Translation Flashcards
(29 cards)
Where does translation occur?
On the ribosome
Does translation occur on the ribosome or in the ribosome?
On the ribosome
What is a ribosome?
large complex of four RNAs and more than 80 proteins
Th ribosome has a 3 sites which are between the large and small subunit of a ribosome. What are the sites?
- E site
- P site
- A site
What is the large subunit of ribosome made up of?
49 proteins and 3 RNA molecules
What is the small subunit of ribosome made up of?
33 proteins and 1 RNA molecule
What is the E site?
exit site
What is the P site?
peptidyl-tRNA site
What is the A site?
aminoacyl-tRNA site
What are the stages that translation can be broken down into?
- Initiation
- Elongation
- Termination
Describe the initiation stage of translation:
- In eukaryotes, translation usually initiates at the first AUG codon in the mRNA
- Initiator tRNAmet bind to AUG start codon to small subunit
- Large subunit can bind and the ribosome to assemble
- P-site is filled by initiator leaving A site empty
What will always be the first amino acid in the polypeptide chain?
Methionine
In what order does translation occur of the three sites on a ribosome?
A to P to E
Describe the elongation stage of translation:
- tRNA with anticodon that is complementary to codon in A site binds
- Amino acid on tRNA in P site is transferred onto the amino acid on tRNA in the A-site
- The empty tRNA mores to E site and is released
- There is a peptide tRNA in the A-site
- Ribosome slides down mRNA so tRNA with growing peptide can more to P-site
- A-site is free to bind another tRNA
- The cycles repeat until ready for termination stage
Describe the termination stage of translation:
- At the end of the coding region of mRNA there is a STOP codon.
- No tRNA with STOP codon
- Translation ends
- Subunits disassemble and release the newly synthesised protein
How do tRNA bound to amino acids?
Specific enzymes
The binding of the tRNA and amino acid causes the tRNA to become?
Charged
What part of the charged tRNA binds with the codon on the mRNA?
anticodon site on the tRNA
How many bases correspond to an amino acid (thought experiment)?
- 4 types of nucleic acids
- 20 types of amino acids in proteins
- so 4^2 = 16 4^3 = 64
- Therefore, at least 3 amino acids
- If call combinations used then code must be degenerate
How do we know codes don’t overlap?
As base mutations only ever affect one amino acids
Describe the Crick, Brenner et als experiment:
- used bacteriophage T4 which infects Escherichia coli
- generated mutants in RII gene in bacteriphage
- distinctive large plaque
- Generated mutants in rII gene of bacteriophage T4 using proflavin
What is proflavin?
- Planar molecule
- Intercalates between base pairs in DNA and can cause insertion or deletion of single base
What is a codon?
Set of three nucleotides
Can amino acids have more than one tRNA?
Yes
