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USMLE Biochemistry > Translation > Flashcards

Translation Flashcards

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USMLE® Step 1 flashcards
1
Q

What do ribosomes contain?

A

rRNA and proteins

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2
Q

How are ribsomes measured?

A

In Svedberg units

- Rate of sedimentation by centrifugation

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3
Q

How many svedberg units are prokaryotes?

A

70S

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

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4
Q

What antibiotics target the 50S subunit?

A
  • Erythromycin (macrolides)
  • Chloramphenicol
  • Clindamycin
  • Lincomycin
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5
Q

What antibiotics target the 30S subunit?

A
  • Tetracyclines
  • Spectinomycin
  • Streptomycin
  • Gentamicin
  • Kanamycin
  • Amikacin
  • Nitrofurans
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6
Q

How many svedberg units are eukaryotes?

A

80S

  • Small unit 40S
  • Large 60S
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7
Q

What enzyme synthesises tRNA to mRNA?

A

RNA polymerase III

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8
Q

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

A

N,N dimethyl Guanosine

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9
Q

How many NTs make up tRNA?

A

70-90 NTs (tiny)

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10
Q

What is the structure of tRNA?

What are the different components?

A

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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11
Q

What does the D loop contain?

A

Dihydrouridine

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12
Q

What enzyme recognises the D loop on t-RNA?

A

Aminoacyl-tRNA synthetase

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13
Q

What does the T loop allow for?

A

tRNA ribosome binding

- Contains TpsiC sequence, contains many altered bases

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14
Q

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

A

Always ends in CCA

- Hydroxyl (OH) of A attaches to amino acid

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15
Q

What is charging?

A

The process of linking amino acids to tRNA

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16
Q

What enzyme does charging? (amino acid binding to 3’ end (OH) on tRNA)

A

Aminoacyl-tRNA synthetase (different types, one enzyme per amino acid)
- Requires ATP

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17
Q

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

A

Aminoacyl group

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18
Q

An intermediate step in charging where ATP is added to the amino acid creates what?

A

Amino acid AMP

- Once the amino acid is bound to tRNA by Aminoacyl-tRNA synthetase the AMP breaks off

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19
Q

What is the process called by which a mischarged tRNA (wrong amino acid for the anticodon on tRNA) is corrected?

A

Hydrolic editing

  • Aminoacyl-tRNA synthetase scrutinises amino acid
  • If incorrect -> hydrolyses from AMP or tRNA
20
Q

What end of the amino acid binds to the OH group on the 3’ end of the tRNA?

A

C-terminal end (COOH) group

21
Q

What are the 3 major stages of protein synthesis?

A
  • Initiation
  • Elongation
  • Termination
22
Q

What are the 4 binding sites on ribosomes?

A
  • 1 for mRNA

- 3 for tRNA: A-site, P-site, E-site

23
Q

What binds on the A-site on the ribosome?

A

Amino acid (charged tRNA)

24
Q

What happens at the P-site?

A

tRNA attached to growing protein chain

- methionine or N-formylmethionine

25
Q

What happens at the Esite?

A

Exit of tRNA

26
Q

What codon codes for initiation on mRNA?

A

AUG

27
Q

What does AUG code for?

A

Methionine or N-formylmethionine (fMet)

  • Binds directly to P-site
  • Initiation of translation (
28
Q

AUG codes for N-formylmethionine (fMet) in what type of cells usually?

A

Prokaryotes

- Acts as a chemotactoc agent for neutrophils (innate immunity)

29
Q

What does intiation require in addition to methionine/fMet? (which binds to P site)

A
  • GTP hydrolysis

- Initiation factors (proteins) which assemble ribosomes and tRNA

30
Q

What proteins are involved in elongation?

A

Elongation factors

31
Q

What do elongation factors do?

A

Hydrolyze GTP to GDP

32
Q

What are the EF in bacteria?

A

EF-Tu and EF-G

33
Q

What are the EF in eukaryotes?

A

EF1 and EF2

34
Q

What bacterial toxins target EF2?

A
  • Diptheria toxin
  • Exotoxin A (pseudomonas aeruginosa)

They inhibit protein snthesis

35
Q

What are the 4 steps involved in elongation?

A
  • 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
36
Q

What is the function of peptidyl transferase?

A

Catylises linkage of amino acid in a site to protein chain in P site

37
Q

Stop codons code for what amino acid?

A

None

- It is not recognised by tRNA

38
Q

What binds to ribosome at stop codons?

A

Releasing factors

- Add water to end of protein chain

39
Q

What does phosphorylation (post-translational modification) involve ?

A

Amino acid residue phosphorylated

- Protein kinase enzymes add phosphate group

40
Q

What does glycosylation (post-translational modification) involve ?

A

Formation of sugar-amino acid linkages

  • Many linkages (N, O, C) linked glycosylation
  • Creates glycoprotiens
41
Q

Hydroxylation of what amino acids is important in collagen synthesis?

A

Proline and lysine residues

42
Q

Acetylation is what?

A

Addition of acetyl (CH3CO) group

43
Q

What is ubiquitination?

A

Addition of ubiquitin (small protein)

- Tags protein for destruction in proteosome

44
Q

What is the function of chaperones?

A

Proteins that facilitate folding

- Bind to other proteins -> ensures proper folding

45
Q

Give an example of chaperones?

A

Heat shock proteins

  • Increase expression with stressors (pH shift, heat, hypoxia)
  • Stabilize proteins - maintaining structure which helps then survive environmental stress

USMLE Biochemistry (44 decks)

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