Gene Products and Protein synthesis Flashcards
The code is read in triplets. How many different possibilities are there of triplets are there? And what does this say about the degenerate code?
There are 64 possibilities
20 Amino acids
The code is degenerate- one amino acid is coded by more than one triplet.
What impact does a change in reading frame have
Most likely cause changes in the amino acid sequence which causes a change in amino acid sequence
This changes primary structure
This changes structure of the protein
This changes the function of the protein
What are examples of frameshift mutations
Insertion
Deletion
What is required for translation to occur ?
mRNA- carries sequence of information to make protein
tRNA- bring individual amino acids to the sites of protein synthesis
Ribosome- site of translation
Contains rRNA and ribosomal proteins
Describe the structure of tRNA
Single stranded- BUT tRNA has intramolecular double stranded feature- extensive internal base pairing
Clover leaf shaped
On the end of the 3’ there is a CCA-OH
Anticodon- on the central loop- which is complementary to bases of the codon
Amino acid attached to the 3’-
forming specific amino acyl tRNA- each tRNA can only accept one amino that is appropriate
Amino acid + tRNA +ATP —-> aminoacyl tRNA + PPi + AMP
Describe what is meant by the term “wobble base pairing”
The idea that the last base on the codon loop can form non Watson-Crick pairs
Does not alter the amino acid sequence of the protein
Therefore allows for a single tRNA species to recognise more than one codon
Means that there are less than 61 tRNAs- instead there are 20 classed by their AA
Ribosome- Ecoli
70s Complex – > Large Subunit (23s rRNA, 55 rRNA, 34 proteins)
—> Small subunit (16s rRNA, 21 proteins)
Name the 3 sites of the ribosome (L–>R)
E- site
P-site
A- site
Initiation
1) 30s binds to IF 1 and IF 3
2) This complex then binds to mRNA
3) fmet-tRNA ^fmet binds to GTP-IF2, entering the P site of the 30s
IF2 is activated by the binding GTP
4) fmet-tRNA ^fmet anticodon loop lines up with the AUG initiation coodon
5) Binds to 50s complex whilst GDP and pi is released
Comment on the site of initiation
at the Shine- Dalgno sequence
sequence upstream of AUG sequence binds to 16s rRNA
This ensures that translation is in frame translation
Polycystemic
Allows for multiple proteins to be translated- in typical bacteria mRNA
Describe Elongation
Activated amino acid binds to elongation factor (EF-Tu GTP) enters the A site of ribosome
Energy required for proof reading provided by GTP hydrolysis to GDP
Peptide bonds form between amino acids in the P and A site
EF-G binds and ribosome translocates (GTP hydrolysis and due to peptidyl transferase) A site is free again
Termination
Stop codon presented on the A site
Release factor binds to the stop codon
Hydrolysis of protein from tRNA
Ribosome complex dissociated
Requires IF3 and ribosomal recycling factor and GTP hydrolysis
