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- Herausgeber: John Wiley & Sons
- Kategorie: Wissenschaft und neue Technologien
- Sprache: Englisch
- Veröffentlichungsjahr: 2020
Your insider guide to the stuff of life 3.8 billion years old and counting, there's more than a little to know about the fundamentals of how life works. This friendly guide takes you from the primordial soup to the present, explaining how specialized cells have given rise to everything living, from the humblest amoeba to walking, talking human beings. Whether you're enrolled in a cell or molecular biology course and need a straightforward overview, or are just curious about the latest advances, this fully updated edition is your all-access ticket to our inner world. Molecular & Cell Biology For Dummies decodes jargon and theories that can tax even the most devoted student. It covers everything from basic principles to how new technology, genetic testing, and microarray techniques are opening up new possibilities for research and careers. It also includes invaluable tips on how to prepare for--and ace--your exams! * Explore the structure and function of the cells--and find out why cellular context is crucial to the study of disease * Discover how molecular biology can solve world problems * Understand how DNA determines traits and is regulated by cells * Enhance your knowledge and results with online resources and study tips From microscopic details to macro concepts, this book has something for you.
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Molecular & Cell Biology For Dummies®, 2nd Edition
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Published simultaneously in Canada
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Library of Congress Control Number: 2020904255
ISBN 978-1-119-62040-2 (pbk); ISBN 978-1-119-74865-6 (ebk); ISBN 978-1-119-74866-3 (ebk)
Molecular & Cell Biology For Dummies®
To view this book's Cheat Sheet, simply go to www.dummies.com and search for “Molecular & Cell Biology For Dummies Cheat Sheet” in the Search box.
Table of Contents
Cover
Introduction
About This Book
Foolish Assumptions
Icons Used in This Book
Beyond the Book
Where to Go from Here
Part 1: The World of the Cell
Chapter 1: Exploring the World of the Cell
Cells and Viruses: Discovering the Inhabitants of the Microscopic World
The Life of a Cell: How Cells Get What They Need to Survive and Reproduce
Sexual Reproduction: Shuffling the Genetic Deck for the Next Generation
DNA to Protein: Following the Instructions in the Genetic Code
DNA Technology: Tackling the World’s Problems
Chapter 2: Take a Tour inside the Cell
Admiring the Unity and Diversity of Cells
Finding Common Ground: Structures in All Cells
Your Body, Your Cells: Eukaryotic Cells
Tiny but Mighty: Prokaryotic Cells
Chapter 3: Dead or Alive: Viruses
Viruses: Hijackers of the Cellular World
War on a Microcosmic Scale: Viruses of Bacteria
I’ve Got a Cold: Viruses of Eukaryotes
Part 2: Molecules: The Stuff of Life
Chapter 4: Better Living through Chemistry
Life Really Matters
It’s Elemental: Atoms That Make Up Living Things
Let’s Bond: How Atoms Are Attracted to Each Other
Blue Planet: The Ocean inside Your Cells
Chain, Chain, Chain: Building and Breaking Polymers
Chapter 5: Carbohydrates: How Sweet They Are
CH
2
O: Structure of Carbohydrates
Sticky and Sweet: Functions of Carbohydrates
Chapter 6: Proteins: Workers in the Cellular Factory
Get into Shape: Levels of Protein Structure
Jacks of All Trades: The Many Functions of Proteins
Get ’Er Done: Enzymes Make Things Happen
Gatekeepers: Membrane Proteins
I’m in Charge: DNA-Binding Proteins
Chapter 7: DNA and RNA: Instructions for Life
It’s Puzzling: Structure of Nucleic Acids
Making DNA and RNA
Breaking the Code: The Function of DNA and RNA
Chapter 8: Lipids: Waterproof and Energy Rich
Hydrocarbons: Structure of Lipids
You Say Fat Like It’s a Bad Thing: Functions of Lipids
Part 3: The Working Cell
Chapter 9: Hello, Neighbor: How Cells Communicate
Shipping and Receiving: Transport across Membranes
