The Cytoskeleton

Cytoplasm = consists of all the contents that we can find within the plasma membrane excluding the cell nucleus (includes organelles)

Cytosol = gel- like, semifluid material that surrounds the membranous organelles

pH 7.2 maintained in a range of 7.0-7.4 by antiporter and anion exchanger membrane proteitns

Key Functions of Cytosol

Transport of metabolites

Site of protein biosynthesis (translation)

Involved in signal transduction

Forms the basis of the cytoskeleton

Three main polymers of cytoskeleton

Microtubules

Actin filaments

intermediate filaments

Functions

Structure and support

Intracellular support

Contractility and motility

Spatial organisation

Differences that distinguish the cystoskeletal polymer types are networks they form are:

Mechanical stiffness

Dynamics of their assembly

Their polarity

Type of molecular motors with which they associate

Most rigid, have the most complex assembly, have filament flexibility that increases with length, can form almost linear tracks that span the length of a animal cell

Hollow rods 25 nm diameter, 200nm to 25 um long

Composed of a protein: tubulin = globular protein

Composed of dimers of alpha and beta tubulin. Once the heterodimer is formed it does not come apart

It is a polymer

Are polarised

Functions

Shaping the cell

Strength + rigidity

Seperate chromosomes during cell division

guiding movement of organelles

Cell motility in cilia and flagella

Can grow out of the centrosome region

Centriole

Composed of 9 triplet MTs,

Cylindrical structures

Duplicates once each cell cycle

Motor proteins

Able to bind a polarised cytoskeletal filament

8 - 12 nanometers

a helical proteins, divided into six major classes or types on the basis of similarities in sequence.

Functions

Maintenance of cell shape

anchorage of nucleus and other organelles

Formation of nuclear lamina

Link to extracellular matrix

Most dynamic (can grow. shrink quickly)

Provide mechanical support to cells. Connect the contents of the cytoplasm with cell membrane in order to support signal transduction

Vesicles + organelles moved along micro filament tracks (transport myosins)

Functions

Maintenance of cell shape

Changes in cell shape

Muscle contraction

cytoplasmic streaming

cell motility

Cell division

Made up of identical actin proteins arranged in a long spiral chain

Polarity. (plus and minus ends) ATP powered growth occurring at plus end

Solid rods 7nm diameter, form a 3D network

motor protein associated with actin = Myosin