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Flashcards in Hettema lecture 4 Deck (16)
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1

Give 3 reasons why proteins undergo glycosylation?

- promote protein folding
- stabilise secretory proteins
- involved in cel-cell interactions

2

What drug inhibits protein glycosylation of haemagglutinin?

tuicamycin

3

Which residue is involved in N-linked glycosylation?

asparagine

4

At which point is the precursor molecule attached to the unfolded protein during N-linked oligossacharide processing?

precursor attached to unfolded protein cotranslationally

5

Which molecule is involved in disulphide bond formation in the ER?

PDI - can be oxidised/reduced

6

Give the names of the proteins involved in aiding protein folding in the ER?

Chaperones -> Hsp70 / BIP (in ER)

7

How are different targeting sequences added to each end of the a.a. sequence?

Alternative splicing generates targeting sequences either at N/C terminus

8

Describe the process of protein import into the mitochondrial matrix (6 steps ish)

1 - unfolded precursor in cytosol is kept unfolded by Hsp70 proteins
2 - targeting sequence binds to mitochondrial outer membrane receptor
3 - polypeptide inserted into outer membrane translocon
4 - simultaneously threads through inner membrane translocon (lined up with each other)
5 - Hsp70 within matrix pulls the polypeptide through (energy provided by ATP hydrolysis)
6 - protein folds into active conformation

9

Describe the process that was used to show that only UNFOLDED proteins could enter the mitochondrial matrix

an unfolded DHFR enzyme sequence can enter the matrix easily - with the correct MTS
however, adding MTX (methotrexate - an inhibitor) binds DHFR and locks it in a folded conformation. This prevents the crossing of the folded protein across both the inner and outer membrane

10

Does mitochondrial import occur post-translationally/co-translationally?

Post-translational

11

What is the structure of the MTS and where is it located?

N-terminus
20-50 a.a.
amphipathic helix

12

What is the structure of the PTS and where is it located?

C-terminus
3 a.a. (SER-LEU-LYS-COOH)

13

At what point of the process involving the import of folded proteins into the peroxisomal matrix is ATP required?

ATP hydrolysis occurs after the protein has been imported into the matrix. ATP released causes the receptor to dissociate from the plasma membrane and to be recycled to go and pick up more folded proteins

14

What is the structure of the ERTS and where is it located?

N-terminus
core of 6-12 hydrophobic a.a
preceded by a few positively charged a.a. (Lys, Arg)

15

What is hyperoxaluria?

Build up of calcium oxalate
Kidney stones
AGT enzyme is mistargeted to mitochondria rather than peroxisomes

16

What is the result of a mutation in the glycosylation site in HA?

HA is not glycosylated therefore cannot be folded -> accumulation of unfolded HA in ER