ribosomes and protein synthesis 2

what are eukaryotic tRNAs synthesised by?

RNA polymerase III

what is splicing catalysed by?

endonucleases

what are the 2 mechanisms in which editing is checked?

favourable binding

hydrolytic editing

what is the favourable binding mechanism?

checking correct amino acid has the highest affinity for active side pocket of synthetase

what is the hydolytic editing mechanism?

when tRNA binds, the synthetase tries to force adenylated amino acids into a second editing pocket

what happens during elongation of the chain in protein synthesis?

peptide bond formation

large unit translocation

small subunit translocation

ribosome moves 3 nucleotides along

which is the start coding sequence?

AUG

what are the 3 stop codons?

UAA

UAG

UGA

what happens at a stop codon?

release factors bind to the ribosome with the stop codon at the A site

this forces the peptidyl transferase to add a water molecule instead of aa

this frees the carboxyl end of the pp chain and the chain is released into the cytoplasm

what is the structure of the proteosome?

central hollow cylinder

contains 6 subunit protein rings

what are the most common modifications of proteins?

glycosylation

phosphorylation

what is the function of chaperones?

help newly made or partly folded proteins to follow the right path, avoids mistakes

what is the shape and functions of HSP 60?

barrel-shaped chamber

where proteins fold

what is the function of HSP 70?

binds and stabilises growing or misfolded proteins

why are some proteins eliminated?

misfolded or abnormal

damaged

alteration of cell state

what are the general mechanisms for protein destruction?

activation of ubiquitin ligase

activation of degradation signal

creation of a ubiquitinylation site in response to intracellular or extracellular signals

what is the carboxyl terminus?

a cleavage site where protease action removes the sequence after the protein is imported to the ER

what do all signal sequences have?

10-15 hydrophobic amino acid residues

one or more positively charged residues

a short sequence at the carboxyl terminus

what is N-linked glycosylation?

the attachment of an oligosaccharide to N

where do modified proteins move to?

intracellular destinations