THE PLASMA MEMBRANE

I. MAINTAINING A BALANCE Homeostasis: the ability of an cell to maintain a constant internal/external environment – This is the plasma membrane’s job in a cell To control what can enter, and what can leave

Where is the Plasma Membrane?

I. MAINTAINING A BALANCE A. Why Cells Must Control Materials Plasma membrane: a flexible boundary between a cell and it’s environment – Allows a steady supply of nutrients to come in/out of a cell Plasma membrane is selectively permeable – Allows some molecules to pass through, while keeping others out.

I. MAINTAINING A BALANCE A. Why Cells Must Control Materials Molecules that can freely enter/leave – Water Molecules that are “selectively” allowed to enter – Calcium [Ca] – Sodium [Na] – Glucose [C 6 H 12 O 6 ] – Oxygen/Carbon Dioxide

II. STRUCTURE OF A PLASMA MEMBRANE Phospholipid: has a glycerol backbone, 2 fatty acid chains, and a phosphate group Plasma membrane is a phospholipid bi-layer – Two layers of back-to-back phospholipids

II. STRUCTURE OF A PLASMA MEMBRANE A. The Phospholipid Bi-Layer 2 fatty acid tails are non-polar Phosphate group is the “polar head”

II. STRUCTURE OF A PLASMA MEMBRANE A. The Phospholipid Bi-Layer Polar head allows p-lipid to interact with water (remember, water is polar too!) Fatty acid tails avoid water – Water insoluble in the middle Fluid mosaic model: the modern day model of a plasma membrane

II. STRUCTURE OF A PLASMA MEMBRANE B. Other Components of the Plasma Membrane Cholesterol: prevent fatty acid tails of p-lipid from sticking together. Transport/Membrane Proteins: help move “large” particles in/out of cells Carb chains: located on outside of cell on plasma membrane – Used in identifying chemical signals