Cellular Transport (Part IV) Cellular Membrane LIFE, ORGANELLES, CELL MEMBRANE, CELLULAR TRANSPORT

Part 4 The Plasma Membrane

1. Function of the Plasma Membrane A. Homeostasis is the internal balance of a cell, including pH, temperature, and water and nutrient content. Homeostasis is primarily maintained by the cell membrane.

1. Function of the Plasma Membrane B. The cell membrane is selectively permeable. Some items are blocked from entering or leaving the cell, while others can enter or leave the cell easily. Analogy: Fish are blocked by a fish net while water and debris pass through easily.

2. Structure of the Plasma Membrane A. Recall that lipid molecules have a triglyceride backbone and three long fatty acid hydrocarbon chains. When one fatty acid chain is replaced with a phosphate group, a phospholipid is made. Circle the phosphate group below. Draw a squiggly line around the glycerol. Box the fatty acid chains.

2. Structure of the Plasma Membrane B. The plasma membrane is composed of a phospholipid bilayer, in which two layers of phospholipids are arranged tail-to-tail. In the plasma membrane, phospholipids arrange themselves in a way that allows the plasma membrane to exist in the watery environment.

2. Structure of the Plasma Membrane C. The Phospholipid Bilayer 1. The phosphate heads are polar, and therefore attracted to another polar molecule: water. 2. The fatty acid chains are non-polar, repelled by the polar phosphate heads. 3. When water soluble items try to enter the cell, they are blocked by the non-polar fatty acid chains.

2. Structure of the Plasma Membrane D. Other Components of the Plasma Membrane 1. Cholesterol floats among the phospholipids, and is nonpolar. They help prevent the fatty acid chains of phospholipids from sticking together. 2. Carbohydrates stick out of proteins and help create and identify cell signals.

2. Structure of the Plasma Membrane D. Other Components of the Plasma Membrane 3. Proteins help with cell signals, provide cell support, and act as tunnels, called transport proteins, allowing certain molecules in the cell like nutrients and let other molecules out like waste.

2. Structure of the Plasma Membrane D. Other Components of the Plasma Membrane 4. Phospholipids, cholesterol, proteins, and carbohydrates float like apples in a barrel to create the cell membrane. The idea that these molecules float in a cell membrane “sea” is called the fluid mosaic model.