1. The Plasma Membrane – Gateway to the Cell
4/23/2017
The Plasma Membrane – Gateway to the Cell
G. Podgorski, Biol. 1010

2. The Plasma Membrane is Semipermeable
4/23/2017
The Plasma Membrane is Semipermeable
The physical properties of phospholipids account for membrane assembly and many of its properties.
Small molecules and larger hydrophobic molecules move through.
Ions, hydrophilic molecules larger than water, and large molecules such as proteins do not move through the membrane on their own.
G. Podgorski, Biol. 1010

3. Plasma Membrane Functions
The Plasma Membrane
4/23/2017
Plasma Membrane Functions
Maintain a high concentration of materials in the cell.
Keep harmful materials out.
Control the movement of materials into and out of the cell.
Let the cell sense its environment.
G. Podgorski, Biol. 1010

4. Membrane Components Phospholipids Proteins (peripheral and integral)
The Plasma Membrane
4/23/2017
Membrane Components
Phospholipids
Proteins (peripheral and integral)
Cholesterol
Carbohydrates
G. Podgorski, Biol. 1010

5. Proteins Are Critical to Membrane Function
The Plasma Membrane
4/23/2017
Proteins Are Critical to Membrane Function
G. Podgorski, Biol. 1010

6. Transport Processes - Diffusion
The Plasma Membrane
4/23/2017
Transport Processes - Diffusion
Solutes move down a concentration gradient until they are evenly distributed. This is diffusion.
Another way of saying this is that solutes move from a region of higher concentration to a region of lower concentration until there is no difference in concentration.
G. Podgorski, Biol. 1010

7. Three Forms of Transport Across the Membrane
The Plasma Membrane
Three Forms of Transport Across the Membrane
4/23/2017
G. Podgorski, Biol. 1010

8. Three Forms of Transport Across the Membrane
The Plasma Membrane
Three Forms of Transport Across the Membrane
4/23/2017
Example: Oxygen or water diffusing into a cell and carbon dioxide diffusing out.
G. Podgorski, Biol. 1010

9. Three Forms of Transport Across the Membrane
The Plasma Membrane
Three Forms of Transport Across the Membrane
4/23/2017
Examples: Glucose or amino acids moving from blood into a cell.
An nerve electrical impulse results from opening protein channels for ions that move by facilitated diffusion.
G. Podgorski, Biol. 1010

10. Three Forms of Transport Across the Membrane
The Plasma Membrane
Three Forms of Transport Across the Membrane
4/23/2017
Examples: Pumping Na+ (sodium ions) out and K+ (potassium ions) in against strong concentration gradients.
G. Podgorski, Biol. 1010

11. The Plasma Membrane
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Moving the “Big Stuff”
Large molecules move in via one of three forms of endocytosis.
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12. Pinocytosis This is the most common form of endocytosis.
The Plasma Membrane
4/23/2017
Pinocytosis
This is the most common form of endocytosis.
Pinocytosis takes up most proteins and other large molecules.
G. Podgorski, Biol. 1010

13. Pinocytosis mature transport vesicle pinocytic vesicles forming
The Plasma Membrane
4/23/2017
Pinocytosis
mature transport vesicle
pinocytic vesicles forming
Transport into a capillary cell (blue).
G. Podgorski, Biol. 1010

14. Receptor-Mediated Endocytosis
The Plasma Membrane
4/23/2017
Receptor-Mediated Endocytosis
Receptor proteins make this a highly specific form of transport.
Cholesterol is taken-up this way.
G. Podgorski, Biol. 1010

15. Receptor-Mediated Endocytosis
The Plasma Membrane
4/23/2017
Receptor-Mediated Endocytosis
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16. The Plasma Membrane
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Cholesterol Delivered to Cells is Carried to Cells in a Low-Density Lipoprotein (LDL) Particle
The LDL particle is taken-up by receptor-mediated endocytosis.
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17. Endocytosis – Phagocytosis Transports Large Particles
The Plasma Membrane
4/23/2017
Endocytosis – Phagocytosis Transports Large Particles
G. Podgorski, Biol. 1010

18. In Preparation for Phagocytosis
The Plasma Membrane
4/23/2017
In Preparation for Phagocytosis
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19. The Plasma Membrane
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The Threshold of Phagocytosis - Capture of a Yeast Cell (yellow) by Membrane Extensions of an Immune System Cell (blue)
G. Podgorski, Biol. 1010

20. Moving the “Big Stuff” Exocytosis: moving things out.
The Plasma Membrane
4/23/2017
Moving the “Big Stuff”
Exocytosis: moving things out.
Molecules are moved out of the cell by vesicles that fuse with the plasma membrane.
This is how many hormones are secreted and how nerve cells communicate with one another.
G. Podgorski, Biol. 1010

21. The Plasma Membrane
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Exocytosis
Exocytic vesicle immediately after fusion with plasma membrane.
G. Podgorski, Biol. 1010

22. Exocytosis and Nervous System Function
The Plasma Membrane
4/23/2017
Exocytosis and Nervous System Function
A nerve cell communicates to another cell by releasing chemicals via exocytosis at the synaptic terminal.
G. Podgorski, Biol. 1010

23. Exocytosis and Chemical Communication at the Synapse
The Plasma Membrane
4/23/2017
Exocytosis and Chemical Communication at the Synapse
The synapse is the region where a nerve cell and its target cell are closely apposed.
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24. Black Widow Spider Venom and Exocytosis
The Plasma Membrane
4/23/2017
Black Widow Spider Venom and Exocytosis
Black widow spider venom causes massive exocytosis of neurotransmitter into the synapse.
G. Podgorski, Biol. 1010

25. Botulism and Exocytosis
The Plasma Membrane
4/23/2017
Botulism and Exocytosis
Botulism is caused by botulinim toxin – a protein produced by a bacterium that sometimes contaminates foods.
Botulinim toxin blocks exocytosis at the synapse and causes paralysis.
Mechanism of botulinum toxin.
Mechanism of botulinum toxin web site.
G. Podgorski, Biol. 1010