Homework

• Get lab safety contract signed• Read Chapter 7: Membrane Structure and

Function

Cell Membrane

Ms. KlinkhachornNovember 15, 2010

AP Biology

Cell Membranes

• Also called the plasma membrane• All cells have cell membranes – can be

compared to the skin on our bodies• Thin film – need to stack 8,000 to equal the

thickness of a page

Plasma Membrane

• It is selectively permeable– Some materials go through the membrane a lot

easier than others– Some materials can’t go through at all

• What kind of materials need to be able to go in to the cell? Go out of the cell?

Other Membranes

• Membranes can also surround organelles– These organelles are membrane-bound – Create compartments within the cell itself that

have different environments

• What type of cell has membrane-bound organelles?

• What are some examples of membrane bound organelles?

Cell Membrane – What’s what?

Membrane Composition

• Membrane composition depends on the type of cell and the kind of organelle

• Membranes are made up of the following:– Phospholipids– Proteins– Carbohydrates/glycoproteins– Cholesterol

What’s in a membrane?

How do these parts behave?

• Fluid-Mosaic Model – states that components of the membrane are able to move two dimensionally without restraint– Membranes are fluid/dynamic.

• Mosaic = collage– membranes are composed of a variety of

components

How can we remember this?

• “Sea” of phospholipids – move about freely, just like water

• Proteins are like boats or icebergs – half in the water, half out

Root Words!

• What do the following root words mean? What are examples of each?– “Hydro”, “Hydr”– “Phobic”, “Phobia”, “Phobe”– “Phile”, “Philic”, “Philia”

DNA – November 16, 2010

1. Why are cell membranes said to be fluid and mosaic?

2. Cell membranes are selectively permeable. Describe what this means, and explain what would happen to your cells if they weren’t permeable.

Who does this look like?

Phospholipids

• Type of lipid– 2 fatty acids (lipids)

make up the tail– Phosphate group makes

up the head

• Use the roots to figure out the characteristics:– Hydrophobic, nonpolar

tails– Hydrophilic, polar heads

Phospholipid Bilayer

• The cell membrane is organized into two layers of phospholipids called the phospholipid bilayer

• It’s like a sandwich

Phospholipid Structure

Head

Tails

Cell Membrane Components

Cholesterol

• Found imbedded in the lipid bilayer between phospholipids

• Also has a hydrophobic and hydrophilic end

Not all cholesterol is bad

• Helps stabilize the membrane

• Prevents the membrane from being TOO flexible

• Also prevents the membrane from being TOO stiff

Cell Membrane Components

Carbohydrates/Glycoproteins

• Carbohydrates are made up of sugar molecules– Good energy supply

• Glycoproteins are when these carbs are attached to the proteins– not actually inside the bilayer

Carbohydrate Function

• Help with cell-cell recognition– Cell’s ability to distinguish neighboring cells– Helps cells figure out how to sort into tissues and

organs– Cell recognize each other based on the

carbohydrates on the surface of the cell membrane

Types of Glycoproteins/Glycolipids

• Glyco = Sugar• Glycoproteins: carbs

bonded to proteins• Glycolipids: carbs bonded

to lipids

Examples

Blood Types: A, B, AB, and O Immune System Rejection

Cell Membrane Components

Proteins

• Proteins control the day-to-day functions of an organism

• Functions of membrane proteins:– Transport materials in and out of the cell– Messenger systems/Cell Signaling– Enzyme activity for chemical reactions– Cell Recognition

Proteins

• Two Main Kinds of Protein– Integral Proteins• Penetrate the hydrophobic

core• Can be transmembrane

– Peripheral Proteins• Not imbedded in the

membrane• Sit on the outside