Cell Membrane Structure and Function Flashcards by Sophie Hurley

what are the fundamental units of specialised functions in living organisms

cells

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The cell membrane is a ____ 8nm, flexible and ____ barrier that _____ the cytoplasm of a cell

The cell membrane is a (thin), 8nm, flexible and (sturdy) barrier that (surrounds) the cytoplasm of a cell

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Describe the membrane structure

Fluid mosaic model

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What does this mean about the proteins of the membrane “sea of lipids in which proteins float like icebergs”

Proteins are free to move around

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What type of bonds hold membrane proteins and lipids together?

hydrogen bonding

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The membrane is 50% ___ and 50% ___

The membrane is 50% (lipid) and 50% (protein)

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The lipid bilayer is a selectively permeable barrier for the entry/exit of…

The lipid bilayer is a selectively permeable barrier for the entry/exit of (polar substances)

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What are gatekeepers in the membrane that regulate how things move across lipid barrier

Proteins

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What are scattered among double row of phospholipid molecules (embedded in phospholipids)

Cholesterol & glycolipids

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___ back-to-back layers of ___ types of ___ molecules

(2) back-to-back layers of (3) types of (lipid) molecules

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cell membrane equation?

Cell membrane = proteins + (phospho)lipids

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what acts as a barrier; isolates cells from their external environment

cell membrane

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the membrane controls passage of subst. in/out of cells to allow for…
1. Maintain…
2. Spacial…
3. Control…
4. Develop…

Maintain conc. gradient
Spacial organisation of chemical/physical processes in cell
Control uptake of nutrients + discharge of waste products + secretion of molecules
Develop membrane potential

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What comprises 75% lipids

Phospholipids

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___ has 2 parallel layers of molecules

Phospholipid bilayer = 2 parallel layers of molecules

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If a molecules has polar (charged) and nonpolar (uncharged) regions it is said to be…?

Amphipathic

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how phospholipids orient themselves?

Spontaneously form stable bilayers, polar head exposed to water non-polar tails shielded in the interior

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what provides highly impermeable barrier to passage of charged ions

hydrophobic core (fatty acid chains)

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membranes are ___ structures and ___ can move around within the plane of the membrane ____

membranes are (fluid) structures and (lipids) can move around within the plane of the membrane (leaflet)

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true or false
lipids often flip flop between membrane leaflets therefore lipid composition of leaflets can be symmetric

FALSE
lipids RARELY flip flop between membrane leaflets therefore lipid composition of leaflets can be ASYMMETRIC

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membrane fluidity is determined by…

lipid tail length&raquo_space; longer tail = less fluid
# of double bonds&raquo_space; more double bonds = more fluidity
amount of cholesterol&raquo_space; more decreases fluidity

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what proteins are amphipathic and stuck in lipid bilayer

integral transmembrane proteins

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integral proteins have hydrophobic regions that span hydrophobic core of lipid bilayer
- what do these regions consist of?

non polar amino acids coiled into helices

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where are peripheral proteins attached to membrane and are they removed easily?

inner or outer surface of membrane
removed easily

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way to easily remove peripheral protein

exposure to salt treatment to break protein-protein bonds

how is membrane spanning protein attach to cytoskeleton and what for?

associated proteins; for bending shape of membrane

features of integral proteins

1. amphipathic 2. hydrophobic regions (non-polar amino acids coiled into helices) span hydrophobic core of lipid bilayer 3. hydrophilic ends interact with aqueous solution

functions of membrane proteins

- receptor proteins - cell identity markers - linkers - enzymes - ion channels - transporter proteins

what protein functions to "allow specific substance to move through water-filled pore"

Channel membrane protein

function of transporter membrane protein

Transport specific subst. across membrane by changing shape

x3 things permeability depends on

1. shape 2. charge 3. lipid solubility

what is governed by laws of diffusion

selective permeability

The lipid bilayer is permeable to 3 things what are they?

1. Nonpolar, uncharged molecules (O2, N2, Benzene) 2. Lipid soluble molecules (steroids, fatty acids, some vitamins) 3. Small uncharged polar molecules (H2O, urea, glycerol, CO2)

The lipid bilayer is IMpermeable to 2 things what are they?

