Warm Up What is meant by concentration gradient? Which direction do materials diffuse across the gradient? What is passive transport? What are two examples of passive transport?

3.5 Active Transport, Endocytosis, and Exocytosis

Moving against the concentration gradient Cells need some materials that cannot passively diffuse across the membrane Proteins can help transport materials against the concentration gradient. These proteins are often called pumps

Active Transport Drives molecules across a membrane from a region of lower concentration to higher concentration (opposite of passive transport, different from facilitated diffusion) Uses transport proteins Requires energy Allows cells to get necessary materials regardless of concentration gradient

Transport Proteins Found in membrane Most change shape when they bind to a specific molecule What do we call a change in shape? Some bind to only one type of molecule, some bind two different kinds Those that bind two may move both types in the same direction or in opposite directions

Transport Proteins: key point Using energy to move molecules against the concentration gradient Most use energy from a molecule called ATP (adenosine triphosphate) In what ways are active transport proteins similar to enzymes?

Vesicles A cell can use energy to move a large substance or large amount of a substance in a vesicle Allows substances to enter/exit a cell without crossing through the membrane

Endocytosis Large molecules or liquids are engulfed by the membrane Something like a little capsule forms The capsule breaks off inside of the cell forming a vesicle Vesicle fuses with lysosome which breaks down the membrane capsule and allows contents to be released into cell

Phagocytosis Type of endocytosis Literally means “cell eating” Key role in immune system Macrophages are special white blood cells that perform an interesting form of phagocytosis Video: watch the macrophage engulf invaders

Exocytosis Opposite of endocytosis Release of substances from cell by way of a vesicle fusing with the membrane Example: every move you make! nerve impulses travel along nerve cells as an electrical signal This electrical signal must be converted into a chemical signal to jump the small gap between nerve cells These chemicals are stored in vesicles Video clip: endocytosis and exocytosis