Essential Cell Biology, Fourth Edition

1 Edition . Fourth . Fourth Edition . Essential . CELL BIOLOGY. CELL BIOLOGY. Essential . Fourth Edition . GARLAND SCIENCE Essential CELL BIOLOGY. A. R. ER TS WALTE. LBE. RT. S BRAY. ROB.. ALBERTS BRAY HOPKIN JOHNSON. HO. LEWIS RAFF ROBERTS WALTER.. PK. FF. IN. RA.. JO S.. HN W I. SON L E. ISBN 978-0-8153-4455-1. 9 780815 344551 ECB4 interactive DVD-ROM inside 1 11/09/2013 13:25. Fourth Edition . Essential . CELL BIOLOGY. ALBERTS BRAY HOPKIN JOHNSON LEWIS RAFF ROBERTS WALTER. Garland Science Essential Cell Biology Website Vice President: Denise Schanck Artistic and Scientific Direction: Peter Walter Senior Editor: Michael Morales Narrated by: Julie Theriot Production Editor and Layout: Emma Jeffcock of EJ Publishing Producer: Michael Morales Services Illustrator: Nigel Orme Developmental Editor: Monica Toledo About the Authors Editorial Assistants: Lamia Harik and Alina Yurova Bruce Alberts received his PhD from Harvard University Copy Editor: Jo Clayton and is the Chancellor's Leadership Chair in Biochemistry Book Design: Matthew McClements, Blink Studio, Ltd.

2 And Biophysics for Science and Education, University of Cover Illustration: Jose Ortega California, San Francisco. He was the editor-in-chief of Authors Album Cover: Photography, Christophe Carlinet; Science magazine from 2008 2013, and for twelve years Design, Nigel Orme he served as President of the National Academy of Indexer: Bill Johncocks Sciences (1993 2005). Dennis Bray received his PhD from Massachusetts Institute of Technology and is currently an active emeritus professor at the University of Cambridge. Karen Hopkin received her PhD in biochemistry from 2014 by Bruce Alberts, Dennis Bray, Karen Hopkin, the Albert Einstein College of Medicine and is a science Alexander Johnson, Julian Lewis, Martin Raff, Keith Roberts, writer in Somerville, Massachusetts.

3 She is a contributor to and Peter Walter Scientific American's daily podcast, 60-Second Science, and to 2010 by Bruce Alberts, Dennis Bray, Karen Hopkin, E. O. Wilson's digital biology textbook, life on Earth. Alexander Johnson, Julian Lewis, Martin Raff, Keith Roberts, Alexander Johnson received his PhD from Harvard and Peter Walter University and is Professor of Microbiology and Immunology 2004 by Bruce Alberts, Dennis Bray, Karen Hopkin, at the University of California, San Francisco. Alexander Johnson, Julian Lewis, Martin Raff, Keith Roberts, Julian Lewis received his DPhil from the University of and Peter Walter Oxford and is an Emeritus Scientist at the London Research 1998 by Bruce Alberts, Dennis Bray, Alexander Johnson, Institute of Cancer Research UK.

4 Julian Lewis, Martin Raff, Keith Roberts, and Peter Walter Martin Raff received his MD from McGill University and is at the Medical Research Council Laboratory for Molecular Cell Biology and Cell Biology Unit at University College London. Keith Roberts received his PhD from the University of This book contains information obtained from authentic and Cambridge and was Deputy Director of the John Innes highly regarded sources. Every effort has been made to trace Centre, Norwich. He is currently Emeritus Professor at the copyright holders and to obtain their permission for the use of University of East Anglia. copyright material. Reprinted material is quoted with permis- Peter Walter received his PhD from The Rockefeller sion, and sources are indicated.

