NOTE: Translation occurs 3’5’ and mRNA is read 5’3’ , opposite of replication/transcription
Fx
RNA TRANSLATION
Prokaryotes
Eukaryotes
Initiation
Binding of Ribosome
5’ End of mRNA positioned on 30 S subunit
Shine Dalgarno site/sequence in 5’ end of
mRNA allows 16S rRNA 3’ leader to base pair
(part of 30S Subunit)
1) P220+4F*=Cap-Binding
Complex, binds to secondary
structure at 5’Cap of mRNA
*4F=eIF4F-Euk. Initiation factor
4F
2) Cap-Binding Complex recruits
4A and 4B** via ATP
** helicase activity, denature the
secondary structure—afterwards
they are released
3) Pre-Initation Complex forms:
40S +Met tRNA (GTP)
4)nmRNA binds to PIC= Initiation
Complex
5) 60 S Subunit binds
(GTP)=active 80 S Initiation
Complex
6) Met-tRNA moves to P site
7)Complex scans to Kozak
Consensus containing AUG start
codon
Elongation
eEF=eukaryotic Elongation Factor
1) eEF-1 binds tRNA to its AA
(GTP)
2) tRNA+AA binds to mRNA
3) Peptidyl Transferase in P site
forms peptide bond b/w AA1 and
AA2 (AA2 N binds to C=O on AA11)
4) eEF-2 translocates tRNA-AA2 +
chain to P site (GTP)
Termination
1) A site reaches STOP Codon
(UAA, UAG, UGA)
2) eRF + GTP bind to A site
3) H20 + Peptidyl Transferase
hydrolyze bond b/w tRNA (P site)
and last AA (carboxyl end of chain
released)
4) Chain and eRF are released
5) 40S and 60S subunits dissociate
Start of PRO = N Terminus End of PRO = C Terminus
5’ end of mRNA =N Terminus
3’ end of mRNA = C terminus
Signal Peptide—Pre-PRO w N-terminal sequence designating where it goes, signal is cleaved in ER
--can go to ER membrane or plasma membrane
Modification of Pre-Pro:
Phosphorylation—Protein Kinases (Ser, Thr, Tyr-all have OH) vs. Phosphatases
-controls activity of enzymes, TFs, subcellular localization of PROs
Attachment of FA chains
--attachment of H20 soluble PRO to cell membrane via adding FA to N-terminus
--attachment of PRO to ER via C Terminus (ex. Protein P21)
EX) ras protein (form amide link b/w terminal amino and myristate-FA (via myristyl CoA)
Protein Glycosylation—attach sugars to PRO destined for cell surface and secretion
 N-Linked Glycosylation—Glycosyl Transferase
o single type of oliggosacch. Transferred to amino group of Asparagine (Asn) AA in growing
peptide chain (Asn-X-Thr or Asn-X-Ser)
 O-Linked Glycosylation—oliggosacch. Added to OH of Serine (Ser) or Threonine (Thr)
Proteolytic Processing
-converts inactive precursors to active form in ER or GOLGI
--cleavage at pairs of BASIC residues (Arg-Arg, Lys-Arg, etc)Cleaves large polypeptides
Pre—pro—Protein pre is usually signal peptide, cleave at each – in order
Ex) Insulin and transforming growth factor beta (TGF-)
Protein Degradation:
1) ATP-Independent
 Uses lysosomes—which are full of proteases
 For membrane-bound and long-lived proteins
2) ATP-Dependent
 Uses Ubiquitin to conjugate with proteins at  amino group of Lys and tag them for degradation
 For abnormal or other short-lived proteins
Roles of PRO modification summary:
1) Normal processing required for activity
 Lipid addition for membrane anchoring
 Glycosylation of membrane PROs
 Proteolytic processing of precursors (Insulin)
2) Modulation of protein activity
 Phosphorylation of enzyme
 Acetylation and methylation of histones
3) Regulation of PRO turnover—Ubiquitination