Chatting through Cellular Connections
Sending and Receiving Signals
Chapter 10: Metabolism: Transferring Energy and Matter
Revving Up Your Metabolism
Stayin’ Alive: Cellular Work and the Laws of Thermodynamics
One Step at a Time: Metabolic Pathways
Chapter 11: Cellular Respiration: Every Breath You Take
Cellular Respiration: An Overview
Gimme a Break: Glycolysis
The Wheel of Fire: Krebs Cycle
Taking It to the Bank: Chemiosmosis and Oxidative Phosphorylation
Breaking Down Complex Carbohydrates, Proteins, and Fats
It’s a Two-Way Street: Connections between Metabolic Pathways
Chapter 12: Photosynthesis: Makin’ Food in the Kitchen of Life
Photosynthesis: An Overview
Shine on Me: The Light Reactions
The Circle of Life: Calvin Cycle
Got Food? Photosynthesis in the Real World
Chapter 13: Splitsville: The Cell Cycle, Cell Division, and Cancer
Reproducing the Cell
Drifting Apart: Binary Fission
Red Light, Green Light: The Cell Cycle
The Dance of the Chromosomes: Mitosis
Breaking Up Is Hard to Do: Cytokinesis
Keeping It under Control
Cancer: The Enemy Within
Part 4: Genetics: From One Generation to the Next
Chapter 14: Meiosis: Getting Ready for Baby
Let’s Talk about Sex, Baby: Reproduction
Homologous Chromosomes
Going Separate Ways: Meiosis
Shuffling the Genetic Deck: Crossing Over
Why Two Divisions Are Better than One
It Was All a Mistake: Nondisjunction
Chapter 15: Genetics: Talkin’ ’Bout the Generations
Pass the Peas, Please: Mendel and Segregation of Single Gene Traits
I Can Go My Own Way: Independent Assortment
It’s News to Mendel: Inheritance beyond Simple Dominance
Almost Inseparable: Linked Genes
Mama’s Boy: Sex-Linked Inheritance
Part 5: Molecular Genetics: How Cells Read the Book of Life
Chapter 16: DNA Replication: Doubling Your Genetic Stuff
DNA Replication: An Overview
Everybody Lend a Hand: Enzymes Involved in DNA Replication
It Takes a Village: Events at the Replication Fork
Keeping It Together: Leading and Lagging Strands
Chapter 17: Transcription and Translation: What’s in a Gene?
File It under Genes: The Blueprints for RNA and Proteins
Make a Copy, Please: Transcription
Finishing Touches: RNA Processing in Eukaryotes
Making a Protein: Translation
Don’t Drink and Drive: Mutation
Chapter 18: Control of Gene Expression: It’s How You Play Your Cards That Counts
Controlling the Situation: Gene Regulation and Information Flow
I Can Be Flexible: Gene Expression in Bacteria
The Master Plan: Gene Expression in Eukaryotes
Learning from Experience: Epigenetics
Part 6: Molecular Biology: Harnessing the Power of DNA
Chapter 19: The Book of You: Reading Your Genes
Copying a gene with PCR
Sorting molecules using gel electrophoresis
Reading a gene with DNA sequencing
I Read the Whole Thing: Sequencing Genomes
Beyond Genomics: Systems Biology and Epigenomes
Chapter 20: Rewriting the Code of Life: Recombinant DNA Technology and Genome Editing
Piecing It Together: Recombinant DNA Technology
Changing the Plan: Using Recombinant DNA Technology to Solve Problems
Hitting the Bull’s-Eye with Genome Editing
Part 7: The Part of Tens
Chapter 21: Ten Important Rules for Cells to Live By
The Cell Theory
The First Law of Thermodynamics
The Second Law of Thermodynamics
The Theory of Evolution by Natural Selection
The Law of Conservation of Matter
Nucleic Acids Pair in Antiparallel Strands
Central Dogma
Protein Shape Is Essential to Their Function
Law of Segregation
Law of Independent Assortment
Chapter 22: Ten Ways to Improve Your Grade
Monitor Your Learning
Study Smarter
Actively Participate in Class
Schedule Your Study Time
Give Your Brain a Well-Rounded Workout during Study Sessions
Get Creative with Memory Tricks
Recognize the Difference between Levels of Understanding
Remember the Supporting Material
Use Your First Test as a Diagnostic Tool
Get Help Sooner Rather than Later
Index
About the Author
Connect with Dummies
End User License Agreement
List of Tables
Chapter 17
TABLE 17-1 Relating Rules for English to Rules for mRNA
List of Illustrations
Chapter 1
FIGURE 1-1: The organization of living things.
