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BMS242 Cell and Molecular > L25 - Protein Trafficking > Flashcards

L25 - Protein Trafficking Flashcards

1
Q

Where are cytosolic proteins made

A

In the cytosol

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2
Q

Where are membrane and secreted proteins made

A

RER

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3
Q

The RER is studded by

A

Ribosomes

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4
Q

Where are nuclear proteins made

A

The outer nuclear membrane

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5
Q

Describe what happens to the common pool of ribosomes

A

Form either a polyribosome in the cytosol

Form a polyribosome bound to the RER membrane

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6
Q

Describe how the polyribosome on the RER membrane forms

A

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

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7
Q

WHat occurs at the RER

A

Protein synthesis

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8
Q

What occurs at the SER

A

Lipid synthesis and formation of vesicles

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9
Q

What is a heavy microsome

A

One made from the RER - studded with ribosomes

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10
Q

What is a smooth microsome

A

From the smooth ER - no ribosomes

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11
Q

Describe how you may separated rough and smooth microsome

A

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

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12
Q

What is the role of the golgi

A

Final addition of sugars and sorting

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13
Q

Describe the organisation of the golgi

A

Cis to trans golgi network

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14
Q

Describe what happens during the maturation of vesicles

A

Proteases act to trim and activate hormones and enzymes

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15
Q

A sequence of positive AA targets the protein to

A

the nucleus

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16
Q

What does an SRP have

What does this allow

A

Hinge region

Means that it is able to travel with the ribosome

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17
Q

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

A

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

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18
Q

What enzyme catakyses cleavage of the signal sequence

A

Signal peptidase

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19
Q

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

A

Large SU faces the translocator

Small SU faces the cytosol

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20
Q

Describe how a protein is inserted into the ER membrane

A

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

21
Q

What is a GPI anchor

A

Glycosylaphosphatidyllinositol anchor

22
Q

What does a GPI anchor allw

A

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

23
Q

Once the signal sequence has been cleaved what happens

A

Conformational maturation

24
Q

Conformation maturation involves the formation of ____________

Where do these form

What is the function

A

Disulphide bridges

From between cystenines

Solidify

25
Q

Where do DS bridges NOT form

A

In the cytosol since it is a reducing environment

26
Q

What is the role of standard glycosylation

A

Quaity control

27
Q

Describe how glycosylation acts as quality control

A

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

28
Q

What (3) is glycosylation important for

A

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

29
Q

What sugar do humans use

What sugar do other animals use

What is the different

A

B-galactose

A-galactose

At C1 OH and H are in differnent positions

30
Q

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

A

N-linked - from asparagine

O linked - from thereonine

31
Q

What three molecules are contained in the quality control tag

A

Glucose
Mannose
N-acetylglucosamine

32
Q

Trimming and growth of carbohydrate chain proceeds in a

A

Step-by step in each individual cisternae

33
Q

Each glycosylation step takes place in …

What is the importance of this

A

A sepaate golgi compartment

Keeps the specific glycoylaion enzymes away from one another

34
Q

Describe why animal organs are rejected when transplanted into humans

A

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

35
Q

Describe how the problems of organ transplant can be overcome

A

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

36
Q

Describe the processing of insulin

A

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

37
Q

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

A

Specific proteases

38
Q

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

A

Disulphide bonds between the two chains

39
Q

Describe Type 1 diabetes

A

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

40
Q

A patient with type 1 diabetes will have

A

Increased levels of blood glucose

41
Q

Different cells cotnain ____________ which cleave the protein into ____________________

A

Different enzymes

Different hormones

42
Q

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

A

Pro-opiomeanocortin

43
Q

ERresident enzymes have what

A

KDEL sequence

44
Q

What is the role of the KDEL sequence

A

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

45
Q

What is the KDEL seq

A

Lys - Asp - Gly - Leu

46
Q

What can Pro-opiomeanocortin be cleaved to in the pittuitry

A

B-lipotrophin

Corticotrophin

47
Q

What can Pro-opiomeanocortin be cleaved in in neurones

A

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

48
Q

When do neurones produce B-endorphin

A

In response to excersise and stress

49
Q

Describe what happens upon binding of insulin to its receptor

A

Causes downstream signalling

Increased transport of glucose transports into the PM of muscle cells

BMS242 Cell and Molecular (26 decks)

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