Membrane Function and Structure Flashcards
Membrane Functions
Homeostasis/Compartmentalization
Transport
Intracellular Communication
Compartmentalization - def
Maintaining concentration differences between compartments
Intracellular Communication - types
gap junctions transmitters receptors synaptic transmissions excitablity
Transporters (Cell Membrane)
Responsible for maintaining concentration differences across cell membranes
Extracellular Fluid Concentrations
Na+ = 135-145 mM K+ = 3.5-5.0 mM Ca2+ = 2.0-2.6 mM Cl- = 98 -106 mM
Intracellular Fluid Concentrations
Na+ = 10 -15 mM K+ = 140 mM Ca2+ = 50 mM Cl- = 10 mM
Which ion concentrations are greater in extracellular fluid?
Na+ , Cl-
Movement of Solutes - methods
Bulk Flow
Diffusion
Electrical Migration
Excitable Cells use … to communicate
Action potentials, synaptic juntions
Bulk Flow
bulk movement of solutions by hydrostatic pressure
Used for big disctances
Diffusion - caused by, results in
Random thermal motion of molecules
Results in directed (net) movement of solutes when concentration differences exsist
Larger molecules diffuse more slowly than smaller ones
Time to travel particular distance (x)
x2
Very inefficient over large distances
Electrical Migration
Charge movement in response to an electric field.
Electrodiffusion
Ions diffuse both by concentration and electrical attraction
Flux
quantity that moves over a specified period of time
quantity/time
Fick Law
Flux = P x A x deltaC
permeability x area x concentration difference
Non Polar lipid soluble solutes
High permeability
Local anesthetics
alcohol
O2, Co2
Ion permeability
Need help crossing membranes - use proteins (ion channels)
Ionic Channels - factors affecting ion movement
chanels, conductance (ions/sec), Open probablity
Protein mediated Transport - types
Facilitated Diffusion
Active Transport
Facilitated Diffusion - def, types
Does not involve any use of metabolic energy
Channels
Carriers
Channels - def, characteristics, amount
membrane protein molecules - pore that spans membrane
Open State & Closed State
Show specificity, saturation and competition
Millions of ions/second
Carriers - def, method, amount
Membrane protein molecules
Binds solute to be transported, changes confirmation allowing solute to cross membrane
Show specificity, saturation and competition
thousands of ions/second
Saturation - Tm, Vmax
Carrier will reach Tm, or transport maximum, with further increases in concentration not leading to increases in transport.
Vmax = maximum rate of reaction reached at high substrate levels where addition of substrate will no longer increase rate of reaction
Active Transport - def
transport that can proceed AGAINST an electrochemical potential difference or can move transported solute ‘uphill’
Requires energy, usually ATP
Active Transport - types
Primary AT
Secondary AT
Primary AT - def, types
directly utilize metabolic energy = an ATPases or pump e.g. Na+/K+ pump Ca2+ pump H+ pump
Na+/K+ pump - action, location
3 Na+ out of cell, 2K+ into cell
Basolateral membrane
Ca2+ pump - location, action
ER of most cells (SR of muscle cell) ,
Keeps Ca2+ within cell ?
H+ pump - location, action
Basolateral membrane of specialized stomach cells or tubular cells of kidney
Results in secretion of HCl during digestion.
Secondary Active Transport - types
Co-transporters
Counter Transporters
Co-Transporters
Move both solutes in the same direction
Secondary Transporters - method, e.g.
Uphill movement of solute coupled with downhill movement of another solute (usually Na+)
Na/glucose
Counter Transporters - def., a.k.a
Move solutes in opposite directions
a.k.a exchangers
Vesicle Mediated Transport - types
Exocytosis
Endocytosis
What undergoes Exocytosis ?
synaptic transmitters, hormones and some digestive enzymes
Receptor mediated endocytosis
material to be transported first binds to a receptor and the substance-receptor complex is ingested by endocytosis
Osmosis - def. how,
Diffusion of water
through lipid bylayer, ionic chanels and aquaporins
measurning water concentration
measured in terms of concentration of dissolved solute particles
Osmolarity
solution of concentration of dissolved particles in the solution
physical property
labeling osmolarity is relative
Tonicity
based on steady state cell volume
biological property
affected by permeability
