Translation Flashcards
What are the 4 key features of the genetic code
61 of a possible 64 codons specify an amino acid
Most amino acids are coded for by more than one codon
Three condones specify stop (UAA, UAG, UGA)
One codon specifies start (AUG - also codes for amino acid methionine)
What is tRNA
The ‘Adaptor’ molecule
Single strand of RNA
70-80 nucleotides long
At least one tRNA for each amino acid
Each tRNA has a region which can bind an amino acid and a region which can interact with mRNA.
Does the amino acid attach to the 5’ or 3’ end of tRNA
3’
Which way does the anti codon run
tRNA is anti parallel to mRNA, thus it is run/read in the 3’ to 5’ direction
What are the steps involved in charging a tRNA molecule
Amino acid and tRNA enter active (binding) site
Using ATP, aminoacyl-tRNA synthetase catalyses covalent bonding between amino acid and the respective tRNA
Aminoacyl (charged) tRNA is released
What is translation
Translation is the syntheses of proteins by ribosomes using mRNA as a set of instructions
Outline the anatomy of a ribosome
Small and large subunit
mRNA binding site on the small subunit
A site (aminoacyle tRNA binding site), P site (peptidal tRNA binding site), E site (exit site) on large subunit
Where are ribosomes found
Bound to the rER - synthesise proteins that are used within the plasma membrane or exocytosed from the cell
Free floating in cytosol - syntheses of proteins that are released into the cytosol and function within the cell
What are the 3 stages of translation
Initiation
Elongation
Termination
Outline the process of initiation
A specific initiation tRNA (codes for methionine) binds to small ribosomal subunit
Small ribosomal subunit/initiator tRNA identifies the 5’ G-cap and attaches to the mRNA
The small ribosomal subunit/initiator tRNA moves along mRNA (5’ to 3’) until it finds the initiation AUG codon
Complex stops. Initiator tRNA carrying methionine is in P site
Large ribosomal subunit attaches
Summarise elongation
Charged tRNA, with anticodon complimentary to A site codon, lands in the A site
As the ribosome moves along the mRNA by 3 nucleotides (5’ to 3’), the ribosome breaks bond binding amino acid to tRNA in P site and transfer the amino acid to newly arrived amino acid (attached to the tRNA in A site), and forms a peptide bond between them
Uncharged/spent tRNA ejected from E site
New charged tRNA with an anticodon complimentary to the next A site codon enters the ribosome at the A site
Elongation processes continues
Summarise termination
When ribosome reaches a stop codon, a protein called release factor enters the A site
The release factor breaks the bond between P site tRNA (using water) and the final amino acid. Polypeptide chain detaches from tRNA and newly made polypeptide is released
Small and large sub units dissociate from the mRNA and each other
What is a genotype
Set of genes and/or DNA combinations that are responsible for a particular trait
Determined at DNA level
What is a phenotype
The physical expression, or characteristic of a genotype. Observable traits or characteristics
Defined by what happens at the protein level (together with environmental influences)
