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93 Cards in this Set

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  • Back

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


longer chains of fatty acids are ________ fluid than shorter chains


unsaturated carbon chains are _______ fluid than saturated chains


higher temperature, ______ fluid



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


one or more short carb chains covalently bonded to protein


carb covalently bonded to lipid


protein with even more, longer carb chains attached

why do membranes constantly change?


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


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


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


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


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

cell shrivels


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


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


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?


do carrier proteins require energy input?


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 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


how do larger molecules cross membrane?

exocytosis and endocytosis


movement of large molecules into cell

involves vesicles

3 kinds: phagocytosis, pinocytosis, receptor-mediated endocytosis



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

phagosome fuses with lysosome and is digested



vesicles bring fluids and dissolved substances in


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


in receptor-mediated endocytosis

covers cell surface exposed to cytoplasm

stabilizes vesicle


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


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


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


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?


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)


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


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.


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 _________


adenylyl cyclase


epinephrine binding to receptor leads to ___________

more cAMP production