DNA, genetics etc Flashcards
Transcription (in detail - 7 points)
1) RNA polymerase binds you the promoter region of a gene
2) this causes helicase to unwind the DNA double helix
3) RNA polymerase moves along the anti-sense strand in a 5’ —> 3’ direction
4) free RNA nucleotides are attracted to the exposed nucleotides on the antisense DNA strand (complimentary base pairing occurs)
5) as RNA polymerase moves onto another region of the antisense strand, the double helix reforms behind it.
6) when the RNA polymerase reaches the terminator region (stop codon) it causes the enzyme to detach and the pre mRNA molecule to peel away from the DNA strand
5) introns present in the preMRNA are removed by splicing, using a complex called a spliceosome.
6) the adjacent exits are then spliced together to form mature RNA (mRNA)
7) mRNA travels through nuclear pores into the cytoplasm to the ribosomes
Describe transcription (ms version - 8 points)
1) helicase unwinds double helix
2) breaking hydrogen bonds between complimentary base pairs
3) only on strand of DNA acts as a template
4) RNA free nucleotides are attracted to exposed bases
5) nucleotides bind according to complimentary base pairing
6) RNA polymerase joins RNA nucleotides together
7) pre RNA spliced to remove introns
8) mRNA forms and travels through nuclear pores into the cytoplasm to the ribosomes
Basic understanding
Chromosome = double helix DNA all scrunched and curled around itself (and histone proteins) to form the shape of a chromosome
Gêne = section of thé double hélix
When a gene is switched on RNA polymerase attaches to the start of the gene and moves along that section of DNA making a strand of RNA from the free based and nucleotides in the nucleus.
(Where do these free bases and nucleotides come from?)
Then the mRNA peels off again so u have mRNA and then the two strands of DNA - or do the two strands recoils again ???
Before mRNA can be used as template it must be processed (informs taken out etc)- mRNA then into cytoplasm. Ribosomes bons to messenger RNA
Translation:
tRNA has an anticodon that is complimentary to a codon and on its other end of the tRNA molecule is an amino acid binding site where the amino acid that correspond with that anticodon is.
Thé anticodon on the tRNA binds is complimentary to the codon of the mRNA and the amino acid is joined to other amino acids (AA leaves the tRNA and empty tRNA goes away to get more amino acids)
Once the last amino acid has been added the chain folds into a complex 3D shape to form the protein
So does this mean for proteins with 4 polypeptide chains u need one bit of mRNA = 4 chains
Or 4 mRNA = 4 chains ?
mRNA always translated from right to left (5’ to 3’)
If the mRNA is exactly the whole strand of mRNA you want to translate why is there a start codon? Surely the mRNA can just go to the ribosome and as soon as the top of the strand enters it begins ? Why does it have to look for the start codon ???
Initiation - small ribosomal subunit binds to initiateur tRNA carrying initiator amino acid met. This complex attached to the cap structure at the 5’ end of mRNA and scans for the start AUG codon. Does this mean mutations occur where proteins don’t get made if there is no start codon ???
At the start codon the large ribosomal subunits joins the complex and all initiator factors released.
A site - entry site for new tRNA
P site - tRNA that carries growing chain
E site - exit site for tRNA afte rit has delivered the amino acid
Initiator tRNA positioned in the P site
When a tRNA molecule with the correct anticodon and this the correct amino acid enters the A site it means that AA is now adjacent to the AA attached to the tRNA in the P site so a peptide bons forms between the two
tRNA in P site release amino acid which is now bonded to the amino acid on the tRNA in the P site. The tRNA at the P site carries the growing peptide chain.
Ribosome moves one triplet forward so now A site is empty for another tRNA to come in.
Termination when one of the three stop codons is positioned in the À site. No tRNA can fit in the A site at that point as no tRNA that have anticodons complimentary to AUG codon,
Instead a release factor protein binds to this codon which catalysés cleavage of bond between tRNA and peptide (tRNA has been carting growing chain this whole time) which releases the whole polypeptide chain
Ribosome disassociates into its subunits
