Cell Membrane The Door to the Cell

Structure of the Cell Membrane

1.PHOSPHOLIPID Head region is outward facing Tail region is inward facing Naturally forms 2 layers in water known as a phospholipid bilayer It is fluid! Permeable only to small molecules like H 2 O, O 2, and CO 2

2. CHOLESTEROL imbedded in the phospholipid bilayer to add strength and stability to the membrane 3. CYTOSKELETON fibers in the cytoplasm of the cell that help support and give strength to the phospholipid membrane

4. CHANNEL PROTEINS (blue) Create ‘doorways’ through the membrane for larger molecules like C 6 H 12 O 6 Each protein is a specific shape and only allows certain molecules into or out of the cell Semi-permeable

OTHER PROTEINS: 5. RECEPTORS – Pick up chemical messages from other cells. This triggers a reaction from the cell. (like antennae) 6. MARKERS (self-antigens) – identify cells (like dog-tags)

A real cell membrane The arrow is pointing to the cell membrane The dark black lines are the two layers of lipids Outside the cell Inside the cell

SOME SUBSTANCES, ARE SMALL ENOUGH TO MOVE THROUGH THE SPACES BETWEEN THE LIPIDS. NAME 4 EXAMPLES.

OTHER MATERIALS ARE TOO LARGE TO FIT THROUGH THE SPACES. NAME 3 EXAMPLES.

Movement of Molecules Molecules are in constant motion. They naturally move from high concentration to low concentration or you could say that molecules like to spread out. High concentration Here! Low concentration here

This type of movement is called PASSIVE TRANSPORT. It does NOT require any energy to move. Can you think of a time you move but do not require energy?

Concentration Gradient This refers to a gradual change in concentration from one area to another. When you hear this term think of the “hill” A concentration gradient is what causes passive transport to occur

3 TYPES OF PASSIVE TRANSPORT 1.Diffusion: the process by which molecules spread from areas of high concentration to areas of low concentration. 2.Facilitated Diffusion (to “facilitate” means to help) diffusion helped by channel proteins 3.Osmosis: movement of water through a membrane

When the molecules are even throughout a space - it is called EQUILIBRIUM DIFFUSION

Why is it hard for people to “sneak” a cigarette? The smoke molecules move from high concentration (the cigarette) to low concentration (out into the hallway)

What about perfume or cologne?

Water will move across membrane until the concentration of ‘free’ water molecules are equal

ISOTONIC SOLUTION Since the solute concentration is equal on the inside and the outside of the cell, the net movement of water is equal. Most cells exist in this type of environment

How diffusion and osmosis effect cells: HYPOTONIC/HYPERTONIC/ISOTONIC? Water will move into the cell until it reaches equilibrium If this happens long enough, an animal cell explodes. This is called cytolysis. (lysis means to break) What type of solution is this cell in?----

How diffusion and osmosis effect cells: Since there are more solutes on the outside of the cell water will move out of the cell until it reaches equilibrium What type of solution is this cell in?----HYPOTONIC/HYPERTONIC/ISOTONIC? What happened to the cell wall and the cell membrane?

More Practice What type of passive transport is this? Does it require energy?

More Practice Look at this one carefully. What type of passive transport is this? What side is hypotonic and which is hypertonic? Does it require energy?