BIOC520: Medical Biochemistry			
L-46/47: TRANSLATION

Objectives:

1.	To understand how polypeptides are produced.
2.	To know the major features of the genetic code.
3.	To understand how translation is similar and different in
prokaryotes and eukaryotes.
4.	To know how various inhibitors of translation work.

I.	General Scheme for Translation (Fig. 30.7  Voet; Fig. 14.7  Marks)
  A.	Requires tRNAs, ribosomes, mRNAs, aa pools, proteins
  B.	mRNA read 5' ® 3'; polypeptide synthesized NH2 ® COOH
  C.	Requires ability to recognize specific sequences in mRNA
  D.	Both ATP and GTP essential


II.	Genetic Code (Table 14.1  Marks)
  A.	Trinucleotide sequences in mRNA that specify amino acid
  B.	Features: degenerate, non-overlapping, commaless, wobble, nearly
universal


III.	Translation in Prokaryotes (Table 14.3, 14.4, 14.7)
  A.	Ribosome Structure - formation of ribonucleoprotein complexes
(Fig. 30.25, 30.26; Table 30.6)
  B.	tRNA Structure
  C.	Amino Acid Activation - joins appropriate aa to corresponding tRNA
(Fig. 30.16)

	Aminoacyl - tRNA synthetase

	Enzyme + amino acid + ATP ® enzyme-(aminoacyl-AMP) + PPi
	tRNA + enzyme-(aminoacyl-AMP) ® aminoacyl-tRNA + AMP + enzyme

	Amino acid + ATP + tRNA ® aminoacyl-tRNA + AMP + 2Pi

	two ~ P/amino acid

  D.	Initiation (Fig. 14.8 and 14.9; 30.43)
    1.	Recognition of 5' end of mRNA
	a.	initiation codons			1 ~ P used
	b.	upstream sequences
    2.	Formation of Initiation Complexes
  E.	Elongation (Fig. 14.10, 14.11, 30-44)
    1.	 Delivery of aa-tRNA complex to A site
    2.	Peptide bond formation				2 ~ P used
    3.	Translocation
  F.	Termination (Fig. 30.48)
    1.	Termination codons				1 ~ P used
    2.	Release factors


IV.	Translation of Eukaryotes
Mechanically identical to prokaryotic translation, but differs in
complexity and detail
  A.	Spatial and temporal differences
  B.	Ribosomes
  C.	Initiation
    1.	Initiator codon/aa
    2.	Start signals
    3.	Initiation complexes
  D.	Elongation
  E.	Termination


V.	Inhibitions of Translation (Tables 14.6 and 30.9)
  A.	Streptomycin
  B.	Tetracycline
  C.	Chloramphenicol
  D.	Erythromycin
  E.	Puromycin 
  F.	Cycloheximide
  G.	Diphtheria Toxin