Lecture 19: Endocytosis, Autophagy, Cytoskeleton

Coatomer: Clathrin and AP complex

• AP = Clathrin Adaptor Proteins

• AP/Clathrin-coated vesicles:

  1. move from TGN to other vesicles (e.g. lysosomes, endosomes, plant vacuoles)

  2. helps form endocytic vesicles to move vesicles from

     plasma membrane to endosomes or lysosomes

Key features of lysosomes

• Digestive organelles.

• Size: 25 nm to 1 μm.

• Internal pH of 4.6 (proton pump or H + -ATPase). Contains hydrolytic enzymes: acid hydrolases.

• Lysosomal membrane is composed of glycosylated proteins that act as a protective lining next to acidic lumen

Cytoskeleton

dynamic network of interconnected filaments and tubes that extends
throughout the cytosol (and some organelles) of eukaryotes

1. structural support

2. spatial organization within cell

3. intracellular transport,

4. contractility and motility

Microtubules (MT)

• Largest cytoskeletal element (25 nm diameter).

• Polymer of two different proteins (monomers): α-tubulin and β-tubulin.

• 2 major types:

  • Axonemal MT:

    • Highly organized, stable

    • Part of structures (axoneme) involved in cell movement (e.g cilia, flagella)

  • Cytoplasmic MT

    • Loosely organized, very dynamic

    • Located in cytosol

Microtubule-associated proteins (MAPs)

Two classes of MAPs
1. Non-Motor MAPs:
• Control MT organization in cytosol (e.g. Tau protein in neurons).
• Defective Tau protein → neurofibrillary tangles → Alzheimer’s disease (right image, top).
2. Motor MAPs:
• Two main types—kinesin and dynein.
• Use ATP to generate force.
• Can move material along MT track.
• Can generate sliding force between MTs