ch 8 - Biological Membranes Flashcards
Lipid rafts
collections of similar lipids with or without associated proteins. serve as attachment points for other biomolecules; often serve roles in signaling
Flippases
specialized enzymes that assist in the transition (or flip) between layers in membrane
Fatty acids
carboxylic acids that contain a hydrocarbon chain and terminal carboxyl group
Triacylglycerols
also called triglycerides - storage lipids involved in human metabolic processes. Contain three fatty acid chains esterified to a glycerol molecule
Unsaturated fatty acids
one or more double bonds and exist in liquid form at room temp; in plasma membrane these characteristics impart fluidity
two important essential fatty acids for humans
alpha-linolenic acid and linoleic acid
saturated fatty acids
main components of animal fats; solid at room temp; decrease membrane fluidity
chylomicrons
the rest of unsaturated fatty acids come from essential fatty acids in the diet that are transported as triacylclycerols from the intestine inside these
glycerophopholipid
commonly called phospholipid - born of a substitution of one of the fatty acid chains of triacylglycerol with a phosphate group, a polar head group joins the nonpolar tails
micelles
phospholipids spontaneously form into these; small monolayer vesicles or liposomes (bilayered) due to hydrophobic interactions
Sphingolipids
do not contain glycerol; similar in structure to glycerophospholipids in that they contain a hydrophilic region and two fatty acid-derived hydrophobic tails.
types of sphingolipids
ceramide, sphingomyelins, cerebrosides, gangliosides
cholesterol
regulates membrane fluidity; necessary in synthesis of steroids; contains both a hydrophilic and hydrophobic region. prevents formation of crystal structures in membrane by stabilizing adjacent phospholipids and occupying space between them at lower temps and higher temps helps keep membrane intact; 20%of cell membrane; by mole fraction about half
waxes
extremely hydrophobic and rarely found in cell membranes of animals; sometimes in cell membrane of plants. Composed of long chain fatty acid and a long chain alcohol, which contribute to high melting point.
Fluid mosaic model
theory underlying structure and function of cell membrane; accounts for presence of 3 types of membrane proteins: transmembrane, embedded, and membrane associated (peripheral)
transmembrane proteins
pass completely through lipid bilayer
embedded proteins
associated with only the interior (cytoplasmic) or exterior (extracellular) surface of the cell membrane
integral proteins
transmembrane and embedded proteins are considered this because of association with interior of plasma membrane, which is usually assisted by one or more membrane associated domains that are partially hydrophobic
membrane-associated (peripheral) proteins
bound through electrostatic interactions with the lipid bilayer, especially at lipid rafts, or to other transmembrane or embedded proteins like the G proteins found in G protein coupled receptors
membrane receptors
tend to be transmembrane proteins that can activate or deactivate some transporters for facilitated diffusion
cell adhesion molecules (CAM)
proteins that allow cells to recognize each other and contribute to proper cell differentiation and development
gap junctions
cell-cell junctions that allow for direct communication, often found in small bunches together; also called connexons; formed by the alignment and interaction of pores composed of six molecules of connexin
tight junctions
prevent solutes from paracellular leaking into the space bt cells; watertight seal; found in epithelial cells; physical link bt cells as they form single layer of tissue; can limit permeability enough to create a transepithelial voltage difference on either side of epithelium
desmosomes
bind adjacent cells by anchoring to their cytoskeletons; formed by interactions bt transmembrane proteins associated with intermediate filaments inside adjacent cells; found in interface bt two layers of epithelial tissue
hemidesmosomes
similar function to desmosomes but their main function is to attach epithelial cells to underlying structures, especially basement membrane
passive transport
spontaneous processes that do not require energy (negative delta G) proceed this way
active transport
nonspontaneous processes that require energy (positive delta G) proceed this way
simple diffustion
passive transport - substrates move down their concentration gradient directly across the membrane. There is potential and as they “fall”, energy is given off. only particles that are freely permeable to membrane
osmosis
