Protein Translation and Post-Translational Processing

Question 1

Do both subunits of ribosomes have enzymatic function? If not, which one does?

Answer 1

No, only large subunit does

Question 2

What is the ternary complex?

Answer 2

eIF2a-GTP bound to initiator methionine-tRNA

Question 3

What is the pre-initiation complex?

Answer 3

ternary complex bound to small subunit + mRNA

Question 4

What is the initiation complex?

Answer 4

pre-initiation complex bound to large subunit

Question 5

The energy needed to bind to large subunit comes from what?

Answer 5

hydrolysis of eIF2a-GTP

Question 6

What site is methionine-tRNA in?

Answer 6

P site of large ribosomal subunit

Question 7

How much energy is required to elongate one amino acid?

Answer 7

2 GTP is needed: one to bind tRNA to the A site (charged tRNA) and another to move ribosome one codon over

Question 8

When does translation terminate?

Answer 8

once a stop codon has reached the A site

Question 9

What pairs with the stop codon in termination of translation?

Answer 9

a protein, eRF (eukaryotic release factor)

Question 10

Does termination of translation require energy?

Answer 10

yes, when the peptide is release from the P site, provided by the hydrolysis of eRF-GTP
- ribosomal subunits separate from each other

Question 11

Which antibiotic binds to ribosomes and causes mistranslation of codons?

Answer 11

neomycin and gentamicin

Question 12

Which antibiotic binds to small subunit and inhibits initiation?

Answer 12

streptomycin

- also causes mistranslation

Question 13

What anitibiotic prevents peptidyl bond formation?

Answer 13

chloramphenicol

Question 14

Which antibiotic blocks the A site and prevents rRNA binding?

Answer 14

tetracycline

Question 15

Which toxin removes adenine bases from various positions of the rRNA in the large subunit?

Answer 15

ricin

Question 16

Which toxin inactivates EF-2 by ADP-ribosylation?

Answer 16

Diptheria toxin

Question 17

What are two ways to regulate translation (gene expression)?

Answer 17

1) prevent recognition of start codon by binding a protein to the 5’ UTR of mRNA
2) phosphorylate eIF-2a (initiating factor), becomes inactive

Question 18

Where does protein folding occur (organelle)?

Answer 18

cytosol and ER

Question 19

Where does N-linked glycosylation occur?

Answer 19

ER, before protein folding is complete

Question 20

In N-linked glycosylation, sugar is added to what residue in protein?

Answer 20

asparagine

Question 21

Where is dolichol phosphate located (organelle)?

Answer 21

ER

Question 22

Where does modification of oligosaccharide occur?

Answer 22

Golgi

1) high mannose type (bulky)
2) complex type

Question 23

What disorder affects N-linked glycosylation?

Answer 23

congenital disorder of glycosylation (CDG)

Question 24

Which disorder has defective trimming of oligosaccharide chain?

Answer 24

CDG II

Question 25

Which disorder has defective synthesis of lipid-linked oligosaccharide precursor?

Answer 25

CDG I

Question 26

Where does O-linked glycosylation occur?

Answer 26

Golgi

Question 27

Which residues are sugar added to in O-linked glycosylation?

Answer 27

glycosyltransferases transfer sugars to serine or threonine of fully folded proteins

Question 28

What is the first sugar of O-linked glycosylatoin?

Answer 28

N-acetylgalactosamine

Question 29

What sugar does the H-antigen of the A type RBC?

Answer 29

GalNac

Question 30

What sugar does the H-antigen of the B type RBC?

Answer 30

Gal

Question 31

What is used to signal proteins to be directed to lysosomes?

Answer 31

phosphorylated mannose

Question 32

Which disease is a result from non-phosphorylated mannose of lysosomal proteins leading to accumulation of these proteins in the serum?

Answer 32

I-cell disease

- also causes accumulation of undegraded proteins in lysosomes because it’s missing proteins to properly degrade

Question 33

What disorder is caused by a mutation in TIM component that impairs cellular energy production by preventing assembly of fully functional mitochondria?

Answer 33

Deafness-dystonia syndrome

Question 34

How is CF also a protein sorting disorder?

Answer 34

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

Question 35

Which residues at the N-terminal makes the protein less stable thus shortening its life?

Answer 35

arginine and lysine

Question 36

Which residues at the N-terminal makes the protein more stable thus prolonging its life as a protein?

Answer 36

serine and methione

Question 37

Sequence elements such as what attracts proteases?

Answer 37

PEST - Pro, Gln, Ser, Thr