ch7 membrane structure and function

the plasma membrane is the boundary that separates the ____ from its ____

living cell; nonliving surroundings

the plasma membrane exhibits selective permeability, which is what?

allowing some substances to cross it more easily than others

cell membranes are ____ ____ of lipids and proteins

fluid mosaics

_____, the most abundant lipid in the plasma membrane, are ____ molecules, which contain ____ and ____ regions

phospholipids; amphipathic; hydrophobic; hydrophilic

the fluid mosaic model states that a membrane is a ____ structure with a "mosaic" of various _____ embedded in it

fluid; proteins

why do we die from dehydration?

water can not bring things to cells

Singer & Nicolson proposed what?

fluid mosaic model - membrane is mosaic of proteins dispersed/inserted into phospholipid bilayer w/only hydrophilic regions exposed to water

in the fluid mosaic model, the membrane contains multiple types of ____ sandwiched btwn two layers of ____

proteins; phospholipids

_____ form the basic structure of a cellular bilayered membrane, and ____ traverse through it

phospholipids; proteins

_____ studies of the plasma mem supported the fluid mosaic model. what do these studies include?

freeze-fracture; specialized prep technique that splits in middle of phospholipid bilayer

the extracellular layer of the fluid mosaic model has _____ proteins than the cytoplasmic layer

less

phospholipids in the plasma mem can ____ within the bilayer.

most lipids and some proteins ___ ___.

a molecule flip-flops transversely across the membrane _____

move

drift laterally

rarely

temperature affects membrane ____.

as temps cool, membranes switch from a ____ state to a ____ state

fluidity; fluid; solid

the temp that a membrane solidifies at depends on the types of ____ in the mem.

membranes rich in ____ are more fluid than those rich in ____

lipids

unsat fatty acids; sat fatty acids

cholesterol effects at warm temps vs cool temps

warm:

restrains phospholipid movement

cool:

maintains fluidity by preventing tight packing

cell membranes must be fluid to ____; they are usually as fluid as _____

work properly; salad oil

some proteins in the plasma mem can ____ within the bilayer. proteins are much ____ than lipids and move more ____

drift; larger; slowly

how did researchers investigate whether membrane proteins moved?

fused mouse cell + human cell and watched what happened to proteins from each cell

a membrane is a collage of different ____ embedded in the fluid matrix of the lipid bilayer. these determine what?

proteins; membrane's specific functions

peripheral vs integral proteins

peripheral: not embedded (on top or bottom)

integral: penetrate hydrophobic core + span membrane

transmembrane proteins are integral proteins that:

span the membrane

the hydrophobic regions of an integral protein consist of 1 or more stretches of ______ coiled into ____.

nonpolar amino acids; alpha helices

the ribbons of a transmembrane protein are _____. these allow:

hydrophilic; things to go in/out of the mem

fave 3 major functions of membrane proteins + examples

1. transport

- Na/K pump (passage and gate)

2. signal transduction

- hormones (hits receptors in brain that make u tired)

3. cell-cell recognition

- WBCs recognize germ antigens

other 3 major functions of membrane proteins + examples

4. enzymatic activity

- adenylate cyclase catalyzes ATP to cAMP

5. intercellular joining

- desmosomes like cell buttons

6. attachment (to cytoskeleton and ECM)

- help things stick

how do cells recognize each other?

binding to surface molecules (membrane carbohydrates) on plasma membrane

membrane carbs may be covalently bonded to lipids (forming ____) or more commonly to proteins (forming ____)

glycolipids; glycoproteins

external carbs on the plasma mem ____ among species, individuals, and cell types in an individual

vary

2 distinct faces of membranes

inside (intracellular)

outside (extracellular)

the ____ distribution of proteins, lipids, and carbs in the membrane is determined when?

asymmetrical; membrane is built by ER and golgi

how do cells grow in size? stopping this process may be beneficial for who?

what cells grow faster than others?

vesicles from golgi merge with cell mem; ppl with cancer

cells that send things often (mucous membranes)

the plasma membrane controls what?

membrane structure results in ____ ___, which regulates the cell's ___ ___

exchanging materials btwn cell/surroundings; selective permeability; molecular traffic

do polar or nonpolar molecules cross the membrane readily?

nonpolar (hydrophobic): dissolve in lipid bilayer + pass thru easily

ex. hydrocarbons

polar: do not pass easily

ex. sugars

transport proteins allow passage of ____, ____ substances where?

hydrophilic, polar; across membrane

channel proteins vs carrier proteins

channel: hydrophilic channel/tunnel for molecules or ions

- like tunnels, limit shape of molecules that fit thru but do not change shape themselves

carrier: bind to molecules + change shape to shuttle them across membrane

- like gates, open/shut/open other way

a transport protein is ____ for the substance it moves.

ex. aquaporins are ____ proteins that facilitate the passage of ___

specific; channel; water

passive transport is ____ of a substance across a membrane ____ energy

diffusion; without

diffusion is the tendency for molecules to ______ into available space.

although each molecule moves randomly, diffusion of a ____ of molecules may exhibit a ____ movement in one direction

spread out evenly

population; net

what happens at dynamic equilibrium?

as many molecules cross one way as cross in the other

substances diffuse _____ (____) their conc gradient (the diff in ____ of a substance from one area to another).

is this passive or active transport? why?

down (high to low)

concentration

passive; requires no energy/work from cell

diffusion says if material can flow it flows from ____ conc to ___ conc until ____

high; low; equilibrium

diffusion of two substances occurs as ____ reactions until each reaches ____

separate reactions; dynamic equilibrium

what is osmosis?

