cytoskeleton

microtubules

• component of cytoskeleton

• regular, non-branching polymers of tubulin

  • recall “polymer”

• hollow tubes (diameter 20-30 nm, inner diameter 14 nm)

• highly dynamic, microtubules can be polymerized and depolymerized rapidly

• “grow” from the microtubule organizing center (MTOC)

what are tubules exhibiting? meaning?

• they exhibit dynamic instability

• meaning they are constantly remodeling

what is control of polymerization and depolymerization dependent on?

• temperature

• presence of GTP and Mg2+

• presence of microtubule association proteins (MAPs)

what do microtubules do?

• serve as infrastructure for molecular motor proteins (dyeins and kinesins)

• mitotic spindle

• cell elongation and migration

• movement of cilia and flagella

where do kinesin and dyein move

• kinesin moves toward positive end towards outside of cell away from MTOC

• dynein moves toward negative end towards MTOC

• 

describe structure of actin filaments and talk ab what cells have them. differences bn microtubules

• all cells have actin

• actin molecules polymerize to form actin chains, two chains wrap around eachother forming actin filament (6-8 up in diameter)

• they are thinner, shorter, and more flexible than microtubules

what are actin filaments called when free or polymerized? what must be present for polymerization? what does ABP do?

• free = G-actin (globular actin)

• polymerized = F-actin (filamentous)

• F-actin has fast growing end (+ barbed) and slow growing end (- pointy)

• ATP, Mg2+, K+ required for polymerization

• actin binding proteins influence structure and function of actin filaments

microfilament roles

• anchorage and movement of membrane protein

• comprise the core of microvilli (a cell modification for absorptive cells, especially intestinal cells)

• locomotion of cells and migration via lamellipodia

  (cells crawl)

• extension of filopodia

intermediate filaments: size, dynamicism, role

• heterogenous group of similarly sized filaments

• subunits are diverse but size remains the same

• less dynamic that actin filaments or microtubules

• between microfilaments and microtubules in size

• role is structure and anchoring (keep membranous organelles in place)

what is the MTOC? centrioles and their structure

• MTOC region in cytoplasm surrounded the centrioles where microtubules originate

• centrioles observable under light microscope as paired short cylinders

  • comprised of 9 microtubule triples

structure of MTOC

• tubulins

• microtuble

• pericentriolar matrix

• gamma-tubulin ring

• nucleus

• - end and + end

• nucleus-basal body connector (NBBC)

centriole axoneme structure

• 9+2 arrangement

cell surface specializations`

• cilia and flagella (sperm)

what is the mechanism of axoneme movement

what is immotile cilia syndrome?

• defect in ciliary dynein

• respiratory tract infections

• male infertility