8-membrane transport ii
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Membrane Transport and Permeability II
Outline for Today
I. IntroductionII. Passive Processes
A. Simple diffusionB. OsmosisC. FiltrationD. Facilitated diffusion
III. Active TransportA. IntroductionB. Solute pumping
1. Na+/K+ ATPase pump
C. Bulk transport1. Endocytosis2. Exocytosis
Active Transport
• Cells must use energy since the movement is non-favorable– ATP ADP + Pi
• Non-favorable means it goes against the concentration gradient
ATP
ADP
Pi
EnergyPi
Energy
Introduction
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Na+/K+ ATPase
K+
K+
K+K+
K+K+
K+
Na+
Na+
Na+
Na+ Na+
Na+
Na+
Na+
ATP
ADP + Pi
K+
Cytoplasm
Extracellular fluid
Gradient for Na+
Gradient for K+
Na+Na+Na+
Electrogenic Pump!!!
Na+Solute Pumping
Na+/K+ ATPase pump
• Movement of materials against the gradient
Solute Pumping
Fig. 3.19
Na+/K+ ATPase pump
• Transmembrane• Pump moves both
Na+ and K+
• Antiport• Enzyme catalyzes the
degradation of ATP• This pump never
stops– Can burn energy while
asleep
Solute Pumping
Fig. 3.19
Na+/K+ ATPase pump
• It maintains a high extracellur and low intracellular [Na+] by moving Na+ (blue) outside
• It maintains a low extracellur and high intracellular [K+] by moving K+ (yellow) inside
• Mnemonic
Solute Pumping
Fig. 3.19
Mnemonic
Potassium -does it go in or out?
Sodium -does it go in or out?
Kin Kout Nain Naout
K goes in so Na must go out of the cell
Solute Pumping
Another way to think of it
• Life began in the sea• The sea is very salty
– Salt has a tendency to enter the organisms/cells so we tend to be bathed in it
• Na tends to enter the cells so we must find a way to get rid of it
• Pump Na+ out of cell
Na+/K+ ATPase pump
• Notice #’s– Moves 3 Na+ outside– Moves 2 K+ inside– mnemonic- 2 letters in “in”
and 3 letters in “out”• Creates a charge
difference– Inside becomes negative– Cell becomes polarized– Can conduct electricity– Called electrogenic pump
Solute Pumping
Fig. 3.19
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Na+/K+ ATPase
K+
K+
K+K+
K+K+
K+
Na+
Na+
Na+
Na+ Na+
Na+
Na+
Na+
ATP
ADP + Pi
K+
Cytoplasm
Extracellular fluid
Gradient for Na+
Gradient for K+
Na+Na+Na+
Electrogenic Pump!!!
Na+Solute Pumping
Na+/K+ ATPase pump
• Regulation of cell volume– Where Na+ goes water
follows– Prevents the cell from
swelling
Solute Pumping
Fig. 3.19
Na+/K+ ATPase pump• Secondary Active
Transport– e.g. sodium glucose
transport protein (SGLT)– Pump maintains low
intercelluar Na+ levels• Pump on basal end
– SGLT, in bringing Na back into the cell (down concentration gradient) , carries glucose with it
• SGLT on apical end– Saves glucose from being
dumped out of the body with urine
Solute Pumping
Fig. 3.20
Na levels low
Na+/K+ ATPase pump
• Heat Production– Thyroid hormone
stimulates cells to make more Na+/K+ ATPase pumps
– As they use ATP they release heat
Solute Pumping
Fig. 3.19
Na+/K+ ATPase pump
• Maintain Membrane Potential– Established concentration
gradients for Na+ and K+ across the membrane
• Also, 3 Na+ out and only 2 K+ in
• Charges of cell– Crucial for excitable cells– Like two poles of a battery
Solute Pumping
Nerve Cell
Introduction
• Energy is required for this process
• Movement of large macromolecules
• Types defined by the direction of movement– Endocytosis
• Intake– Exocytosis
• Output (e.g. secretion or excretion)
Fig. 3.21
Bulk Transport
Endocytosis
• Three different types– Phagocytosis– Pinocytosis– Receptor mediated
endocytosis
Bulk Transport
Fig. 3.21
Phagocytosis
• Literally means cell eating
• Usually a protective function
• Not all cells are phagocytic
• May bring in cell debris for clean up
Bulk Transport
Fig. 3.21
fusion
excretion
Bulk Transport
Fig. 3.21
Phagocytosis• Extends pseudopods
around the particle• Pseudopods meet and
package the material into a vessel (phagosome)
• Processes ingested material by fusion of phagosome with lysosome (phagolysosome)
• Residue is released by excretion (via exocytosis)– Can go into blood and be
filtered by the kidney
Bulk Transport
Fig. 3.21
Phagocytosis
• Phagocytes– Cells’ function is
phagocytosis– Found in almost every
tissue compartment but only in specialized cells
• Lungs, for example, are rich in macrophages which are phagocytes
Bulk Transport
Fig. 3.21
Pinocytosis
• Pino = tiny• “cell drinking”• Little pockets or divots
form invaginations in the membrane
• Typically get this occurring in all human cells
• Extracellular fluid with whatever molecules were there at the time
http://academic.brooklyn.cuny.edu/biology/bio4fv/page/endocytb.htm
Bulk Transport
Receptor Mediated Endocytosis
• More selective than the other types– Specific molecules without a lot of fluid
• Particles bind to specific receptors
• Membrane protein called clatharin• When the clatharin and LDL’s (for example) are taken inside there is
a clatharin coated vesicle• Can serve as an address label to tell it where to go in the cell
Bulk Transport
Fig. 3.22
Receptor Mediated Endocytosis
• Example is LDL (low density lipoproteins) and insulin• Familial hypercholesterolemia
– Low number of LDL receptors so the cholesterol stays in the blood
– 1200 mg/dL – Can have heart attacks before age 20 and usually die before
age 30
Bulk Transport
Fig. 3.22
Exocytosis
• Secreting or excreting materials from the cell– e.g. release of insulin, milk release from breast tissue, hormone
release • Like endocytosis in reverse• Both endocytosis and exocytosis subtract from and add
to the cell membrane so the amount is relatively constant
Bulk Transport
Fig. 3.24
ID 12051--- where the last three is your test number
Your lab section you attend: A=001, B=002, etc. A list will be on the exam.