protein synthesis Flashcards
What happens in transcription
- Section of DNA arhat contains the gene unteists and unzips ( DNA helicase), beginning at the START codon
Breaking H bonds - Antisense and sense strand
- Free nucleotides(mRNA) will pair with complementary bases exposed on the anti sense strand when the DNA unzips
- PHOSPHODIESTER bonds are formed between DNA neuclotides ( RNA polymerase), transcription STOPS at the end of the gene and the completed short strand of RNA . Same base sequence as sequence making up the gene of dna But U instead of T
- The mRNA then detaches from the dna template and leaves the nucleus through the nuclear pore - the dna double helix reforms and this mRNA then travels to a ribose
What is the sense strand
Contains the protein to be synthesised
Coding strand
RUNS FROM
5’ to 3’
Antisense strand
TEMPLATE
Complementary copy of the sense strand
So that the complementary RNA strand contains same base sequence as the sense strand
MRNA neucleotides
Activated
Ready in nucleus
2 extra phosphates
What are the RNA neucleotides
ATP
GTP
CTP
UTP
What hapoena when neighbouring activated neucleotides are bonded by RNA polymerase
2 phosphates are released
When ATP is dephosphorylated, it releases energy for bonding adjacent neucleotides
What are ribosomes made up of and where are they made
- made in nucleolus
- made up of 2 subunits, one small and one large
These subunits are made of protein and r RNA
properties of rRNA
Maintains the structural stability of the prelim synthesis sequence and plays a biochemical role in catalysing the reaction
What happens when mRNA leaves the nucleus
Bonds to a specific site on the SMALL subunit of a ribosome
A ribosome holds mRNA in position while it’s decided into a sequence of amino acids
What is tRNA
Single stranded
In parts, there’s complementary base pairing and it binds to itself
CLOVER leaf shape
3 based ( anticodon) are at one end of the molecule, this anticodon will bind to complementary codon on mENA and the tRNA molecule Carry amino acid corresponding to that codon
What happens when the tRNA bind to complementary codons
Amino acids brought together in the correct sequence to form the primary structure of the protein coded for by mRNA
Cannot happen all at once - amino acids are added 1 at a time
What happens in translation
The mRNA binds to the small subunit of the ribosome at its start codon ( AUG)
A tRNA with the complementary anticodon ( UAC ) binds to the mRNA start codon - carries the amino acid that is complementary to anticodon METHIONINE
another tRNA carries an amino acid, a maximum of 2 tRNAS can be bound at the same time - ribosome slides along to read next codon
Second tRNA binds to this codon and a peptide bond forms between the 2 amino acids ( peptidyl transferase)
The ribosome moves along the mRNA, deasj g the 1st tRNA, second tRNA becomes first
Stages 3-5 repeated until the ribosome reaches end of mRNA at stop codon and polypeptide is released
How are polypeptides synthesised simultaneously
Many ribosomes can follow on the mRNA behind the first so that multiple identical polypeptides can be synthesised simultaneously
rRNA
Bonds to tRNA
Complementary base pairing
Why are there different ribosomal sites - cytoplasm And ER
- free floating ribosomes - produce proteins for use in cell
ER- produce proteins to export from the cell
