Membrane Structure and Function PDF

05_Chapter_Outline Print Download Chapter 5 The Working Cell Introduction: Turning on the Lights to Be Invisible Some...

05_Chapter_Outline Print Download Chapter 5 The Working Cell Introduction: Turning on the Lights to Be Invisible Some organisms use energy-converting reactions to produce light A. Examples are organisms that live in the ocean and use light to hide themselves from predators Energy conversion involves not only energy but also membranes and enzymes B. So, production of light involves all of the topics covered in this chapter C. MEMBRANE STRUCTURE AND FUNCTION 5.1 Membranes are a fluid mosaic of phospholipids and proteins Membranes are composed of phospholipids and proteins A. Membranes are commonly described as a fluid mosaic This means that the surface appears mosaic because of the proteins embedded in the phospholipids and fluid because the proteins can drift about in the phospholipids Many phospholipids are made from unsaturated fatty acids that have kinks in their tails B. This prevents them from packing tightly together, which keeps them liquid This is aided by cholesterol wedged into the bilayer to help keep it liquid at lower temperatures Membranes contain integrins, which give the membrane a stronger framework C. Integrins attach to the extracellular matrix on the outside of the cell as well as span the membrane to attach to the cytoskeleton Some glycoproteins in the membrane serve as identification tags that are specifically recognized by membrane proteins of other cells D. For example, cell-cell recognition enables cells of the immune system to recognize and reject foreign cells, such as infectious bacteria Carbohydrates that are part of the extracellular matrix are significantly involved in cell-cell recognition Many membrane proteins function as E. enzymes, others in signal transduction, while others are important in transport Because membranes allow some substances to cross or be transported more easily than others, they exhibit selectively permeability Nonpolar molecules (carbon dioxide and oxygen) cross easily Polar molecules (glucose and other sugars) do not cross easily