University:
The University Of Western Ontario
Course:
Biology 2290F | Scientific Method in Biology
Academic year:

2021
Views:

283

Pages:

12
Author:

Kyuwon J.

Components of the translation machinery TRNAs(transfer RNAs) ● TRNAs are adapter modules that decodes the genetic code ○ Adept Nucleotide message to protein message ● Bring the amino acid to the growing polypeptide chain ● All have a similar structure(ribosome) ● Have distinguish features to be triplets and amino acid specific ● Stem-Loop structure due to internal base pairing ● Bases tRNAs are highly modified ● In 3D the tRNAs look like an L ○ All tRNA should be similar in structure or would not be able to identify 2 key single stranded regions ● 3` acceptor site ● Anticodon Wobble ● Most organisms have fewer than 45 different tRNAs ● How can all 61 codons be used ○ Not 64 because 3 of them are stop codons. ● For some tRNAs base pairing between the anticodon and the codon only requires matching at two positions. Molecular basis of Wobble ● There is only one type of tRNA for Ph ● It has a GAA anticodon Base pairin interactions for the two Phe codons Aminoacyl tRNA synthetase Couple the 3` end of a tRNA to is correct amino acid The aminoacyl-tRNA Synthetase Reaction Charging of tRNAs ● Store energy from ATP in a high energy ester linkage ● Have proofreading function TRNA-aminoacyl tRNA synthetase complex Ribosome ● Brings everything together ○ MRNA ○ TRNAs ● ● ● ● ● ● ● ● Catalyze protein synthesis Consist of a large and a small subunit Are made of many RNAs and proteins Three sites of binding tRNAs on the ribosome A site that binds aminoacyl-tRNA P site that binds peptidyl-tRNA E site from which tRNA exits MRNA is bound close to the A and P site Steps in translation First- the general mechanism Initiator tRNA ● The first Amino Acid of every protein is a “special” Methionine ○ F-Met ● All other methionines are regular methionines ● Slightly modified ○ Have floro group Step 1 of translation ● An aminoacyl-tRNA binds to the P site of the ribosome ● Requires basepairen between the tRNA and the codon Step 2 ● The energy from the ester bond of the peptidyl-tRNA in the P site is used to form a new peptide bond between the amino acids in the A and P sites ● Red arrows shows the newly added amino acids The peptidyl Transferase Reaction Step 3 ● Peptide bond formation is coupled to a conformational change in the ribosome that shifts the large subunits forwards ● This conformational change reposition the tRNAs ● The former peptidyl tRNA 3 move from P to E site ○ Detach from amino acid and ready to leave the ribosome ● Former aminoacyl tRNA4 from A to P site Step 4 ● The small subunit moves forward(towards the 3` end) exactly 3 bases ● The spent tRNA leaves the E site ● Step 1 is repeated Key point for translation 1. Translation occurs in the cytoplasm-both for prokaryotes and eukaryotes 2. Occurs in 5`=>3` direction along the mRNA making a protein from N to C terminus 3. The mRNA is decoded one codon at a time 4. Energy for peptide bond synthesis comes from the high energy aa-tRNA charging 5. Compex reaction involving a. Both RNA and proteins molecules b. Conformational (shape) changes in the ribosome 6. Specify comes from the a. Aminoacyl tRNA synthetase b. Requirement for base pairing in the A site of the ribosome