Biochemistry Chapter 5: Membranes and Signal Transduction (PDF)

Chapter 5 Membranes and an Introduction to Signal Transduction Biochemistry First Edition John Tansey Lecture PowerPoints Tanea Reed/ Dr. Jose Sapien Chapter 5 Outline 5.1 Membrane structure and function 5.2 Signal transduction Copyright © 2019 John Wiley & Sons, Inc. Section 5.1 Learning Obje...

Chapter 5 Membranes and an Introduction to Signal Transduction Biochemistry First Edition John Tansey Lecture PowerPoints Tanea Reed/ Dr. Jose Sapien Chapter 5 Outline 5.1 Membrane structure and function 5.2 Signal transduction Copyright © 2019 John Wiley & Sons, Inc. Section 5.1 Learning Objective ▪ Illustrate how the structure of a membrane dictates the functions of a membrane. Copyright © 2019 John Wiley & Sons, Inc. Copyright © 2019 John Wiley & Sons, Inc. Lipids Defined ▪ Lipids are hydrophobic molecules. • Polar lipids are found in cell membranes. o Contain water soluble functional groups • Can be amphipathic o Can have both polar and nonpolar components Copyright © 2019 John Wiley & Sons, Inc. Membranes Defined ▪ People often see membranes as something static, such as the skin of an onion or the thin layer of connective tissue on a piece of meat. ▪ These structures are dynamic, fluid, and only a few molecules thick. ▪ Membrane fluidity is enhanced at higher temperatures and is also affected by the composition of the bilayer. Copyright © 2019 John Wiley & Sons, Inc. ▪ Membranes in the cell are comprised of two main components: lipids and proteins. ▪ Lipids are hydrophobic molecules ▪ Polar lipids in the membranes are amphipathic, an important property in forming a membrane. Copyright © 2019 John Wiley & Sons, Inc. ▪ These lipids have two acyl chains (long-chain fatty acids) esterified to a glycerol backbone. Copyright © 2019 John Wiley & Sons, Inc. Plasma Membrane ▪ Contains two sheets of phospholipids • Leaflets are diverse and asymmetrical. ▪ This is a fluid (mosaic) structure. Figure 5.2 Plasma membrane. Copyright © 2019 John Wiley & Sons, Inc. Types of Lipids ▪ Phospholipids • Contain phosphate group ▪ Glycerophospholipids • Contain glycerol backbone ▪ Sphingolipids • Sphingosine backbone ▪ Cholesterol • Steroid containing (If cholesterol increases, the fluidity decreases) Copyright © 2019 John Wiley & Sons, Inc. Copyright © 2019 John Wiley & Sons, Inc. Diffusion Defined ▪ Diffusion is the movement of particles down a concentration gradient. • Depends on several factors: o Size o Shape o Solvent viscosity o Temperature • Illustrates the second law of thermodynamics Copyright © 2019 John Wiley & Sons, Inc. From: https://microbenotes.com/simple-diffusion/ Image Source: Khan Academy Copyright © 2019 John Wiley & Sons, Inc. Copyright © 2019 John Wiley & Sons, Inc. Components of Cell Membranes Figure 5.3 Membrane proteins and the plasma membrane. Copyright © 2019 John Wiley & Sons, Inc. Integral Membrane Proteins ▪ Proteins embedded in the plasma membrane ▪ Can be subclassified as: • Monotopic (One side of the bilayer) • Ditopic (transmembrane) Copyright © 2019 John Wiley & Sons, Inc. Seven-Transmembrane Receptors ▪ An example of membrane-spanning proteins ▪ Contain seven transmembrane α helices that span the membrane ▪ Examples include: • Integrins • Aquaporins Copyright © 2019 John Wiley & Sons, Inc. Peripheral Membrane Proteins ▪ Associated with the surface of the membrane ▪ Can be linked through a hydrophobic anchor ▪ Not embedded in the plasma membrane ▪ Can be dissociated from the membrane by: • changes in pH • salt • urea • guanidinium hydrochloride Copyright © 2019 John Wiley & Sons, Inc. Copyright © 2019 John Wiley & Sons, Inc. Transporters ▪ Methods for molecules to pass in and out of the cell or organelle ▪ Three systems are involved • Uniporter • Symporter • Antiporter Copyright © 2019 John Wiley & Sons, Inc. Example of Transporters Figure 5.4A Transporters, pumps, and channels. Copyright © 2019 John Wiley & Sons, Inc. Copyright © 2019 John Wiley & Sons, Inc. Active Transport ▪ Energy is required. ▪ Molecules move up a concentration gradient. • Can be primary or secondary o Primary—ATP is used directly to drive ion movement o Secondary—gradient pumps a second molecule across the membrane Copyright © 2019 John Wiley & Sons, Inc. Passive Transport ▪ Molecules move down a concentration gradient. ▪ Can occur through channels Copyright © 2019 John Wiley & Sons, Inc. Channels ▪ Can be gated or regulated Figure 5.4B,C Transporters, pumps, and channels. Copyright © 2019 John Wiley & Sons, Inc. Osmosis Defined ▪ The movement of solvent through a semipermeable barrier from a region of low to high solute concentration Copyright © 2019 John Wiley & Sons, Inc. Lipid Rafts Defined ▪ Lipid rafts are structures composed of cholesterol and sphingolipids that aggregate in the plasma membrane. ▪ They are involved in cell signaling and tethering cell membranes. Copyright © 2019 John Wiley & Sons, Inc. Lipid Rafts Figure 5.5 Other aspects of membrane biology. Copyright © 2019 John Wiley & Sons, Inc. Membrane Fusion and Budding Figure 5.7 Fusion and budding. Copyright © 2019 John Wiley & Sons, Inc. ▪ Membranous structures can either fuse together when a hormone or neurotransmitter is secreted from the cell or they can bud or bleb off from an existing structure Copyright © 2019 John Wiley & Sons, Inc. Copyright Copyright © 2019 John Wiley & Sons, Inc. All rights reserved. Reproduction or translation of this work beyond that permitted in Section 117 of the 1976 United States Act without the express written permission of the copyright owner is unlawful. Request for further information should be addressed to the Permissions Department, John Wiley & Sons, Inc. The purchaser may make back-up copies for his/her own use only and not for distribution or resale. The Publisher assumes no responsibility for errors, omissions, or damages, caused by the use of these programs or from the use of the information contained herein. Copyright © 2019 John Wiley & Sons, Inc.