Module 7 — Lesson 2: Lipids & the Plasma Membrane
1. Lipids
* Lipids are large molecules composed of glycerol and three fatty acids.
* If a phosphate group replaces one fatty acid, a phospholipid forms.
* A phospholipid consists of:
* 1 glycerol backbone
* 2 fatty acid chains
* 1 phosphate-containing group
Phospholipid Properties
Head:
* Polar
* Hydrophilic → attracted to water
* Lipophobic → repelled by lipids
Tails:
* Nonpolar
* Hydrophobic → repel water
* Lipophilic → attracted to lipids
2. Plasma Membrane
* The plasma membrane is a thin, flexible boundary between the cell and its environment.
* It allows nutrients into the cell and waste out of the cell.
* It is made of a phospholipid bilayer.
* A phospholipid bilayer consists of two layers of phospholipids arranged tail-to-tail.
Selective Permeability
* Selective permeability allows some substances to enter the cell while keeping others out.
3. Plasma Membrane Proteins
Receptors
* Receive and transmit signals to the cell.
Anchors
* Attach organelles to the plasma membrane.
* Help give the cell its shape.
Transport Proteins
* Create tunnels/channels that allow substances to move across the membrane.
* Help substances enter the cell and waste leave the cell.
4. Homeostasis
* Homeostasis is the process of maintaining balance in an organism’s internal environment.
* It is essential for cell survival.
* The plasma membrane plays an important role in maintaining homeostasis by controlling what enters and leaves the cell.
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