Cell Transport

Plasma membrane is used to maintain homeostasis (maintain a constant internal environment) Plasma Membrane = “selectively permeable” (lets certain things in & keeps others out) Made up a phospholipid bilayer and proteins Phospholipids have hydrophilic heads and hydrophobic tails Proteins help move large molecules or aid in cell recognition

Three types of membrane proteins include: Peripheral proteins that are attached on the surface of the membrane(inner or outer) Integral proteins are embedded in the membrane but do not completely cross through the membrane Transmembrane proteins that completely cross the membrane and can serve as transport or channel proteins

Fluid Mosaic Model FLUID- because individual phospholipids and proteins can move around freely within the layer, like it’s a liquid. MOSAIC- because of the pattern produced by the scattered protein molecules when the membrane is viewed from above.

Types of Cell Transport 2 Main Types: Passive Transport – movement of a substance through a cell membrane without using any energy Active Transport - using energy to transport particles through a membrane against a concentration gradient (lesser concentration to greater concentration)

Types of Passive Transport 1. Diffusion = movement of particles from high concentration to low concentration difference in concentration is called a concentration gradient diffusion occurs until equilibrium is reached

Simple Diffusion

2. Facilitated Diffusion = transport of particles through a membrane by a channel protein (No energy needed!) Types of transport Proteins Channel proteins are embedded in the cell membrane & have a pore for materials to cross Carrier proteins can change shape to move material from one side of the membrane to the other

Types of Passive Transport 3.) Osmosis = diffusion of water through a selectively permeable membrane from an area of high water concentration to an area of low water concentration Solute = a substance dissolved in another substance (ex. Kool-Aid) Solvent = a substance that does the dissolving (ex. Water) Solution = mixture of solutes & solvents

Isotonic Solution = concentration of solutes is same inside & outside of a cell (at equilibrium)

Hypotonic Solution = low solute, high solvent Ex. Cell swells when placed in a hypotonic solution

Hypertonic Solution = high solute, low solvent Ex. Cell shrinks when placed in a hypertonic solution

so, hypo, & hyper refer to the solutes!!

Types of Active Transport Sodium/Potassium (NA+/K+) Pump Moves 3 Na+ out of a cell and 2 K+ into the cell against (up) the concentration gradient Requires ATP

Types of Active Transport Exocytosis Molecules are moved out of the cell by vesicles that fuse with the plasma membrane. This is how many hormones are secreted and how nerve cells communicate with one another.

Exocytic vesicle immediately after fusion with plasma membrane.

Types of Active Transport Endocytosis – Movement of large molecules into the cell Two forms Pinocytosis Phagocytosis

Pinocytosis – Cell forms an invagination Materials dissolve in water to be brought into cell Called “Cell Drinking”

Phagocytosis Used to engulf large particles such as food, bacteria, etc. into vesicles Called “Cell Eating”