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SGU: Cytoskeleton
Histology: Cytoskeleton
| Question | Answer |
|---|---|
| What are the three major components of the cytoskeleton? | actin filaments (microfilaments), intermediate filaments and microtubules |
| What is the function of the cytoskeleton? | maintains cell shape and support, provides the mechanisms for cell movement, acts as tracks for motor proteins that help move materials within cells |
| Describe actin filaments | F-actin that is ATP dependent. 7nm. Polarized:fast growing + and slow growing - |
| Functions of microfilaments | anchorage, structural core of microvilli, locomotion, extension of cell processes |
| Describe microvilli | cyclindrical, membrane-bound cytoplasmic projections of a core 25-30 actin microfilaments. The actin is crosslinked by villin anchored to the terminal web. |
| Describe Intermediate filaments | 8-12nm, rope-like, formed from non-polar and variable subunits |
| Functions of intermediate filaments | stabilize cell structure: maintain nuc and organelle position, resist shearing force:connects with desmosomes and hemidesmosomes across the cytoplasm, essential for integrity of cell-cell and cell-ECM junctions |
| What are the 4 intermediate filaments? | keratins, vimentin & vimentin-like, neurofilaments, lamins |
| Describe keratins | diverse group with >50 isoforms, found in different cells of epithelial origin |
| Describe vimentin | most abundant in mesoderm-derived cells |
| Describe vimentin-like | desmin in muscle cells, glial fibrillary protein in glial cells and astrocytes, peripherin in neurons |
| Describe neurofilaments | formed from a group of neurofilament triplet proteins, extend from cell body into the ends of axons and dendrites, provide structural support |
| Describe lamins | associated with nuc envelope, Lamin A & B, found in nucleoplasm |
| Describe the stucture of a centriole | 9 triplets of microtubules arranged around a central axis. Each triplet consists of 1 complete and 2 incomplete microtubules fused |
| Function of centriole | organizes the centrosome, provide basal bodies necessary for assembly of cilia and flagella, formation of centrosome & alignment of the mitotic spindle during cell division |
| What is the structure of the centrosome/MTOC? | pair of centrioles perpendicular to each other with an amorphous protein matrix and gamma-tubulin ring complexes where microtubules grow from |
| Function of MTOC? | initiate microtubule formation: positive ends point out and grow toward the cell periphery |
| Structure of microtubules? | non-branching, rigid, hollow tubes made up of alpha and beta tubulin subunits with a positive and negative end |
| Which cytoskeletal component is "dynamic"? | microtubules because the assemble and disassemble as the needs of the cell change |
| Functions of microtubules | intracellular transport, cell motility, mitotic spindle, rigid intracellular skeleton to main cell shape and polarity |
| Describe the polymerization of microtubules | directed by MTOCs, dependent on GTP, can be highly dynamic or relatively stable, fast grow at positive end and slow growth/disassembly at negative end |
| controller of microtubule lenght | environment and microtubule associated proteins |
| Function of cilia | move fluid and particles along epithelial surfaces |
| How are cilia anchored to the cell? | basal body |
| What are primary cilia? | antennae-like structures, 9+0, develops from one centriole following division |
| What sensory organelles are derived from primary cilia? | outer segment of rods, chemoreceptors in olfactory neurons, mechanoreceptors on epithelial cells of kidney to monitor fluid flow. |
| What defect arises from polycystic kidney disease? | primary cilia defect |
| What is part of the actin based molecular motor family? | myosin |
| What is part of the microtuble based molecular motor family? | kinesin, dynein |
| Structure of myosin II? | 2 heavy chains and 4 light chains, tail-tail interactions result in the formation of bipolar thick filaments, head binds and hydrolyzes ATP |
| Describe the kinesin family of molecular motors | positive end directed motors, binding sits for vesicles, organells or other microtubule, ~40 kinesins in humans |
| Describe the dynein family | negative end directed motors, binding sites for vesicles, organelles and another microtubule, largest and fastest |
| What are the two branches of dynein | cytoplasmic and axonemal |
| What are the 3 steps of cell motility? | protrusion, attachement, contraction |
| Describe protrusion | actin-rich structures pushed out at the front of the cell |
| Describe attachment | actin cytoskeleton connects across PM to substratum |
| Describe contraction | bulk of the trailing cell cytoplasm in drawn forward |
| What are the 3 different types of protusion | filopodia, lamellipodia, pseudopodia |
| Describe filopodia | 1 dimen., core o long, bundled actin filaments ex. fibroblasts |
| Describe lamellipodia and examples | 2 dimens. sheet like structures, ex. fibroblasts, epithelial cells, neurons |
| Describe pseudopodia | 3 dimensional projections, ex. neutrophils |
| Desribe in detail PM protrusion | actin polymerization: actin filaments oriented with plus end forward and minus end attached to sides of other actin by ARP complexes, treadmilling: assemble at front, disassembling at rear |
| What proteins are involved in cell motility? | monomeric GTPases, Rho, Rac, Cdc24 |
| Function of Rho | bundling of actin filaments with myosin II, clustering of integrins to form focal contacts |
| Function of Rac | actin polymerization at periphery |
| Function of Cdc24 | actin polymerization and bundling to form filopodia/microspikes |
| What are the three methods of neutrophil migration | neutrophil extravasation, transmigration, chemotaxis |
| Describe neutrophil extravasation | movement from blood to tissues through blood vessels. EC selectin receptors bind neutrophils |
| Describe transmigration | diapedesis: extension of a pseudopod between endothelial cells. |
Created by:
mnoronha
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