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 Transport Active 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.