MCB Lec 8

- Actin filament
- Intermediate
- Microtubules

- organizes and supports cytoplasm
- guides intracellular traffic (mostly Microtubules)
- Pulling apart of chromosomes in mitosis (microtubules)
- muscle cell contraction

- thinnest
- highly concentrated in the cortex
- supports shape of plasma membrane

- globular protein with 375 residues
- contains a cleft that binds to ATP

- G-Actin
- F-Actin
- Polymerization

Associate to form polymer with subunits added to both ends
- subunits add more rapidly to + end
- shrinking occurs in - end

Filamentous form

process to create polymers
- reversible
- constantly grows and shrinks

growth rate is equal to shrink rate

- largest of the 3
- POLYMERS of tubulin (dimer of alpha and beta subunits).
- bind to G nucleotide

- A-tubulin
- B-tubulin

inaccessible and always stays as GTP

more exposed to the solvent and can be hydrolyzed from GTP to GDP

Spindle that splits chromosomes during Mitosis
When this spingle grows instead of shortening it is cancer

Vincristine: inhibits polymerazation by binding tubilin before its able to make microtubules.
Paclitaxel: stabalized the polymerized state of microtubules so chromosomes are unable to seperate

can be made from all sorts of protiens, typically fibrous

Lamins: form nuclear lamina and defines the shape of the nuclear membrane
Keratin: Helps form the skins outer layer of hair and nails

Progeria produces defective lamina because of mutated Lamin A gene

2 a-helixes forming a left handed coil, ideal version is Heptad Repeat (Leucine residues, in position 4, every 7 away)
Every 3.6 residues make a turn and hydrophobic interactions coil them together

- Crucial for extracellular matrix and connective tissue,
- 3 polypeptide chains (triple-helix),
- every 3rd residue is glycine
glycine --> flexible = collagen

(Gly-Pro-Hyp) found in collagen
Vitamin C is required as a cofactor for proline> hydroxyproline

- ATP hydrolysis to carry out mechanical work
- actin and microtubules

Muscle contractions (myosin) and intercellular transport (kinesin)

- 2 heads long tail so ATP can bind
ATP hydrolysis drives the physical movement of myosin along the actin filimanet in contraction

1. Relaxed: release of ADP and the ATP binding alters the conformation so the actin is not connected
2. Contracted: hydrolysis of ATP> ADP+Pi and triggers the myosin to bind to actin

- acts on microtubule
- two heads for tubulin and ATP