Zaidi Lecture 9/28 Trafficking

Question 1

Lysosomes

Answer 1

Membrane enclosed compartments filled with hydrolytic enzymes; important for intracellular digestion of macromolecules; derived from late endosomes

Question 2

Vacuolar ATPase Pump

Answer 2

Pumps H+ ions into lysosomes to maintain the acidic pH and to drive transport of small metabolites

Question 3

Transport from Trans Golgi Network to Lysosomes

Answer 3

Pathway that delivers membrane proteins and hydrolases to lysosomes

Question 4

Sorting Signal for Lysosomal Hydrolases

Answer 4

Mannose-6-phosphate, which is attached in the Cis Golgi Network; M6P receptors in Trans Golgi Network recognize the sugar to be packaged into clathrin coated vesicles that bud off from TGN

Question 5

Hurler’s Disease

Answer 5

Mutation in the enzyme required to break down glycosaminoglycan chains

Question 6

Inclusion Cell Disease

Answer 6

All of the lysosomal hydrolases are missing in many cell types; undigested substrates accumulate as “inclusions”

Question 7

Endocytosis

Answer 7

Uptake of macromolecules from exterior across plasma membrane; material is progressively enclosed by a portion of plasma membrane

Question 8

Phagocytosis

Answer 8

Large particles ingested by vesicles called phagosomes; carried out by phagocytes, macrophages, neutrophils; phagosomes fuse with lysosomes and ingested material is degraded; undigested material secreted out by exocytosis

Question 9

Pinocytosis

Answer 9

Small particles ingested by pinocytic vesicles; occurs continuously in all eukaryotic cells

Question 10

Receptor-mediated Endocytosis

Answer 10

Used to import select macromolecules from outside cell; uptake of cholesterol is done in this way; blockage of this pathway results in atherosclerosis

Question 11

GLUT 4

Answer 11

Glucose transporter 4; only one that is insulin sensitive

Question 12

Exocytosis

Answer 12

Transport vesicles move from TGN to plasma membrane; membrane proteins and lipids in the vesicles are destined for plasma membrane while soluble proteins are secreted out of cells

Question 13

Constitutive Secretory Pathway

Answer 13

Operates continuously

Question 14

Regulated Secretory Pathway

Answer 14

Triggered by signals

Question 15

Process of Endocytosis

Answer 15

1. Material is progressively enclosed by a portion of the plasma membrane
2. Plasma membrane invaginates and then pinches off to form endocytic vesicle

Question 16

Process of Receptor-mediated Endocytosis

Answer 16

1. Molecules bind to receptors on membrane surface
2. Accumulate in clathrin-coated pits
3. Enter cell as receptor-macromolecular complex in clathrin-coated vesicles
4. Provides selective concentration mechanism

Question 17

Process of Phagocytosis

Answer 17

1. Triggered by binding of particle to receptors on phagocyte surface
2. Receptors functionally linked to cellular response machinery
3. Antibodies bind to microbe, Fc chain recognized by Fc receptor on surface of macrophages/neutrophils
4. Binding triggers formation of pseudopod which engulfs the particle and forms phagosome
5. Pseudopod formation driven by localized actin polymerization and reorganization
6. Controlled by Rho GTPases and phosphoinositide signaling

Question 18

Process of Pinocytosis

Answer 18

1. Process begins at clathrin-coated pits
2. Membrane invaginates and pinches off to form clathrin-coated vesicle
3. Extracellular fluid with various solutes trapped in pits as they invaginate

Question 19

Process of Pinocytosis through Caveolae

Answer 19

1. Caveolae invaginate into membrane by virtue of lipid composition and not the protein coat
2. Caveolae pinch off from plasma membrane by dynamin to form caveosome (endosome-like compartment)
   * DO NOT CONNECT WITH LYSOSOMES*

Question 20

Caveolae

Answer 20

Flask-shaped invaginations in plasma membrane enriched in cholesterol and glycosphingolipids and GPI-anchored membrane proteins; major structural protein is caveolin

Question 21

Formation of Secretory Vesicles

Answer 21

Proteins destined for secretion packed into secretory vesicles in TGN
Involves selective aggregation/clumping of proteins, but mechanism not fully understood
Vesicle membrane proteins may have receptors for aggregated proteins or undergo phagocytosis like mechanism