Secretory pathways I & II Flashcards Preview

Thanh Cell Physiology Unit III > Secretory pathways I & II > Flashcards

Flashcards in Secretory pathways I & II Deck (20)
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1
Q

Proteins move between compartments using what 3 fundamental mechanisms?

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

6 major functions of ER

Do you remember? DO YOU?!

A
  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
3
Q

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

A

signal recognition particle (SRP)

  • looks like poop
4
Q

What does the SRP bind to?

A
  1. signal sequence of nascent pp
  2. ribosome
  3. SRP receptor on ER membrane
5
Q

What is a translocon?

A

a protein channel allowing pp chain to enter ER

aka translocator

6
Q

What is co-translational translocation?

A

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

-ribosomes synthesizing the protein are membrane bound

7
Q

Describe steps in co-translational translocation

A
  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
8
Q

List major functions of Golgi

A
  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
9
Q

3 well studied vesicle coats and movement

A
  1. COPII
    • (ER to golgi)
  2. COPI
    • (Golgi to ER)
  3. Clathrin
    • (golgi to plasma membrane)
    • (plasma membrane to interior)
10
Q

What important protein is used in cholesterol sensing?

A

SCAP protein that binds SREBP

11
Q

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

A

Lined by methionines, becomes flexible

12
Q

How many residues in the signal peptide?

A

8 or more nonpolar residues

13
Q

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

A

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

14
Q

What determines the orientation of the transmembrane protein?

A

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.

15
Q

Describe how Clathrin forms a vesicle

A
  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

16
Q

What happens in the cis face of the golgi?

A

lysosomal targeting of proteins

closest to nucleus

17
Q

What happens in the trans face of the golgi?

A

most of the sulfates are being added to proteins

18
Q

KDEL function

A

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
19
Q

What does Mannose-6-phosphate do?

A

It is a sorting signal for lysosomal proteins.

20
Q

Congenital disorder of glycosylation caused by?

A

defects in forming N-linked glycosylation