CH 14 Genetics

Components of translation

Components of translation

amino acids, mRNA, ribosomes, translation factors, tRNA, enyzmes

what is different about tRNA bases?

they have modified ones – I being imporntant

EF-Tu

GTPase that transports charged aminoacyl tRNA to A site

EF-G

Hydrolyzes GTP after peptide bond formation, conformation change in EF-G causes movement of small subunit relative to large subunit

Aminoacyl tRNA synthetase

charges tRNAs, is specific to each amino acid

Svedberg unit

measurable size and shape, found via sedimentation

Translation is dependent on what energy source

GTP

Shine-Dalgarno sequence

base pairs with some of small subunit, allows for internal ribosome initiation, allows for translation of polycistronic mRNAs, made of purines, allow for being polycistronic

Initiation

starts with AUG and Shine-Dalgarno sequence ( if bacteria ), Ifs bind to small subunit and attract mRNA, charged fmet tRNA binds to AUG codon of mRNA in P site, forming initiation complex

Elongation

second charged tRNA enters A site facilitated by EF-Tu, peptide bond forms between AAs facilitated by EF-G, uncharged tRNA then moves to E site and out of ribosome

Termination

signaled by UAG, UAA, UGA. GTP dependent release factors cleave polypetide chain from tRNA and releases it from the translation complex

Are Prokaryotes polycistronic or monocistronic?

polycistronic

Are Eukaryotes polycistronic or monocistronic?

monocistronic

Polysomes

mRNAs with several ribosomes translating at once

How does translation differ in eukaryotes

closed loop translation and no shine-dalgarno sequence

Closed loop translation

mRNAs forms loop that is closed by Poly-A binding proteins bind to the cap binding proteins, allows for regulators of translation after stop codon

Sir Archibald Garrod

studied alkaptonuria

What happens when blocks occur in a pathway

build up of harmful intermediate

AKU

single chemical, familial basis

Beadle and Tatum Neurospora experiment

nutritional requirements were specific and single gened, layed groundwork for Srb and Horowitz

Auxotroph

Does not have ability to synthesize one or more essential substances for growth

ONE GENE: ONE ENZYME HYPOTHESIS

Srb and Horowitz, Hemoglobin

Srb and Horowitz

ordering the intermediates in a pathway even when ones not involved, arginine mutants, found correlation between biochemical pathway and genetics

amino acid types

nonpolar/hydrophobic, Polar/hydrophilic, polar and positive, polar and negative

peptide bonds

covalent bond between the carboxyl group of one AA and the amino group of another

secondary

folding into alpha helix and beta pleated sheet, caused by hydrogen bonding along alpha carbon backbone

tertiary

based on R groups

stabilizing factors

covalent disulfide bonds between close cytosine residues, ionic bonds, hydrophilic R on surface and hydrophobic R on interior, Van der Waals interactions

Post transcriptional modification

N-terminus amino acid removed or modified, individual AA modified (phosphate addition by kinases), polypeptide cleaved to make active form