Secretory pathways I & II

Question 1

Proteins move between compartments using what 3 fundamental mechanisms?

Answer 1

1. gated transport between cytosol and nucleus
2. transmembrane transport in cytosol (mitochondria, protein synth)
3. vesicular transport

Question 2

6 major functions of ER

Do you remember? DO YOU?!

Answer 2

1. synthesis of lipids
2. control of cholesterol homeostasis
3. storage of Ca2+
4. synthesis of proteins on membrane bound ribosomes
5. co-translational folding of proteins and early posttranslational modification
6. quality control

Question 3

What recognizes the signal sequence that emerges from a newly formed polypeptide?

Answer 3

signal recognition particle (SRP)

• looks like poop

Question 4

What does the SRP bind to?

Answer 4

1. signal sequence of nascent pp
2. ribosome
3. SRP receptor on ER membrane

Question 5

What is a translocon?

Answer 5

a protein channel allowing pp chain to enter ER

aka translocator

Question 6

What is co-translational translocation?

Answer 6

the cell begins to import most proteins into the ER before complete synthesis of PP chain

-ribosomes synthesizing the protein are membrane bound

Question 7

Describe steps in co-translational translocation

Answer 7

1. ER signal seq (hydrophobic rich) emerges from ribosome
2. SRP binds to the signal and ribosome and directs it to the translocon on the ER membrane
3. Translocon forms a pore for the pp to be translocated into ER lumen
4. Signal peptidase cuts signal sequence during transloation
5. Mature protein is released into the lumen of ER

Question 8

List major functions of Golgi

Answer 8

1. synthesis of sphingolipids from ceramide backbone
2. additional post-translational modification of proteins and lipids
   
   • such as sugar addition
3. proteolytic processing
4. sorting proteins/lipds for post golgi compartments

Question 9

3 well studied vesicle coats and movement

Answer 9

1. COPII
   
   • (ER to golgi)
2. COPI
   
   • (Golgi to ER)
3. Clathrin
   
   • (golgi to plasma membrane)
   • (plasma membrane to interior)

Question 10

What important protein is used in cholesterol sensing?

Answer 10

SCAP protein that binds SREBP

Question 11

Signal sequence binding pocket lined by what? Gives it what property?

Answer 11

Lined by methionines, becomes flexible

Question 12

How many residues in the signal peptide?

Answer 12

8 or more nonpolar residues

Question 13

Type I transmembrane proteins have what special feature that the other types do not?

Answer 13

N-terminal signal sequence (gets localized/sits in lumen)

Question 14

What determines the orientation of the transmembrane protein?

Answer 14

Which ever side the positive charges (Lys/Arg) is sitting relative to the membrane. The side with the positively charged AA will sit in the cytosolic side.

Question 15

Describe how Clathrin forms a vesicle

Answer 15

1. coat assembly (clathrin and adaptor protein) and cargo selection
2. Bud formation
3. coated vesicle formation
4. Uncoating (loss of clathrin coats)

= free vesicle

Question 16

What happens in the cis face of the golgi?

Answer 16

lysosomal targeting of proteins

closest to nucleus

Question 17

What happens in the trans face of the golgi?

Answer 17

most of the sulfates are being added to proteins

Question 18

KDEL function

Answer 18

Retrieves ER membrane proteins

C-terminal end of some ER proteins

• –> binds to KDEL receptor in golgi
• –> Using COPI and gets recycle back to ER

Question 19

What does Mannose-6-phosphate do?

Answer 19

It is a sorting signal for lysosomal proteins.

Question 20

Congenital disorder of glycosylation caused by?

Answer 20

defects in forming N-linked glycosylation