Membrane structure Plasma membrane: helps cells regulate and adjust to continuously changing environment The cell needs to keep its internal concentration of substances (water, glucose, etc) constant or homeostatic

Phospholipid Bilayer The plasma membrane is a bilayer of phospholipids The polar head are on the outside and inside of the cell The nonpolar tails turn inward toward each other The bilayer has the consistency of olive oil

Phospholipid Structure

Membrane structure Also embedded in the plasma membrane are cholesterol molecules and proteins The cholesterol provide structure Proteins provide channels

Fluid Mosaic Model Because there are proteins, cholesterol and other substances embedded in the phospholipids, the plasma membrane is often referred to as a fluid mosiac.

Selective Permeability selective permeability: the property that allows some material to pass through the membrane while keeping other materials out

Transport of Materials Active vs. Passive Transport PASSIVE Diffusion - high to low no energy required With the concentration gradient Facilitated diffusion channels needed but no energy requirement; still considered passive ACTIVE Active transport Moving substances from low to high concentration Against the concentration gradient requires energy from ATP

Passive vs. Active transport Movement through the plasma membrane

The function of Proteins Channel Proteins Allow a particular molecule or ion to cross the plasma membrane freely Example: hydrogen ions

Function of Integral Proteins Carrier Proteins Specifically interact with a specific molecule or ion so that it can cross the plasma membrane More selective than the channel protein Example: sodium and potassium ions across a nerve cell membrane May require energy (ATP)

Carrier protein

Function of Integral Protein Cell Recognition Proteins Glycoproteins that help the body recognize when it is being invaded by pathogens so that an immune reaction can occur.

Function of Integral Protein

Receptor Proteins Have shape that allow a specific molecule to bind to it. The binding causes the protein to change shape and brings a cellular response Example: the liver stores glucose after it is signaled to do so by insulin

Receptor Proteins

Function of Integral Protein Enzymatic Protein Carry out metabolic reactions directly.

Selectivity of Plasma membrane What determines what is passively transported and what is actively transported across the membrane? 1. Size: small, nocharged molecules are able to pass through more easily (Oxygen, Carbon dioxide, alcohol and water) 2. Need of the cell: cells often need things (potassium) in the cell so it has to actively pump it in. It also pumps sodium out even though it is more concentrated on the outside (requires energy) 3. Charge/solubility: the charge of the molecule or if it is soluble in water (mixes with water) Ions and polar molecules are often assisted across the membrane by a carrier protein 4. Temperature/Pressure: Warmer temperature causes faster movement of particles and colder..slower.

Active Transport

Homeostasis The goal is for cells (and organisms) to regulate their internal environment despite changes in their external environment. This is known as homeostasis