Cell Structure and Function Lecture 14 & 15

Cytoskeleton 

a network of interconnected filaments and tubules extending through the cytosol, playing a role in cell movement and division

True or False: Cytoskeleton is dynamic and changeable.

true

What are the three basic types of cytoskeletal elements of eukaryotes?

microtubules, microfilaments, and intermediate filaments

Microtubules

composed of tubulin subunits and are about 25 nm in diameter

Microfilaments (actin filaments)

7 nm wide, are composed of actin subunits, the smallest of the filaments and are best known for their role in muscle contraction, involved in cell migration, amoeboid movement, and cytoplasmic streaming

Intermediate Filaments 

8-12 nm, are variable in composition, keratin-like organization 

Septins

located within cells, a network composed of proteins

Actin

a very abundant protein in all eukaryotic cells, once synthesized it folds into a globular-shaped monomer that can bind ATP or ADP

G-actin

globular actin, polymerize to form microfilaments, F-actin

How are actins broadly divided? 

into muscle-specific actins (α-actins) and non muscle actins (β- and γ-actins)

Where do β- and γ-actins localize?

to different regions of a cell

G-actin monomers

can polymerize reversibly into filaments with a lag phase and elongation phase 

F-actin filaments

are composed of two linear strands of polymerized G-actin wound into a helix

True or False: Not all the actin monomers in the filament have the same orientation 

false