Membrane Structure & Function
Membrane Models
1935-1970SandwichModel
1972- PresentFluid-MosaicModel
Membrane Transport(Passive)
Glucose, amino acids
1 2
Diffusion
• Steepness of concentration
gradient• Temperature• Mass of diffusing
substance• Surface area• Diffusion
distance
2 types of membrane transportPassive vs Active
Channel-mediated Facilitated Diffusion of Potassium ions through a Gated K +
Channel
Glucosetransporter
Glucosegradient
Glucose
Extracellular fluid Plasma membrane Cytosol
1
Glucosetransporter
Glucosegradient
Glucose
Extracellular fluid Plasma membrane Cytosol
1
2
Glucosetransporter
Glucosegradient
Glucose
Glucose
Extracellular fluid Plasma membrane Cytosol
1
2
3
http://trc.ucdavis.edu/biosci10v/bis10v/media/ch04/tonicity.html
Crenation
HemolysisCytolysis
Plasmolysis – the shriveling of the cell membrane due to loss of water (osmosis)
Turgor pressure – the force directed against the cell wall after the influx of water (osmosis)
Filtration is movement of water and solute molecules across the cell membrane due to hydrostatic pressure generated by the cardiovascular system.
Requires Energy:ex.: thyroid gland concentrates Iodine glucose is completely absorbed by digestive tract sodium potassium pump
Active TransportI. Solutes are transported across plasma membranes with the use of energy, from an area of lower concentration to an area of higher Concentration *Sodium-potassium pump*Thyroid gland*Intestines (glucose)II. 2 sources of energy
1. ATP (Primary active transport)2. Energy stored in Ion concentration gradients (Secondary active transport)
**40% of a cell’s ATP is used for Primary active transport Cyanide shuts down active tranport by turning off ATP production
1
3 Na+
K+
gradient
Cytosol
1
3 Na+ expelled
3 Na+
ADP P
P
2 K+
importedK+
gradient
Na+
gradientNa+/K+ ATPase
Extracellular fluid
Cytosol
2K+
ATP2 3 4
18
Secondary Active Transport Mechanisms
• Antiporters carry two substances across the membrane in opposite directions (Digitalis)
• Symporters carry two substances across the membrane in the same direction
Endocytosis – taking in large amounts of material (bulk flow)
• Ex. LDL cholesterol (bad cholesterol)