DNA replication & Cell processes - Protein Synthesis Flashcards
Define translation
Process by which a sequence of amino acids is formed from a polypeptide strand
Describe tRNA
tRNA + Amino acid = Amino acyl tRNA
tRNA has 5’ + 3’ strand Amino acid is added to 3’ strand (ACC base sequence on tRNA).
Anticodon is found on the loop of the structure binds to codon on mRNA.
In amino acid addition hydrolysis takes place.
Four helices form the secondary structure of tRNA.
Anticodon loop contains anticodon.
CCA arm is what attaches the amino acid.
What are the features of the genetic code?
Non overlapping – Each codon is read only once
Degenerate – each amino acid has more than one codon
Stop codon – doesn’t code for any protein
Universal – same DNA structure for all organisms (except mitochondria)
Describe ribosome structure
Prokaryotes = 70s (50s + 40s subunits)
Eukaryotes = 80s (40s +60s subunits)
Ribosomes are made from a mix of both RNA + Proteins (peptide bond forming site = RNA)
Describe peptide chain growth
Polypeptides are formed due to continuous addition of amino acids to the PP chain (to the carboxyl end peptide bonds form between NH2 and COOH
Error rate is 1x10^-4 (fast addition of polypeptides and low chance of inserting wrong one)
Name the modified tRNA nucleotides
Methylionosine Dihydrouridine Ribothymidine Pseuridine Methyl Guanosine Dimethyl Guanosine
What is Amino acyl tRNA synthetase?
Enzyme that attaches amino acid to CCA arm of tRNA reads anticodon
If anticodon corresponds with the the amino acid, it is added
Hydrolyses and removes the wrong amino acids (wrongly charged tRNA)
How does editing occur using amino acyl tRNA synthetase?
CCA arm is flexible Moves AA between editing site & Activation site
If editing occurs, the amino acid is removed via hydrolysis
What are polysomes?
Found in Eukaryotes and Prokaryotes
1 mRNA has many ribosomes found on the mRNA strand (polysomes)
Higher amount of ribosomes binding more protein synthesis (regulates gene expression)
What happens in initiation?
AUG binding site on mRNA where ribosomes bind (larger the binding site greater the ribosome affinity) (16s RNA from 30s RNA joins from 70s RNA) this regulates gene expression
Protein initiation factors aid in the assemble of initiation complexes (such as 30s and 70s)
The small sub units (40s and 30s) join at the binding site moves to TIS At TIS corresponding codon joins (AUC) with tRNA carrying methionine- eukaryotes + formylmethionine-prokaryotes
At TIS the large subunit binds (50s + 60s)
What happens in elongation?
Ef-Tu aids in elongation brings amino acyl tRNA to the ribosome
What are the stages of elongation?
3 sites (A site, P site and E site)
Aminoacyl tRNA containing methionine is present in the P site (due to initiation)
Another amino acyl tRNA enters the A site (EF-Tu)
A peptide bond forms between both amino acids
Ribosome then moves along to net codon (translocation)
The A site is now free for another amino acyl tRNA to come in & the deacylated tRNA dissociates from the ribosome
The 50s ribosome contains a tunnel, to allow the growing polypeptide chain to leave
Describe termination
Termination occurs when the stop codon is reached, there is no corresponding RNA
Release factors bind to the A site instead of a tRNA, this causes the polypeptide chain to be cleaved from the ribosome so the large subunit and small subunit also dissociate from each other
What is the wobble hypothesis?
Idea that unconventional base pairing occurs at the 3rd base of the codon (due to 16s RNA not being able to identify if the charged between base pairs are correct)
What bases can U bind to if at the third spot
A G
