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93 Cards in this Set

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fluid mosaic model

phospholipid bilayer as lipid "lake" in which variety of proteins "swim"

where are hydrophilic portions?

exposed to water on one/both sides




in cytosol or on extracellular surface

where are hydrophobic portions?

within plasma membrane

bilayer organization

hydrophobic nonpolar fatty acid tails associate and hydrophilic polar heads face out

what influences fluidity of membrane

chain length of fatty acid tails




presence of polar groups




degree of saturation




temperature

longer chains of fatty acids are ________ fluid than shorter chains

less

unsaturated carbon chains are _______ fluid than saturated chains

more

higher temperature, ______ fluid

more

steroids

family of carbon compounds with multiple linked rings




ex. cholesterol- helps maintain membrane fluidity

peripheral membrane proteins

loosely associated with hydrophilic end




not embedded in bilayer




lack hydrophobic groups, do not cross into core of bilayer

integral membrane proteins

cross into hydrophobic portion of bilayer




cannot be removed without disrupting whole membrane




both hydrophilic and hydrophobic portions

transmembrane protein

integral protein that completely crosses entire membrane




protrudes on both sides

anchored membrane proteins

membrane proteins with fatty acids or other lipid groups covalently attached to them

can all proteins move within bilayer?

no, some can but others cannot because they are impeded by other proteins OR attached to cytoskeleton

glycoprotein

one or more short carb chains covalently bonded to protein

glycolipid

carb covalently bonded to lipid

proteoglycan

protein with even more, longer carb chains attached

why do membranes constantly change?

dynamic




ability of lipids to spontaneously associate with each other

selective permeability

some can enter others can't

examples of permeable substances

oxygen and CO2




can cross through simple diffusion

examples of non-permeable substances

large molecules, polar molecules, charged molecules, glucose, potassium, sodium, H ions, chloride, magnesium, calcium




cannot diffuse without transporter

passive transport

diffusion across membrane




no need for energy input





types of passive transport

simple diffusion




facilitated diffusion

diffusion

tendency of molecules to spread out in available space in random movement towards equilibrium




net movement high to low concentration

simple diffusion

passive diffusion across phospholipid bilayer



no protein transport




no energy input



what affects diffusion speed?

diameter of molecules: smaller=faster




temp: higher=faster




concentration gradient: greater difference=faster

natural tendency to go high to low concentrations does what in terms of free energy and entropy?

releases free energy




entropy increases

osmosis

diffusion of WATER through semipermeable membrane




higher solute conc. = lower H2O conc.

osmotic pressure

pressure that needs to be applied to solution to PREVENT flow of H2O across membrane by osmosis




pi= cRT

hypotonic

solution that is hypotonic to another solution has LOWER conc. solutes than other




cell will expand, can burst!

turgor pressure

pressure that builds up against cell wall as water flows inside cell




keeps green plant parts upright




if enough water leaves cell, turgor pressure drops, plant wilts

when is plant cell healthiest? when is animal cell healthiest?

plant: when turgid (firm state when cell in HYPOtonic environment and water is pushing out onto cell wall)




animal: isotonic environment

hypertonic

solution that is hypertonic to another solution has HIGHER conc. solutes than other




cell shrivels

isotonic

solution is isotonic to another solution if both have SAME conc. solutes




stable size

facilitated diffusion

passive movement of molecules down conc. gradient using TRANSPORT PROTEIN

types of transport proteins

channel proteins




carrier proteins

channel proteins

type of transport protein under facilitated diffusion



integral membrane proteins that form hydrophilic channels across membranes




do NOT change shape




two kinds: gated channels and aquaporins



types of channel proteins

gated ion channels




aquaporins

gated ion channels

channel protein that opens and closes in response to a stimulus, selectively allowing ions to move down conc. gradient




2 kinds: ligand-gated and voltage-gated

ligand-gated channel

type of gated ion channel, which is a type of channel protein, which is a transport protein all under facilitated diffusion



respond to ligand (chemical signal that binds and sets off response)

voltage-gated channel

type of gated ion channel, which is a type of channel protein, which is a transport protein all under facilitated diffusion



responds to change in voltage (electrical charge) along membrane

aquaporins

type of channel protein, which is transport protein under facilitated diffusion




channels that allow large amounts of water to move down conc gradient

which protein changes shape to transport molecules into the cell?

carrier proteins

carrier proteins

transport protein that takes in polar molecules like sugars and aminos




CHANGES SHAPE, allows molecules inside

what affects rate of facilitated diffusion? when does it reach max?

saturation of carrier molecules




rate of diffusion reaches maximum when ALL carrier molecules fully saturated (loaded w solute molecules)

do channel proteins require energy input?

no

do carrier proteins require energy input?

no

active transport

movement of substance against normal flow, against conc. gradient




energy input!




