Marc McLaughlin - How Cells Send, Receive, and Process Information

Published in 2015 by Britannica Educational Publishing (a trademark of Encyclopdia Britannica, Inc.) in association with The Rosen Publishing Group, Inc.

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First Edition

Britannica Educational Publishing

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Rosen Publishing

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Library of Congress Cataloging-in-Publication Data

McLaughlin, Marc, author.

How cells send, receive, and process information/Marc McLaughlin, Michael Friedman, and Brett Friedman.First edition.

pages cm.(The Britannica guide to cell biology)

Includes bibliographical references and index.

ISBN 978-1-6227-5801-2 (eBook)

1. CytologyJuvenile literature. 2. Cell interactionJuvenile literature. 3. NeurotransmittersJuvenile literature. 4. HormonesJuvenile literature. I. Friedman, Michael, 1955 author. II. Friedman, Brett, author. III. Title.

QH582.5.M315 2015

571.6dc23

2014021398

Cover (cell illustration) Mopic/Shutterstock.com; cover (background), pp. 1, 3, 4, 5 Sebastian Tomus/Shutterstock.com

CONTENTS

C ells are the building blocks of the living world. Living things as different as bacteria, archaea, algae, fungi, protozoans, animals, and plants all consist of one or more cells. Cells are made up of parts that help living things to eat, respire, excrete wastes, and perform all the necessary functions of life. The parts are organized to fit and work together. For this reason, living things are called organisms.

The activities of the cells are controlled by the cells genetic materialits deoxyribonucleic acid (DNA). DNA controls how the cell reproduces and functions and determines which traits are inherited from previous generations. In some types of organisms, called eukaryotes, the DNA is contained within a membrane-bound structure called the nucleus. In eukaryotic cells, most specialized tasks, such as obtaining energy from food molecules and producing material for cell growth, occur within a number of enclosed bodies called organelles. Plants, animals, fungi, and many microorganisms are eukaryotes.

Other microorganisms, namely bacteria and archaea, are unicellular (consisting of a single cell) and lack a distinct nucleus and organelles. These organisms are called prokaryotes. Some prokaryotic organisms, such as cyanobacteria (also called blue-green algae), can photosynthesize food; their food-making chlorophyll is scattered throughout the cell. In eukaryotic photosynthesizing organisms, such as plants and algae, the chlorophyll is contained within chloroplasts.

The parts of a multicellular organism are controlled so that they work together to keep the organism alive and aid in reproduction. In multicellular animals, such as humans, hormones regulate growth, keep muscles in condition, and perform many similar tasks. Other controls are carried out by nerve cells, also called neurons, via impulses to and from various parts of the body. These impulses can indicate that something has been seen, felt, or heard. They also make muscle cells contract or relax, so that animals can run, lie down, catch food, and do countless other things. Nerve cells may even deliver the impulses that stimulate hormone production. These specialized cells have most of the same features as other cells but have certain adaptations that help them do their respective jobs. Humans have many kinds of specialized cells, including red blood cells that transport oxygen throughout the body, skin cells that help to protect the body, muscle cells that contract and relax to move parts of the body, nerve cells that transport information from one part of the body to another, and pancreatic cells that produce compounds such as insulin. Specialized cells work with other similar cells to carry out their specific functions.

An animal cell (left) and a plant cell contain an array of organelles. Some organelles and structures are specific to either cell, while others are found in both types. Encyclopdia Britannica/Universal Images Group/Getty Images

A cell functions similarly to the way in which a factory makes a product, with each factory worker performing a vital role. The most significant job performed in this so-called cell factory is the making of proteins. In eukaryotic cells, a variety of organelles, including the nucleus, ribosomes, Golgi apparatus, and endoplasmic reticulum, work together to manufacture proteins. These and other organelles enable the cell to send, receive, and process information so that it can maintain a stable equilibrium.

T he cells of every living organism contain DNA, which determines how that organism will look and function. In humans, for instance, DNA tells the body what color an individuals eyes should be and how big that persons feet will grow, and it controls a variety of characteristics at a cellular level. Each different piece of information is carried on a specific segment of the DNA known as a gene, each of which contains biochemical codes for the synthesis of specific proteins.

DNA is a nucleic acid made up of two strands of biochemical units called nucleotides. Each nucleotide consists of a phosphate, deoxyribose (a sugar), and one of four nitrogen-bearing bases: adenine, guanine, cytosine, or thymine. Chemical bonds connect bases on one strand with bases on the other, forming base pairs. The molecule resembles a ladder with the two DNA strands for sides and chemical bonds forming steps. The nucleotide ladder winds around itself, forming a double helix. This configuration makes the DNA molecule very stable.

The nucleus of a eukaryotic cell contains structures called chromosomes. Each chromosome is made up of strands of DNA. A gene is a short section of DNA. Encyclopdia Britannica, Inc.

THE PRODUCTION OF DNA, THE GENETIC CODE, AND DNAS WORK

When extra copies of DNA molecules are neededas occurs before cell divisionthe molecule undergoes replication. In this process the two DNA strands separatethat is, the rungs of the ladder are broken. Each freed strand then serves as a template, or pattern, from which a new strand is produced. After the new strands are completed, each bonds to its respective template strand. This produces two new, identical DNA molecules, each consisting of one old strand and one new strand. This method of replication is a key factor in the stable transfer of genetic traits from one generation of cells to the next.