The document discusses the structure and function of cell membranes, emphasizing the fluid-mosaic model which describes membranes as flexible and composed of various molecules. It highlights the selectively permeable nature of membranes, dictated by factors like size and polarity, and explains the roles of phospholipids, cholesterol, and different types of proteins in membrane function. Additionally, it describes how proteins contribute to cell identification and signal reception.

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