5 A wide variety of references are University in New York and is Professor of the Department listed. Reasonable efforts have been made to publish reliable of Biochemistry and Biophysics at the University of data and information, but the author and the publisher cannot California, San Francisco, and an Investigator of the Howard assume responsibility for the validity of all materials or for the Hughes Medical Institute. consequences of their use. All rights reserved. No part of this book covered by the copy- right hereon may be reproduced or used in any format in any form or by any means graphic, electronic, or mechanical, in- cluding photocopying, recording, taping, or information storage and retrieval systems without permission of the publisher.

6 ISBNs: 978-0-8153-4454-4 (hardcover); 978-0-8153-4455-1. (softcover). Library of Congress Cataloging-in-Publication Data Alberts, Bruce. Published by Garland Science, Taylor & Francis Group, LLC, Essential cell biology / Bruce Alberts [and seven others]. an informa business, 711 Third Avenue, New York, NY 10017, -- Fourth Edition . USA, and 3 Park Square, Milton Park, Abingdon, OX14 4RN, UK. pages cm. ISBN 978-0-8153-4454-4 (hardback). 1. Cytology. 2. Molecular biology. 3. Biochemistry. I. Title. Printed in the United States of America 2013. 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 2013025976. Visit our website at CHAPTER SEVEN. 7. From DNA to Protein: How Cells Read the Genome Once the double-helical structure of DNA (deoxyribonucleic acid) had FROM DNA TO RNA.

7 Been determined in the early 1950s, it became clear that the hereditary information in cells is encoded in the linear order or sequence of the four different nucleotide subunits that make up the DNA. We saw in FROM RNA TO PROTEIN. Chapter 6 how this information can be passed on unchanged from a cell to its descendants through the process of DNA replication. But how does RNA AND THE ORIGINS OF life . the cell decode and use the information? How do genetic instructions written in an alphabet of just four letters direct the formation of a bac- terium, a fruit fly, or a human? We still have a lot to learn about how the information stored in an organism's genes produces even the simplest unicellular bacterium, let alone how it directs the development of com- plex multicellular organisms like ourselves.

8 But the DNA code itself has been deciphered, and we have come a long way in understanding how cells read it. Even before the DNA code was broken, it was known that the information contained in genes somehow directed the synthesis of proteins. Proteins are the principal constituents of cells and determine not only cell struc- ture but also cell function. In previous chapters, we encountered some of the thousands of different kinds of proteins that cells can make. We saw in Chapter 4 that the properties and function of a protein molecule are determined by the sequence of the 20 different amino acid subunits in its polypeptide chain: each type of protein has its own unique amino acid sequence, which dictates how the chain will fold to form a molecule with a distinctive shape and chemistry.

9 The genetic instructions carried by DNA must therefore specify the amino acid sequences of proteins. We will see in this chapter exactly how this is done. 224 CHAPTER 7 From DNA to Protein: How Cells Read the Genome gene DNA DNA does not synthesize proteins itself, but it acts like a manager, del- 5 3 egating the various tasks to a team of workers. When a particular protein 3 5 is needed by the cell, the nucleotide sequence of the appropriate segment RNA SYNTHESIS of a DNA molecule is first copied into another type of nucleic acid RNA. nucleotides TRANSCRIPTION (ribonucleic acid ). That segment of DNA is called a gene, and the result- RNA. ing RNA copies are then used to direct the synthesis of the protein. Many 5 3 thousands of these conversions from DNA to protein occur every sec- ond in each cell in our body.

10 The flow of genetic information in cells is PROTEIN SYNTHESIS. TRANSLATION. therefore from DNA to RNA to protein (Figure 7 1). All cells, from bacte- ria to humans, express their genetic information in this way a principle PROTEIN. so fundamental that it has been termed the central dogma of molecular H2N COOH. biology. amino acids In this chapter, we explain the mechanisms by which cells copy DNA. Figure 7 1 Genetic information directs into RNA (a process called transcription) and then use the information the synthesis of proteins. The flow of genetic information from DNA to RNA in RNA to make protein (a process called translation). We also discuss (transcription) and from RNA to protein a few of the key variations on this basic scheme. Principal among these (translation) occurs in all living cells.