Vesicle Transport

Question 1

How do budding and fusion of vesicles occur? •

Answer 1

Transfer of soluble components from one lumen to another • Membrane proteins transferred, with same domain always oriented to the cytosol.

Question 2

Describe each vesicular transport pathway

Answer 2

Biosynthetic secretory pathway - enters pathway via ER, goes to Golgi, then Endosome, then plasma membrane (via constitutive or regulatory pathway) or lysosome.

Endocytic pathway- Plasma membrane to endosome, can end up in lysosome, recycled in plasma membrane, or transcytosis.

Retrieval pathway - backward in biosynthetic pathway, recycling in endocytosis pathway

Question 3

How does vesicular transport work?

Answer 3

Compartments have chemically distinct characteristics and vesicles deliver components to each compartment with different “addresses”

Question 4

What is the function of coated vesicles

Answer 4

concentrates membrane proteins in specialized patches, molds the vesicle, different coats for different compartments.

Question 5

Where do clathrin coated vesicles originate and end up?

Answer 5

Clathrin with adaptin 1: starts in golgi apparatus and ends in lysosome via endosomes
Clathrin with adaptin 2: starts in plasma membrane and ends in endosomes.

Question 6

Describe cop1 and cop2.

Answer 6

Cop1 starts in golgi and ends in er. Cop2 starts in er and ends in golgi.

Question 7

What are the characteristics of clathrin?

Answer 7

Subunit composed of 6 polypeptides, important for endocytosis.

Question 8

What do adaptor proteins do?

Answer 8

Bind clathrin coat to membrane and trap proteins in forming vesicle. Provide specificity.

Question 9

What does dynamin do?

Answer 9

Recruits proteins for pinching off

Question 10

What are rab proteins?

Answer 10

Monomeric GTPases that mediate vesicle targeting. includes inactive/cytosolic Rab-GDP and active, membrane bound Rab GTP that recruits Rab effectors.

Question 11

What is the function of SNARES?

Answer 11

brings membranes together for fusion.

Question 12

describe the different snares.

Answer 12

V-snares on vesicle membrane, single polypeptide. T-snares on target membrane, 2-3 polypeptides.

Question 13

Describe membrane fusion.

Answer 13

SNARE complex brings membranes together, H2O is forced out, noncytosolic leaflets fuse and cytosolic leaflets fuse.

Question 14

Describe transport from ER to Golgi.

Answer 14

Happens via cop2 vesicles. Proteins must be properly folded/assembled for transport.

Question 15

What do KDEL and KKXX do?

Answer 15

KDEL functions as an ER retrieval signal on soluble proteins, binds receptor. KKXX functions as ER retrieval signal on membrane proteins, binds COP1 coat.

Question 16

Describe the golgi apparatus -

Answer 16

composed of membrane enclosd compartments call cisternae, located near nucleus, site of o-linked glycolysation, includes cis and trans network

Question 17

Describe lysosomes:

Answer 17

sites of intracellular digestion, acidity maintained by H+ ATPase, low in pH,

Question 18

How does transport of lysosomal hydrolases occur?

Answer 18

M6P added to lysosomal hydrolases. • M6P receptor in trans Golgi recognizes M6P to target proteins to the endosomes

Question 19

What are the pathways to the lysosome?

Answer 19

Phagocytosis (take up of large particles or microorganisms), endocytosis (take up of molecules from extracellular fluid), autophagy (disposal of cell parts)

Question 20

What are exocytosis and endocytosis?

Answer 20

Exocytosis - delivery to membrane/extracellular space, endocytosis - internalization from the membrane/extracelullar space.

Question 21

What are the different types of exocytosis?

Answer 21

Unregulated exocytosis where all cells are continuous (constitutive secretion). Regulated exocytosis where specialized cells secrete hormones, NTs, and digestive enzymes (regulatory secretion)

Question 22

What are the different ways of sorting in the Golgi?

Answer 22

Signal mediated diversion to lysosomes, signal mediated diversion to secretory vesicles, and constitutive secretory pathway (default)

Question 23

How does exocytosis happen in mast and parasitic islet cells?

Answer 23

Causes release of histamine in allergic response and insulin release from pancreatic beta-islet cells.

Question 24

What is phagocytosis?

Answer 24

Cell eating” • Ingestion of large particles like microorganisms/dead cells by specialized cells

Question 25

What is pinocytosis?

Answer 25

cell drinking, ingestion of fluid and small solutes.

Question 26

What is receptor mediated endocytosis?

Answer 26

Endocytosis of macromolecules bound to receptors via clathrin-coated vesicles.

Question 27

What are the fates of endocytosed transmembrane proteins?

Answer 27

Recycling, degradation, transcytosis (movement from one extraceullar space to another)