Bios 3200 Exam 3

plasma membrane

surrounds cell, defines boundaries; separates intracellular fluid from extracellular fluid

what does the plasma membrane control?

passage of solutes into/out of cell

the plasma membrane is made of membrane ______ & _______ that are critical to cell function

lipids, proteins

explain why phospholipids are amphipathic

phosphate head is hydrophilic; fatty acid tails are hydrophobic

how do phospholipids contribute to the structural function of the cell membrane?

create the phospholipid bilayer

saturated fatty acids

lack double bonds, rigid

unsaturated fatty acids

one or more double bonds, fluid

what does the degree of saturation of fatty acid tails affect?

the tightness of packing and the fluidity of the membrane

what are the 4 parts of the structure of a phosphatidyl-x? (phospholipid subtype)

“x” group (choline, serine, ethanolamine, etc.), phosphate group, glycerol, two fatty acids

what are 3 membrane lipids?

phospholipids, glycolipids, cholesterol

glycolipids

have short carbohydrate on ECF face, used for cell recognition, embedded in phospholipid bilayer

______ contribute to glycocalyx (on surface of some cells), which protects cells and prevents cell ______

glycolipids, fusion

what is the function of cholesterol?

reduces membrane fluidity by holding phospholipids still and stiffening membrane; “fills the gap” between two phospholipid molecules

true or false: membrane components are homogenous

false

how do enzymes that interact with the plasma membrane recognize it?

recognize hydrophilic head groups

what are the 3 enzymes that contribute to the asymmetry of the plasma membrane?

flippase, floppase, scramblase

flippase

move phospholipids from cytosolic side to inside of cell; require ATP

floppase

move phospholipids from inside of cell to cytosolic side; require ATP

scramblase

moves phospholipids bidirectionally; does not require ATP

true or false: the plasma membrane is fluid

true

the plasma membrane is ______ to mechanical force perturbances

refractory

is the plasma membrane uniformly fluid? why or why not?

no, due to lipid rafts

lipid rafts

lipids gathered into rigid patches on plasma membrane

what are the functions of lipid rafts?

cell signaling, forming caveolae, cytoskeleton anchoring

integral proteins _____ the plasma membrane

penetrate

what is the location of transmembrane proteins?

pass completely though plasma membrane

where is the location of hydrophilic regions of integral proteins?

contact aqueous ICF & ECF

where is the location of hydrophobic regions of integral proteins?

pass through phospholipid bilayer

describe peripheral proteins

do not penetrate membrane, only affiliated with one side, usually anchored

what are the functions of membrane proteins?

receptors, second messenger systems, enzymes, channel proteins, carriers, cell identity markers, cell adhesion molecules

the plasma membrane is __________, based on function

compartmentalized

what does compartmentalization of the plasma membrane allow cells to do?

have polarity, which lets different parts of cells to have specific functions

what is membrane transport?

movement of solutes between fluid compartments

movement of solutes between compartments influences movement of _______

water

where is intracellular fluid (ICF) located?

inside cells

where is extracellular fluid (ECF) located?

blood plasma, interstitial fluid

what are the two mechanisms of membrane transport?

passive and active transport

passive transport

no cellular energy required (energetically favorable); typically transporting solutes down/with gradient

active transport

cell energy is required (not energetically favorable); typically transporting solutes up/against gradient

cell membrane is selectively ________

permeable

explain how the cell membrane is selectively permeable

it restricts and regulates what crosses it; some solutes can pass freely across the cell membrane, while others require help of transport proteins

molecules with nonpolar covalent bonds are typically?

hydrophobic and lipophilic

molecules with polar covalent bonds are typically?

hydrophilic and lipophobic

describe the movement of the solute across the cell membrane: hydrophobic (polar) molecules

readily pass through bilayer

describe the movement of the solute across the cell membrane: small uncharged polar molecules

some can pass through without aid of a transport proteins; but it slow and inefficient

describe the movement of the solute across the cell membrane: large uncharged polar molecules

have very low membrane permeability

describe the movement of the solute across the cell membrane: ions

not permeable

what are the 3 types of transport proteins that can be used in passive transport?

channel proteins, gated ion channels, carrier proteins

channel proteins

pores that accommodate size/charge of specific solute

how do channel proteins transport solutes? (passive transport)

via facilitated diffusion and have specificity

osmosis

a specialized form of facilitated diffusion (through channel protein)

_______ protein channels permit transport of water across the _______

aquaporin, membrane

gated ion channels

open and close to control ion passages

how do gated ion channels transport solutes? (passive transport)

require a stimulus to transport solutes via facilitated diffusion and have specificity

what are the 3 types of gated ion channels?

chemically (ligand) gated, voltage gated, mechanically gated

chemically (ligand) gated ion channel

chemical messenger (ligand) binds to protein and induces opening; acts as both receptor and channel

voltage gated ion channel

change in voltage (membrane potential) induces opening of channel protein

mechanically gated ion channel

mechanical force on cell membrane physically opens channel

carrier proteins

specific binding site(s) for solutes; requires conformational change

how do carrier proteins transport solutes?

via facilitated diffusion or active transport and have specificity

where is the energy stored in ATP?

phosphate bonds

what are the 2 types of carrier (transport) protein mechanisms used in active transport?

