A. Active Transport a. Active transport is the transport of a substance across the cell membrane against its concentration gradient (from low to high concentration). b. Active transport requires energy in the form of ATP.

1. Carrier Proteins act as “pumps” a. Bind to a specific substance on one side of cell membrane b. Moves the substance against the concentration gradient c. From low to high concentration

2. Sodium Potassium Pump a. A form of active transport b. Carrier protein transports 3 Na + out of the cell and 2 K + into the cell

c. Both are being moved against the concentration gradient i. Na + is usually more concentrated outside the cell ii. K + is usually more concentrated inside the cell d. Sodium Potassium pump uses ATP as energy source, can use up most of a cell’s ATP

Phosphorylate: attachment of phosphate

removal of phosophate

3. Purpose of the Sodium- Potassium Pump a. The pump prevents sodium from accumulating in the cell thereby preventing excess osmosis into the cell, which could potentially cause the cell to burst. b. The pump maintains the concentration gradients of Na + and K + across the cell membrane, which many cells use to help in the transport of other substances, such as glucose across the cell membrane

B. Bulk Transport a. Movement of large molecules into and out of the cell. b. Molecules that are too large for carrier proteins (e.g. proteins, polysaccharides) c. Transported by vesicles

1. Endocytosis -movement of substance into the cell by vesicle (Endo = in) a. fuse with a lysosome or other organelles b. Two main types of endocytosis: pinocytosis and phagocytosis.

i. Pinocytosis a. Movement of liquid and solutes into the cell b. “cell drinking” c. Example: maturing human egg cells use pinocytosis to take in dissolved nutrients

ii. Phagocytosis a. Movement of food particles into the cell b. “cell eating” c. Example: Amoeba eating or white blood cells engulfing bacteria

2. Exocytosis -movement of substance out of the cell by vesicle (Exo = out) a. vesicle fuses with the cell membrane, releasing contents outside the cell b. cells use exocytosis to export modified contents from Golgi (e.g. proteins)

C. Receptor Proteins a. Binds to a specific signal molecule, allowing the cell to respond Example- Signal molecules tell muscles when to contract and relax b. Binding of a signal molecule to its matching receptor protein causes a change in the activity of the receiving cell.

c. 3 common changes that may occur: 1. changes in permeability a. When paired with an ion channel, signal causes channel to open, allowing ions to cross

2. triggers a second messenger a. Second messenger sends another message to somewhere else in the cell

3. enzyme action a. Binding of signal may speed up chemical reactions in the cell