Unit 4 Cell Membrane Structure & Cell Transport

The Structure and Function of the Cell Membrane Question: What feature does the cell membrane, nucleus, mitochondria, and chloroplast have in common? All have a membrane. The Cell Membrane: 1. The cell membrane is selectively permeable. This means that the cell membrane controls what materials can and can not enter the cell.

2. The cell membrane is made of primarily phospholipids and proteins. Phospholipids: Hydrophilic (Water-Loving) Heads and Hydrophobic (Water-Fearing) Tails

Some proteins are attached to the surfaces of the cell membrane and so are called peripheral proteins. Some proteins are embedded in the lipid bilayer and are called integral proteins. What is the purpose of these integral proteins? To allow molecules to be transported into the cell.

6. With the use of the Scanning Electron Microscope (SEM), scientists now know that the membrane is constantly changing, proteins are moving laterally within the cell membrane and are not stationary. Because of this fluidity and the fact that the cell membrane is composed of many substances, scientists use the “Fluid Mosaic Model” to describe the cell’s membrane.

Cellular Physiology: Membrane Transport Membrane Transport – movement of substance into and out of the cell Transport is by two basic methods Passive transport No energy is required Active transport The cell must provide metabolic energy Slide 3.20 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Selective Permeability The plasma membrane allows some materials to pass while excluding others This permeability includes movement into and out of the cell Slide 3.22 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Passive Transport Processes Diffusion Particles tend to distribute themselves evenly within a solution Movement is from high concentration to low concentration, or down a concentration gradient Figure 3.8 Slide 3.23 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Passive Transport Processes Types of diffusion Simple diffusion Unassisted process Solutes are lipid-soluble materials or small enough to pass through membrane pores Osmosis – simple diffusion of water Highly polar water easily crosses the plasma membrane Facilitated diffusion Substances require a protein carrier for passive transport Slide 3.24a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Diffusion through the Plasma Membrane Figure 3.9 Slide 3.25 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Active Transport Processes Active Transport helps move substances into and out of the cell that are unable to pass by diffusion They may be too large They may not be able to dissolve in the fat core of the membrane They may have to move against a concentration gradient Two common forms of active transport Solute pumping Bulk transport Slide 3.27 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Active Transport Processes Solute pumping Amino acids, some sugars and ions are transported by solute pumps ATP energizes protein carriers, and in most cases, moves substances against concentration gradients Slide 3.28a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Active Transport Processes Figure 3.10 Slide 3.28b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Active Transport Processes Bulk transport Exocytosis Moves materials out of the cell Material is carried in a membranous vesicle Vesicle migrates to plasma membrane Vesicle combines with plasma membrane Material is emptied to the outside Slide 3.29a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Active Transport Processes Figure 3.11 Slide 3.29b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Active Transport Processes Bulk transport Endocytosis Extracellular substances are engulfed by being enclosed in a membranous vescicle Types of endocytosis: Phagocytosis – cell eating Pinocytosis – cell drinking Slide 3.30a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Active Transport Processes Figure 3.12 Slide 3.30b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings