Cytoskeleton and Cell Membrane Flashcards
List the three specific types of structures found in the cytoskeleton.
- Microfilaments
- Intermediate filaments
- Microtubules
Microfilaments are made up predominately of _____
actin
Characteristics of Actin Filaments
7 nm thick, bind to specific transmembrance proteins either directly or indirectly. Exist as monomers and long chains
Actin monomers are called:
g-actin
Actin long chains are called:
f-actin
Taxol will NOT inhibit microtubular polymerization
True
Nuclear lamins are intermediate filaments that:
Line the inner aspect of the nuclear envelope.
____________ initiates growth of f-actin from the sides of existing filament and causes branching
Arp2/3
fibronectin is NOT a type of intermediate filament
True
Low concentrations of G-actin ________ the disassembly of actin filaments
Favor
A dynamic equilibrium is favored when _____________ concentrations of g-actin are present
intermediate
Net addition at both ends of the actin filament are favored when the G-actin concentration is ___________
Higher
Cytochalasins are actin binding proteins that:
bind to the barbed (plus) end and block elongation. They can also inhibit movements, such as mitosis
Actin-binding protein, Phalloidin:
binds to the actin filaments and prevents dissociation. It can be labeled with fluorescent dyes for visualization
Actin-Binding Protein, spectrin:
Is found in RBCs. It binds coritcal cytoskeleton to plasma membrane
Actin-Binding Protein, Dystrophin:
Binds cortical cytoskeleton to plasma membrane. Muscle tissue related
Actin-Binding Protein, Villin and Fimbrin
cross-links microvilli. Links to actin chains
Actin-Binding Protein, Calmoduling and myosin I:
cross-links actin to plasma membrane in microvilli
Actin-Binding Protein: alpha-actinin:
cross-links stress fibers and connects actin to protein-plasma membrane complexes.
Actin-Binding Protein, Filamin:
Cross-links actin at wide angles to form screen-like gels.
Thymosin:
controls treadmilling, captures actin monomers and prevents actin monomers form being polymerized
Profilin:
Bind to actin monomers and prevent monomer from being polymerized. Facilitates exchange of bound ADP for ATP- which favors polymerization. Remember, only ATP-actin monomers can be assembled into f-actin.
Gelsolin:
Treadmilling control; destabilizes f-actin and caps actin filaments, preventing loss and addition of g-actin. In presence of calcium ion, fragments actin filament and remains bound to the plus end.
Cofilin:
Triggers depolymerization of ADP-bound actin at the minus end.
Arp2/3:
Initiates growth of F-actin from sides of existing filament– causing branching.
________ and __________ complex determine where filaments (branching) are formed by facilitating nucleation
Fromin, Arp2/3
Tropomyosins:
Stabilize the actin filaments that are nucleated by Formins
Name the three proteins that are not naturally ocuring in the cell be can be added to effect actin polymerization
cytochalasins, phalloidin, latrunculins
Latrunculins:
come from Red Sea Sponge. Bind to g-actin and induce f-actin depolymerization
Name the two types of actin bundles:
Parallel Bundles and Contractile Bundles
Parallel bundles:
an actin bundle that has closely spaced actin filaments aligned in parallel, all with the same polarity, with the barbed ends adjacent to the plasma membrane.
Contractile Bundles:
actin bundles that are more widely spaced filaments, cross-linked by alpha-actinin. The increasing space allows the motor protein myosin to interact with the actin filaments.
Phalloidin:
Prevents depolymerization by binding to actin filaments
Intermediate Filaments…..
- Provide tensile strength in cells such as neurons and muscle.
- Are abundant in cells subject to mechanical Strength
- Strengthen epithelial cells as desmosomes and hemidesmosomes
- All have a common monomer consisting of central alpha-helix rod flanked by head and tail domains.
The rodlike portion of intermediate filaments…..
- Consists of repeated amino acid segments (heptads)
2. Facilitate formation of coiled-coil-a-helix dimers or parallel intermediate filament proteins.
_______ and ______ terminals for the rodlike proteins (intermediate filaments) form links to other cytoskeletal elements.
