ch 8 - Biological Membranes

Question 1

Lipid rafts

Answer 1

collections of similar lipids with or without associated proteins. serve as attachment points for other biomolecules; often serve roles in signaling

Question 2

Flippases

Answer 2

specialized enzymes that assist in the transition (or flip) between layers in membrane

Question 3

Fatty acids

Answer 3

carboxylic acids that contain a hydrocarbon chain and terminal carboxyl group

Question 4

Triacylglycerols

Answer 4

also called triglycerides - storage lipids involved in human metabolic processes. Contain three fatty acid chains esterified to a glycerol molecule

Question 5

Unsaturated fatty acids

Answer 5

one or more double bonds and exist in liquid form at room temp; in plasma membrane these characteristics impart fluidity

Question 6

two important essential fatty acids for humans

Answer 6

alpha-linolenic acid and linoleic acid

Question 7

saturated fatty acids

Answer 7

main components of animal fats; solid at room temp; decrease membrane fluidity

Question 8

chylomicrons

Answer 8

the rest of unsaturated fatty acids come from essential fatty acids in the diet that are transported as triacylclycerols from the intestine inside these

Question 9

glycerophopholipid

Answer 9

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

Question 10

micelles

Answer 10

phospholipids spontaneously form into these; small monolayer vesicles or liposomes (bilayered) due to hydrophobic interactions

Question 11

Sphingolipids

Answer 11

do not contain glycerol; similar in structure to glycerophospholipids in that they contain a hydrophilic region and two fatty acid-derived hydrophobic tails.

Question 12

types of sphingolipids

Answer 12

ceramide, sphingomyelins, cerebrosides, gangliosides

Question 13

cholesterol

Answer 13

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

Question 14

waxes

Answer 14

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.

Question 15

Fluid mosaic model

Answer 15

theory underlying structure and function of cell membrane; accounts for presence of 3 types of membrane proteins: transmembrane, embedded, and membrane associated (peripheral)

Question 16

transmembrane proteins

Answer 16

pass completely through lipid bilayer

Question 17

embedded proteins

Answer 17

associated with only the interior (cytoplasmic) or exterior (extracellular) surface of the cell membrane

Question 18

integral proteins

Answer 18

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

Question 19

membrane-associated (peripheral) proteins

Answer 19

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

Question 20

membrane receptors

Answer 20

tend to be transmembrane proteins that can activate or deactivate some transporters for facilitated diffusion

Question 21

cell adhesion molecules (CAM)

Answer 21

proteins that allow cells to recognize each other and contribute to proper cell differentiation and development

Question 22

gap junctions

Answer 22

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

Question 23

tight junctions

Answer 23

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

Question 24

desmosomes

Answer 24

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

Question 25

hemidesmosomes

Answer 25

similar function to desmosomes but their main function is to attach epithelial cells to underlying structures, especially basement membrane

Question 26

passive transport

Answer 26

spontaneous processes that do not require energy (negative delta G) proceed this way

Question 27

active transport

Answer 27

nonspontaneous processes that require energy (positive delta G) proceed this way

Question 28

simple diffustion

Answer 28

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

Question 29

osmosis

Answer 29

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

Question 30

hypotonic

Answer 30

conc of solutes inside cell is higher than the surrounding solution; sometimes causes lysing. (ex too much salt in the cell, water rushes in)

Question 31

hypertonic

Answer 31

solution that is more concentrated than the cell; water moves out of the cell

Question 32

isotonic

Answer 32

solutions inside and outside cell are equimolar; movement still occurs but cell will neither gain nor lose water overall

Question 33

osmotic pressure

Answer 33

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

Question 34

van’t Hoff factor

Answer 34

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

Question 35

colligative properties

Answer 35

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

Question 36

facilitated diffusion

Answer 36

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

Question 37

carriers

Answer 37

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

Question 38

channels

Answer 38

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

Question 39

active transport

Answer 39

results in net movement of a solute against its concentration gradient; always requires energy

Question 40

primary active transport

Answer 40

uses ATP or another energy molecule to directly power transport of molecules across a membrane; generally involves use of transmembrane ATPase

Question 41

Secondary active transport

Answer 41

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

Question 42

endocytosis

Answer 42

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

Question 43

pinocytosis

Answer 43

endocytosis of fluids and dissolved particles

Question 44

phagocytosis

Answer 44

endocytosis of large solids like bacteria

Question 45

exocytosis

Answer 45

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

Question 46

membrane potential (V sub m)

Answer 46

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

Question 47

leak channels

Answer 47

ions may passively diffuse through the cell membrane using these; therefore maintaining membrane potential requires energy

Question 48

sodium-potassium pump (Na+/K+ ATPase)

Answer 48

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

Question 49

Nernst equation

Answer 49

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

Question 50

outer mitochondrial membrane

Answer 50

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

Question 51

inner mitochondrial membrane

Answer 51

very restrictive permeability compared to outer membrane; contains numerous infoldings (cristae)

Question 52

mitochondrial matrix

Answer 52

where the citric acid cycle produces high energy election carriers used in the e- transport chain; high level of cardiolipin and no cholesterol