Transport mechanisms Flashcards
(40 cards)
How do we ensure to preserve the constancy of the Milieu Intérieur and the homeostasis?
by exchanging nutrients, salts, gases, and waste in and out of the body
What is the plasma membrane/ cell membrane?
What are its characteristics?
It is the membrane that covers every cell (membrane between ICF and ISF)
Varies depending on the cell
Bimolecular Phospholipid Layer (phospholipid bilayer)
polar/hydrophilic head and non-polar/hydrophobic tail
Phospholipids = 40-50% of plasma membrane by weight
What organs make the link between the plasma and the interstitial fluid?
Lungs and the kidneys
What is the cell membrane permeable/ less permeable and impermeable to?
Highly permeable to :
H2O
Lipid-soluble substances
Dissolved gases(CO2, O2)
Small uncharged molecules
Less permeable to:
Larger molecules
Charged particules
Impermeable to:
Very large molecules (macro-molecules)
What role does cholesterol play in the plasma membrane?
inserted into phospholipid bilayer to reduce packing of fatty acid tails –> increase fluidity of membrane and avoid aggregation
In high temperature, role changes: adds firmness, stabilize cell membrane
What are the different types of protein we can find in the cell membrane and their importance?
25-75% of membrane by weight
Integral proteins:
closely associated with phospholipids, cross membrane (Trans-membrane, amphipathic –> both hydrophilic and hydrophobic parts)
Peripheral proteins:
more loosely associated, mostly on the cytoplasmic side
What is Glycocalyx?
layer of carbohydrates formed by a chain of monosaccharides that extend extracellular surface on cell membrane bound ot proteins
Provides protection from infections
Enable cells to indentify each other and interact
What are the different functions of plasma membrane proteins?
Selective transport channel
Enzyme that catalyse membrane associated ractions (amino acid transport/Na-K pump)
Cell surface receptors for chemical signal of cell environment
Cell surface identity marker
Cell adhesion
Attachement to cytoskeleton
Which are the 2 possibilities for transmembrane transport pathways?
- via phosphilpid bilayer
- via interaction with protein cluster (channel or carrier/trnasporter)
What are the 3 passive transport mechanisms across the cell membrane ?
Energy independent
1. Diffusion (most important)
- Carrier-mediated Facilitated Diffusion (form of diffusion)
3.Osmosis (mvt of water across semi-permeable membrane)
What are the 3 active transport mechanisms across the cell membrane ?
Energy dependent
1.Carrier-mediated Active Transport:
- primary
-secondary
- Pino/phagocytosis
What is simple diffusion
mvt of molecules from on location to another as result of RANDOM THERMAL MOTION
Flux = amount particules crossing surface/ unit of time
Net Flux = high concentration to lower concentration
Equilibrium = when diffusion fluxes are equal and net flux = 0
*Membrane has to be permeable to particles
What happens with diffusion and concentrations when cell is exposed to solute in large extracellular solution?
extracellulare cellular concentration = constante C0
intracellular concentration = Ci
Ci will eventually = C0
because when Ci diffuses, doesn’t change C0 concentration but when C0 diffuses, changes Ci concentration
What is Fick’s Law of Diffusion?
J = PA(C0 - Ci)
J = Net flux: rate of diffusion
P = Permeability/diffusion coefficient
A = surface area of membrane
C0 - Ci = concentration gradient
*Diffusion time increases proportionnally to the square of distance travelled by solute molecule –> effective over short distances –> why many tiny capillaries close to cells
What factors affect diffusion across the cell membrane?
- Mass of the molecule
- Concentration gradient across cell membrane
- Lipid Solubility (if diffusion trough bilayer)
- Electrical charge
- Availability of selective ion channel or membrane carriers (to move olecules through celle membrane)
Which are the 2 ways DIFFUSION particules may penetrate into cell?
- Dissolving in the lipid component (for non-polar molecules) ex: O2, CO2, fatty acids, etc.
- Diffusing through channels (for ions –> polar) (mediated transport?)
Both case, mvt depends on existence on concentration gradient
What is an ion channel?
What are the 3 ways a channel can be gated?
A single protein or clusters of proteins (which cross the membrane multiple times)
Shows selectivity based on their diameter (why small particles enter more easily) and on the distribution of charges
Eache type of selectivity channels has specific ions which go through –> form energy barriers
3 possible ways to channel is gated:
- Ligand-gated
- Voltage-gated (based on resting potential?)
- Mechanically-gated (stress around channels –> pain ex)
What is the electrical gradient?
Mouvement of ions also affected by presence of an ELECTRICAL GRADIENT because inside of cell = negative charge
simultanous existence of concentration + electrical gradient for particular ion = electrochemical gradient
How do voltage gated ion channel work?
4 classes of ion channels:
Na+ channels
K+ channels
Ca+ channels
Cl- channels
total # ions that flow through these channels generate ionic current depending on:
1. channel conductance
2. how often channel opens
3. how long channel says open
What is Mediated Transport Systems?
And its characteristics
mouvement of ions and other molecules (glucose, amino acids) by integral membrane proteins called transporters
Ion mvt across membrane via transporters = much slower that trough ion channels
- Specificity - system transports 1 specific type of molecule only
- Saturation - rate of transport = max when all binding sites on all transporters occupied.
Tm (transport max) for given substance across given membrane - Competition - when (structurally) similar substances compete for same binding site on membrane carrier
*Compared to simple diffusion which increase linearly, mediated-transport curves at asymptote Tm
2 Types:
1. Facilitated diffusion (passive)
- Active transport (active)
- Primary active transport
- Secondary active transport
Which are the factors that determine flux magnitude of mediated-transport systems?
- solute concentration
- Affinity of transporter for the solute
- # transporters
- Rate of transporter conformational change
What is involved in facilitated diffusion?
(mediated-transport)
presence of a transporter/carrier molecule which enable solute to penetrate nore readily than by simple diffusion
- Passive (no energy)
- net flux from high to low concentration (thats why no energy?)
- Hormones may increase # or affinity of transporters
- Solute binds transporter
- Transporter changes configuration
- Solute is delivered to other side membrane
- Transporter resumes original conformation
What is involved in active mediated-transport?
- Transport-mediated
- Requires supply of chemical energy (usually hydrolysis of ATP by carrier)
- Susceptible to metabolic inhibitors
- Can transport solute against concentration gradient (“uphill”)
Primary: ATP
Phosphorylation of transporter changes conformation of transporter and its solute binding affinity
Necessary to maintain concentration gradient between inside and outside of cell (ICF = more K+ than Na+ and ECF = more Na+ so have to go uphill to keep gradient bc naturally goes downhill)
Secondary: use downhill for uphill, electrochemical gradient
- Na+ binds to transporter outside cell (where Na+ concentration = high so downhill) allowing glucose or amino acid to bind to the same carrier
- Through change of configuration, transporter delivers both into cell
- Transporter then reverts to original configuration and Na+ is extruted from cell by Na+/K+ -ATPase (primary)
*Uses energy stored of electrochemical gradient to move Na+ and transport solute.
Creation + maintenance of electrochemical gradient depends on primary active transport
What is Na+/K+ -ATPase?
It is the active mediated-transport of Na+ ouside the cell and K+ inside the cell to keep concentration gradient (uphill) to compensate for simple diffusion goind downhill
Changes in the binding site affinity for a transported solute are produced by phosphorylation and dephosphorylation of the Na+/K+-ATPase.
