5.1- protein synthesis, processing and regulation

Proteins synthesised on free ribosomes

Remain in cytosome or transported to nucleus, mitochondria, chloroplasts, peroxisomes

Proteins synthesised in membrane bound ribosmes

Transported to Golgi body, lysosomes, plasma membranes, ER

Aminoacyl and rna synthases

Attach amino acids to corresponding tRNAs

Non standard base pairing

Wobble- third letter in codon doesn’t need to be complementary so non complementary bases bind together

Shine Dalgarno

Enables initiation of translation by aligning the ribosome with the start codon

Prokaryotic ribosomes

70s, made of 50s and 30s

Eukaryotic ribosomes

80s, made of 60s and 40s

Evidence of rRNA (1)

catalytic activity of other rnas

Evidence of rRNA (2)

Needed for in vitro assembly of functional ribosomes

Evidence of rRNA (3)

Ribosomal proteins absent from peptide bond formation site

Prokaryotic mRNA

1 mRNA codes for more than 1 protein- multicistronic

Eukaryotic mRNA

1 mRNA codes for 1 protein- monocistronic

Regulation of elf4e (increase)

Phosphorylation of 4e bp, dissociates from elf4e, translation can begin

Regulation of elf4e (decrease)

4e bp binds to elf4e, dissociates from elf4g, inhibits translation

What is a chaperone?

Bind to and stabilise unfolded polypeptide, prevents aggregation

Cytosolic chaperones

Maintains polypeptide as it travels unfolded

Mitochondrial chaperones

Finishes folding polypeptide inside mitochondria

Sequential actions of chaperones

Hsp70 proteins stabilise polypeptide, transfer to chaperonin, folding takes place, isolates protein from cytosol

Cystic fibrosis caused by

Mutation of CFTR protein, transfers cl-

What happens in a mutant CFTR?

Increase cl- conc inside, h2o enters, cilia can’t move, high chance of infection

PDI

Catalyses formation of disulphide bonds between cysteine residues

Glycosylation

Adds sugars to proteins

N linked glycoproteins

Sugar joined to nitrogen atom in side chain of asparagine

O linked glycoprotein

Sugar joined to oxygen atom of serine or threonine

Lipid binding

Mark and anchor proteins to membrane

Allosteric regulation

Regulatory molecule binds to enzyme site other than active site- changes shape and activity

Start codon

AUG

Ubiquitin-proteasome pathway

main route of protein degradation in eukaryotes, ubiquitin as a protein marker

Lysosomal proteolysis

misfolded protein moves into lysosome by autophagy