Translation Flashcards
What do ribosomes contain?
rRNA and proteins
How are ribsomes measured?
In Svedberg units
- Rate of sedimentation by centrifugation
How many svedberg units are prokaryotes?
70S
- Small (30S) and large (50S) subunit
What antibiotics target the 50S subunit?
- Erythromycin (macrolides)
- Chloramphenicol
- Clindamycin
- Lincomycin
What antibiotics target the 30S subunit?
- Tetracyclines
- Spectinomycin
- Streptomycin
- Gentamicin
- Kanamycin
- Amikacin
- Nitrofurans
How many svedberg units are eukaryotes?
80S
- Small unit 40S
- Large 60S
What enzyme synthesises tRNA to mRNA?
RNA polymerase III
What is an example of a chemically modified base found on tRNA?
N,N dimethyl Guanosine
How many NTs make up tRNA?
70-90 NTs (tiny)
What is the structure of tRNA?
What are the different components?
Cloverleaf shape (secondary structure)
- 3’ end longer than 5’ at the top of the molecule
- D-loop (part of D arm)
- T loop (part of T arm)
- Anticodon loop at bottom of molecule
What does the D loop contain?
Dihydrouridine
What enzyme recognises the D loop on t-RNA?
Aminoacyl-tRNA synthetase
What does the T loop allow for?
tRNA ribosome binding
- Contains TpsiC sequence, contains many altered bases
What does the 3’ end (at the top of tRNA) contain?
Always ends in CCA
- Hydroxyl (OH) of A attaches to amino acid
What is charging?
The process of linking amino acids to tRNA
What enzyme does charging? (amino acid binding to 3’ end (OH) on tRNA)
Aminoacyl-tRNA synthetase (different types, one enzyme per amino acid)
- Requires ATP
The carboxyl group on the amino acid binds to the OH group on the tRNA to creae what?
Aminoacyl group
An intermediate step in charging where ATP is added to the amino acid creates what?
Amino acid AMP
- Once the amino acid is bound to tRNA by Aminoacyl-tRNA synthetase the AMP breaks off
What is the process called by which a mischarged tRNA (wrong amino acid for the anticodon on tRNA) is corrected?
Hydrolic editing
- Aminoacyl-tRNA synthetase scrutinises amino acid
- If incorrect -> hydrolyses from AMP or tRNA
What end of the amino acid binds to the OH group on the 3’ end of the tRNA?
C-terminal end (COOH) group
What are the 3 major stages of protein synthesis?
- Initiation
- Elongation
- Termination
What are the 4 binding sites on ribosomes?
- 1 for mRNA
- 3 for tRNA: A-site, P-site, E-site
What binds on the A-site on the ribosome?
Amino acid (charged tRNA)
What happens at the P-site?
tRNA attached to growing protein chain
- methionine or N-formylmethionine
What happens at the Esite?
Exit of tRNA
What codon codes for initiation on mRNA?
AUG
What does AUG code for?
Methionine or N-formylmethionine (fMet)
- Binds directly to P-site
- Initiation of translation (
AUG codes for N-formylmethionine (fMet) in what type of cells usually?
Prokaryotes
- Acts as a chemotactoc agent for neutrophils (innate immunity)
What does intiation require in addition to methionine/fMet? (which binds to P site)
- GTP hydrolysis
- Initiation factors (proteins) which assemble ribosomes and tRNA
What proteins are involved in elongation?
Elongation factors
What do elongation factors do?
Hydrolyze GTP to GDP
What are the EF in bacteria?
EF-Tu and EF-G
What are the EF in eukaryotes?
EF1 and EF2
What bacterial toxins target EF2?
- Diptheria toxin
- Exotoxin A (pseudomonas aeruginosa)
They inhibit protein snthesis
What are the 4 steps involved in elongation?
- Charged tRNA binds A-site
- Amino acid joined to peptide chain (catalysed by the ribosome)
- Translocation: ribosome moves down mRNA towards 3’ end
- tRNA leavs E site
What is the function of peptidyl transferase?
Catylises linkage of amino acid in a site to protein chain in P site
Stop codons code for what amino acid?
None
- It is not recognised by tRNA
What binds to ribosome at stop codons?
Releasing factors
- Add water to end of protein chain
What does phosphorylation (post-translational modification) involve ?
Amino acid residue phosphorylated
- Protein kinase enzymes add phosphate group
What does glycosylation (post-translational modification) involve ?
Formation of sugar-amino acid linkages
- Many linkages (N, O, C) linked glycosylation
- Creates glycoprotiens
Hydroxylation of what amino acids is important in collagen synthesis?
Proline and lysine residues
Acetylation is what?
Addition of acetyl (CH3CO) group
What is ubiquitination?
Addition of ubiquitin (small protein)
- Tags protein for destruction in proteosome
What is the function of chaperones?
Proteins that facilitate folding
- Bind to other proteins -> ensures proper folding
Give an example of chaperones?
Heat shock proteins
- Increase expression with stressors (pH shift, heat, hypoxia)
- Stabilize proteins - maintaining structure which helps then survive environmental stress
