Chapter 22

First language v second language

sequence of nuclotides → amino acids

what is a codon

group of 3 nucleotides which speicify a single amino acid

how many total codon combos

64, 61 are amino acids

Start codon

AUG- MET

stop codon

UAG UAA UGA

codon features

highly degenerate, nonrandom code

synonoym

codon specifying same amino acids

which codes usually specify same AA

XYU and XYC

XYA and XYG

How many potential reading frames

3 , this is why mRNA reading is highly regulates

what on TRNA matches with mRNA

anticodon at botom of anticodon loop with codon

tRNA

trasnfer rNA matches mrna with amino acid

what is on each side of trna

anticodon0 on one end and aminoacyl group on other

• terminal 5’ phosphate

  • 3’- CCA-OH acceptor step on 3’ end

how do amino acids attach to the tRNA

ester linkage @ 3’ OH

how is the correct AA attached to tRNA

aminoacyl- trna synthase

the wobble hypothesis

expains why multiple codons can code for a single AA

why is wobble true

one tRNA can recognize and bind to more than one codon bc less precise base pairs arising between the 3rd base of the codon

wobble hyp first 2 codons

normal watson and crick geometry, with third permitting multiple non wc

ribosome function

molecular machine preforming biological protein synthesis

how many trna and mrna can bind to ribosoe

3 TRNA and 1 mRNA

e.coli ribosome

70 S, 30s small and 50s large

mammalian ribosome

80 s, 40s small, 60s large

how many proteins does 50s and 30s contain

50s- 31 30s 21 diff proteins

parts of ribosome

E site- exit

P site- peptidy

A site- accdeptor site

e-site

exite site occupied by tRNA from previous donor

p site

peptidyl site trna growing peptide chain

a site

acceptor site, aminoacylation site

polypeptide synth proceeds in

n term to c term, 5’ to 3’

ribosome function

matches mRNA codon with trna anticodon making peptide bonds between peptidyl tRNA and aminoacyl tRNA

what does chain initation require

initiation factors

IF-3 (step 1)

binds to 30s ribosome and 50s dissasociates

If-2

mRNA and initiator tRNA fmet-tRNA with IF-2 GTP binds to small 30s ribosomal subunit

what is fMET trna

n-formylmethionine

when does formylatino occur

after aminoacylation of tRNA, occurs posttransaltionally

shine dalgarno sequence

found at -7—4 AGGAGG

what is euk shine dalgarno sequence

requires 11 initation factors and starts leading at AUG GCCRCCAUGG

as mRNA and FMEt and IF-2 bind,

if3 and if1 are released, 50s joins 30s relasing IF2

when 5-s subunit and 30 s assocate

If-2 hydrolises its GTP —> fmet TRNA occupies P site making A site accepting

what steps does chain elongation occur in

decoding, transpeptidation, translocation

requirements for peptide elongation

mRNA 70S ribosome peptidyl tRNA complex

aminoacyl tRNA

Elongation factors

GTP

decoding

codon directed binding of incoming aminoacyl-tRNA at A site

transpeptidation

transfer of the peptidyl chain from the TRNA bearing to the -NH2 group of the new amino acid

decoding

aminoacyl-TRNA (aa-TRNA) EF TU GTP complex binds to the ribosome at the A site uncharged tRNA leave the E site

what is decoding driven by

GTP hydrolysis, results in release of EF TU GDP and PI

EF-TU

ensures that polymerization does not occur unless the corect aminoacyl-tRNA positioned at the A site

transpeptidation catalyse

peptide bond formation

peptide bond fomration occurs between

C terminus at P-ste AA and N-term of A site aa

translocation- movement to next codon

peptidyl tRNA and corresponding codon shifts to p-sitr as entire mRNA translocate , needs GTP hydrolysis drives the translocation and EF-G

how does termination occur

release factor binds to stop codon in the A site

what does water do in chain termiantion

ribosomal peptidyl transferase catalyzes the release of nascent peptide

silent mutation

no change in amino acid sequence

missense mutation

amino acid substituion

nonsense mutation

results in stop codon

frame shift mutation

single bases inserted or deleted leadig to non functional protiens

what drugs inhibit protien synthesis

macrolides and tetracyclines

macrolides MOA

bind in the peptide exit tunnel of the 50s subunit

tetracyclins MOA

binds to 30 s subunti and inhibit peptide chain elongation

macrolide example

erythromycin

tetracyclin example

doxycyclin