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.