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
