Previously

2 main types of Endocytosis

3 main trafficking routes for newly internalized receptors and ligands

Now: If there is traffic there must be roadsCellular infrastructure: the components of the cytoskeleton

Molecular Roads and Infrastructure

Bipolar disorder•Is it the cellular equivalent of ‘dead letter box’?

•Are cytoskeletal ‘problems’ a likely cause for for this disorder?

What are the components of the cytoskeletonand what do they do?

Elements of the Cytoskeleton

Intermediate filaments

Microfilaments (actin)

Microtubules

Actin

Fig 18-4

Highly conserved

Most abundant intracellularprotein (in eukaryotes)

Structure of actin

Fig 18-2

Polarity of molecule‘-” and ‘+’ ends

T form and D form

G- actin vs F- actin

Bundles and Networks

What is the benefit of these kinds of associations?

Stability of actin

Stability depends on environment– ion and g-actin concentration

Provides support through DYNAMIC arrangements

including both structure and gel-like qualities of cytosol

Actin filaments dynamics

http://www.bms.ed.ac.uk/research/smaciver/lectures/Cs2.htm

+ vs - end?

Illustration of treadmilling CBI 25.2

Filaments utilizes 3 steps: lag period, elongation, steady state

ATP hydrolysis NOT required for polymerization

ATP hydrolysis changes kinetics of polymerization

Microtubules

Fig 19-5

Fig 19-1

Protofilament:Polymer of

/ tubulin heterodimers

13 protofilaments= microtubule

Stable and unstable populations

Exhibit dynamic instability

Microtubule dynamics

http://www.bms.ed.ac.uk/research/smaciver/lectures/Cs2.htm

+ vs - end

Steps in formationprotofilament formationmicrotubule assemblymicrotubule elongation

Microtubules treadmill AND undergo dynamic instabilityhttp://cryoem.berkeley.edu/video/nogales_400x300_narrated.mov

Factors effecting polymerization/ depolymerization

Critical Concentration: Cc

Actin: ends have different Cc (+) 0.1M(-) 0.8Mcellular concentration 0.5M

Consequences? Microtubules: One end ‘in’ MTOC

Consequences?

Associated proteins

Toxins

And why are we discussing this?

Shmoos form from reorganization of actin cytoskeletonShmoo tip ‘extends’ due to vesicles specifically delivered

via actin bound motor protein

Microtubules are main ‘highway’ vesicular traffic

Cytoskeleton critical for localizationFig 23-30

Actin in development CBI21.5Microtubules in axon core and protein localizationIntermediate filaments in mechanical stability of neurons

But how do the vesicles move?

What makes one MT different from another?

Accessories!Accessories!