Translation Flashcards by Joe Bloggs

What do ribosomes contain?

rRNA and proteins

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How are ribsomes measured?

In Svedberg units

- Rate of sedimentation by centrifugation

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How many svedberg units are prokaryotes?

70S

- Small (30S) and large (50S) subunit

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What antibiotics target the 50S subunit?

Erythromycin (macrolides)
Chloramphenicol
Clindamycin
Lincomycin

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What antibiotics target the 30S subunit?

Tetracyclines
Spectinomycin
Streptomycin
Gentamicin
Kanamycin
Amikacin
Nitrofurans

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How many svedberg units are eukaryotes?

80S

Small unit 40S
Large 60S

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What enzyme synthesises tRNA to mRNA?

RNA polymerase III

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What is an example of a chemically modified base found on tRNA?

N,N dimethyl Guanosine

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How many NTs make up tRNA?

70-90 NTs (tiny)

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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

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What does the D loop contain?

Dihydrouridine

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What enzyme recognises the D loop on t-RNA?

Aminoacyl-tRNA synthetase

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What does the T loop allow for?

tRNA ribosome binding

- Contains TpsiC sequence, contains many altered bases

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What does the 3’ end (at the top of tRNA) contain?

Always ends in CCA

- Hydroxyl (OH) of A attaches to amino acid

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What is charging?

The process of linking amino acids to tRNA

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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

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The carboxyl group on the amino acid binds to the OH group on the tRNA to creae what?

Aminoacyl group

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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

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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