1. Large uncharged polar molecules (glucose, a.a) 2. Ions (Na+, K+, Cl-, Ca2+, H+)

what do membrane proteins mediate

transport of subst. across the membrane that can't penetrate hydrophobic core of lipid bilayer

Membrane proteins ____ the transport of substance across the membrane that ____ permeate the ______ core of the lipid bilayer

Membrane proteins (mediate) the transport of substance across the membrane that (CAN'T) permeate the (hydrophobic core) of the lipid bilayer

Define diffusion

Net diffusion from high concentration to low concentration

Aim of diffusion

To redistribute so substances maintain equilibrium

what way along gradient do molecules move in diffusion

area of high concentration to area of low concentration

what is the "random mixing of particles in a solution as a result of the particle's kinetic energy"

simple diffusion

Principles of diffusion (things that affect diffusion rate)

- greater difference in conc. between 2 sides of membrane = faster rate - higher temp = faster rate - larger subst. = slower rate - increase SA = faster rate - increase diffusion distance = slower rate

physical consequences of diffusion

1. diffusion rate sets limit on size of cells 2. increase diffusion = increase membrane area available 3. membrane thickness > thicker membrane = slower rate 4. very fast over small distances

define concentration gradient

non charged molecules diffuse down their concentration gradients

what does a selectively permeable membrane enable

difference in conc. across membrane to be established

define electrical gradient

ions will be influenced by membrane potential in addition to their concentration gradient

what are movement of ions influenced by

electrochemical gradient

what do membranes mimic and why?

membranes mimic capacitors - can separate + store charge

___ use ~30% of resting energy to maintain ___ and ___ gradients

(cells) use ~30% of resting energy to maintain (conc.) and (electrical) gradients

what do conc. and electrical gradients represent

stored energy

Na+ ion gradient: ___ Na+ conc. in extracellular fluid >> to ___ Na+ conc. in cytoplasm

Na+ ion gradient: (HIGH) Na+ conc. in extracellular fluid >> to (LOW) Na+ conc. in cytoplasm

K+ ion gradient: ___ K+ conc. in extracellular fluid >> to ___ K+ conc. in cytoplasm

K+ ion gradient: (LOW) K+ conc. in extracellular fluid >> to (HIGH) K+ conc. in cytoplasm

Cl- ion gradient ___ ways: ___/___ Cl- conc. in extracellular fluid >> to ___/___ Cl- conc. in cytoplasm

Cl- ion gradient BOTH ways: HIGH/LOW Cl- conc. in extracellular fluid >> to HIGH/LOW Cl- conc. in cytoplasm

what are ions influenced by in their gradients

membrane potential and ion conc. gradient

why are ion gradients kept up

to harness energy stored in ion gradients

define osmosis

net movement of H2O through a selectively permeable membrane from area of HIGH to LOW conc.

true or false "osmosis occurs if membrane is permeable to H2O but not to certain solutes"

TRUE

how can osmotic H2O movement be prevented by opposing force?

hydrostatic pressure (osmotic pressure of solution)

what is osmotic pressure of solution

colligative property > depends on # and not types of particles in solution

what is osmolarity calculated in/

Osmol

membrane permeability to water (Pw) equation

Pw = Pd + Pf

what is Pd

through lipid bilayer - small - mercury insensitive - temp dependent (lipid fluidity)

what is Pf

through water channel - large - mercury sensitive - temp independent

what is mediated by aquaporins (9 isoforms)

cells have different ___ because they express different ___ ___

cells have different (Pw) because they express different (aquaporin) (isoforms)

true or false "different aquaporin = same permeability"

FALSE "DIFFERENT aquaporin = DIFFERENT permeability"

what is osmotic pressure

the pressure applied to a solution to prevent the inward flow of H2O across a semi-permeable membrane

same osmolarity

isosmotic

lower osmolarity

hyposomotic

higher osmolarity

hyperosmotic

define tonicity

effect solution has on cell volume

what does tonicity depend on

membrane permeability of solute

True or false "osmolarity of solution DOESN'T always indicate effect on cell vol."

TRUE osmolarity and tonicity NOT always the same thing

isotonic solution

no change in cell vol

hypotonic solution

cell swells = cell lysis (haemolysis)

hypertonic solution

cell shrinks (crenation)