Unit 3 Translation

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1

Adapter Molecules

AAs can't bind directly to codon; tRNA serves as adapter in translation; bind AA to 3'-end, transport AA to ribosome; Anticodon of tRNA interacts with codon of mRNA

2

Wobble Hypothesis

non-traditional base-pairing of first anti-codon with last base of codon therefore fewer than 64q tRNAs required for translation

3

Specificity, Universality, Redundancy, Nonoverlapping and commaless

*Specificity- one code one AA; Universality- conservation of genetic code (except mito); *Redundancy- more than one code per AA; *Nonoverlapping and commaless- read from fixed starting point and continuous

4

Types of Mutations

*Silent- change code for same AA; *Missense- change code for diff. AA; *Nonsense- change code for termination codon; *Insertions, deletions, frameshift mutations

5

Sicke Cell Anemia

missense mutation: beta-globin GTG (Val) replaces GAG (Glu)

6

Components of Translation

Template mRNA, Ribosomes, tRNAs, AAs, initiation, elongation, and termination factors, ATP (attach AA to tRNA) & GTP (binds aminoacyl-tRNA to A site for translocation) and used in initiation and termination steps

7

What End is the Polypeptide Synthesized From?

The amino-terminal end

8

Aminoacyl-tRNA Synthetases

*recognizes specific AA & corresponding tRNA, *AA attached to 3' end of tRNA, *requires ATP ->AMP, *responsible for specificity and proofreading and high fidelity of translation

9

Fx Components of Ribosomes

A site- binds incoming aminoacyl-tRNA & specifies next AA to be added; P site- peptidyl-tRNA, carries synthesized peptide; E site- occupied by empty t-RNA as it is about to exit

10

Initiation

Prokaryotes: 16S binds Shine-Dalgarno sequence and positions on 30S subunit; Eukaryotes: 40S subunit binds cap of mRNA

11

Initiation Codon

AUG recognition facilitated by IF-2 (e.coli) and eIF (humans). Prokaryotes & Mito- initiator is N-formyl Met, but just Met in eukaryotes.

12

What End are AAs Added to?

Carboxyl terminal by peptidyltransferase (component of 50S ribosomal subunit)

13

Choramphenicol

inhibits prokaryotic peptidyltransferase

14

Tetracyclines

Interact with small ribo subunit blocking access of aminoacyl-tRNA to mRNA-ribosome complex

15

Clindamycin & Erythromycin

Bind irreversibly to 50S subunit of bacterial ribosomes inhibiting translocation

16

Diphtheria Toxin

Inactivates eukaryotic elongation factor eEF-2 preventing translocation

17

Termination

Stop codon moves to A site, *release factors bind A site, *peptidyltransferase hydrolyzes bond between peptide and tRNA

18

Regulation of Translation

*Gene expression regulated on level of transcription, *binding of regulatory proteins to mRNA, *rare codons regulate rate of translation, *siRNA target mRNA for degradation

19

Chaperones

Prokaryotes: DNA J & DNA K; Eukaryotes: Hsp 40 & Hsp 70; mediate folding and prevent improper folding

20

Disulfide Isomerase

catalyzes disulfide bond formation between Cys residues during processing

21

Posttranslational Covalent Modifications

*(de)Phosphorylation of Ser, Thr, & Tyr; *Methylation of Lys & Arg (histone meth. regs transcription); *Hydroxylation of Pro & Lys (stabilization of collagen); *Carboxylation- blood coag clot formation; *Glycosylation of Ser, Thr, Asn of membrane or secreted proteins; *Biotinylation of Lys in carboxylases

22

Targeting Proteins

Synthesis in Cyto: Nuclear Proteins- nuclear localization signal; Mito proteins- mito entry signal; Elongation & release in ER: secreted proteins