1. PART II Why Do Cells Need a Cytoskeleton
PART II Why Do Cells Need a Cytoskeleton? How do cells move vesicles and themselves? CH 15 and a bit of 16 (Last for CH Test #3 Friday) Oct 27, Oct 30 and Nov 1
Cytoskeletal Components: microtubules, microfilaments and intermediate fibers
Cytoskeleton is required by all eukaryotic cells!
Microtubule functions/characteristics
Microfilament functions/characteristics
Intermediate filament functions/characteristics
Calcium, Actin and Myosin=> contraction
Skeletal and Cardiac Muscle VS. Smooth Muscle
Intermediate assembly and hair

2. Important for muscle contraction (actin/myosin)
Microfilaments are the smallest cytoskeletal structures in the cell and form thread-like actin structures in the cytosol.
Important for muscle contraction (actin/myosin)
Important for ameboid motion/cytoplasmic streaming
Organization:
Monomers of G-actin-ATP polymerize into long strands of F-actin (mature actin)
Small: about 7 nm in diameter
Strands form a double helix
Some strands become cross-linked by “filamin” for extra strength!

3. Microfilaments are primarily formed by adding G-actin to the positive “fast-growing” end of the filament. Actin polymerization requires: ATP, K+ and Mg++ What effect does the drug cytochalasin have?

4. Microfilaments can form diffuse gel-like matrices OR they can become tightly cross-linked to form rigid structures like the non-motile microvilli found on intestinal epithelial cells.

5. Microfilaments can also be linked to proteins in the plasma membrane and molecules/materials outside the cell itself by N-CAMS. This is important for attaching the brush border of the mucus membrane to the cell!
Classic Link
Protein Types:
Ankyrin
Spectrin
Band 4.1
Microtubule of G-actin monomers

6. Myosin-I = Monomers + actin
Myosin-II forms large polymers (2H + 4L) for muscle contraction. Myosin-I monomers attach actin to plasma membranes, moving vesicles, and pushing actin “rods” in the direction of cell elongation (have you ever seen a pseudopod on an amoeba?).
These are examples of
Myosin-I = Monomers + actin

7. Awesome review of the cytoskeleton and intracellular transport:

8. Depolarization of the target cell occurs when the ACH in a vesicle is released (exocytosis), diffuses across synapse, and binds/open its receptor (a Ligand Gated-Na+ Channel) This should be review.

9. End Plate “Potential”: One exocytosis may not release enough ACH to open enough ligand-gated channels to create enough depolarization to cause enough depolarization to open the voltage gated channels. Membrane potential changed, but not enough for Na-VGC threshold to be reached. Wait till next exocytosis of ACH to occur.

12. Review of structural organization

13. Smooth muscle cells are found in blood vessels, glands, guts,and other places. SMCs contract using calcium entry/calmodulin binding as a signal to activate myosin light chain kinase (MLCK). MLCK phosphorylates myosin letting it bind actin and contract.

14. Once the myosin in smooth muscle is phosphorylated it binds actin and the cell contracts, contraction ends when Ca++ leaves the cell and MLC-phosphatase removes the phosphate from MYOSIN…leading to SMC relaxation

15. Desmosones and Hemidesmosomes
Intermediate Filaments (polymers) consist of relatively tissue specific proteins and are transcribed from genes only expressed in specific tissues.
Classics:
Desmosones and Hemidesmosomes
Mechanical strength to the cell wall-
Cellular glue!
Keratins:
Mechanical strength to epithelial cells
Form skin and hair!
Desmin:
Attachment of actin from myosin complex to Z-line of cell end plate! STRONG!
Neurofilaments:
Provide strength to the long fragile axons of body!
“Tangles” are one of the prime indicators/causes of the cellular dysfunction that leads to Alzehimers disease

16. 4 main types of cell-cell connection: Tight Junction: prevent chemical diffusion and infection Desmosome: attach neighboring cells Hemidesmosome: attach cells to basement membrane Gap Junction: is a pore (hole) between cells

17. How are intermediate filaments assembled
How are intermediate filaments assembled? MonomerDimerTetramerProtomerFilament (8-10 nm diameter)

18. Hair is formed when epithelial cells in a hair follicle accumulate keratin and die. New cells push the old ones out and you have hair growth! Curls in hair are created when the disulfide-cross links don’t match-up evenly! Perms modify this artificially!

20. Lets consider the transport of materials inside of and along the length of a neuron. How fast and how efficient is the process of molecular/organelle transport?
Soma is the source of mRNA and most biosynthesis.
Axonal transport describes how things get to the synaptic ending (FAST OR SLOW).
Fast axonal transport ( mm/day)
Daily use materials: organelles, vesicles, proteins
Pathogens: Anterograde-to soma Retrograde-away from soma
Herpes Simplex Virus (Nerve soma to skin escape from body/coldsore
Rabies Virus: Dendrite to soma and protection from antibodies within CNS
If you know where the pathogen entered a neuron, you can time the appearance of symptoms in the CNS to the rate of transport!
Slow axonal transport (0.5 to 10mm/day) provides LARGE materials for axonal growth/repair/regeneration or mitochondrial migration
If a nerve was cut at shoulder, how long would it take at minimum to regenerate “finger tip innervation” if distance was 30 cm? 300mm X 0.5mm/day=600days