Chapter 7: Membrane Structure and Function Flashcards
plasma membrane
boundary that separates living cell from its surroundings
most abundant lipid in membrane
phospholipids
amphipathic
contains hydrophilic (head) and hydrophobic (tail) regions
fluid mosaic
membrane is fluid structure with mosaic of protein
who discovered the fluid mosaic model
singer and nicolson
what type of studies supported fluid mosaic model
freeze-fracture
as temp cools what happens to membrane
becomes less fluid, more solid; membrane can solidify
which types of membranes are more fluid
rich in unsaturated fatty acids
function of cholesterol in membrane
prevent membrane from becoming too solid when cold, too lquid when warm
why do variations of lipid composition of membrane occur
adaptations to environment
peripheral proteins
bound to surface of membrane, sticks out on one side
integral proteins
penetrate hydrophobic core (transmembrane)
glycolipid
has carbohydrate chain instead of hydrophilic head
glycoproteins
carbohydrate chain bonded to protein
6 functions of membrnae proteins
transport, enzymatic activity, signal transduction, cell-cell recognition, intercellular joining, attachment to cytoskeleton and extracellular matrix
external carbohydrates may vary among
species, individuals, and cell types
HIV requires what to enter cell
CD4 and CCR5 receptors
why are some individuals resistant to HIV
do not have CCR5 receptors
assymetrical distribution of proteins, lipids,and carbs in membrane determined when
membrane is built by ER and golgi bodies
hydrophobic molecules can
dissolve in lipid bilayer and pas through membrane
what type of molecules do not cross through membrane easily
polar molecules
transport proteins
allow passafe of hydrophilic substances across membran; specific to a substance
two types of transport proteins
channel, carrier
channel protein
have hydrophilic channel that certain molecules/ions can use s tunnel
aquaporins
channel protein for water
carrier protein
bind to molecules, change shape, brins molecules into cell
diffusion
tendency for moecules to spread out evenly into available space
diffusion in relation to concentration gradient
diffuses down gradient
osmosis
diffusion of water across selectively permeable membrane
tonicity
ability of surrounding solution to cause cell to gain or lose water
osmoregulation
control of solute concentration and water balance
paramecium are hypertonic to environment; how do they maintain homeostasis
contractile vacuole
cell wall prevents
lysing
turgid
when no more water can diffuse into the cell (in a hypotonic solution)
flaccid
limp (in an isotonic solution)
plant cell in a hypertonic solution
cells undergo plasmolysis - plant wilts
facilitated diffusion
transport proteins speed passive movement of molecules across membrane
facilitated diffusion makes use of
channel proteins
ion channels
gated channels for specific ions
active transport
moves sustances against gradient, allows cell to maintain gradient different from enviroment
active transport requires
energy
examples of active transport
sodium-potassium pumps
membrane potential
voltage difference across a membrane created by difference in distribution of anions and cations across a membrane
electrochemical gradient drives
diffusion of ions across a membrane
electrogenic pump
transport protein that generate voltage across a membrane
electrogenic pump in animals
sodium-potassium
electrogenic pump in plants,fungi, bacteria
proton pump
electrogenic pumps help store
energy that can be used for work
cotransport
when active transport of a solute indirectly drives transport of other solutes
example of cotransport
plants use H+ gradient generated by proton pump to drive active transport of nutrients into cell
small molecules/water tracel through membrane via
protein
large molecules cross membrane in bulk via
vesicle
bulk trnaspsort requires
energy
exocytosis
transport vesicles outside cells - secretory cells
endocytosis
cells takes in mecromolecules by forming vesicles from membrane
types of endocytosis
phagocytosis, pinocytosis, receptor-mediated
phagocytosis
cell eating - large molecules
pinocytosis
cell drinking - smalll molecules
receptor-mediated
recognizes/bonds to substance that is needed; binding of ligand triggers vesicle formation
ligand
molecule that bonds to receptor