Membrane Transport Flashcards
Plasma Membrane Function
- barrier between intra & extracellular
- precise control movement of substances across or thorugh membrane is fundemental to physiological system processes
Examples of Plasma Membrane Significance for Physiological Systems:
- nurtition absorption from digestive tract into bloodstream
- salt & water balance in kidneys
Solvent Definition:
able to dissolve other substances
Solute Definition:
minor component in a solution dissolved in the solvetn
Aqueous Solution Defintion:
solution of solutes dissolved in water
What are the two main structural components of the Plasma membrane?
- Lipid Bilayer
- Membrane proteins
Lipid bilayer function in the plasma membrane
- made up of phospholipids with fatty acid tails = hydrophobic
- acts as barrier between aqeuous intracellular and extracellular fluid
Membrane protein functions in the plasma membrane
- connects extra and intracellular spaces across lipid bilayer
e. g. channels, carriers, or pumps - provides highly regulated means of transport across membrane
Passive Proccesses of Membrane Transport
- does not require metablic energy (ATP)
- traverse membrane passivley by diffusion (even distribution); down conc. gradient (from high -> low conc.)
Active Processes of Membrane Transport
- requires metabolic energy (ATP)
- molecules transverse membrane against conc gradient (from low -> high conc.)
Diffusion Defintion:
net flow of substances from a region of high concentration to a region of low concentration
Variables that Effect the Rate of Diffusion
- Molecular size: smaller molecules diffuse at faster rates as they bounce further after collision.
- Distance: grater distance = slower rate of diffusion due to less collision
- Conc. Gradient:
- Cell Size: biger cells have larger surface area available for diffusion
Rate of Diffusion is highest when:
concentration gradient, membrane permeability and surface area are increased and molecular weight and distance are decreased.
Equation for rate of Diffusion for any substance:
Fick’s Law:
Q = (C×P×A)/(MW×X)
Q = (C×P×A)/(MW×X)
Where:
Q = rate of diffusion C = concentration gradient P = Permeability A = surface area MW = molecular weight X = distance
Two major mechanisms by which solutes can transverse the plasma membrane by simple diffusion:
- simple diffusion through lipid bilayer
2. simple diffusion through protein channels
Simple Diffusion Through Lipid Bilayer:
Substances with high lipid solubility (O2, COs, N2, alcohol, fatty acids) dissolve in phosphoipds of lipid bilayer & diffuse directly through membrane
higher lipid solubility of susbatnce = faster rate of diffusion through membrane
Simple Diffusion Through Protein Channels:
small water-soluble substances (H+, Na+, K+, Ca2-) transverse membrane through channels. these channels are often ion selective and may be gated
Simple Diffusion:
Molecules transverse the membrane without binding to a carrier protein
Facilliated Diffusion:
molecules that are lipid insoluble or too big o pass through protein channels. transverse the membrane by binding to carrier protein. protein undergoes conformational change. then solute is relesed into cell.
Experiment to determine whether a substance moved across the plasma membrane by simple or facilitated diffusion?
Testing saturation kinetics to see if the rate of transport plateaus or not.
Experiment to determine whether a substance moved across the plasma membrane by simple or facilitated diffusion?
Testing saturation kinetics to see if the rate of transport plateaus or not.
Once carrier proteins are occupied there is no increase in facilitated diffusionand the rate of transport plateaus. for simple diffusion increased conc. increases rate.
the Importance of passive process in terms energy-expenditure by the human body
A great conservation of energy, metabolically friendly, no energy is expanded. allows our cellular energy to be used for other more important purposes
Active Transport
- membrane spanning proteins act as molecular pump - moves substances lik Na+, K+, Ca2+, sugars, most amino acids
- Protein pump has high affinity binding site for a substance on low conc. side of membrane
- Substance binds and protein undergoes conformational change – process is powered by ATP
e. g. Hydorgen pump, sodium potassium exchange pump, cals
Bulk Transport:
- large substances may be too large for diffusion or solute pump
- Substances enter/leave in vesicles by a process powered by ATP
Two Types of Bulk Transport:
- Exocytosis
2. Endocytosis
Exocytosis:
transport of material synthesised by cell from inside to outside. involves migration, fusion, breakdown. release of macromolecule outside the cell
e.g. hormones, neurotransmitters, enzymes
Endocytosis:
transfer of large particles , macromolecules, and extracellular fluid into the cell. process involves a fold of plasma membrane forming around substance to be ingested, forming membrane-bound vesicle
Three Types of Endocytosis:
- Phagocytosis
- Pinocytosis
- Receptor-mediated Endocytosis
Phagocytosis:
specialised cells able to ingest certain large solid particles – extension to form particle containing vesicle.Phagosome fuses with a lysosome that has digestive enzymes – break down debris and releases products into cell’s cytoplasm
Pinocytosis:
involves a small volume of the extracellular fluid being incorporated into a membrane-bound vesicle formed by a small fold in the plasma membrane
Receptor-mediated Endoytosus
the membrane expresses extracellular receptors to which a particular macromolecule binds
Osmosis
movement of any solvent across selectively permeable barrier. Solvent – water; permeable barrier – plasma membrane
How is the plasma membrane highly permeable to water despie the lipid bilayer with a hydrophobic core?
Water molecules are small enough to pass straight through lipid bilayer and protein channels. Water can move down conc. gradient in the same way small ions mov through the membrane via simple diffusion
Appreciate the difference between the movement of water and solutes across the plasma membrane of cells.
diffusion of solutes across the membrane does not result in volume changes whilst osmosis does produce changes in volume as water moves freely across membrane
Osmotic Pressure:
water moves from high -> low conc.
osmotic pressure is the driving force of osmosis. There will be greater water movement by osmosis when the concentration difference of non-penetrating solutes across membrane is high
Osmolarity:
measure of the number of particles in a solution and reflects more accurately its osmotic pressure as it is does not only measure the concentration
Tonicity:
movement of water in and around cells
Formula for Osmolarity:
molarity of solution x no. of particles it dissociates into
- add up molecules
- divide % (multiply by 100) by molecular weight
- multiply by the no. of particles it dissociates into
- multiply by 1000 and rounf to 1 decimal
Isotonic Solution Effect on Cells
- cells intact; ‘normal’ size
- water evenly distributed in and out of cell
- no net movement of water
Hypertonic Solution Effect on Cells
- higher conc of colutes in ICF so water moves out of cell
- cell becomes shrivelled & shrunken
Hypotonic Solution Effect on Cells
lower conc. of solutes than ICF so water flows into cell
- cell becomes swollen, enlarged, and may burst
Equation for Equilibirum Potenital:
Nernst Equation:
E[ion]: -61 x log x (ion[in])/(ion[out])
