Cell Biology Study Guide

The plasma membrane serves as a barrier, composed primarily of phospholipids that form a bilayer.
Key components of the plasma membrane structure include:
- Hydrophilic heads: Polar regions that interact with water.
- Hydrophobic tails: Non-Polar regions that avoid water, forming the interior of the bilayer.
- Cholesterol: Embedded within the bilayer to maintain fluidity.
- Proteins: Integral and peripheral proteins serve various functions.

Fluid Mosaic Model:
- Describes the structure of the plasma membrane as a fluid phospholipid bilayer with proteins embedded within it that can move laterally like boats on a sea of lipids.
Factors influencing fluidity include:
- Temperature: Higher temperatures increase fluidity.
- Fatty Acid Structure:
- Longer tails result in more viscous membranes.
- More unsaturation (double bonds) leads to increased fluidity due to kinking in the tails.
- Cholesterol: Acts as a fluidity buffer:
- At high temperatures: reduces fluidity by restraining lipid movement.
- At low temperatures: increases membrane fluidity by preventing fatty acids from packing too closely.

Types of Membrane Proteins:
- Integral Membrane Proteins:
- Span the entire bilayer and include transmembrane proteins, which have hydrophobic domains.
- Peripheral Proteins:
- Attach to the surface and form noncovalent interactions with lipids and other membrane proteins.
Functions of Membrane Proteins:
- A. Transporters:
- Facilitate movement of molecules across the membrane.
- B. Enzymatic Activity:
- Catalyze reactions at the membrane level.
- C. Signal Transduction:
- Receive and transmit signals from outside the cell.
- D. Cell Surface Attachment/Recognition:
- Enable cells to adhere to one another or to extracellular matrices.