passive transport - specific kind of simple diffusion that concerns water; water will move from a region of lower solute concentration to one of higher solute concentration; inversely, move from a region of high water conc to one of lower water conc down its gradient
hypotonic
conc of solutes inside cell is higher than the surrounding solution; sometimes causes lysing. (ex too much salt in the cell, water rushes in)
hypertonic
solution that is more concentrated than the cell; water moves out of the cell
isotonic
solutions inside and outside cell are equimolar; movement still occurs but cell will neither gain nor lose water overall
osmotic pressure
pi=iMRT where M is the molarity of the solution, R is the ideal gas constant and T is the absolute temp (in kelvin), i is van’t Hoff factor; colligative property and is dependent only on presence and number of particles in solution; pure water will push on a solution and make the solution’s water level rise to the point that solution can push back sufficiently; draws water into cell
van’t Hoff factor
the number of particles obtained from the molecule when in solution; if sodium chloride becomes two ions (Na+ and Cl-) then i of NaCl=2
colligative properties
physical properties of solutions that are dependent on concentration of dissolved particles but not on chemical identity of those dissolved particles. Examples are osmotic pressure, vapor pressure depression (Raoult’s Law), boiling point elevation, and freezing point depression
facilitated diffusion
simple diffusion for molecules that are impermeable to the membrane (large, polar or uncharged); energy barrier is too high for these molecules to pass freely. requires integral membrane proteins to serve as transporters or channels for substrates
carriers
proteins; only open to one side of the cell membrane at any given point; revolving door - binds to transport protein, remains in the transporter during a conformational change (in occluded state and not open to either side during this phase) and then finally dissociates from the substrate-binding site of the transporter
channels
viable transporters for facilitated diffusion; may be in an open or closed conformation; open are exposed to both sides of the cell membrane and are like a tunnel
active transport
results in net movement of a solute against its concentration gradient; always requires energy
primary active transport
uses ATP or another energy molecule to directly power transport of molecules across a membrane; generally involves use of transmembrane ATPase
Secondary active transport
also known as coupled transport; uses energy released by one particle going down its electrochemical gradient to drive a different particle up its gradient; When both particles flow in same direction it is symport, when opposite, antiort
endocytosis
occurs when cell membrane invaginates and engulfs material to bring it into the cell; incased in a vesicle; sunstrate binding to specific receptors embedded within plasma membrane initiates
pinocytosis
endocytosis of fluids and dissolved particles
phagocytosis
endocytosis of large solids like bacteria
exocytosis
occurs when secretory vesicles fuse with the membrane, releasing material from inside the cell to the extracellular; important in the nervous system and extracellular signaling
membrane potential (V sub m)
difference in electrical potential across cell membranes; resting potential for most cells is bt -40 and -80 mV, can rise as high as +35 during depolarization
leak channels
ions may passively diffuse through the cell membrane using these; therefore maintaining membrane potential requires energy
sodium-potassium pump (Na+/K+ ATPase)
regulates concentration of intracellular and extracellular sodium and potassium ions; main role is to maintain a low conc of sodium ions and a high conc of potassium ions intracellularly by pumping three sodium ions out for every two potassium ions pumped in. maintains negative resting potential
Nernst equation
used to determine membrane potential from the intra- and extracellular concentrations of various ions: E=RT/zF In ([ion]outside/[ion]inside)=(61.5/z)log ([ion]outside/[ion]inside)
R = ideal gas constant
T=temp in kelvin
z=charge of ion
F=Faraday constant (96,485 C/mol e-)
simplification to 61.5 in the numerator assumes body temp, 310 K
outer mitochondrial membrane
highly permeable due to large pores that allow for passage of ions and small proteins; completely surrounds the inner mitochondrial membrane with small intermembrane space bt the two layers
inner mitochondrial membrane
very restrictive permeability compared to outer membrane; contains numerous infoldings (cristae)
mitochondrial matrix
where the citric acid cycle produces high energy election carriers used in the e- transport chain; high level of cardiolipin and no cholesterol
