Download Active Transport - PickensAPBiology

Active Transport
 Movement of molecules against the
concentration gradient

“uphill”
 Allows cell to maintain internal
concentrations of small molecules
 Specific proteins embedded in
membranes
 Energy provided by ATP
 Transfer of phosphate to induce
conformational change in the
protein
Types of active transport:
Uniport=movement of a single molecule
Symport=movement of two molecules in the same direction
Antiport=movement of two molecules in opposite directions
An example of active transport:
Membrane potential
 Uneven balance of charged ions across the membrane
-50 to -200 mv
 Cytoplasm is negative compared to outside of cell
 Favors passive transport of cations into cell and anions out
of cell
Electrochemical gradient
 Chemical gradient
 Electrical gradient (follows same principle as chemical
gradient)
Concentration of Na+ in a cell at rest is lower than outside the
cell
Gated channel opens
Sodium “fall” down concentration gradient (toward outside of
cell)





Electrogenic pump
 Na-K pump



Active pump contributes to membrane
potential
3 Na+ out=2 K+ in
Transfer of one (=) charge for every cycle
 Proton pump

Transports protons (H+) out of cell
 Harnesses energy to do work
The Na+/K+ pump in action:
Co-transport
 Flow of one solute
molecule through a pump
indirectly drives movement
of other solutes

Couples downhill diffusion
with uphill tranport
 Examples
 Proton gradient
(established by proton
pump) transports amino
acids, sugars (sucrose)
into cell
 How sucrose is loaded
into cells in the veins of a
plant
Active Vs. Passive Transport:
A Review
Transport of large molecules
 Proteins and polysaccharides
 Exocytosis: removal of particles
 Transport
vesicles produced by golgi
 Fuse with plasma membrane
 Excretory cells
Vesicle-mediated transport:
Exocytosis
Exocytosis in action:
Endocytosis
 Endocytosis: engulfing of particles


Plasma membrane forms a pocket
Pinches inward forming a vesicle
 Phagocytosis
Wrapping pseudopodia around particle
 Forms a membrane enclosed vesicle
 Contents digested by lysosome
 Pinocytosis
 “gulping” droplets of extracellular fluid
 Unspecific transport
 Receptor mediated endocytosis
 Very specific
 Extracellular substances bind to ligands of cell surface
 Enables cell to acquire bulk quantities of specific substances that
may be in low concentration in ECM

Cholesterol buildup in blood vessels
 Cholesterol travels in blood stream in low
density lipoproteins
 LDL’s bind to receptors on membranes and
enter cell by endocytosis
 Defective LDL receptors prevents uptake of
cholesterol by cell
 Results in accumulation in blood stream
 Contributes to atherosclerosis
Vesicle - mediated transport:
Endocytosis  Pinocytosis
Vesicle - mediated transport:
Endocytosis  Phagocytosis
Receptor-mediated endocytosis
Check yourself
 Explain the difference between passive and
active transport and give specific examples of
each
 Explain the difference between gated channels,
electrogenic pumps and cotransport. Give
specific examples of each
 Explain the difference between exocytosis,
pinocytosis, phagocytosis and receptor
mediated endocytosis.
Useful links
 http://www.stolaf.edu/people/giannini/flashanimat/tran
sport/atpase.swf
 http://student.ccbcmd.edu/~gkaiser/biotutorials/photo
syn/atpasep.html
http://www.northland.cc.mn.us/biology/Biology1111/an
imations/active1.swf
 http://highered.mcgrawhill.com/olc/dl/120068/bio04.swf