October 2014

Phospholipid bilayer Hydrophobic (non-polar) & Hydrophilic (polar)

components Transmembrane proteins

3 types: Recognition, Receptor, Transport Cholesterol

Stabilizes membrane

Materials within a cell need to be able to move through the cell in order to complete the functions of life (homeostasis).

There are several ways that cells transport materials.

Two categories:Passive TransportActive Transport

Does not require energy Molecules move from HIGH to LOW

concentrations Three types:

Diffusion Osmosis Facilitated diffusion

Diffusion Molecules moving from an area of

higher concentration to an area of lower concentration

Concentration gradient Difference in concentrations across the

distance the material moves Equilibrium

Endpoint of diffusion Concentration of solution is the same

throughout

Diffusion can occur across a membrane if the molecules can pass through it.

Plasma (cell) membranes are semi-permeable, which means that certain materials can pass into and out of the cells and organelles.

Osmosis Diffusion of water across a membrane

from an area of high concentration of water to an area of low concentration of water.

This is important because water is the most common solvent in organisms (“universal solvent”)

Solvent: a substance that dissolves another. Solute: the substance that is being dissolved

in the solvent. Concentration: the amount of solute

compared to the amount of solvent.EXAMPLE: In 5% salt water, salt is the solute and

water is the solvent. The concentration is 5g of salt and 95 g of water.

Hypotonic: the concentration of solute is lower than that in

the cytoplasm of cells. Hypertonic:

the concentration of solute is higher than that in the cytoplasm of cells.

Isotonic: the concentration of solute is the same as that of

the cytoplasm of cells.

Water flows into cell

Result: Cell lyses (blows up)

Water flows into and out of cell

Result: Equilibrium

Water flows out of cell

Result: Cell shrivels

Turgor Pressure The pressure that the water in a cell exerts

on the cell membrane ▪ Occurs in a hypotonic solution (water flows into

the cell) Plasmolysis

When a cell looses turgor pressure due to the loss of water ▪ Occurs in a hypertonic solution (water flows out

of the cell)

Some molecules are too large to diffuse across a plasma membrane.

This means that even if the concentration gradient is in their favor they could not get in or out.

Carrier proteins: proteins in the cell membrane that can open and close to let these larger molecules pass.

This is called facilitated diffusion.

Active transport is when a cell exerts energy to transport materials.

At times a cell must move material from an area of low concentration to an area of high concentration.

This means that the cell must work against the natural concentration gradient.

Cell membranes have carrier proteins that act as doors to let materials in and out of a cell.

Cells need different concentrations of ions like potassium (needed inside) and sodium (needed outside) in order to function.

Ion pumps use energy produced by the creation of ATP to force sodium out of the cell while taking in potassium against the gradient (Sodium-Potassium Pump).

**This is like the battery in your cell phone

Ions bind to the carrier protein ATP (energy molecule) is altered Energy is produced to alter the shape of

the carrier protein The new shape of the protein can

transport ions from LOW concentrations to HIGH concentrations

Once ions are transported, the carrier proteins are restored to their original shape.

Some molecules are so big that they cannot even pass through the cell membrane through carrier proteins.

Some of the molecules, like proteins, carbohydrates and even other whole cells are needed for survival.

Cells can use their own membrane to create vacuoles (vesicles), or sacs, that can then be brought into the cell.

Endocytosis is the process of taking in food through in-folds, or pockets in the cell membrane.

Exocytosis is the opposite process of endocytosis in which the vacuole fuses with the membrane to release its contents to the surrounding environment.