Cells - Concept 2

4 Functions of the Cell Membrane

1. Containment and separation of cell interior - barrier

2. Material exchange - selectively permeable

3. Information detection and signal transduction (relay) - Membrane has (receptors)(proteins)(lipids)

4. Proteins pull or pinch Membrane for cells to move

What are proteins? NOTES

• Vital Macro nutrients made of building blocks called amino acids

• Make enzymes and hormones (Controls chemical reactions and body signals)

• Cell membrane proteins are vital molecules attached to or embedded within the lipid bi layer of a cell’s plasma membrane or organelle membrane

• Account for half of the cell membrane’s mass, and drive nearly all of the functions of the cell membrane

Fluid Mosaic Model NOTES

• Cell membrane is a dynamic fluid structure composed of a “mosaic” of phospholipids and proteins

• FLUID → Phospholipids and proteins can move laterally within the membrane

• MOSAIC → Various proteins embedded or attached to a double layer (bi layer) of phospholipids

Hydrophobic

Water FEARING (Hydro-Water, Phobia-Afraid of)

Hydrophilic

Water LOVING (Hyrdo-Water, Philic-Having a tendency for)

Amipathic

Contains both hydrophobic and hydrophilic regions (ex. Cell Membrane)

Phospholipid

A class of lipids that make up the cell membrane, an amipathic molecule

Phospholipid Bi Layer

• Hydrophilic Head

• Hydrophobic Tail

• Membrane proteins- These proteins are embedded in the phospholipid bi layer

Is the Cell Membrane Static?

• Membranes are NOT STATIC! They are constantly moving → It is fluid and moving

Cholesterol

• A bidirectional regulator of fluidity, steroid molecule. That prevents fatty acid tails from sticking to each other

• At high temp. → Restricts fluidity (Viscous = limited flow)

• At low temp. → It increases fluidity (Fluid = can flow)

What substances can freely pass through the lipid bi layer?

• Small uncharged polar molecules (urea)

• Small no polar molecules, such as N2, O2, and CO2 across the membrane

NOTE

• Most molecules cannot easily pass through the hydrophobic lipid tails

Channel Proteins

Help molecules pass through the cell membrane without interacting with the fatty acid chains