Cell Membranes And Cytoskeleton Flashcards
Phospholipids
. Most prevalent type of lipid in biological membranes
. Synthesized in sER, transported to Golgi then to plasma/organelles
. Polic, ionic compounds
. Amphiphatic
Phospholipid structure
. Alcohol attached by phosphodiester bridge to carbon3 of glycerol backbone or to sphingosine
. Hydrophobic tail contains 2 fatty acid chains links to carbons 1 and 2 of glycerol backbone
. Number of carbon atoms in fatty acid chain is even
. 1 of the fatty acid chains is unsaturated (1 double bond)
Major membrane phospholipids
. Phosphatidylserine (PS) . Phosphatidylethanolamine (PE) . Phosphatidylcholine (PC) . Phosphatidylinositol (PI) . Sphingomyeline (SM)
T/F membrane phospholipids cannot move
F, capable of many types of motion (rotation, flexion, lat. movement) contributing to membrane fluidity
Areas w/ most cholesterol synthesis
Liver, adrenal cortex, and reproductive tissues
T/F Every human tissue is capable of cholesterol synthesis
T
Cholesterol structure
Polar hydroxyl group and hydrophobic steroid ring and attached hydrocarbon
. Amphiphatic
Cholesterol interaction w/ phospholipid membrane
. Goes btw phospholipids w/ hydroxyl group near polar heads and steroid ring and hydrocarbon tail parallel to the fatty acid chains of phospholipids
Cholesterol function in membrane
Inc packing of phospholipids and slows their lat. mobility
Glycolipids
.minor lipid components in cell membranes
. Have acquired sugar groups in the non-cystolic half of lipid bilayer from golgi so sugar is always displayed on exterior of cell when in the membrane
. Important in cell-cell and cell-matrix interactions
T/F lipids important for membrane structure, protein important for membrane biological functions
T
Integral membrane proteins
. Embedded in phospholipid bilayer
. Can be transmembrane or lipid-anchored
. Rotate along their long axis (lat. movement) w/in membrane but can’t flip form one leaflet to another
Lipid anchored protein
Integral protein covalently attached to lipid w/o entering core of membrane bilayer
Integral membrane protein functions
. Ligand receptors
. Channels and transport proteins
. Cellular identity
Ligand receptors
. External signals (ligand) that bind to protein receptor on cell surface
. Specific receptors for specific ligand
. Cells w/o receptor can’t respond to ligand
Glycoproteins
. Integral proteins w/ carbs attached to them on exterior of cell
. Each cell type has different glycoproteins to give it individual identity
. Individual humans can have different glycoproteins
Peripheral membrane proteins
. Can be removed w/o disrupting bilayer
. Attach to membrane surface via ionic interactions w/ integral protein or via interaction w/ polar head groups of phospholipids
Peripheral membrane protein functions
. Constituents of cytoskeleton: maintain cell shape and form, move chromosomes during cell division, help w/ cell motion
. Signal transduction: enzymes that are active after ligand binding
Asymmetry in membrane
. Different proteins, phospholipids, and glycolipids are presented on the external and internal sides of membrane
. Proteins have specific orientations when embedded into membranes
because of the fluidity of biological membrane ____
. Proteins diffuse in plane of bilayer and interact
. Easy to distribute membrane lipids and proteins through diffusion
. Membranes can fuse w/ one another to allow mixing of molecules
. Insurance that membrane molecules are distributed evenly btw daughter cells during mitosis
Lipid rafts
. Specialized cholesterol-enriched microdomains w/in cell membrane
. Fatty acid chains of phospholipids are extended and more tightly packed
. Float independent w/in fluid created by less ordered lipids in surrounding portions of membrane
Lipid raft function
. Cholesterol transport
. Endocytosis
. Signal transduction
Types of lipid rafts
. Gycosphingolipid-enriched membranes (GEM)
. Polyphosphoinositol-rich
. Caveolae
Caveolae
Flask-shaped invaginations of cell membrane
. Contains protein caveolin that causes local change in morphology of membrane
Major factor in controlling fluidity of membrane and what does it do?