ATP-driven pumps and coupled transporters

what is the energy source of ATP-driven pumps?

chemical energy via ATP hydrolysis

what is the energy source of coupled transporters?

electrochemical gradient of another solute

primary active transport

uses chemical energy from ATP directly to move molecules across a cell membrane against their concentration gradient

secondary active transport

uses electrochemical gradient previously created to move molecules; ATP hydrolysis used indirectly

what are the 2 carrier proteins used in secondary active transport?

symport and antiport

symport

solutes move in the same direction

antiport

solutes move in opposite direction

membrane potential

unequal distribution of charge across membrane; that charge comes from ions dissolved in fluid compartments

what are the uses of membrane potential?

source of potential energy to do work (membrane transport); in electrically excitable cells, can be changed for purpose of cell signaling or changing function

what is the resting membrane potential value?

-60 to -90 mV

portion of the membrane facing the ICF is more ________

negative

portion of the membrane facing the ECF is more ______

positive

how is the resting membrane potential established?

ion concentration gradient and selective ion permeability

what does the ion concentration gradient refer to? (in regards to the establishing the resting membrane potential)

Na+/K+ pump

what are the 6 steps of the Na+/K+ pump?

1. there is a higher concentration of Na+ in the ECF and a higher concentration of K+ in the ICF

2. 3 Na+ in the ICF bind to the pump

3. Na+ binding stimulates phosphorylation of pump by ATP

4. phosphorylation causes pump to change conformation, which expels Na+ to ECF, and opens binding sites for K+

5. 2 K+ in ECF bind to pump, which causes release of phosphate group

6. loss of phosphate group restores original conformation, and K+ are released

what is the result of the Na+/K+ pump?

both Na+ and K+ are moved against their concentration gradients; 3 Na+ moved into ECF and 2 K+ moved into ICF, this causes membrane facing ECF to have a positive charge and membrane facing ICF to have negative charge

what does selective ion permeability refer to? (in regards to the establishing the resting membrane potential)

K+ leak channels

how is the extracellular pool of K+ established?

K+ leak channels allow K+ to move down concentration gradient and exit the cell; contributes to positive charge on ECF side of membrane

how is the intracellular pool of Na+ established?

Na+ enters cell via coupled transport - SGLT1 symport and heart/kidney antiports

SGLT1 symport

uses Na+ gradient (from Na+/K+) pump as energy source to transport both glucose and Na+ into cell; Na+ moves down its gradient

heart/kidney anitports

Na+ moves from ECF to ICF (down concentration gradient), while other solute (Ca2+ or H+) moves from ICF to ECF

how is the electrochemical gradient formed?

by the combined effects of concentration and electric gradients

what is the electrochemical gradient of K+ at equilibrium?

0

when K+ leaves through leak channels it moves _______ downhill, but _______ uphill

chemically, electrically

what type of resting potential must a membrane establish?

one that perfectly opposes the net movement of an ion down its concentration gradient

ions tend to move ____ their concentration gradient until ________ is achieved

down, equilibrium

ions tend to move ____ their electrical gradient until ________ is achieved

down, equilibrium

a stronger electrical field results in a ________ tendency of ions to move down gradient

greater

a weaker electrical field results in a ________ tendency of ions to move down gradient

lesser

describe ion movement due to the electrochemical gradient

at resting membrane potential the draw of an ion to move down its concentration gradient is balanced by its draw into the cell due to its electric potential

why is resting membrane potential close to equilibrium potential for K+?

membrane is more permeable to K+ ions

action potential

rapid change in membrane potential

what is the threshold value for an action potential?

around -45 to -55 mV

rapid change in membrane potential ______ along the length of the cell membrane

propagates

what is the mechanism of membrane potential change in an electrically excitable cell? (3 steps)

1. change membrane permeability for select ions

2. allow those ions to move in/out of cell

3. change membrane potential

what are the 6 steps of an action potential?

1. localized change in membrane potential (small increase)

2. depolarization

3. peak

4. repolarization

5. hyperpolarization

6. return to resting membrane potential

how does a localized change in membrane potential occur during an action potential?

a chemical messenger (ligand/neurotransmitter) binds to a chemically (ligand) gated Na+ channel, this causes a localized increase in Na+ permeability, which locally opens the Na+ channels, allowing Na+ to flow in; causes a small increase in membrane potential

depolarization

membrane potential becomes more positive