Cell Membrane Structure and Function Flashcards
what are the fundamental units of specialised functions in living organisms
cells
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
Describe the membrane structure
Fluid mosaic model
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
What type of bonds hold membrane proteins and lipids together?
hydrogen bonding
The membrane is 50% ___ and 50% ___
The membrane is 50% (lipid) and 50% (protein)
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)
What are gatekeepers in the membrane that regulate how things move across lipid barrier
Proteins
What are scattered among double row of phospholipid molecules (embedded in phospholipids)
Cholesterol & glycolipids
___ back-to-back layers of ___ types of ___ molecules
(2) back-to-back layers of (3) types of (lipid) molecules
cell membrane equation?
Cell membrane = proteins + (phospho)lipids
what acts as a barrier; isolates cells from their external environment
cell membrane
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
What comprises 75% lipids
Phospholipids
___ has 2 parallel layers of molecules
Phospholipid bilayer = 2 parallel layers of molecules
If a molecules has polar (charged) and nonpolar (uncharged) regions it is said to be…?
Amphipathic
how phospholipids orient themselves?
Spontaneously form stable bilayers, polar head exposed to water non-polar tails shielded in the interior
what provides highly impermeable barrier to passage of charged ions
hydrophobic core (fatty acid chains)
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)
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
membrane fluidity is determined by…
- lipid tail length»_space; longer tail = less fluid
- # of double bonds»_space; more double bonds = more fluidity
- amount of cholesterol»_space; more decreases fluidity
what proteins are amphipathic and stuck in lipid bilayer
integral transmembrane proteins
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
where are peripheral proteins attached to membrane and are they removed easily?
inner or outer surface of membrane
removed easily
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
- amphipathic
- hydrophobic regions (non-polar amino acids coiled into helices) span hydrophobic core of lipid bilayer
- 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
- shape
- charge
- lipid solubility
what is governed by laws of diffusion
selective permeability
The lipid bilayer is permeable to 3 things what are they?
- Nonpolar, uncharged molecules (O2, N2, Benzene)
- Lipid soluble molecules (steroids, fatty acids, some vitamins)
- Small uncharged polar molecules (H2O, urea, glycerol, CO2)
The lipid bilayer is IMpermeable to 2 things what are they?
- Large uncharged polar molecules (glucose, a.a)
- 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
- diffusion rate sets limit on size of cells
- increase diffusion = increase membrane area available
- membrane thickness > thicker membrane = slower rate
- 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»_space; to ___ Na+ conc. in cytoplasm
Na+ ion gradient: (HIGH) Na+ conc. in extracellular fluid»_space; to (LOW) Na+ conc. in cytoplasm
K+ ion gradient: ___ K+ conc. in extracellular fluid»_space; to ___ K+ conc. in cytoplasm
K+ ion gradient: (LOW) K+ conc. in extracellular fluid»_space; to (HIGH) K+ conc. in cytoplasm
Cl- ion gradient ___ ways: ___/___ Cl- conc. in extracellular fluid»_space; to ___/___ Cl- conc. in cytoplasm
Cl- ion gradient BOTH ways: HIGH/LOW Cl- conc. in extracellular fluid»_space; 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)
Pf
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)
