Block 1 090612 Endosomes And Lysosomes

Front 1

What are two methods of endocytosis?

Back 1

1. phagocytosis= a cell eat another cell (large particles like bacteria)
2. pinocytosis= a cell uptakes small particles in the ECM like solutes

Front 2

Name the 3 specific types of pinocytosis.

Back 2

1. receptor-mediated endocytosis= ingestion of receptor- bound material covered in clathrin
2. Caveolae= injestion of small vesicles formed by aggregative of Caveolae in lipid rafts
3. Mcaropinocytosis= uptake of liquin in large vesicles

Front 3

What are the 4 general steps of phagocytosis?

Back 3

1. binding of extracellular material on cell membrane
2. extension of pseudopodia by microfilament-dependent movement
3. Formation of phagosomes by fusion of pseudopodia
4. fusion of phagosomes with lysosomes (phagolysosome) for enzymatic digestion

Front 4

Specify the stages of receptor-mediated endocytosis.

Back 4

1. ligands are selectively internalized by binding to cell surface receptors in clathrin-coated pits
2. Pits budding in GTP mediated by Dynamin
3.Clathrin coat dissociates and the material fuses with early endosomes
4.The receptors are recycled and sent back to the plasma membrane and the ligands remain in a vesicle that fuses with late endosomes

Front 5

What is the role of Dynamin?

Back 5

closes off the cell membrane with the clathrin coat using GTP

Front 6

What is the role of AP2?

Back 6

AP2 or adaptor protein that binds to the specific AA sequence on the receptor that has the ligand attached. The AP2 then attaches the receptor to the clathrin coat

Front 7

What is the role and structure of Clathrin?

Back 7

Structure: 3 heavy chains and 3 light chains that forms a cage
FXN: distorts the plasma membrane by budding to produe a vesicle and capture membrane receptors and bound molecule

Front 8

Specify the trafficking steps involved in receptor mediated endocytosis of a ligand from the extracellular space tot eh lumen of a lysosome.

Back 8

1. Clathrin coat dissassociates to expose the receptors and it fuses with the early endosome
2. The receptors are repackaged and send back to the membrane and the ligand is sorted and send to the late endosome
3. The late endosome matures into a lysosome

Front 9

How of the vesicles transported to the early and late endosome?

Back 9

along microtubules using either Dynein motor proteins for kinesins

Front 10

What is the pH of the late endosome and why?

Back 10

5.5, Hydrolytic enzymes tagged with Mannose-6-P fuse the the late endosome so enzymes can be active at this pH

Front 11

How does a late endosome mature into a lysosome?

Back 11

1. sorts the hydrolytic enzymes and recieves them from the golgi which tags the enzymes with mannose-6-P
2. Sends endosomal membrane back to the trans Golgi network
3. enzymes activated by lowered pH

Front 12

What are the different types of ligands that can undergo endocytosis?

Back 12

hormones, growth factors, antibodies, lipoproteins, vitamins, iron binding proteins, toxins, viruses

Front 13

Describe the structure and function of multivesicular bodies.

Back 13

When the receptor shouldn't be recycled and it should be degraded, it is tagged with ubiquitin and sent to the late endosome then budds into a conglomeration called the MVB. THis sorts and degrated integral membrane proteins and by doing this it hormone desensitizes by down regulating the receptor

Front 14

Describe the structure and function of Caveolae

Back 14

**this method of endocytosis DOES NOT require a receptor

They are integral membrane proteins with lots of sphingomyelin + cholestrol = lipid rafts that either
1. Endocytosis:bud as vesicles from the plasma membrane to trap ligands and fuse with either "caveosomes" or early endosomes
2. Transcytosis: bud as veiscles from the cell surface and cross the cella nd fuse the the membrane at another location on the cell surface

Front 15

Where are caveolae abundant?

Back 15

vascular endothelial cells, smooth muscle cells, fibroblast, adipocytes

Front 16

What are the main types of lysosome hydrolases?

Back 16

nucleases, proteases, lipases, glycosidases, phosphatases, phospholipases, sulfatases

Front 17

What are 3 specializations in lysosomal membranes and their functional significance?

Back 17

1. proton pump = lowers pH
2. glycoslyation of membrane proteins protect the membrane from digesting
3. membrane transporters that relase digested products

Front 18

How do lysosomes form?

Back 18

The trans-golgi send a clathrin-coated mannose-6-p linked to lysosomal enzymes that is synthesized in the cis-golgi. It shreds the clathrin coat and fuses with the late endosomes. The mannose-6-p receptors are recycled to the trans golgi and the enzymes lowers the pH so enzymes are active

Front 19

What cellular defects cause I-Cell Disease?

Back 19

There is a defect in processing mannose-6-P tag. This prevents lysosomal enzymes from getting from the Golgi to the late endosomes so there is an accumulation

Front 20

What cellular defects cause Tay-Sachs Disease?

Back 20

The alpha-hexoaminidase A is defected so there is an accumulation of GM2 gangliosides in the brain

Front 21

What cellular defects cause gaucher's disease?

Back 21

The beta-glucocerebrosidase is defected and causes accumulation of glucocerebroside in macrophages which leads to splenomegaly and enlarged liver