Translation Flashcards
What are the three key types of RNA involved in protein synthesis
mRNA, tRNA, rRNA
Which end of tRNA is the AA attached to
3’ end
What is an anticodon
Feature of tRNA which is three bases that pair with a complementary codon on mRNA
How much of total cell RNA does rRNA account for
80%
How many strands of rRNA does the large subunit of the ribosome consist of and what are their sizes
3 strands, 28S, 5.8S, 5S
How many protein molecules are in the large subunit of the ribosome
49
How many protein molecules are in the small subunit of the ribosome
33
How many strands of rRNA does the small subunit of the ribosome consist of and what are their sizes
1 strand, 18S
What is the size difference between the large and small subunit of the ribosome
60S vs 40S
What are the two main functions of rRNA
Maintain ribosome form and catalyse peptide bond formation in protein translation
Define the genetic code in mRNA
The way in which the sequence of the four bases in mRNA correspond to the sequence of the 20 amino acids in proteins
What are triplets
Bases are in trios called codons
What is meant by no overlap in the genetic code
Each codon relates to one amino acid
What are the 6 features of the genetic code
One directional (5’-3’), no ‘punctuation’/modification in sequence, degenerate, no overlap, designated STOP codons, universal
How many codons code for amino acids
61
How many codons are STOP codons
3
What is the designated start codon and what does it code for
AUG- methionine
What is meant by degenerate
Most amino acids are encoded by more than one codon as there are more codons than amino acids
Which two amino acids only have one codon
Tryptophan and methionine
What are Aminoacyl tRNA synthetases
Enzyme that catalyses the aminoacetylation of tRNA
What are the 4 steps of aminoacetylation of tRNA
1) AAs attached to specific tRNA
2) AA is esterified and activated so it can form a peptide bond
3) tRNA+AA= aminoacyl tRNA (catalysed by aminoacyl tRNA synthetase and use of energy from ATP)
4) the AA in aminoacyl tRNA will be incorporated into a growing polypeptide at a posterior determined by it’s anticodon on tRNA
What are the 4 steps of translation initiation
1) small ribosomal subunit joins with special initiator tRNA carrying methionine (so anticodon matches AUG start codon on mRNA)
2) attaches to cap structure at 5’ end of mRNA and scans for AUG start codon
3)At the start codon the large subunit binds to them to form the initiation complex
4) the special initiator tRNA occupies the P (peptidyl) binding site of the ribosome
What are the 4 steps of translation elongation
1) second aminoacylated tRNA enters A (aminoacyl) binding site of ribosome, it,s anticodon matches the mRNA codon at the A site
2) peptide bond is formed between the two adjacent AAs, initiator tRNA releases it’s AA (Met) onto the new tRNA
3)Ribosome shifts along the mRNA to the next codon (now deacylated) and the initiator tRNA is at the E (exit) binding site of the ribosome where it exits
4) another aminoacylated tRNA enters the A site of the ribosome and another peptide bond is formed (cycle repeats)
What are the 4 steps of translation termination
1) mRNA STOP codon enters A site
2) no tRNAs can match STOP sequence so no tRNA approaches A site
3) release factor binds to codon instead, leading to the breaking of the bond linking tRNA and the polypeptide
4) polypeptide is released from the ribosome and disassociates into it’s subunits until it is required again
Where does post translational modification occur
Endoplasmic reticulum
What 3 ways can proteins be modified post translation
Folding, formation of disulphide bonds, glycosation
What is glycosation
Addition of sugar group to form a glycoprotein
What are the 5 steps of post translational modification
1) signal sequence emerges from ribosome and is recognised by a signal recognition particle (SRP) which binds to it, stopping elongation of a polypeptide
2) SRP brings the entire ribosome and incomplete polypeptide to join with a peptide translocation complex on the outer ER surface
3)SRP disassociates itself from ER surface and elongation resumes with the polypeptide being fed from ribosome into ER until complete
4)signal sequence is removed by signal peptidase in ER lumen
5)PP now free in ER lumen, ribosome disassociates and is recycled
Does post translational modification happen to all proteins
No, some remain in the cytoplasm while others are transferred to the ER for PTM
