1. The Plasma Membrane also called the cell membrane -
1/18/2019
The Plasma Membrane also called the cell membrane -
Gateway to the Cell
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G. Podgorski, Biol. 1010

2. Photograph of a Cell Membrane
The Plasma Membrane
1/18/2019
Photograph of a Cell Membrane
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G. Podgorski, Biol. 1010

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The Plasma Membrane
1/18/2019
Cell Membrane
The cell membrane is flexible and allows a unicellular organism to move
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G. Podgorski, Biol. 1010

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The Plasma Membrane
1/18/2019
Homeostasis
Balanced internal condition of cells
Also called equilibrium
Maintained by plasma membrane controlling what enters & leaves the cell
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G. Podgorski, Biol. 1010

5. Functions of Plasma Membrane
The Plasma Membrane
1/18/2019
Functions of Plasma Membrane
Protective barrier
Regulate transport in & out of cell (selectively permeable)
Allow cell recognition
Provide anchoring sites for filaments of cytoskeleton
copyright cmassengale
G. Podgorski, Biol. 1010

6. Functions of Plasma Membrane
The Plasma Membrane
1/18/2019
Functions of Plasma Membrane
Provide a binding site for enzymes
Interlocking surfaces bind cells together (junctions)
Contains the cytoplasm (fluid in cell)
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G. Podgorski, Biol. 1010

7. Structure of the Cell Membrane
The Plasma Membrane
1/18/2019
Structure of the Cell Membrane
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G. Podgorski, Biol. 1010

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Membrane Components
The Plasma Membrane
1/18/2019
Phospholipids
Proteins (peripheral and integral)
Cholesterol
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Carbohydrates (glucose)
G. Podgorski, Biol. 1010

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The Plasma Membrane
1/18/2019
Phospholipids
Make up the cell membrane
Contains 2 fatty acid chains that are nonpolar
Head is polar & contains a –PO4 group & an alcohol (glycerol)
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G. Podgorski, Biol. 1010

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The Plasma Membrane
1/18/2019
FLUID MOSAIC MODEL
FLUID- because individual phospholipids and proteins can move side-to-side within the layer, like it’s a liquid.
MOSAIC- because of the pattern produced by the scattered protein molecules when the membrane is viewed from above.
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G. Podgorski, Biol. 1010

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The Plasma Membrane
Cell Membrane
1/18/2019
Polar heads are hydrophilic “water loving”
Nonpolar tails are hydrophobic “water fearing”
Makes membrane “Selective” in what crosses
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G. Podgorski, Biol. 1010

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The Plasma Membrane
1/18/2019
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G. Podgorski, Biol. 1010

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The Plasma Membrane
Cell Membrane
1/18/2019
The cell membrane is made of 2 layers of phospholipids called the lipid bilayer
Hydrophobic molecules pass easily; hydrophilic DO NOT
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G. Podgorski, Biol. 1010

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The Plasma Membrane
1/18/2019
Solubility
Materials that are soluble in lipids can pass through the cell membrane easily
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G. Podgorski, Biol. 1010

16. Semipermeable Membrane
The Plasma Membrane
Semipermeable Membrane
1/18/2019
Small molecules and larger hydrophobic molecules move through easily.
e.g. O2, CO2, H2O
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G. Podgorski, Biol. 1010

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The Plasma Membrane
Semipermeable Membrane
1/18/2019
Ions, hydrophilic molecules larger than water, and large molecules such as proteins do not move through the membrane on their own.
copyright cmassengale
G. Podgorski, Biol. 1010

18. The Fluidity of Membranes
Phospholipids in the plasma membrane Can move within the bilayer two ways
Lateral movement
(~107 times per second)
Flip-flop
(~ once per month)

19. The Fluidity of Membranes
The type of hydrocarbon tails in phospholipids Affects the fluidity of the plasma membrane
Fluid
Viscous
Unsaturated hydrocarbon
tails with kinks
Saturated hydro-
Carbon tails

20. The Fluidity of Membranes
The steroid cholesterol Has different effects on membrane fluidity at different temperatures
Figure 7.5
Cholesterol

21. Membrane Proteins and Their Functions
A membrane is a collage of different proteins embedded in the fluid matrix of the lipid bilayer
Fibers of
extracellular
matrix (ECM)

22. Types of Membrane Proteins
Integral proteins
Penetrate the hydrophobic core of the lipid bilayer
Are often transmembrane proteins, completely spanning the membrane
EXTRACELLULAR
SIDE

23. Transport Proteins Transport proteins
Allow passage of hydrophilic substances across the membrane

24. Types of Membrane Proteins
Peripheral proteins
Are appendages loosely bound to the surface of the membrane

25. The Role of Membrane Carbohydrates in Cell-Cell Recognition
Is a cell’s ability to distinguish one type of neighboring cell from another
Membrane carbohydrates
Interact with the surface molecules of other cells, facilitating cell-cell recognition