Lecture 8: Vesicular Transport Pt.3

Endocytosis

• process by which cells take in cargo through sticking it through the membrane e

• BOX & bud 

• done by clathirin coated vesicles 

All Endocytosed Cargo Things

• receptors ligand complexes

• nutrients & carriers

• extracellular matrix components

• cell debris

• bacteria and viruses

• cells themselves (phagocytes)

Clathirin Coated Vesicles

• basket like network on the systolic surface of the membrane that form vesicles that perform endocytosis

Mechanism of Cathrin Mediated Endocytosis

1. Adaptins select cargo molecules for transport

2. Cathrin Coats the Vesicle

3. The soccer ball is formed

4. Dynamin pinches the neck

Adaptins (wife) 

• select cargo molecules for transport & secure clathrin to the membrane 

• clathirirn goes on top of the adaptin 

Dynamin

• GTPase that hydrolyzes GTP to GDP allowing pinching

• a protein that pinches the neck of the vesicle formed by clathrin

Types of Endocytosis

1. Pincocytosis

2. Receptor Medicated Endocytosis

3. Phagocytosis 

Pincocytosis 

• indiscriminate & continuous

• involves ingestion of fluid & molecules via small vesicles (<150nm) 

• Party Bottom

T Or F, The rate of endocytosis equals the rate of constitutive exocytosis 

TRUE 

Receptor Mediated Endocytosis

• efficient way to take up SPECIFIC macromolecules from extracellular fluid 

How Receptor Mediated Endocytosis happens 

• specific MMs bind to complementary membrane proteins accumulating in the vesicle

How Cholesterol gets into the cell 

1. LDL’s carry it and bind to LDL receptors on the cells extracellular surface 

2. The LDL + Receptor get into the cell and bind to the endososme where the receptor lets go and is sorted

LDLs

Low Density Lipoprotiens that hold cholesterol due to it’s amphipathic properties

Why the LDL receptor let’s go when in the endosome

the endesome has a lower pH than cytosol, causing the receptor’s confirmation to change 

True or False: Does the LDL Receptor Process happen regardless of of whether or not LDL is there?

true

How does the endesome sort 

• It has two domains, vascular and tubular.

• Things are sent their way depending on the size

Vacular Domain of the endosome

where FAT things go and get sent to the lysosome

Tubular Domain of the endosome

where SKINNY things go to get sen too the plasma membrane

Fates of a Receptor 

• Recycled:bak to teh PM

• Degraded: taken to the Lysosome

• Transcytosis (trafficked to the PM) 

Phagocytosis 

• specialized form of endocytosis where cells use large vesicles called phagosomes to eat up large particles

• size of phagosome is proportional to what its eaten

• defends against infection

Lysosome

the cells stomach, where the pH is low so acid hydrolyses can get to degrading macromolecules 

Acid Hydrolases

proteins within the lysosome that work best at a low pH to degrade macromolecules

V-ATPases 

proteins that pump the Lysosome with H+ to maintain acidity

Acid Hydrolayses Journey

• they are tagged with specific AZUCARES in the ER& cis Golgi, allowing them to be sorted & modified at the trans-golgi 

• modified in the Golgi because if not it’d be eating 24/7 (ms.gyatt) 

Autophagy

• self eating

• autophagsosmal membrane is induces and vesicles create and autophagsosome

Types of Autophagy & why they happen

• selective autophagy

• non-selective autophagy

Selective Autophagy

• a selective cargo is packaged into autophagosomes that contain LITTLE cytosol

• mediates the amount of worn out/unwanted organelles

• mitophagy

Non-Selective Autophagy

• a lot of the cytoplasm is in side the autophagaosme

• occurs especially when resources are limited (drinking your own piss, your not selective) 

Endesome 

where macromolecules go after receptor mediated endocytosis to then be further sorted 

Transcytosis

one of the three fates of a receptor once is goes to the endesome where it is then pushed to a new membrane