Protein Translation and Post-Translational Processing Flashcards
Do both subunits of ribosomes have enzymatic function? If not, which one does?
No, only large subunit does
What is the ternary complex?
eIF2a-GTP bound to initiator methionine-tRNA
What is the pre-initiation complex?
ternary complex bound to small subunit + mRNA
What is the initiation complex?
pre-initiation complex bound to large subunit
The energy needed to bind to large subunit comes from what?
hydrolysis of eIF2a-GTP
What site is methionine-tRNA in?
P site of large ribosomal subunit
How much energy is required to elongate one amino acid?
2 GTP is needed: one to bind tRNA to the A site (charged tRNA) and another to move ribosome one codon over
When does translation terminate?
once a stop codon has reached the A site
What pairs with the stop codon in termination of translation?
a protein, eRF (eukaryotic release factor)
Does termination of translation require energy?
yes, when the peptide is release from the P site, provided by the hydrolysis of eRF-GTP
- ribosomal subunits separate from each other
Which antibiotic binds to ribosomes and causes mistranslation of codons?
neomycin and gentamicin
Which antibiotic binds to small subunit and inhibits initiation?
streptomycin
- also causes mistranslation
What anitibiotic prevents peptidyl bond formation?
chloramphenicol
Which antibiotic blocks the A site and prevents rRNA binding?
tetracycline
Which toxin removes adenine bases from various positions of the rRNA in the large subunit?
ricin
Which toxin inactivates EF-2 by ADP-ribosylation?
Diptheria toxin
What are two ways to regulate translation (gene expression)?
1) prevent recognition of start codon by binding a protein to the 5’ UTR of mRNA
2) phosphorylate eIF-2a (initiating factor), becomes inactive
Where does protein folding occur (organelle)?
cytosol and ER
Where does N-linked glycosylation occur?
ER, before protein folding is complete
In N-linked glycosylation, sugar is added to what residue in protein?
asparagine
Where is dolichol phosphate located (organelle)?
ER
Where does modification of oligosaccharide occur?
Golgi
1) high mannose type (bulky)
2) complex type
What disorder affects N-linked glycosylation?
congenital disorder of glycosylation (CDG)
Which disorder has defective trimming of oligosaccharide chain?
CDG II
Which disorder has defective synthesis of lipid-linked oligosaccharide precursor?
CDG I
Where does O-linked glycosylation occur?
Golgi
Which residues are sugar added to in O-linked glycosylation?
glycosyltransferases transfer sugars to serine or threonine of fully folded proteins
What is the first sugar of O-linked glycosylatoin?
N-acetylgalactosamine
What sugar does the H-antigen of the A type RBC?
GalNac
What sugar does the H-antigen of the B type RBC?
Gal
What is used to signal proteins to be directed to lysosomes?
phosphorylated mannose
Which disease is a result from non-phosphorylated mannose of lysosomal proteins leading to accumulation of these proteins in the serum?
I-cell disease
- also causes accumulation of undegraded proteins in lysosomes because it’s missing proteins to properly degrade
What disorder is caused by a mutation in TIM component that impairs cellular energy production by preventing assembly of fully functional mitochondria?
Deafness-dystonia syndrome
How is CF also a protein sorting disorder?
CFTR1 protein is normally trafficked to the cell surface, but a mutation causes it to be not properly glycosylated thus it gets move to the cytoplasm where it is degraded instead
Which residues at the N-terminal makes the protein less stable thus shortening its life?
arginine and lysine
Which residues at the N-terminal makes the protein more stable thus prolonging its life as a protein?
serine and methione
Sequence elements such as what attracts proteases?
PEST - Pro, Gln, Ser, Thr
