Cell Membranes

• Separates the Inside of the cell from the outside of the cell

Permeability

Permeable Membrane—a membrane which allows particles to travel freely through the membrane (they can go back and forth)

Impermeable Membrane—a membrane which DOES NOT allow particles to travel freely through the membrane (they are stuck on one side or the other)

Selective Permeability

• Characteristic of cell membranes

• Ability to regulate the passage of molecules

• Allows some molecules to pass through the membrane, but not others

The Cell Membrane

• Known as the “Lipid Bilayer”

• Composed of fat (lipid) molecules

• Lipid molecules drift randomly in the planeof the membrane(they aren’t attached)

The Lipid BilayerExterior Layer

• Part of the fat molecules that LIKE water are located on the outside (the round heads)

• They are calledPolar Molecules

The Lipid BilayerInternal Layer

• Part of the fat molecules that DON’T LIKE water are located on the inside

• They are called Non-Polar Molecules

• Prevents Water-Soluble (things that dissolve in water) molecules from passing through the membrane

• Fat-Soluble moleculespass through easily!

One Exception!

• Water molecules CAN pass through the membrane

• Very SMALL molecules

• VERY SLIGHT electrical charge

Proteins

• Large molecules made up of amino acids that are linked together to form a long, folded chain

• These are the bigmasses that stick outof the membrane

• Act as Receptors

Receptors

• Bind specifically to molecules, such as hormones, that act as chemical messengers

• Receptors receive a message

Hormones attach to receptors

Triggers the cell to respond to some body condition

Protein Function Cont.

• Allow specific molecules to move in and out of the cell

• Allow the membrane to be Selectively Permeable (It can choose what it wants to go in and out)

Protein Function #2

• Form Specific Protein Channels

– Gives Large Molecules a way to pass through the lipid bilayer

– Ex. Glucose and Sugar

– Ion Channels• Ions molecules with an

electric charge

• Need a channel b/c fat cells repel their charge

Parts of the Lipid Bilayer

You don’t have to sketch this, but make sure that you are familiar with it!