Protein Targeting

Question 1

So proteins destined for the cytoplasm have a signal?

Answer 1

No they are made on free ribosomes and require no transportation.

Question 2

Are proteins made in there active state?

Answer 2

No, some proteins have to made I in and inactive state and activated just prior to secretion.

Question 3

How are proteins activated?

Answer 3

Cleavage of amino acid residues.

Chemical modification

Question 4

Proteins destined for the membrane or secretion are made where? From there where do they travel?

Answer 4

Made by ribosome and move into RER through to Golgi cis face and out of trans face

Question 5

Where do proteins from the Golgi trans face go?

Answer 5

Lysosomes, membrane and secretory vesicles

Question 6

What does a protein need to get to its destination?

Answer 6

A signal that’s intrinicpsc to the protein.
A receptor to recognise the signal.
Translocation machinery
Energy to transfer the protein

Question 7

Describe the four essential elements for proteins destined for peroxisomes.

Answer 7

SKL sequence at the C terminus. This is also known as PTS.
Recognised by pex5 receptor in cytosol.
Pex5 binds to the 13 per protein channel in peroxisomes to open channel to transport into peroxisome.
ATP hydrolysed to allow PTS recycling.

Question 8

Pamela a disorder of peroxisome targeting faults.

Answer 8

Rhizomelic chondrodysplasia punctata

Question 9

Describe the secretory pathway of proteins

Answer 9

Cotranslational transport of protein being manufactured by ER bound ribosomes into the RER.
Budding and fusion of protein carrying vesicle from RER to cis Golgi.
ER destined proteins dent back to ER.
Other proteins progress through cisternae.
At the trans face the protein can undergo
-sorting to lysosomes
-regulated secretion
-constitutive secretion

Question 10

Give an example of constitutive secretion.

Answer 10

Fibroblasts making collagen

Question 11

What cells under go regulated secretion?

Answer 11

Endocrine, exocrine and neurocrine cells

Question 12

Where is the signal for secretion found on proteins?

Answer 12

N terminus 5-30 amino acid sequence

Makes and alphahelical with a central hydrophobic residue to aid membrane permeability.

Question 13

How do proteins get made into the ER?

Answer 13

Signal sequence recognised by protein complex and this pauses translation until. The machinery attaches to the RER the signal is cleaved and the protein is made and fed into the ER

Question 14

How do you get a transmembrane protein?

Answer 14

Stop transfer sequence halts the peptide manufacture accross the membrane, the alpha helix holds it in the membrane with the n terminus on the inside.

Question 15

What does the endoplasmic reticulum do?

Answer 15

Inserts membrane proteins 
Proteolytic cleavage 
Glycosylation 
Disulphide bond formation 
Protein folding 
Multi subunit protein assembly 
Hydroxylationnof proline and lysine so selectively

Question 16

Why add a sugar to a protein?

Answer 16

Stabilisation and to ensure correct folding

Question 17

Why is adding a sugar to a protein termed n linked glycosilation?

Answer 17

Add the sugar to th N of the amino group of an asparginine residue

Question 18

Which amino acid residue readily forms disulphide bonds?

Answer 18

Cysteine

Question 19

What type of reaction forms disulphide bonds.?

Answer 19

Oxidation

Question 20

If a folding problem happens in the ER what mechanism helps to correct it?

Answer 20

ER chaperone proteins

• BiP binding immunoglobulin protein
• calmed in and calrectilin

These will force the protein to sty in the ER and monitor the level of misfolds get to regulate translation.

Question 21

If the protein is kept in the ER due to misfolds go what may result?

Answer 21

Towiic level of misfolds do protein in ER gives disease,

Question 22

Glycosilation in the Golgi is what type of glycosilation?

Answer 22

O linked it attaches the sugar to the -OH

Question 23

Which amino acid residues are prone to o linked glycosilation and why?

Answer 23

Serine and threonine needed in proteogkycans and mucus secretions.
The OH in the r group of these amino residues makes this possible

Question 24

What well known portion is an example of ER and Golgi modifications?

Answer 24

The signal peptide is cute as it enters the ER then the disulphide bonds are made before the beta chain is removed and the carboxyll termini trimmed in the Golgi

Question 25

Why are proteolytic activities so variable

Answer 25

One peptide could have multiple protein products dependent on the tissue its in so cells need to make the right one