two types: primary and secondary

difference between passive and active transport

active transport requires energy (ATP) and REDUCES entropy




passive transport does not require energy and INCREASES entropy

types of active transport

primary




secondary

primary active transport

involves direct hydrolysis of ATP to generate energy necessary to move substance vs conc. gradient

sodium-potassium pump

membrane protein that uses 1 ATP to pump 3 sodiums OUT and 2 potassiums IN, against their conc. gradients





secondary active transport

indirectly uses ATP to set up gradient




involves coupling of downhill diffusion of one substance and uphill transport of another against conc. gradient




move against gradient by "hitching a ride" with other ions moving down gradient OR by transport protein

protein transporters only effective for _______ molecules

small

how do larger molecules cross membrane?

exocytosis and endocytosis

endocytosis

movement of large molecules into cell




involves vesicles




3 kinds: phagocytosis, pinocytosis, receptor-mediated endocytosis

phagocytosis

"cell-eating"




binding of ligand and receptor causes cell to engulf particle, forming a phagosome




phagosome fuses with lysosome and is digested

pinocytosis

"cell-drinking"




vesicles bring fluids and dissolved substances in




nonspecific

receptor-mediated endocytosis

ligands bind to receptors on cell membrane and trigger vesicle formation




highly specific




receptors located in coated pits with clathrin




inside cell, loses clathrin

clathrin

in receptor-mediated endocytosis




covers cell surface exposed to cytoplasm




stabilizes vesicle

exocytosis

movement of large molecules out of cell via vesicles that fuse with cell membrane

where do the coated vesicles go?

fuse with lysosome OR eventually with cell membrane

example of receptor-mediated endocytosis in mammalian cells

cholesterol located in LDLs, circulated in blood




LDL binds to receptors that recognize protein




clathrin molecules coat interior membrane, bend, and form vesicle




inside, coat comes off, fuses with endosome (receptors go back to membrane)




endosome fuses with lysosome, cholesterol released in cytosol

signal transduction pathway

series through which signal binds to receptor and causes response




signal, receptor, response

autocrine signaling

affects the same cell that releases it




self-stimulation

paracrine signaling

diffuse to and affects adjacent cells

endocrine signaling

hormone secreted through bloodstream to reach distant cells

juxtracrine signal

requires direct contact between signaling and responding cell




interaction btw signaling molecules bound to cell surfaces

ligand

chemical signal that binds to receptor noncovalently (weak) and reversibly




highly specific




does not contribute further, simply "knocks on the door"

allosteric regulation

alteration of 3D shape of protein as result of binding to non-active site




triggers signal transduction, can cause short or long term response

cytoplasmic receptors

located in cytoplasm or nucleus

membrane receptors

located on membrane

what kinds of molecules would have membrane receptors?

large or polar signal molecules... CANNOT cross membrane!



what kinds of molecules would have cytoplasmic receptors?

small hydrophobic signal molecules... CAN cross membrane




steroids and thyroid hormones (estrogen, testosterone, cortisol)

transcription factors

turn on specific genes





antagonist/inhibitor

binds to receptor and prevents ligand binding

ion channel receptors

on plasma membrane




changes shape when ligand binds to it, either allows or restricts flow of ions into cell




ligand-gated ion channel receptors such as acetylcholine receptor control sodium flow

do ion channel receptors require energy?

no!




they are not pumps, they control flow down conc. gradient

protein kinase receptors

on membrane, also changes shape




can initiate multiple signal transduction pathways at one time




ligand binding activates phosphorylation (addition of phosphate groups)

kinase

molecule that phosphorylates other molecules

example of protein kinase receptor

tyrosine kinase receptor




two membrane proteins come together, tyrosines are phosphorylated


ATP + protein ---> ADP + phosphorylated protein




phosphorylated tyrosine heads activate different types of relay proteins that attach to them, resulting in different responses

G protein linked receptors

on membrane




what sticks out into extracellular surface is receptor, what extends into cytoplasm interacts with G protein

G protein

bound to cytoplasmic side of membrane




bound to GDP= inactive


bound to GTP= active




can bind to receptor, GDP and GTP, and effector protein (amplifies signal)

what happens when G protein linked receptor activated?

GTP replaces GDP, effector protein activated=amplification




eventually, G protein acts as GTPases and turn themselves off- self regulation

second messengers

small nonprotein water soluble molecules or ions that acts as intermediate btw activated receptor and cascade of events




ex. cAMP

cAMP

cyclic AMP




created by adenylyl cyclase (enzyme in plasma membrane)




activates protein kinase by noncovalent bonding, changes shape! (kinase goes on to phosphorylate others and amplify signal)

cellular responses

opening ion channels




alterations in gene expression (on/off)




alteration of enzyme activity

which is fastest cell response

alteration of enzyme activity

true or false.


same signal can lead to different response.

TRUE




epinephrine ACTIVATES signal transduction in heart m. cells but INHIBITS target enzyme in digestive tract

what determines cellular response?

balance btw signal enzymes and regulating enzymes




cells alter balance by synthesis/breakdown of enzymes OR activation/inhibition of enzymes by other molecules

adenylyl cyclase

enzyme in plasma membrane




makes cAMP from ATP with liberation of pyrophosphate

if conc. of epinephrine drops, cAMP conc. in liver cells expected to _________ because ____________ activity would _________

decrease


adenylyl cyclase


decrease

epinephrine binding to receptor leads to ___________

more cAMP production