The Cell Membrane

Functions of the cell membrane

-Selectively isolates the cell from the external environment

-Regulate the exchange of essential substances between the cell and the extracellular fluid

-Communication between cells

-Create attachments within and between cells

-Regulate biochemical reactions

Cell membranes are a phospholipid bilayer

A phospholipid has a hydrophilic (Water liking) Head and a hydrophobic (Water hating) Tail

-These two features of a phospholipid are extremely important. they are the reason that cells can exist.

-The cell membrane is like a drop of oil floating in water. It is not very strong and can easily tear open.

-The chemical properties of lipids is what allows some things in and others not...also known as selectively permeable

Class discussion - What is a fluid mosaic model?

Membrane proteins

-The phospholipid bilayer is not the only thing that makes up the cell membrane.

-There are also membrane proteins embedded in the bilayer

-Attachment Proteins

Attachment proteins attach the cell to other cells. It is what holds them in place. You would not want your heart cells floating off.

-Recognition Proteins

A recognition protein is like a name tag. Most cells have a name tag. Heart cells say hello my name is heart. Skin cells say hello my name is skin. Your blood type is a recognition protein.

-Receptor Proteins

A receptor protein receives signals and messages. This is where hormones will bind and other messages sent throughout the body.

-Transport Proteins

Transport proteins transport things in and out of the cell. Since many things cannot cross the phospholipid bilayer, the transport proteins bring in and remove what the cell needs.

Diffusion

-Diffusion is the movement from an area of high concentration to an area of low concentration

-In order to understand diffusion we need to remember that atoms are always moving. Hot atoms move fast. Because atoms are always moving they tend to bounce off each other. Once they collide and bounce off each other they then head in the opposite direction. All of this bouncing off of each other causes atoms to spread out. This is diffusion.

SO WHAT! Who cares about diffusion?

Diffusion is the reason everything in biology works. At the heart of almost all biological processes is diffusion.

-Passive Transport (Does not require energy)

-Simple Diffusion

-Facilitated Diffusion (Diffusion that needs a little help)

-Osmosis (Diffusion of water)

Demonstration:

-The teacher sprays body spray in the front of the classroom and then continues to lecture. As the students become able to smell it they raise their hands. This continues until the body spray can be smelled from the back of the room.

-How did the spray make it to the back of the room?

Real World Application:

-When you wear cologne or perfume do you spray it on your clothes or on your skin? Why do you do that? Do you have a reason for doing one or the other?

-Heat speeds up the rate of diffusion because the hotter a molecule is the more energy it has. The molecules can travel faster when they are heated up.

-If you spray perfume on your skin, your skin heats the perfume causing it to diffuse faster which means it can reach further distances faster. If you are in a room and perfume is on your skin then everyone in the room can smell you. The draw back is that the perfume does not last as long because the rate of diffusion is happening so fast.

-If you spray perfume on your clothes the perfume will stay with you much longer but only people right next to you can smell you.