Lecture 13: Endomembrane System Part II

Question 1

Endocytosis

Answer 1

cells take up cell components from extracellular fluid using endocytic vesicles

endocytosed cargo includes nutrients, macromolecules, and membrane componets

Question 2

Most endocytic vesicles fuse with

Answer 2

early endosome where cargo is sorted
as endosome matures, it fuses with other endosomes and matures into lysosome

Question 3

Pinocytosis

Answer 3

continuous ingestion of small amounts of extracellular fluid
default pathway
counteracts constitute secretory pathway helps cell maintain size

Question 4

Phagocytosis

Answer 4

selective ingestion of large particles or cells; only performed by specialized cells (macrophages)

Question 5

Clathrin coated vesicles

Answer 5

move materials from:
plasma membrane to endosome (endocytosis), golgi to lysosome, and golgi to secretory vesicles (exocytosis)

Question 6

Receptor mediated endocytosis

Answer 6

specific molecules are bound by receptors at plasma membrane to concentrate molecules from extracellular fluid

able to bring in low density lipoproteins (LDL)

Question 7

Low density lipoproteins (LDL)

Answer 7

transports cholesterol in blood to provide cells with important membrane component
composed of cholesterol, triacylglycerol, and lipid monolayer
protein (apolipoprotein B) makes LDL water soluble

Question 8

LDL recognized by

Answer 8

LDL receptor for protein-protein interaction

Question 9

Cells can increase intake of cholesterol by increasing number of

Answer 9

LDL receptors

Question 10

LDL is not ___ but _____

Answer 10

cholesterol
cholesterol carrier

Question 11

Critical steps for LDL Endocytosis

Answer 11

LDL receptor on plasma membrane binds to LDL in extracellular fluid
Adaptor and clathrin coat proteins form protein coat for formation of vesicle
2. Clathrin coated vesicle buds off plasma membrane, vesicle loses protein coat before fusion
3. Vesicle fuses (via Rab and Snare proteins) to early endosome
As endosome matures it lowers pH to activate enzymes and become lysosome
LDL receptor disassociates from LDL because of low pH
4. LDL receptor recycled to plasma membrane; lipoprotein is degraded by proteasome in lysosome; cholesterol transported to plasma membrane and ER
proteasome digest LDL to release cholesterol