Homeostasis and Transport

Moving Cellular Materials Passive Transport- The movement of substances through the cell membrane without the use of energy.

Types of passive transport Diffusion Osmosis Facilitated Diffusion Ion Channels

Diffusion Diffusion- Materials that move from high concentrations to low concentrations. The difference between the concentration of molecules across a space is the called the concentration gradient.

Diffusion

Equilibrium Diffusion will eventually cause the concentration of the molecules to be the same throughout the space the molecules occupy, this is known as equilibrium.

Osmosis Osmosis- When water moves from high concentration to low concentration. The direction of osmosis depends on the concentration of solutes on both sides of the membrane.

Osmosis Hypotonic – concentration of solute molecules outside the cell are lower therefore water moves into the cell. Hypertonic - concentration of solute molecules outside the cell are higher therefore water moves out of the cell. Isotonic – this is when the concentration of the solutes are equal on the inside and outside of the cell.

Facilitated Diffusion This process is used for molecules that cannot diffuse rapidly through cell membranes. The movement of these kinds of molecules across the cell membrane is assisted by specific proteins called carrier proteins.

Carrier Protein

Carrier Proteins The molecule enters the protein. The carrier protein then changes shape to protect the molecule from the hydrophobic interior of the lipid bilayer. The molecule is then pushed through to the other side of the cell membrane. This process is still considered passive transport.

Ion Channels Ex: Sodium (Na+), potassium (K+), Calcium (Ca+), chloride (Cl-) Ions cannot diffuse through a lipid bilayer Each channel is specific to a certain type of ion.

Active Transport When the cell spends energy to bring materials into and out of the cell. Three types: Endocytosis Exocytosis Sodium-Potassium pump

Endocytosis Process by which a cell takes in a substance by surrounding it with the cell membrane. These substances are enclosed around the cell membrane. The cell then forms a pouch. The pouch then pinches off and becomes enclosed in a membrane bound structure called a vesicle. Two types of endocytosis based upon the type of material taken in Pinocytosis Phagocytosis

Exocytosis Process by which a cell gets rid of substances from the cell. During this process vesicles in the cytoplasm fuse with the cell membrane. They then release the contents into the cell’s external environment.

Sodium-Potassium Pump Only transports sodium and potassium. Three sodium ions bind to the carrier protein on the cytosol side of the membrane. At the same time a phosphate molecule is taken from ATP and binds to the carrier protein. The ATP molecule supplies the necessary energy to change the shape of the carrier protein. With its new shape the carrier protein carries the sodium ions across the cell membrane and releases them outside.

Na+ enters the carrier protein A p-group from ATP is added to the protein. The protein changes shape and the Na+ ions are released out of the cell. K+ ions now enter and bind to the protein. The p-group unbinds with the protein; which changes the shape. K+ ions are then released by the protein into the cell.