Part 1

Radioisotopes and Life Processes

The Understanding the Atom Series

Nuclear energy is playing a vital role in the life of every man, woman, and child in the United States today. In the years ahead it will affect increasingly all the peoples of the earth. It is essential that all Americans gain an understanding of this vital force if they are to discharge thoughtfully their responsibilities as citizens and if they are to realize fully the myriad benefits that nuclear energy offers them.

The United States Atomic Energy Commission provides this booklet to help you achieve such understanding.

Edward J. Brunenkant, Director Division of Technical Information

UNITED STATES ATOMIC ENERGY COMMISSION

Dr. Glenn T. Seaborg, Chairman James T. Ramey Wilfrid E. Johnson Dr. Theos J. Thompson Dr. Clarence E. Larson

Radioisotopes AND LIFE PROCESSES

by Walter E. Kisieleski and Renato Baserga

CONTENTS

INTRODUCTION 1 CELL THEORY: DNA IS THE SECRET OF LIFE 2 RADIOACTIVE ISOTOPES: THE BIOLOGICAL DETECTIVES 10 DNA SYNTHESIS: THE AUTOBIOGRAPHY OF CELLS 15 RNA SYNTHESIS: HOW TO TRANSLATE ONE LANGUAGE INTO ANOTHER 25 PROTEIN SYNTHESIS: THE MOLECULES THAT MAKE THE DIFFERENCE 35 CELL CYCLE AND GENE ACTION: LIFE IS THE SECRET OF DNA 37 ISOTOPES IN RESEARCH: PROBING THE CANCER PROBLEM 43 CONCLUSIONS 45 SUGGESTED REFERENCES 47

United States Atomic Energy Commission Division of Technical Information Library of Congress Catalog Card Number: 66-61908 1966; 1967(Rev.)

THE COVER

The cover design portrays the inter-relationships suggested by the title of this booklet: On a trefoil symbolizing radiation are superimposed a dividing cell, a plant, an animal, and a double helix of a molecule of deoxyribonucleic acid, a material unique in and fundamental to all living things.

THE AUTHORS

Radioisotopes AND LIFE PROCESSES

By WALTER E. KISIELESKI and RENATO BASERGA

INTRODUCTION

Here and elsewhere we shall not obtain the best insight into things until we actually see them growing from the beginning.

Aristotle

The nature of life has excited the interest of human beings from the earliest times. Although it is still not known what life is, the characteristics that set living things apart from lifeless matter are well known. One feature common to all living things, from one-celled creatures to complex animals like man, is that they are all composed of microscopic units known as cells.

The cell is the smallest portion of any organism that exhibits the properties we associate with living material. In spite of the immense variety of sizes, shapes, and structures of living things, they all have this in common: They are composed of cells, and living cells contain similar components that operate in similar ways. One might say that life is a single process and that all living things operate on a single plan.

The past few years have been a time of rapid progress in our understanding of the mechanisms that control the function of living systems. This progress has been made possible by the development of new experimental techniques and by the perfection of instruments that detect what happens in the tiny world of molecules. Prominent among the methods that have contributed to the explosive growth in our understanding of biology is the use of radioactive isotopes as laboratory tools.

In this booklet we shall attempt to give an account, in chemical terms, of the materials from which living matter is made and of some of the chemical reactions that underlie the manifestations and the maintenance of life. To accomplish this, we have chosen to describe three types of molecules that have become the basis of modern biology: deoxyribonucleic acid (DNA), ribonucleic acid (RNA), and proteins. We will show how radioactive isotopes can be used to pry into the innermost secrets of these substances. Before we can understand the function of these precious molecules, however, it will be necessary to review the structure of a cell and the physical nature of radioactive isotopes.

CELL THEORY: DNA IS THE SECRET OF LIFE

We have seen that all organisms are composed of essentially like parts, namely cells; that these cells are formed and grow in accordance with essentially the same laws; hence that these processes must everywhere result from the operation of the same forces.

Theodor Schwann

Unit of Life