The Plasma Membrane and The Plasma Membrane and HomeostasisHomeostasis

Homeostasis – Maintaining a Homeostasis – Maintaining a BalanceBalance

Cells must keep the proper Cells must keep the proper concentration of nutrients and concentration of nutrients and water and eliminate wastes.water and eliminate wastes.

Cells die without homeostasis.Cells die without homeostasis. The plasma membrane is The plasma membrane is

selectively permeable – it will selectively permeable – it will allow some things to pass allow some things to pass through, while blockingthrough, while blocking other other things.things.

phospholipid bilayer

PLASMA MEMBRANEPLASMA MEMBRANE

Two layers of phospholipids embedded Two layers of phospholipids embedded with proteinswith proteins

Selectively permeableSelectively permeable Fluid mosaic model – made of similar Fluid mosaic model – made of similar

molecules free to move sidewaysmolecules free to move sideways Surround organelles and cellsSurround organelles and cells Permeability of membranes differ Permeability of membranes differ

because each has their own unique because each has their own unique proteins and fatty acidsproteins and fatty acids

Cholesterol increases the stability of the Cholesterol increases the stability of the membranemembrane

What’s a Phospholipid?What’s a Phospholipid? It’s a pair of fatty acid chains and a It’s a pair of fatty acid chains and a

phosphate group attached to a glycerol phosphate group attached to a glycerol backbone.backbone.• Polar (water-soluble, hydrophilic) Polar (water-soluble, hydrophilic)

phosphate heads face out phosphate heads face out • Nonpolar (hydrophobic) fatty acids Nonpolar (hydrophobic) fatty acids

hang inside hang inside

Membrane ProteinsMembrane Proteins

1. Determine what particles can 1. Determine what particles can pass through the membrane.pass through the membrane.

2. Serve as enzymes (may speed 2. Serve as enzymes (may speed reactions).reactions).

3. Act as markers that are 3. Act as markers that are recognized by chemicals and recognized by chemicals and molecules from the inside and the molecules from the inside and the outside of the cell (the immune outside of the cell (the immune system).system).

MEMBRANES OF A CARIBOUMEMBRANES OF A CARIBOU

In caribou, an arctic animal, membranes of cells near the animal’s hooves have phospholipids with many unsaturated fatty acids. Unsaturated fatty acids remainliquid at low temperatures. The unsaturated lipids allow the caribou's feet and legs to drop to almost 00C in the arctic winters andstill maintain plasma membrane function.The cell membranes of the rest of the caribou's body have more saturated lipids.

AURIVOIR