Lecture 3 Flashcards
Mreb
- prokaryotic ancestor of actin
- give rod-shaped bacteria structure
Microfilaments
- made up of actin (alpha muscle, beta/gamma non)
- abundant in all tpyes of eukaryotic cells
- 4 muscle, 2 non
- actin is highly conserved
Cytochalasins
- bind to barbed end
- block elongation
- can inhibit mitosis
Phalloidin
- prevents dissociation
- can be labeled with fluorescent dyes
Spectrin
- found in RBCs
- binds cortical cytoskeleton to plasma membrane
- ghost RBCs after bursting
Dstrophin
- binds cortical cytoskeleton to plasma membrane
- muscular dystrophy gets name from this
Villin and Fimbrin
-cross-links in microvilli
Caalmodulin and Myosin 1
-cross-links actin to plasma membrane in microvilli
alpha-actinin
- cross-links stress fibers and connects actin to protein-plasma membrane copes
- adaptor for integrins to interact with F-actin
Filamin
- cross-links actin at wide angles to form screen-like gels
Thymosin
- controls treadmilling
- captures actin monomers and prevents from being polyerized
Profilin
- binds to actin monomers, prevents polymerization
- controls treadmilling
- facilitates exchange of bound ADP for ATP
- *only ATP-actin monomers can assemble into F-actin
Gelsolin
- controls treadmilling
- destabilizes F-actin and caps filaments, prevents loss and addition of G-actin
- in presence of Ca, fragments actin filament and remains bound to plus end
Cofilin
- controls tread
- triggers depolymerization of ADP-bound actin at minus end
Arp 2/3
- initiates growth of F-actin fro sides of existing filament
- causes branching
- nucleation (3 actin monomers coming together) is rate-limiting
Formin
- and Arp 2/3 complex determine where filament are formed
- large dimers that bind initial monomer, and move along the growing filament
- nucleate long unbranched actin filaments, many stabilized by tropomyosin
Laatrunculins
- bind to G-actin and induce F-actin depolymerization
- non native proteins, used in research to break down filaments
Parallel Bundles
- closely spaced actin filaments aligned in parallel
- barbed ends adjacent to plasma membrane
Contractile Bundles
- more widely-spaced filaments, cross-linked by alpha-actinin
- allows motor protein myosin to interact with actin
Intermediate Filaments
- abundant in cells subject to mechanical stress
- provide tensile strength to cells such as neurons and muscle
- strengthen epithelial cells such as desmo and hemi
- common monomer consisting of central a-helix rod flanked by head and tail domains
Intermediate Assembly
- 2 antiparallel dimers form staggered tetramer
- form spontaneously, doesn’t require ATP
- formed by poly of long, rodlike proteins
- repeated AA segents (heptads)
Intermediate Filament Associated Proteins (IFAPs)
- stabilize filament
- may cap to prevent further elongation
- filaggrin, epinemin, paranemin, plectin, synemin
Intermediate Filament Types
- Type I: acidic keratins, associaed with plaques of desmo and hemi
- Type II: neutral to basic keratins
- Type IV: neurofilaments, axons and dendrites
- Type V: nuclear lamins, mechanical support for nuclear envelope
- Type VI: nestin, associated with CNS stem cells
Microtulues
- thick, composed of tubulin dimers
- consist of 13 protofilaments
- plus end grows more rapidly in presence of low Ca
Factors Inhibiting Microtubule Polymerization
- colchicines, used to create karyotype
- colcemid
- vincristine and vinblastin, anti-cancer
- taxol stabilize
Cilium Structure
- 9 peripheral doublets + central pair of microtubules
- each doublet has alpha tubule (13 protofilaments) and beta (10-11)
Fatty Acid Characteristics
- long-chain pack well together and limit movment
- short are more limited but create spaces which other chains can move
- saturated has no double bonds, max H+
Outer Leaflet of Phospholipid bilayer
- Cholesterol
- phosphatidylcholine
- sphingomyelin
Inner Leaflet of Phospholipid bilayer
- cholesterol, phosphatidylethanolamine, phosphatidylserine (- charge)
- phosphatidylinositol, - charge, important in cell signaling, only in inner
Glycolipids
-outer leaflet with carbohydrate portion facing extracellular, forms glycocalyx
Cholesterol
- High temps, interfers with FA chain movement, makes membrane less fluid, reduced permeability to small molecules
- low temps, prevents membranes form freezing
Glycocalyx
- not integral part of membrane
- carb coat composed of carb portions of glycolipids and glycoproteins
Lipid Rafts
- small patches of cholesterol and sphingolipids
- no proteins, smooth surface
Peripheral Proteins
-can be removed by altering pH or ionic content of environment
Integral Proteins
- Embedded, extracellular portion typically glycolsylated
- can only be removed by detergents
Transmembrane Proteins
- integral that pass completely through both layers
- channel or transporter proteins
- 1 hydrophobic and 2 philic domains
- membrane-spanning portions usually a helix with 20-25 hydrophobic AA (glycophorin, band 3 anion tranporter for Cl ions)
Single Pass Transmembrane Proteins
- single hydrophobic domain passes through layer only once
- enzyme-like receptrors (receptor tyrosine kinases)
- glycophorin (RBC membranes)
Multiple-pass Transmembrane Proteins
- use two or more hydrophobic domains
- activated by add of phosphate
- G-protein-linked receptors (7 trans domains)
- Large transporter and channel proteins (porin has 12 trans domains as does glucose)