Cholesterol
. Inc. cholesterol: less fluid outer surface but more fluid in hydrophobic core
Spur cell anemia
. Erythrocyte has inc. cholesterol and dec. membrane fluidity causing dec. ability to negotiate micocirculation
. Causes premature destruction of cells
Intoxicating ethanol effects on nervous system from caused by ____
Modification of membrane fluidity and alteration of receptors and ion channels
Abetalipoproteinemia
Altered phospholipids in membranes causing dec. membrane fluidity
Reason RBC dies in 120 days
. Loss of membrane fluidity preventing them from negotiating microcirculation
Hereditary spherocytosis
Reduction in erythrocytic spectrin content
. Creates spherical fragile rbcs and hemolytic anemia
Hereditary elliptocytosis
. RBCs are elliptical and fragile
. Spectrin can’t bind protein 4.1 or form stable spectrin-4.1-actin complex
Functions of actin in non-muscle cells
Regulation of physical state of cytoplasm, cell movement, formation of contractile rings in cell division
Polymerization fo actin
. Actin filaments (F-actin) are polymers of actin monomers (G-actin)
. Each G-actin monomer has ATP bound to polymerize onto F-actin
Diameter of actin filament
8nm
Stages of actin filament formation
. Lag
. Polymerization
. Steady state
Lag phase of actin filament formation
3 G-actin monomers w/ bound ATP join to form nucleation site
. ATP is hydrolyzed and G-actin is added to end of F-actin
Steady state in actin formation
. Actin monomers added at one end at same rate as they are being removed from other end
. Treadmilling
Actin-binding proteins
.regulate structure of actin by controlling polymerization and breakdown of actin
. Regulate gel-state of cytosol: more structured actin more firm gel, less structured (more fragmented) more soluble
. Spectrin and dystrophin important ones
Muscular dystrophy diseases
. Deletion in dystrophin gene
. X-linked recessive
. Duchene: no functional dystrophin, rapid severe muscle degeneration
. Becker: partially functional dystrophin, slowly progressive muscle weakness
Intermediate filaments
. Intermediate in thickness btw actin and microfilaments (10nm)
. Rope-like appearance
. Fibrous protein subunits that form fibrous heteropolymers
. Structural function
. Assoc. w/ nuclear envelope and plasma membrane
Types of intermediate filaments
. Acidic and basic keratin . Desmin and vimentin . Neurofilaments, synemin, syncollin . Nuclear lamina . Nestin
Microtubule function
. Ciliary and flagella motility
. Mitotic and meiotic chromosomal movement,
. Intracellular vesicles transport and secretion
Principle component of microtubules
Tubulin
Tubulin structure
Globulin protein heterodimer w/ alpha and beta subunits
T/F GTP not required for dynamic instability of microtubules
F, need GTP bound to tubulin for assembly and disassembly
Assembly and disassembly process of microtubules
. GTP hydrolyzed to GDP after tubulin addition to microtubule
. Disassembly peels back protofilaments and begins once GTP cap is hydrolyzed to GDP from plus end (beta side)
Microtubule-protein interaction
Motor proteins associate w/ them to position membrane-bound organelles w/in cell
Spectrin
Actin-binding protein that strengthens and supported membranes
. Important in erythrocytes
Dystrophin
. In Skeletal muscle cells
. Links actin to supporting structures w/in and strengthens muscle fibers
FRAP experiment
Showed that phospholipids were mobile
. Bleach a spot of cell that has fluorescence and if it has lateral mobility the bleached part will regain it’s fluorescence
Which phospholipids are on inner leaflet?
. Phosphatidylethanolamine
. Phosphatidlinositol
. Phosphatidylserine
Phospholipids on outer leaflet
. Phosphatidylcholine
. Sphingomyelin
