This presentation is done by Orji Jonathan Orji with the guidance of Tamriko valishvili, Associate Prof. Doctor of medicine. Is very educative, well organized and a good learning material, enjoy it to the fullness. Comment, like and share if you fine it useful.

1. ORJI JONATHAN ORJI
MD, phD
Kutaisi 2013
ACTIN FILAMENT

2. Actin filaments are thin and
flexible
7 nm in diameter
Less rigid than
microtubules
Plus end - fast growing
Minus end - slow
growing
Monomers polymerize
into a helical chain

3. Actin and microtubules
polymerize using similar
mechanisms
Monomeric actin binds
to ATP
Upon polymerization,
actin ATPase activity
cleaves ATP to ADP
ATP hydrolysis acts as a
molecular “clock”
Older actin filaments
with ADP are unstable
and disassemble

4. Myosins are actin-based motor
proteins
Myosins convert ATP hydrolysis into movement along
actin filaments
Many different classes of myosins (>30 in humans)
Some myosins move cargoes, other myosins slide
actin (as in muscles)
Actin & ATP binding sites in N-terminal head domain

5. Contraction is activated by calcium
release from the sarcoplasmic
reticulum

6. Contraction is regulated by a Ca+2-
mediated change in the
conformation of troponin

7. Contraction is regulated by a Ca+2-
mediated change in the
conformation of troponin