Translation of mRNA Flashcards
(16 cards)
What is the Central Dogma?
DNA –> mRNA –> Protein:
Genetic information is transcribed into mRNA, which is translated into protein
What are the three stages of mRNA translation?
1 - Initiation - Ribosome binds mRNA at start codon (AUG)
2 - Elongation - Polypeptide chain growns by adding amino acids
3 - Termination - Ribosome encounters a stop codon, releasing the polypeptide
What are the main molecules involved in translation?
mRNA - Template for protein synthesis (500-10,000 bases)
tRNA - Matches codons to their amino acids (74-95 bases)
Aminoacyl-tRNA synthetases (aaRS) - Enzymes that charge tRNAs with the correct amino acids
Ribsome - Ribonucleoprotein complex (rRNA + proteins)
Translation factors:
Initiation (IF/eIF)
Elongation (EF/eEF)
Termination (RF/eRF)
What are polysomes?
Multiple ribosomes translating the same mRNA simultaneously
What are the three ribosomal sites?
A-site (Arrival) - Where new aminoacyl-tRNA binds
P-site (Paste) - Where peptide bonds form
E-site (Exit) - Where deacylated tRNA leaves
What does tRNA do?
Links codon to amino acids, using anticodon complementary to the mRNA codon
What is the structure of tRNA?
Cloverlead shape, small (<100 bases)
Amino acid attaches at the 3’ end (CCA)
What are isoacceptor tRNAs?
Different tRNAs charged with teh same amino acid but recognising different codons (e.g., Serine tRNAs recognise 6 codons)
Why are tRNAs highly modified?
Enhances stability, recognition, codon pairing (15-20% of based modified)
What is the Wobble Hypothesis?
Relaxation of standard base-pairing rules allowing one tRNA anticodon to recognise multiple codons while inserting the same aino acid
What are the key steps in translation?
1 - Arrival at A-site - New aminoacyl-tRNA binds
2 - Peptide Bond Formation - Polypeptide transferred from P-site tRNA to A-site amino acid
3 - Large Subunit Translocation - Ribosome moves one codon forward (5’ to 3’)
4 - Small Subunit Translocation - Deacylated tRNA exits via E-site, A-site is vacated
What is the role of Peptidyl Transferase Center (PTC)?
Catalyses peptide bond formation (part of ribosome)
How does the ribosome locate the start codon (AUF)?
Via the Ribosomal Binding Site (RBS), only required in prolaryotes
What are the prokaryotic initiation factors (IFs)?
IF1 - Prevents premature binding of tRNA
IF2 - Helps initiator tRNA bind AUG
IF3 - Stabalises 30S subunit, prevents premature 50S binding
How does initiator tRNA (Met-tRNAf) differ from elongator tRNA?
Initiator Met-tRNAf is formylated (fMet)
Elongator - Met-tRNAm is unmodified
Why is fMet important?
Directs polypeptide chian growth, distinguishing start codon translation from normal elongation
