Cytoskeleton Actin Structure
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What is the width and subunit composition of Microfilament (2), Microtubule (3), and IF(4)?
- Actin (/MreB): 7-9 nm
- Alpha + Beta Tubulin dimer: 25 nm (hollow)
- Lamins, Desmin, Keratin, Neurofilaments: 10 nm
Specifications of Actin:
- Highly conserved
- Most abundant Eukaryotic protein
- G-Actin + F-Actin forms
- Complexed with ATP-Mg or ADP-Mg
G and F- Actin sturcture
- G-Actin: Monomer with 4 domains. domains II+IV= (-) end I+III=(+) end and a cleft for ATP on the (+) end
- F-Actin: Homomer made of G-Actin monomers the form a left handed helix (pointed end = (-); Barbed end = (+))
+/- side characteristics + [Cc]
- Cc: the concentration of G-actin required for monomer assembly into filaments.
- + side has a lower Cc which allows it to assemble in one direction
- [+] = .12 uM [-] = .6 uM
Different Cc allow for ______ which is the process by which a cell moves its membrane.
Treadmilling: Cc of cell is inbetween + and - end which allows forward movement and is powered by ATP hydrolysis
The 3 phases of Actin polymerization are:
Nucleation - Elongation - Stablization
Drugs that restrict actin assembly include:
- Cytocholasin D: Bocks + end assembly
- Latrunculin: Blocks G-actin addition
Drugs that stabalize actin fimalaments:
Phalloidin: Used as actin specific stain
2 proteins that regulate actin polymerization are:
- Thymosin Beta: binds G-Actin 1:1 and prevents assembly
- Profilin: Promotes ATP binding (+ end assembly) and binds to PIP2 at membrane
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