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