L25 - Protein Trafficking

Question 1

Where are cytosolic proteins made

Answer 1

In the cytosol

Question 2

Where are membrane and secreted proteins made

Answer 2

RER

Question 3

The RER is studded by

Answer 3

Ribosomes

Question 4

Where are nuclear proteins made

Answer 4

The outer nuclear membrane

Question 5

Describe what happens to the common pool of ribosomes

Answer 5

Form either a polyribosome in the cytosol

Form a polyribosome bound to the RER membrane

Question 6

Describe how the polyribosome on the RER membrane forms

Answer 6

Signal sequence of a protein destined for the ER is translated
This is recognised by a signal recognition particle (SRP)
SRP bins to an SRP receptor particle on the ER membrane

Question 7

WHat occurs at the RER

Answer 7

Protein synthesis

Question 8

What occurs at the SER

Answer 8

Lipid synthesis and formation of vesicles

Question 9

What is a heavy microsome

Answer 9

One made from the RER - studded with ribosomes

Question 10

What is a smooth microsome

Answer 10

From the smooth ER - no ribosomes

Question 11

Describe how you may separated rough and smooth microsome

Answer 11

Differnetial centrifugation
Establish concentration gradient of sucrose solution (high at the bottom)
Rough microosmes are heavier so wil lfloat at higher concnetrations of sucrose - at the bottome of the tube

Question 12

What is the role of the golgi

Answer 12

Final addition of sugars and sorting

Question 13

Describe the organisation of the golgi

Answer 13

Cis to trans golgi network

Question 14

Describe what happens during the maturation of vesicles

Answer 14

Proteases act to trim and activate hormones and enzymes

Question 15

A sequence of positive AA targets the protein to

Answer 15

the nucleus

Question 16

What does an SRP have

What does this allow

Answer 16

Hinge region

Means that it is able to travel with the ribosome

Question 17

Describe the process of a signal sequence targetting a protein to the ER

Answer 17

Signal sequence is produced through translation
SRP binds to sig seq and the ribosome
Translation slows
SRP then captured by the SRP receptor protein and protein translocated
Polypeptide is made through the trnalsocator into the ER
Signal peptidase catalyes cleavage of the signal sequence

Question 18

What enzyme catakyses cleavage of the signal sequence

Answer 18

Signal peptidase

Question 19

What is the topology of the ribosome once it has bound to the translocator

Answer 19

Large SU faces the translocator

Small SU faces the cytosol

Question 20

Describe how a protein is inserted into the ER membrane

Answer 20

At the start there is a start-transfer sequence - hydrophobic
This is cleaved by a signal peptidase
Stop-transfer sequence marks the transmembrane domains

Question 21

What is a GPI anchor

Answer 21

Glycosylaphosphatidyllinositol anchor

Question 22

What does a GPI anchor allw

Answer 22

Attachement of a protein to the membrane without the need for a transmembrane doamin

Question 23

Once the signal sequence has been cleaved what happens

Answer 23

Conformational maturation

Question 24

Conformation maturation involves the formation of ____________

Where do these form

What is the function

Answer 24

Disulphide bridges

From between cystenines

Solidify

Question 25

Where do DS bridges NOT form

Answer 25

In the cytosol since it is a reducing environment

Question 26

What is the role of standard glycosylation

Answer 26

Quaity control

Question 27

Describe how glycosylation acts as quality control

Answer 27

If the protein is in the incorrect shape then the sugar cant be attached at the correct place - if this happens the protein is degraded

Question 28

What (3) is glycosylation important for

Answer 28

Protein stability in a harsh EC environment Cell-cell recognition Cross species separation

Question 29

What sugar do humans use What sugar do other animals use What is the different

Answer 29

B-galactose A-galactose At C1 OH and H are in differnent positions

Question 30

What are the two linkages of glycosylation - from which AA does each occur

Answer 30

N-linked - from asparagine O linked - from thereonine

Question 31

What three molecules are contained in the quality control tag

Answer 31

Glucose Mannose N-acetylglucosamine

Question 32

Trimming and growth of carbohydrate chain proceeds in a

Answer 32

Step-by step in each individual cisternae

Question 33

Each glycosylation step takes place in ... What is the importance of this

Answer 33

A sepaate golgi compartment Keeps the specific glycoylaion enzymes away from one another

Question 34

Describe why animal organs are rejected when transplanted into humans

Answer 34

Humans use B-galactose whilst animals will make a-galacose | Humans make antibdodies agaisnt a-galactose - so the animal derived organ will be rejected by the humn

Question 35

Describe how the problems of organ transplant can be overcome

Answer 35

Using an organsism which doesnt have the enzymes required for the synthesis of a-galactose So there is no a-galactose produced s no antibodies produced

Question 36

Describe the processing of insulin

Answer 36

Preproinsulin translation occurs in the ER - cleaveage of insulin leads to the production of proinsulin Proinsulin is transported to the golgi where it is packaged into sec vesicles Proinsulin cleaved to mature insulin and a C peptide

Question 37

What enzymes are required for the cleavage of prepro-insulin and pro-insulin

Answer 37

Specific proteases

Question 38

Even though two chains of insulin are separate how are they held together

Answer 38

Disulphide bonds between the two chains

Question 39

Describe Type 1 diabetes

Answer 39

Misfolding of proinsulin in the ER due to mutation Protease in secretory vesicles unable to cleave the C peptide Secretion of dyfunctional proinsulin Antibodies make agaisnt pancreatic cells Destruction of pancreatic cells

Question 40

A patient with type 1 diabetes will have

Answer 40

Increased levels of blood glucose

Question 41

Different cells cotnain ____________ which cleave the protein into ____________________

Answer 41

Different enzymes Different hormones

Question 42

What is an example of a large protein which can be cleaved into many different proteins

Answer 42

Pro-opiomeanocortin

Question 43

ERresident enzymes have what

Answer 43

KDEL sequence

Question 44

What is the role of the KDEL sequence

Answer 44

KDEL sequence of ER resident enzymes binds to the KDEL receptor Ensures that they return to the ER instead of entering the secretory pathway

Question 45

What is the KDEL seq

Answer 45

Lys - Asp - Gly - Leu

Question 46

What can Pro-opiomeanocortin be cleaved to in the pittuitry

Answer 46

B-lipotrophin | Corticotrophin

Question 47

What can Pro-opiomeanocortin be cleaved in in neurones

Answer 47

B-endorphin B-MSH A-MSH Gama-lipotrophin

Question 48

When do neurones produce B-endorphin

Answer 48

In response to excersise and stress

Question 49

Describe what happens upon binding of insulin to its receptor

Answer 49

Causes downstream signalling | Increased transport of glucose transports into the PM of muscle cells