Protein synthesis and sorting Flashcards
ribosomes
carry out the process of polypeptide synthesis
tRNA molecules
align the amino acids in the correct order
aminoacyl-tRNA synthetases
attach amino acids to their appropriate tRNA molecules
mRNA molecules
encode the amino acid sequence information
facilitate some of the steps of translation
protein factors
made up of two dissociable subunits that resemble rRNA and proteins
bacterial ribosome
(A) aminoacyl site
binds each newly arriving tRNA with its attached amino acid
(P) peptidyl site
where the tRNA carrying the growing polypeptide chain resides
(E) exit site
from which tRNAs leave the ribosomes after they have discharged their amino acids
what directs the order of amino acids in a polypeptide?
sequence of codons in mRNA
nuclear export signals
for transport of mRNA through the nuclear pores
start codon
first to be translated
-usually AUG
step 1 of translation in bacteria
IF1,2,3 and GTP bind to small ribosomal subunit
step 2 of translation in bacteria
aminoacyl tRNA and mRNA are attached and bind to small ribosomal units
step 3 of translation in bacteria
large subunit joins and complex resulting 70S ignition complex and GTP is hydrolyzed
tRNA met
imitator in eukaryotes that carries methionine
-doesn’t become formylated
cap-binding initiation factor, eIF4F
recognizes the 5’ end of the mRNA
kozak sequence
AUG, start codon sequence
what must be attached to the start codon for the large subunit to bind to the complex and start initiating?
initiator tRNA met
aminoacyl tRNA binding
the ribosome bringing a new amino acid
peptide bond formation
links this amino acid to the growing polypeptide chain
translocation
moving the mRNA 3 nucleotides ahead to bring the next codon into position for translation
release factors
protein that recognizes a stop codon in the A site
hydrolysis
releases the polypeptide
chemical modification in bacteria so to return to normal function after translation
N-formyl group and Met are removed
chemical modification in eukaryotes so to return to normal function after translation
Met is removed
internal stretches of amino acids
removed to produce an active protein
two types of splicing
intermolecular and intramolecular
inteins
remove certain amino acid sequences from poylpeptides
cotranslational import
movement of the polypeptide across or into the ER membrane
-directly coupled to the translational process
post translational import
polypeptides which are destined to cell organelles, required a special targeting signal
molecular chaperones
facilitate protein folding and assembly
protein folding is accompanied by the formation of what?
disulphide bonds between Cys in the pp chain
unfolded protein response (UPR)
detects misfiled proteins and enhances pathways for protein folding
ER-associated degradation (ERAD)
recognizes misfiled proteins and exports them back to cytosol for degradtion
glycoproteins
proteins synthesized on rough ER
where does initial glycosylation take place?
ER
where does further glycosylation occur?
golgi complex
what is the default pathway for soluble proteins?
golgi complex- secretory vesicles
-move to cell surface and fuse with palm membrane for secretion from the cell
