The cell membrane is composed of a fluid-mosaic structure containing phospholipids, cholesterol, and proteins. Phospholipids form a bilayer with hydrophobic tails facing inward and hydrophilic heads facing outward. Cholesterol maintains membrane fluidity at different temperatures. Membrane proteins perform important functions like recognition, signaling, and selectively transporting substances into and out of the cell based on size and polarity.

1. Cell Membrane
Structure and Function

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Membrane Design
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 fluid-mosaic model
a. Fluid = pliable/easily moved
b. Mosaic = made of many different
molecules (lipids, proteins, carbohydrates)
Cell Membrane Animation

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Predict the two reasons things can’t directly go through
the membrane:
Selectively Permeable
1) Size (duh)
2) Polarity (from last unit)

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The cell membrane only lets certain substances in and
out of the cell
Selectively Permeable

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Phosopholipid Bi-Layer
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-polar heads are hydrophilic “water loving”
-tails (fatty acids) are hydrophobic “water fearing” and face inward

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Cholesterol
 Type of steroid (lipid)
 Changes fluidity of cell membrane
 Higher temps – stiffens membrane
 Lower temps – prevents membrane from freezing

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Proteins
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 Recognition Proteins
 Proteins that have carbohydrate
chains attached
 Carbohydrate chains aid in cell
identification
 “Name Tags”
 Example: Red Blood Cells (A, B),
Identify Viruses as foreign
 Receptor Proteins
 Proteins that receive chemical
signals from other cells
 Such as nervous system cells

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 Channel Proteins
 Proteins that involved in letting certain substances in and out
of cells
 Aquaporins- let water in and out of cells
Proteins

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 Integral
 Proteins that cross both layers of the phosphoplipid
bilayer
 Peripheral
 proteins that are only on the top half or bottom half
of the phospholipid bilayer
Proteins