Protein Synthesis Flashcards
How are amino acids bound to their cognate tRNA
- The amino acid must be activated by the addition of ATP
2. The binding of the activated amino acid (AMP complex) to its tRNA is catalyes by a specific tRNA synthetase
Initiation
- ribosomes first attached to mRNA here at start codon
1. Small subunits complexes with initiation factos and base pairing occurs between the small subunits and a special sequence on the mRNA
2. Start codon (AUG) of mRNA is positioned in the ribosomal P site and formyl-methionyl tRNA
3. Large subunit joins, GTP is hydrolysed , and initiation factors leave the ribosome
Elongation
- movement of ribosomes
Ribosome is a ribozyme
The ribosome has 3 sites where tRNA can bind if which 2 are usually occupied at one time
The ribosome does not act on: all stages require additional factors
A site- Aminoacyl acceptor site (IN)
P site - peptidyl site ( bond formation)
E site - Exit site (OUT)
The growing peptide chain is in the A site afte peptide formation
The final step is translocation
- the ribosome moves 1 codon towards the 3’ end of mRNA so that the growing peptide chain moves A to the P site. This means that unloaded tRNA now moves to E site. The A site is now empty, then it all happens again
Termination
- Synthesis continues until a stop codon is reached (UAA, UGA or UAG(
- a special release factor (RF) binds in the A site
- polypeptide in the P site is then hydrolysed from its tRNA and leaves via the exit tunnel, the tRNA then exists the ribosome
Commonly used antibiotics work by binding to bacterial ribosomes
Tetracycline
- prevents tRNA binding to the A site
- (tetracycline =4 rings)
- the most common current use in the treatment of moderately severe acne
Commonly used antibiotics work by binding to bacterial ribosomes
Chloramphenicol
- inhibition of peptide bond formation
- chloramphenicol is effective against wide range of bacteria. However, because of resistance, it is no longer a first- line agent for infection in developed nations, except for topical treatment of bacteria conjunctivitis
Commonly used antibiotics work by binding to bacterial ribosomes
Erthromycin
- blocking the exit tunnel of the ribosome
- ethromycin is a macrolide antibiotic and is often prescribed for people who have an allergy to penicillins
Mutation….
The mutation of just a single base in the RNA or single amino acid in a ribosomal protein can cause antibiotic resistance
What happens after protein synthesis.. Post- translation modification (PTM)
- is the enzymatic(convalent) modification of a protein after its translation
- it is the way in which on polypeptide chain can be modified to give many different versions of the same protein
- understanding post-translation modification of proteins help diagnose patient disease thro proteomics
PMT : phosphorylation
- kinases add phosphate groups for activation or inactivation
- phoshatases hydrolyze the phosphate group (remove it)
- phosphorylation, principally on the serine, threonine or tyrosine reudues, is critical in the regulation of many cellular processes including cell growth, apoptosis and signal transduction pathways
PMT : glycosylation
- one of the major PMT, with significant effects on protein folding, conformation, distribution, stability and activity.
Common types of PMT
- Lipidation
- Phosphorylation
- Glycosylation
- Acetylation
- Ubiquitnation
- Methylation
Other
Identification if PTM in study of disease
- patient serum sample collected
- (proteins)
- fractionation
- digested with proteolytic enzymes
- (peptides)
- seperated by chromatography
- analysed by mass spectroscopy
- protein spectra
- analysed algorithm to generate a cancer-associated pattern
