1. The Plasma Membrane – Gateway to the Cell
8/29/2018
The Plasma Membrane – Gateway to the Cell
G. Podgorski, Biol. 1010

2. The Plasma Membrane is Semipermeable
8/29/2018
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
8/29/2018
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
8/29/2018
Membrane Components
Phospholipids
Proteins (peripheral and integral)
Cholesterol
Carbohydrates
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5. Proteins Are Critical to Membrane Function
The Plasma Membrane
8/29/2018
Proteins Are Critical to Membrane Function
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11. Transport Processes - Diffusion
The Plasma Membrane
8/29/2018
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

12. Three Forms of Transport Across the Membrane
The Plasma Membrane
Three Forms of Transport Across the Membrane
8/29/2018
G. Podgorski, Biol. 1010

13. Three Forms of Transport Across the Membrane
The Plasma Membrane
Three Forms of Transport Across the Membrane
8/29/2018
Example: Oxygen or water diffusing into a cell and carbon dioxide diffusing out.
G. Podgorski, Biol. 1010

14. Three Forms of Transport Across the Membrane
The Plasma Membrane
Three Forms of Transport Across the Membrane
8/29/2018
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

15. Three Forms of Transport Across the Membrane
The Plasma Membrane
Three Forms of Transport Across the Membrane
8/29/2018
Examples: Pumping Na+ (sodium ions) out and K+ (potassium ions) in against strong concentration gradients.
G. Podgorski, Biol. 1010

17. 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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18. Pinocytosis This is the most common form of endocytosis.
The Plasma Membrane
8/29/2018
Pinocytosis
This is the most common form of endocytosis.
Pinocytosis takes up most proteins and other large molecules.
G. Podgorski, Biol. 1010

19. Pinocytosis mature transport vesicle pinocytic vesicles forming
The Plasma Membrane
8/29/2018
Pinocytosis
mature transport vesicle
pinocytic vesicles forming
Transport into a capillary cell (blue).
G. Podgorski, Biol. 1010

20. Receptor-Mediated Endocytosis
The Plasma Membrane
8/29/2018
Receptor-Mediated Endocytosis
Receptor proteins make this a highly specific form of transport.
Cholesterol is taken-up this way.
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21. Receptor-Mediated Endocytosis
The Plasma Membrane
8/29/2018
Receptor-Mediated Endocytosis
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22. Endocytosis – Phagocytosis Transports Large Particles
The Plasma Membrane
8/29/2018
Endocytosis – Phagocytosis Transports Large Particles
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23. In Preparation for Phagocytosis
The Plasma Membrane
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In Preparation for Phagocytosis
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24. 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)
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25. Moving the “Big Stuff” Exocytosis: moving things out.
The Plasma Membrane
8/29/2018
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.
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26. The Plasma Membrane
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Exocytosis
Exocytic vesicle immediately after fusion with plasma membrane.
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27. Exocytosis and Nervous System Function
The Plasma Membrane
8/29/2018
Exocytosis and Nervous System Function
A nerve cell communicates to another cell by releasing chemicals via exocytosis at the synaptic terminal.
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28. Exocytosis and Chemical Communication at the Synapse
The Plasma Membrane
8/29/2018
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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29. Black Widow Spider Venom and Exocytosis
The Plasma Membrane
8/29/2018
Black Widow Spider Venom and Exocytosis
Black widow spider venom causes massive exocytosis of neurotransmitter into the synapse.
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30. Botulism and Exocytosis
The Plasma Membrane
8/29/2018
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.
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32. ENZYMES
Definition: A protein that speeds up chemical reactions WITHOUT being changed. (catalyst)

33. Enzymes Speed Biochemical Reactions
Energy and Enzymes
8/29/2018
Enzymes Speed Biochemical Reactions
Enzymes are biological catalysts – substances that speed a reaction without being altered in the reaction.
Most enzymes are proteins, some are RNA.
Model of the surface of an enzyme.
Enzymes are essential for life.
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34. Enzymes Lower a Reaction’s Activation Energy
Energy and Enzymes
8/29/2018
Enzymes Lower a Reaction’s Activation Energy
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35. Energy and Enzymes
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Enzyme Action
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36. The Fit Between Enzyme and Substrate is Critical and Precise
Energy and Enzymes
The Fit Between Enzyme and Substrate is Critical and Precise
8/29/2018
Hexokinase, an enzyme (blue), binding its substrate, glucose (yellow).
G. Podgorski, Biol. 1010

38. Substrate: Substance acted upon by the enzyme.
ENZYMES
Substrate: Substance acted upon by the enzyme.

40. Products: substances resulting from enzyme action.
ENZYMES
Products: substances resulting from enzyme action.

41. Substrate(s)
+ Enzymes
Product(s)

42. Enzymes
Lock and Key – Enzymes are like a key that can ONLY fit a certain lock or substrate.

43. Enzymes
Active site – site on an enzyme molecule directly responsible for the chemical change.

44. Many Enzymes Work by Altering the Shape of Their Substrates
Energy and Enzymes
8/29/2018
Many Enzymes Work by Altering the Shape of Their Substrates
The active site of an enzyme is where substrate is bound.
G. Podgorski, Biol. 1010

45. The “Nature of Life” – Coupling Favorable to Unfavorable Reactions
Energy and Enzymes
8/29/2018
The “Nature of Life” – Coupling Favorable to Unfavorable Reactions
G. Podgorski, Biol. 1010

46. ATP - Life’s Energy Currency
Energy and Enzymes
8/29/2018
ATP - Life’s Energy Currency
Energy is released when ATP is hydrolyzed (broken down) to ADP.
ATP is restored from ADP and an input of energy.
ATP’s energy is used to drive endergonic (energy-requiring) reactions.
G. Podgorski, Biol. 1010