Chapter 17 Cytoskeleton
Cytoskeleton
Set of formed elements (consisting of proteins) that perform a variety of tasks
Microtubules
Actin microfilaments
Intermediate filaments
Plants/Animals have these elements
Prokaryotes don’t endosymbiosis? (centrioles can replicate)
Functions (9)
Skeletal framework of cell
Supports and moves organelles
Movement
Amoeboid type
Cilial/flagella
Cell junctions
Specialized structures
Spindle fiber
Contractile rings
Muscle fibrils
Exocytosis/endocytosis
Cell shape changes spindle fibres
Shows array of green microtubules
Red are mostly actin microfilaments
Centrosome area of intense microtubule activity
Pair of centrioles
Formed Elements: microtubules Actin microfilaments Intermediate filaments

Intermediate Filaments (simplest)
Protect cells from mechanical stresses
Resist stretching
Keep connection to other cells
Structural
See array of intermediate filaments making connections to other cells
Intermediate filament proteins important in cell junctions
Desmosomes, tight junctions

Intermediate Filaments (10-12 nm in diameter)
Made up of polypeptide chains coiled together staggered to make longer (C N staggered with NC)
8 tetramer combinations make up filament (48 nm long)
Protein Families
Keratin, desmin, vermentin, lamin
Tissue Specific
Intermediate filaments strengthen cell structure
Responses to mechanical stresses
Functions of Intermediate Filaments
Lamins form meshlike surface of nuclear envelope
Framework of cytoskeleton
Intermediate filamentsstay same

Blues are supporting intermediate filaments

Microtubules (25 nm in diameter)
Length is variable
Family
α,β and γ
Tubulin Dimers α, β monomers polymerize, add more dimers to the wall
Centrosomes- microtubules push out
Basal body in ciliated cell analogous to centriole
Microtubules all look same (human, yeast, cow etc)
Made up of protofilaments
13 arranged around diameter
Polarity (top and bottomes) βplus endexploratory extensions α minus endcentrosome
Cells are added and taken away from plus end
Minus end as well but much slower..
Nucleating sites (γ tubulin dimers)
Where projections of microtubules leave centrosomes from
Dynamic instability
Processes of how microtubules are always polymerized and depolymerised
Microtubules can only be added with GTPase activity
Β monomer binds and hydrolyses

Microtubule associated proteins (MAPs)
Stabilize position of microtubules (cap ends)
Prevent from depolarizing
Can also lead to cross linking thanks to stability
Microtubule tracts
Stabilized by capping proteins
Motor Proteins
Type of MAP
Dynein + - end
Inward traffic flow
Kinesin - +
Motor Proteins move vesicles proteins and even mitochondria
Can be behind two sides
Microtubule side and vesicle side
Move along microtubule from binding site to binding site
Walking
Traffic Flow

Arrangement of microtubules with intermediate filaments
Movement of golgi
Also transport synaptic vesicles
Experiment to show motor proteins carry things of no need
High Powered micrograph of connection between kinesin microtubules and cargo
Cilia and flagella
Move synchronously
Stroke similar to in cilia and flagella
Power stroke followed by return stroke
Oar like
Uniform Arrangement

Christina’s notes. Last day
Microfilaments
Smallest division of the formed elements
2 intertwined strands of actin dimers (α and β)

Dimers Polymerize and depolarize
Β Subunits bind ATP
Basis of Filapodia, pseudopodia, lammelapodia
Microvilli, shape formation, cell cortex just below cell matrix gel like consistency
Shows microvilli, structure, amoeboid movement and cell division
Actin