Lecture 12 - the endomembrane system 2

Bio 201

Exocytosis

Releases material out of cell

Inner membrane of the vesicle becomes part of the outer surface of the plasma membrane

Exocytosis of many materials is regulated by extracellular signals

Many cells only release materials to a specific surface

• polarized secretion

Endocytosis

Endocytosis has the opposite effect on the membrane composition as exocytosis

• removes lipids and proteins

“membrane flow”

• movement of proteins and lipids into and out of the plasma membrane

What is phagocytosis?

ingestion of large particles

What happens after unicellular eykaryotes take in food particles?

endocutic vesicle fuses with a late endosome or matures into a lysosomes

What engulfs pathogens?

Macrophases and neutrophils

Receptor mediated endocytosis

Usually receptors from the plasma membrane are recycles due to acidification of the early endosome

Fate of ligand in vesicle?

1. carried to a lysosome for degradation

2. carried to the TGN, where they enter a variety of pathways

3. carried to a different region of the plasma membrane, then secreted (transcytosis)

Coated vesicles in transport

layers of proteins cover the cytosolic surfaces of most vesicles involved in protein and lipid transfer

Most common types of coat proteins?

• clathrin

• COPI

• COPII

• caneolin

Wht does type of coat on vesicle help determine?

• determine vesicle destination

• induce vesicle cutvature

• cytoskeletal interactions

Clathrin-Coated vesicles

Movement to endosomes

What are clathrin coated vesicle made of?

clathrin and adaptor protein (AP)

What are adaptor protein complexes?

Helps in:

• promoting assembly of clathrin coats

• clathrin binding to membrane proteins

Four types of AP complexes (basic structure)?

• two adaptins

• medium chain

• small chain

ATP/GTP helped provide energy for what in clathrin coated vesicles?

• binding of AP complexes to PM

• concentrating receptors/receptor ligand complexes

Wht is Dynamin?

Required for constricting and closing the vesicle as clathrin accumulated around the budding vesicle

Dynamin is a cytosolic GTPase…

• GTP hydrolysis tightens dynamin rings which are rings of proteins that get tighter as hydrolyzed

• seperares vesicles from plasma membrane

Eventually clathrin is removed from fully formed vesicles by?

also known as “uncoating” and done by energy

COPI coated vesicles are involved in transport from…

golgi to er and within golgi

COPI vesicles are coated with:

• COPI

• ARF (ADP ribosylation factor) —-helper protein

How is coat assembly mediated by ARF?

• ARF activated by GEF proteins which have an on/off switch and turns off when GTP hydrolyzed by GDP and turned back on when GDP bound to protein (GDP→GTP)

• activated ARF attaches to lipid bilayer

COPII have a role in transport from…

ER to golgi

COPII coat is assembled from protein complexes….

• Sec13/31 and Sec23/24

• sarl is similar to ARF

What are SNARE proteins?

• mediate fusion between vesicle and target membranes

• SNAP receptor proteins (SNARE)

Where are V-snares found?

• on vesicles

• Vesicle-SNAP receptors

Where are T-snares found?

• target membranes

• Target-SNAP receptors

what helps SNARES come together?

Rab GTPases

SNARE release is mediated by…

• NSF

• SNAPs

Tethering proteins may also play a role in vesicle targeting over long distances…

• goglins

• exocyst complex