Transcript Cell Membrane & Transport

Membrane Structure &
Function
Membrane Models
1935-1970
Sandwich
Model
1972- Present
Fluid-Mosaic
Model
Membrane Transport
(Passive)
1
2
Glucose,
amino acids
Diffusion
• Steepness of
concentration
gradient
• Temperature
• Mass of
diffusing
substance
• Surface area
• Diffusion
distance
2 types of membrane transport
Passive vs Active
Channel-mediated Facilitated Diffusion of
Potassium ions through a Gated K +
Channel
Extracellular fluid
Glucose
1
Plasma membrane
Glucose
transporter
Glucose
gradient
2
3
Glucose
Cytosol
http://trc.ucdavis.edu/biosci10v/bis10v/media/ch04/tonicity.html
Crenation
Hemolysis
Cytolysis
Turgor pressure – the force
directed against the cell wall after
the influx of water (osmosis)
Plasmolysis – the shriveling of the cell
membrane due to loss 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 Transport
I. 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
Extracellular fluid
Na+
gradient
Cytosol
K+
gradient
Cytosol
K+
gradient
3
Na+
Na+/K+ ATPase
3 Na+ expelled
2K+
1
P
3 Na+
1
ATP
2
ADP
3
P
+
4 2K
imported
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
18
Endocytosis –
taking in large
amounts of
material (bulk flow)
• Ex. LDL cholesterol (bad cholesterol)