The Cell Membrane

The Cell Membra

ne

I.) What is the cell membrane?

A. AKA: Plasma membraneB. The boundary between the cell and

the environmentC. Does every cell have a cell

membrane?1. Yes, Each and every cell has a cell

membrane.

Cell membranes help maintain homeostasis, what is that?

Cells b

reathing

Cells g

etting b

lood t..

.

Cells m

aintai

ning in...

Cells r

epro

ducing

0% 0%

100%

0%

1. Cells breathing2. Cells getting

blood to them3. Cells

maintaining internal conditions

4. Cells reproducing

II.) How do cell membranes help to maintain

homeostasis?A. The cell membrane allows

nutrients to come into the cell1. Examples: sugar, proteins,

fats

B. Selective Permeability: the cell membrane lets some molecules in and keeps others out

C. The cell membrane removes waste

III.) Structure of the Cell Membrane

What does the cell membrane look like up close?

Lets look at one of these

structures up close

III.) Structure of Cell Membrane

A.Phospholipids1. Phosphate head

a. Polarb. Hydrophilicc. Make up the outer borders

of the membrane2. Glycerol

3. 2 Fatty acid tails (lipids=fats, oils, etc)

a. Nonpolarb. Hydrophobicc. Make up the

inner part of the membrane

Structure of Phospholipid

4. Why are the phospholipids arranged tail to tail? a. Water is inside and outside the

cell b. Phosphate group is hydrophilic

(polar) end1. Attracts water

c. Fatty acid tail end is hydrophobic (nonpolar)

1. Repels water

III.) Structure of Cell Membrane (cont.)

B. Phospholipid Bilayer1. 2 layers of phospholipids make up

a cell membrane2. Remember polar heads and

nonpolar tails!

3. Arrangement of phospholipids “tail to tail” due to water inside & outside the cell

Let’s Begin to Build Our Membrane!

1. Take 1 bag with materials for you & your partner

2. You are going to build your phospholipids firsta. Marshmallows represent your

phosphate headb. Toothpicks represent your fatty acid

tails1. Break these in half. Please

include unsaturated fatty acid tails.

c. Make sure to line up the phospholipid bilayer correctly! Think polar & nonpolar!

When something is hydrophilic, it…

Has a

chem

ical m

ake..

Has a

chem

ical m

ake..

6%

94%1. Has a chemical makeup that likes to be around water

2. Has a chemical makeup that does not like to be around water

Where would you expect to find water in this cell

membrane?

Here Here

6%

94%1. Here2. Here

Structure of Cell Membrane (cont.)

C.Cholesterol1. Helps to

stabilize the phospholipids and keep them from sticking together

Building Time!1. Now let’s add your cholesterol

into the membrane2. Use the gummy bears that are in

your bags to represent the cholesterol

a. Be sure to place them correctlyb. Check with your teacher once your

group has completed this3. We will stop here for today. Please

put your group’s name on the bag and put your phospholipids and cholesterols back in bag

Bell Work1. Please put the parts of the cell

membrane that we built yesterday back together

a. Phospholipid bilayerb. Cholesterols

Structure of the Cell Membrane (cont.)

D. Proteins: Regulate which molecules enter and which molecules leave a cell.

1. Types of proteins in the cell membrane

a. Carrier Protein1. Allow needed substances or

waste materials to move through the cell membrane

2. Molds around the molecule to bring molecule into the cell

Let’s Build It! Take your Pretzel Twist out of the

bag. This will represent the carrier

protein. Keeping in mind what we just talked

about in class, think of a way you can turn this into what a carrier protein is.

Types of proteins (cont.)

b. Channel protein1. Hydrophilic

channel--allows hydrophilic substances to pass in and out of cell through hydrophobic tails of phospholipids

2. Allows molecules to easily flow into and out of cell

Let’s Build It!1. Take the Twizzler out of your

bag.2. This represents the channel

protein. 3. You will need to split this in half

in order to represent both sides of the channel.

Types of proteins (cont.)d. Receptor Protein

1. These have binding sites for molecules such as hormones or substrates to bind to

Let’s Build It! Take your 2 hard

fruit candies out of the bag.

This will represent your receptor protein.

Leave the wrapper on! This will provide the unique shape that will serve as the receptor site.

Arrangement of cell surface proteins

Structure of Cell Membrane (cont.)

E. Nonpolar interior zone- true barrier that separates the cell from its surroundings

1. Many polar particles like sugars, proteins, ions, & most cell wastes cannot cross this zone because they are repelled by the nonpolar region

IV.) Fluid Mosaic Model of Cell Membrane

A. Lipid bilayer is not strong & firm like a hard shell, but it is fluid like a soap bubble

1. Often called a fluid mosaic model

B. Individual phospholipids, arranged side by side, float within the bilayer

1. Cholesterol prevents phospholipids from sticking together

Cell Membrane Structure Overview