Protein Processing

Question 1

In which 2 places can ribosomes be?

Answer 1

attached to RER or in cytosol

Question 2

Where would the ribosome be if the protein being synthesised was destined for secretion or the membrane?

Answer 2

attached to RER

Question 3

Where would the ribosome be if the protein being synthesised is destined for the cytosol or organelles?

Answer 3

In the cytosol

Question 4

Where on the protein is the signal if it is destined to go to the ER?

Answer 4

N terminus

Question 5

If destined for the ER, is the protein folded during transfer and what are the specialised proteins required?

Answer 5

No - it is unfolded during transfer

SRP - signal recognition protein
SRP receptor

Question 6

Is the signal cleaved if destined for the ER?

Answer 6

Yes - by signal peptidase

Question 7

Does protein transfer to the ER require energy?

Answer 7

Yes - GTP

Question 8

What do we call the signal if the protein is destined for the nucleus?

Answer 8

NLS - nuclear localising signal

Question 9

Where is the NLS found?

Answer 9

On the surface of the folded protein

Question 10

What are the 2 important proteins for processing into the nucleus and what do they do?

Answer 10

Importin - recognises NLS and mediates transport

RanGTP - displaces importin in the nucleus

Question 11

Is the signal cleaved in nuclear transport?

Answer 11

No - the signal is retained because it is needed in cell division

Question 12

What kind of signal is required for mitochondrial transport and where is it located?

Answer 12

Amphipathic signal

N terminus

Question 13

Is the protein folded during transport to the mitochondria?

Answer 13

No

It is held partially unfolded by a chaperone protein (MSF)

Question 14

What does MSF stand for?

Answer 14

Mitochondrial-import stimulating factor

Question 15

What specialist proteins are required for transport into the mitochondria?

Answer 15

MSF: chaperone protein
TOM: transport channel on outer membrane
TIM: transport channel on inner membrane

Question 16

Is the signal cleaved during mitochondrial transfer?

Answer 16

Yes

Question 17

Is energy required for mitochondrial transfer?

Answer 17

Yes - ATP

Question 18

What is the signal for transport to lysosomes?

Answer 18

mannose-6-phosphate

Added post-translation

Question 19

Is the protein folded during transfer to lysosomes?

Answer 19

Yes - it is delivered in a vesicle

Question 20

Where is the M-6-P receptor?

Answer 20

Trans-Golgi

Question 21

Is the signal removed after transport the lysosomes?

Answer 21

Yes - the phosphate is cleaved by phosphatase

Question 22

Is energy required for transport to lysosomes?

Answer 22

Yes - ATP

Question 23

What and where is the signal for retention in the ER?

Answer 23

KDEL signal

C terminus

Question 24

What is constitutive secretion?

Answer 24

When something is being secreted all the time. It does not rely on stimulation.

Question 25

Is the protein folded during retention in the ER?

Answer 25

Yes - it is transported via vesicle

Question 26

What and where is the receptor for the KDEL signal?

Answer 26

KDEL receptor | Cis-Golgi

Question 27

Is the signal cleaved for retention in the ER?

Answer 27

No - is required to keep the process going

Question 28

Is energy required for retention in the ER?

Answer 28

No Except a very small amount is required for the budding off of vesicles

Question 29

How could someone have pyruvate dehydrogenase deficiency due to a fault in the protein processing?

Answer 29

If there is a mutation in the mitochondrial targeting sequence on pyruvate dehydrogenase then it cannot enter the mitochondria.

Question 30

What is Swyer Syndrome?

Answer 30

The loss or mutation of NLS in the sex determining region of the Y protein. You would be outwardly female as there is no testis differentiation.

Question 31

What is the SHOX transcription factor required for?

Answer 31

Skeletal development

Question 32

What are the functions of the ER?

Answer 32

``` insertion of proteins into membranes specific proteolytic cleavage glycosylation formation of disulfide bonds folding of proteins assembly of some multi subunit proteins hydroxylation of selected Lys and Pro residues ```

Question 33

What is glycosylation important for?

Answer 33

correct folding, stability and interaction with other molecules

Question 34

How does N-linked glycosylation work?

Answer 34

Sugars are added to an asparagine side chain.

Question 35

What does the enzyme protein disulfide Isomerase do?

Answer 35

Forms disulfide bonds in the ER

Question 36

How does O-linked glycosylation work?

Answer 36

Attachment of sugar to the -OH group of serine or threonine in the Golgi.

Question 37

What is tropocollagen?

Answer 37

the basic unit of collagen | 3 polypeptide alpha chains in a triple helix

Question 38

Which 2 enzymes are important in collagen synthesis and what do they do?

Answer 38

Prolyl hydroxylase - hydroxylation of selected Pro and Lys residues Lysyl oxidase - allows covalent cross-linking of collagen molecules to form fibres

Question 39

Which enzyme requires vitamin C?

Answer 39

Prolyl hydroxylase

Question 40

What is the simple sequence of events for collagen synthesis?

Answer 40

1. Enters RER 2. Cleavage of signal 3. Hydroxylation 4. N linked glycosylation 5. Addition of galactose 6. Disulfide bond formation 7. Triple helix formation 8. Addition of glucose 9. Vesicle to exocytosis 10. Terminal propeptide removal 11. Covalent cross-linking 12. Aggregation of fibrils to fibres

Question 41

What are the 2 causes of Ehlers-Danos Syndrome? (Stretchy skin)

Answer 41

mutation in type III or V collagen | Lysyl oxidase deficiency