Carboxyl, Amino
Explain Intermediate filament assembly
you have two antiparallel dimer form a staggered tetramer. The non-polar tetramers bind end-to-end and for a helical filament. This spontaneous formation does not require ATP or GTP
Intermediate Filament Associated Proteins (IFAPS)
Stabilize filaments by cross-linking adjacent filaments or by linking to other cytoskeletal elements, and may cap filaments to prevent further elongation.
List the five IFAPs
Filaggrin, epinemin, paranemin, plectin, synemin.
Type I Intermediate Filament
Acidic Keratins: with type II these for the intermediate filaments of the epithelial cell cytoskeleton. Associated with plaques of desmosomes and hemidesmosomes
Type II Intermediate Filament
Neutral to Basic keratins.
Type IV Intermediate Filament
Neurofilaments: found in axons and dendrites
Type V Intermediate Filament
Nuclear lamins: Provide mechanical support for inner membrane of nuclear envelope and bind chromatin
Type VI Intermediate Filament
Nestin: associated with CNS stem cells
Microtubules
are composed of tubulin dimers, alpha and beta units. Have a dynamic instability
Microtubules consist of ___ ________ arranged parallel to form a cylinder with a hollow core.
13 protofilaments
The microtubule plus end grows more rapidly than the minus end in presence of _________ [ ]
low calcium ion
Define MAPs
Microtubule-associated proteins
Protofilaments are longitudinal rows of…..
Tubulin dimers
Factors that inhibit microtubule polymerization
colchicines- arrest in metaphase to photograph karyotypes. Colcemide. Vincristin and vinblastin are anti-cance drugs
Factors that stabilize microtubles
Taxol- binds to MTs to prevent depolymerization. Disrupts mitosis
Structure of Cilium
9+2 config. 9 peripheral doublets + central pair of microtubules. Each doublet consist of the alpha tubule and Beta tublue
Explain the alpha and beta tubule of cilium doublets
Alpha: Consist of 13 profilaments, radial spokes extending to sheath around central pair, Pairs of dynein arms projecting to beta unit of next doublet
Beta: 10-11 protfilaments
What is a protofilament?
a vertical linear array of tubulin units alpha and beta alternating along its length.
List some functions of the cytoskeleton
cell movement, spindle formation and function, support and strength for the cell, phagocytosis, cytokinesis, cell-to-cell and cell-to-ECM adherence, changes in cell shape, intracellular transport.
Outer leaflet of phospholipid bilayer contains….
cholesterol, phosphotidylcholine, sphingomyelin
inner leaflet of phospholipid bilayer contains….
cholesterol, phosphotidylethanolamine, phosphatidylserine (-), phosphatidylinositol (-) and important in cell signaling.
Glycolipids:
are found only in the outer leaflet with carbohydrate portion facing the extracelluar environment.
Cholesterol:
within the phospholipd bilayer, moderates membrane fluidity. At high temp it interferes with FA chain movement making outer part less fluid reducing permeability to small molecules.
At low temp it prevents membranes from freezing and maintains membrane fluidity.
Glycocalyx:
Not an integral part of membrane. Carbohydrate coat on the extracellular surface of cell membrane composed of carbohydrate portions of glycolipids and glycoproteins.
Lipid Rafts
small patches of: cholesterol and sphingolipids (sphingomyelin and glycolipds)
Peripheral Proteins:
are found on both the inner and outer leaflets of the cell membrane facing either the extracellular or intracellular fluid. Can be removed by altering pH or ionic content of environment
Integral Proteins:
Embedded within the phospholipid bilayer, extracellular portion is typically glycolsylated. These proteins can only be removed by detergents.
Transmembrane proteins;
Integral proteins that pass completely through both phospholipid layers, typically server as channel and transporter proteins and must have at least one hydrophobic and two hydrophilic domains. i.e glycophorin and band 3
Glycophorin and Band 3 are examples of what?
transmembrane proteins.
Single pass transmembrane proteins:
have single hydrophobic domain that passes through the bilipid layer only once. Includes enzyme linked receptors and glycophorin
Multiple-pass transmembrane proteins
multiple passes through the cell membrane using two or more hydrophobic domains. Typically activated by the addition of a phosphate. Includes g-protein-linked receptors (7 domains), and larger transporter proteins and channel proteins. Porin has 12 domains.
