Lecture 1

what mRNA is like after initiation

circular, 5’ cap and poly-A tail, exported from nucleus, near 5’ cap is start codon, stop codon is at the end

what is needed for translation

a code (genetic code)

adaptor (tRNA)

scaffold and catalyst (ribosome)

energy

genetic code is

non-overlapping

universal

highly degenerate

how many codons

64 - 61 for amino acids and 3 stop codons

tRNA production

tRNA gene transcribed by RNA Pol II to produce tRNA precursor

this is then processed through cleavage events, addition of bases at 3’ end, and modification of bases to produce mature tRNA

tRNA secondary structure

clover leaf

tRNA tertiary structure

L shaped

wobble base

3rd base of codon and 1st base of anticodon

modified bases can recognise >1 base in this position, when multiple bases in the 3rd position code for the same amino acid

helps with fidelity of the genetic code

isoacceptor tRNAs

carry the same amino acids but have different anticodons

aminoacyl tRNA synthetases (aaRS)

catalyse formation of ester bond between an amino acid and its appropriate tRNA molecule

each one is specific to one amino acid but may recognise more than one tRNA

terms for when amino acid is added to tRNA

amino acid becomes activated, tRNA becomes charged

reaction catalysed by aaRS enzymes (charging tRNA) - step 1

amino acid is adenylated - AMP is added from ATP (get 2 phosphates)

reaction catalysed by aaRS enzymes (charging tRNA) - step 2

enzyme transfers adenylated amino acid from AMP to 3’OH of tRNA

reaction catalysed by aaRS enzymes (charging tRNA) end result

tRNA with amino acid attached and AMP

tRNA is ready to be used in translation

role of protein in ribosomes

scaffold

role of rRNA in ribosome

catalyst

where is rRNA transcribed

nucleolus

G proteins

essential for protein synthesis

have GTPase activity

cellular work is changing their conformation

EF-Tu

when bound to GTP it has a binding site for tRNA, when it is hydrolysed to GDP the protein changes shape and no longer has a tRNA binding site

GEFs

guanine exchange factor - can replace GDP with GTP to activate something

GTPyS

non-hydrolyseable GTP analogue used to study G proteins