Forces acting across membranes Flashcards
What is the basic structure of the membrane
- Double layer of phospholipids
- Embedded with proteins (aquaporin)
What are the characteristics of a membrane
- Selective barrier
- Permeability can vary
- Dynamic
- Very thin bilayer
- Very flexible because of fatty acids
- Insulators against ion movement
What is the function of the membrane
Selectively permeable barrier between ICF and ECF
Provide binding sites for chemical signals
Differences in membrane proteins responsible for varied charteristics
What are the different types of membrane proteins
- Integral - Span hydrophobic core of phopholipid bilayer
- Periphrial - interact only with phosphates of bilayer and do not penetrate hydrophobic region
What are the functions of membrane proteins
- Receptors
- Transport
- Enzymes
- Maintenence of cell structure
- Communication
What are the concentrations of ions in cellular fluid
What are the differences in membrane protein content
Myelin - low protein content 18%, high lipid content good insulator
Plasma membrane - protein content 50%
Membranes for energy transduction - high protein content 75%
What is the elctrochemical gradient
Combination of chemical gradient and electrical gradient
What are the mechanisms of movement across membranes
- Diffusion
- Active transport
- Osmosis
- Filtration
What is Endocytosis
Invagination of cell membrane to form a vesicle which disintegrates on inisde, releasing contents that migrate to destination
Common mechanism to terminate signals from extracellular ligands
What is exocytosis
Vesicles merge with plasma membrane on inside and release contents outside of cell
Many proteins synthesized inside cell are released this way
What is diffusion across membranes
Molecules move from high concentraition to low concentration down concentration gradient
What types of diffusion is there
- Passive
- Facilitated
Describe passive diffusion
Substances move directly through lipid bilayer
Molecules need to be: small, uncharged and Lipophilic
Describe facilitated diffusion
Substances require assistance from membrane proteins to cross lipid bilayer
Membrane proteins can be channels or mediated transport proteins
What type of channels proteins are there
Voltage gated - electric potential
Ligand gated - ligand binding
Describe Transporters
Open to one side of ECF or ICF at a time
What is active transport
Movement of molecules against concentraition gradient with energy
Describe the Na+/K+ pump
1.Maintains high Na+ outside cell and high K+ concentration inside
2.Pumps 3 Na+ out and 2 K+ inside
3.Net movement of positive charge out cell = electrogenic pump
4.40% of resting energy is used by pump
What is osmosis
Net movement of H2O from high concentrations to low concentrations of water
What is the difference between osmosis and diffusion
Osmosis - Net movement of water form high concentration to low
Diffusion - Net movemet of solutes from high solute concentration to low
Describe osmosis
Membranes permiable to only water will have equal concentrations on both sides of membrane but different volumes
Describe diffusion
Membranes permiable to water and a solute will have equal concentrations on both sides and equal volume
What is osmolarity
Total number of solute particles in solution (after they dissociate), not nature of particles
What is Tonicity
Total number of non-penatrating particles in solution (particles unable to cross membrane)
What is the importance of tonicity
If a solute cannot cross a membrane, a change in its concentration will cause osmotic flux and change volume of cell
Describe an isosmotic solution
Describe an isotonic solution
Give examples of penetrating and non-penetrating particles
Penetrating - water, urea
Non-penetrating - ions
What is the Osmolarity of human plasma
285mosmol/l, same as osmolarity of cells
What happens to cells in hypotonic and hypertonic solutions
Hypotonic - swell because water enters cell down conc. gradient
Hypertonic - shrink because water leaves down a chemical gradient
Why is osmosis important when prescribing fluids
Cause cells to burst
Lysed cells introduce proteins to ISF, uncontrolled increase of ECF tonicity
Fluids must have the appropriate tonicity
Brain is most sensative to change in tonicity
