in through the entry site which are stitched together to make the polymer - RNA.
The polymerase continues until it hits the termination sequence which tells it where to stop.
How do we stop - Transcription
Hairpin structure - when we have a particular series of bases that we can read the same backwards and forwards creating these hairpin structures in which we can get hydrogen bonds forming between complementary strands. When the rna polymerase hits one of these sequences hairpin structures form in the exit channel and the rna polymerase starts to stall.
The other way to do this is by another stop sequence which is recognised by a protein called Rho → atpase that moves along the strand and once it catches up it binds to the rna polymerase that triggers the dissociation as
Translation
we can make a copy of rna and use that as a template to start making copies of some proteins.
Transcription in plants and animals
more is done to the mRNA as well. Processing of the mRNA - there is a cap at one end and a poly-a tail at the other end (string of A residues). This capping increases the stability of the mRNA molecule if it doesn’t have the cap or tail it will become degraded really quickly. The cap helps make sure that the mRNA is transported safely out of the nucleus.
tRNA is the adaptor molecule
Transfer rna - amino acid attaches at one end and an anticodon at the other end and the trna uses some base pairing between the rna that makes it up to recognise the codon and bring in the right amino acid.
Ribosomes in translation
2 subunits of ribosomes - the large and the small subunits. The ribosome is mostly amde of ribosomal RNA - (rRNA). Can do recognition and catalysis - ribosomal RNA. when the two molecules (large and small subunit) come together there is an area at the bottom for the recognition and then an acitvie site at the top.
Binding in translation
Make sure that we have the right reading frame - there are multiple reading frames so need to make sure we have the correct arrangement at the start.
We always have AUG as the start codon - always the first tRNA that comes in and starts recognising the start codon.
We get a particular region on the mRNA called the ribosome binding site, the ribosomal RNA in the small subunit can form some hydrogen bonds with a sequence of nucleotides at the ribosme binding site and that helps make sure that we’ve got a pattern.
So we have an mrna binding site where we get complementary hydrogen bonding between the ribosomal rna and the small subunit. The small subunit binds to the mRNA and then the tRNA comes in aswell.
Once its worked out where to start the large subunit comes in on top and we can start making our protein. We need energy to power these steps, when the ribosome is making proteins it uses GTP - g base instead of the a base.
COVID’s genome
COVID has an RNA genome with a 5 prime cap and the poly A tail. Our cells will only take in a RNA genome with the cap and tail, so when it enters the cells it gets recognised and proteins start getting made immediately. Hijacks the ribosomes to make its own stuff in the cell.
Which mutations are we more likely to see?
Adenine and guanine and pyrimidine with two ringed structures. Cytosine and thymine and single ringed structures. You are far more likely to see the changes between the A’s and G’s and C’s and T’s - transitions and not transversions.
Mutations
We can get change to base, insertion/deleltion, breakage.
Nucleotide pair substitution
Silent mutation - at the three prime end - change of sequence but still the same amino acid.
Missense - different amino acid.
Nonsense mutation - stop codon - much shorter protein
Multiples of three - one amino acid is missing
