Intro to Cell Membrane

Function of the Cell Membrane What does it do? Cells maintain homeostasis by keeping a balance of macromolecules, water, gases, etc. The cell membrane regulates (controls) what enters and leaves the cell. It is like the security guard of the cell!

Function of the Cell Membrane What does it do? To regulate, the cell membrane is selectively permeable: allows some things to pass through, while blocking other things. Welcome to our cell! Get Out!

Structure of Cell/Plasma Membrane What does it look like? The cell membrane is made of many different macromolecules. The main macromolecule found in the cell membrane are special types of lipid called phospholipids. Can you use the picture above to fill out your chart?

Structure of Cell/Plasma Membrane What does it look like? NOTE: This is called a lipid bilayer, or a fluid mosaic model.

So… What’s a Phospholipid Anyway?

So… What’s a Phospholipid Anyway? Phospholipid: A special lipid with 2 fatty acids attached to glycerol plus a phosphate group. Glycerol P

So… What’s a Phospholipid Anyway?

So… What’s a Phospholipid Anyway? Phospholipids have 2 parts: 1. Glycerol & Phosphate (HEAD) HYDROPHILIC which means: LOVES water 2. Fatty Acid (TAIL) HYDROPHOBIC which means: FEAR of water P Animation with table doesn’t work very well

Hydrophilia & Hydrophobia IN ACTION!! What can molecules do when they are both hydrophilic and hydrophobic? Water Mixtures Soap Mixtures What does it mean when a molecule “LOOOVES” another molecule? What about when they FEAR each other? Aarrggh!

Part I. Water Mixtures Water + Alcohol Fill in your charts. Water + Oil Put ONE drop of blue food coloring into about 100 mL of water. Put ONE drop of red food coloring into about 50 mL of alcohol. Mix 50mL blue water + 50mL red alcohol (should turn purple mixes b/c hydrophilic) Mix 50mL blue water + 50mL vegetable oil (doesn’t mix hydrophobic)– Just like GANGS! They want to stay with their own kind…

But what is it like to be BOTH hydrophilic and hydrophobic at the same time???

Part II. Soap Mixtures If oil and water don’t mix, how do you wash grease off your hands? BACKGROUND INFORMATION: Soap also has a hydrophilic head and one hydrophobic tails. I don’t like my tail! I want to be with more heads! We just saw something that was hydrophobic, and we also saw something that was hydrophilic. Now we are going to see what it’s like to be BOTH hydrophilic and hydrophobic at the same time. I am going to give you some info and YOU have to figure out what is going on! I don’t like my head! I want to be with more tails!

H2O H2O oil H2O This picture did not explain the activity that well. Students still have no clue what is happening in the activity. H2O H2O

H2O H2O oil H2O H2O H2O

Quick Check-In A B C

Structure of Cell/Plasma Membrane What does it look like? The glycerol likes water (hydrophilic). (Draw & Label this pic!) Outside cell (~80% water) Inside Cell Cytoplasm (~80% water)

Why is it two layers? The fatty acid chains hate water (hydrophobic). Outside cell (~80% water) Inside Cell - Cytoplasm (~80% water) The fatty acid chains hate water (hydrophobic). Like Oil!