Lecture 6 Flashcards
1
Q
Specifying amino acids
A
- mRNA can’t act as a physical template for amino acids
- Adaptors required to link mRNA and amino acids
- This where tRNA comes in
2
Q
tRNA structure
A
- 80 nucleotides long
- Single stranded
- Anti-codon at one end
- Clover leaf structure folds into L shaped molecule
- Amino acid attachment site in the 3’ hydroxyl group at RNA chain end
3
Q
tRNA specificity
A
- Each tRNA is specific for one amino acid. Determined by anticodon
- Specific attachment carried out by amino-acyl tRNA synthestases (activating enzymes)
- one for each amino acid
- has binding sites for tRNA, amino acid and ATP
4
Q
Binding amino acid to tRNA
A
- ATp hydrolsysed and amino acid joined to AMP
- Correct tRNA binds to Amino-acryl and amino acid transferred from AMP to tRNA
5
Q
Ribosome
A
- Composed of ribosomal RNA and proteins
- Two subunits - one large and one small
- Binds mRNA and amino-acyl tRNAs
- Moves in 5-> 3 direction along mRNA
- Catalyses formation of peptide bonds
6
Q
Protein synthesis (intiation)
A
- Small subunit binds to mRNA near the 5’ end
- Intiator amino acyl-tRNA binds to AUG start codon
- Large subunit binds so initiator tRNA fits in P sites
- Requires energy from GTP hydrolysis and proteins called initation factors
7
Q
Elongation
A
- tRNA base pairs with codons in A site
- Peptide bonds formed between amino groups of amino acid and the COOH group of the last amino acid-catalysed by peptidyl transferase
- Growing peptide chain now in A site
- T RNA in P site is ejected, ribosomes moves along one codon
- Growing chain in P site, A site free to accept next amino acyl tRNA
8
Q
Termination
A
- Stop codon in A site
- Release factor enters A site
- Water added to polypeptide chain end
- Completed polypeptide chain released form tRNA in P site
9
Q
Polyribosomes
A
When mRNA is being translated simulataneously by several ribosomes