diffusion of WATER across selectively permeable mem

what is the direction of osmosis determined by?

diff in total solute concentration

how does water diffuse? what does this show?

from region of LOWER SOLUTE to region of HIGHER SOLUTE until equal conc of solute are on each side of membrane

- force of diffusion is greater than gravity

how to get a high concentration vs low concentration solution

HIGH: increase solute or decrease solvent

LOW: decrease solute or increase solvent

tonicity is the ability of a solution to cause a cell to:

gain/lose water

isotonic vs hypertonic vs hypotonic solutions

isotonic: solute conc. same inside/outside; no net movement

hypertonic: solute conc. GREATER outside than inside; cell loses water

hypotonic: solute conc. LESS outside than inside cell; cell gains water (hypo hippo)

____ and organisms without ____ have osmotic problems in hyper/hypotonic environments and must have adaptations for _____ (_____).

example?

animals; rigid cell walls

osmoregulation (control of water balance)

ex. Paramecium in hypotonic ponds have contractile vacuole to pump out water when it comes in

cell walls help maintain _____.

what happens to animal cells in hypo, iso, and hypertonic solutions?

water balance

animal: lysed, normal, shriveled

what happens to a plant cell in a hypotonic solution?

turgid (firm/normal)

- cell swells until wall opposes uptake

what happens to a plant cell in an isotonic solution?

flaccid (limp)

- no net movement of water into cell; plant may wilt

what happens to a plant cell in a hypertonic solution?

plasmolysis (lethal)

- mem pulls away from wall; cells lose water

facilitated diffusion is ____ transport aided by ____.

transport proteins ____ movement of molecules across membrane

passive; proteins

speed

channel proteins provide ______ that allow _____ molecules or ions to cross the membrane.

carrier proteins undergo a ____ in ___ that translocates the ____ across the membrane

corridors; specific

subtle change; shape; solute-binding site

do channel proteins or facilitated diffusion carrier proteins require energy?

no; stuff moves based on diffusion

active transport uses ____ to move solutes ____ their gradients (___)

energy; against (low to high)

facilitated diffusion is still passive because the solute ____________.

moves down its concentration gradient

some transport proteins ____ in the membrane can move solutes against their conc gradients via ______, which requires _____/____

embedded; active transport; energy/ATP

the proteins that function for active transport are _____ proteins. ____ proteins CANNOT be used for active transport

carrier; channel

_____ is one type of active transport system. what are its 6 steps?

sodium-potassium pump

1. cytoplasmic Na bonds to pump

2. Na binding stimulates phosphorylation by ATP

3. phosphorylation causes protein to change conformation, releasing Na outside

4. extracellular K binds to protein, releasing phosphate

5. loss of phosphate restores protein's og conformation

6. K released inside, Na sites are receptive + cycle repeats

explain the conc in/out of the cell with a Na/K pump

Na high/K low outside cell

- pumps 3 Na out + 2 K in constantly

how is the Na/K pump related to charges?

- pump pumps chemicals to each side of mem + establishes electrochemical gradient which generates electricity

- Na/K both pos charged, but outside of cell is very pos and inside is very neg

- kind of makes a battery w/a pos end/neg end

- when a conductor connects these neg charges to the pos ones u create a current

- means ur cell mems have voltage (diff in charges) that are connected via stimulation

ex. touch sends signals to ur brain

what is membrane potential?

how does transport maintain membrane potential?

voltage/charge difference across a membrane

- ion pumps

passive diffusion review

high to low conc, no energy

ex.

- diffusion

- facilitated diffusion

--- channel proteins/carrier proteins

active diffusion review

low to high conc, uses energy

ex.

- carrier proteins

- pumps

what are the 2 combined forces (______) that drive the _____ of ions across a membrane?

(electrochemical gradient); diffusion

- chemical force (ion's conc gradient)

- electrical force (effect of membrane potential on ion's movement)

what is an electrogenic pump?

what is the main electrogenic pump of plants, fungi, and bacteria?

transport protein that generates voltage across membrane

- proton pump

explain what a proton pump does

- materials go in one direction, releasing H+

ex.

- stomach is acidic & H+ is released to incr. it (pos charge lowers pH)

- stomach receives alkaline food & H+ help to lower food pH similar to stomach

- if proton pumps are too active, stomach can be too acidic leading to digestion of ur own stomach (ulcers) or acid reflux

what is cotransport? when does it occur?

coupled transport by membrane protein

- occurs when active transport of a solute indirectly drives transport of another solute

what is an example of cotransport?

- proton pump pumps out H+ which wants to come back to lower conc

- H+ links w/sucrose in sucrose-H+ cotransporter

-- lock/key system where both must bind to go into cell

plants use the gradient of H+ ions generated by ____ to drive ________

proton pumps; active transport of nutrients into cell

bulk transport across the cell mem occurs by ___ and __

exocytosis; endocytosis

small molecules/water enter/leave the cell through (2)

large molecules (polysaccharides/proteins) cross the mem via (1)

lipid bilayer or transport proteins

vesicles

many secretory cells use ____ to export their products. explain this process

exocytosis

- transport vesicles migrate and fuse to membrane and release their contents

_____ is a reversal of exocytosis, involving different proteins. explain this process

endocytosis

- cell takes in macros by forming vesicles from the plasma mem

3 types of endocytosis

1. phagocytosis "cellular eating"

- cell engulfs particle in vacuole

2. pinocytosis "cellular drinking"

- cell creates vesicle around fluid

3. receptor-mediated endocytosis

- ligands bind to receptors + triggers vesicle formation

ex. viruses (keys) use receptors to get into cells