Chapter 2
FIGURE 2-1: The fluid-mosaic model of plasma membranes.
FIGURE 2-2: Structures in a typical animal cell.
FIGURE 2-3: Structures in a typical plant cell.
FIGURE 2-4: The nucleus.
FIGURE 2-5: The endomembrane system.
FIGURE 2-6: The mitochondrion.
FIGURE 2-7: The chloroplast.
FIGURE 2-8: The cytoskeleton.
FIGURE 2-9: Structure of cilia and flagella.
FIGURE 2-10: The extracellular matrix of animal cells.
FIGURE 2-11: Structures in a typical prokaryotic cell.
Chapter 3
FIGURE 3-1: Structure and shapes of viruses.
FIGURE 3-2: Multiplication cycles of bacteriophage.
FIGURE 3-3: The multiplication cycle of the human immunodeficiency virus (HIV).
Chapter 4
FIGURE 4-1: The Periodic Table of Elements.
FIGURE 4-2: Atoms and chemical bonds.
FIGURE 4-3: The formation of a covalent bond in hydrogen gas.
FIGURE 4-4: Polar covalent bonding in water.
FIGURE 4-5: Hydrogen bonding between water molecules.
FIGURE 4-6: The pH scale.
FIGURE 4-7: Condensation and hydrolysis.
FIGURE 4-8: Functional groups.
Chapter 5
FIGURE 5-1: Carbohydrate molecules.
FIGURE 5-2: Cellulose and starch.
Chapter 6
FIGURE 6-1: Amino acid structure.
FIGURE 6-2: The four levels of protein structure (conformation).
FIGURE 6-3: The formation of a peptide bond.
FIGURE 6-4: Interactions between R groups.
FIGURE 6-5: Enzyme catalysis.
FIGURE 6-6: Enzyme inhibition.
FIGURE 6-7: Feedback inhibition.
FIGURE 6-8: Membrane proteins.
FIGURE 6-9: DNA-binding domains.
Chapter 7
FIGURE 7-1: Structure of a nucleotide (adenosine monophosphate).
FIGURE 7-2: The nitrogenous bases.
FIGURE 7-3: Synthesis of a polynucleotide chain.
FIGURE 7-4: The twisted ladder model of the double helix of DNA.
Chapter 8
FIGURE 8-1: Saturated and unsaturated bonds in a typical fat.
FIGURE 8-2: The formation of a fat or oil.
FIGURE 8-3: A phospholipid.
FIGURE 8-4: The structure of estrogen, a sterol.
Chapter 9
FIGURE 9-1: Membrane permeability.
FIGURE 9-2: Diffusion of molecules.
FIGURE 9-3: Transport across membranes.
FIGURE 9-4: The sodium-potassium pump.
FIGURE 9-5: Types of junctions between animal cells.
FIGURE 9-6: Connections between plant cells.
FIGURE 9-7: Signal transduction.
FIGURE 9-8: Signal transduction pathways.
Chapter 10
FIGURE 10-1: A metabolic map showing the molecules (dots) and chemical reaction...
FIGURE 10-2: Spontaneous versus nonspontaneous reactions.
FIGURE 10-3: Changes in free energy during spontaneous and nonspontaneous react...
FIGURE 10-4: The energy carrier adenosine triphosphate (ATP).
FIGURE 10-5: The ATP/ADP cycle.
FIGURE 10-6: Metabolic pathways.
FIGURE 10-7: Energy of activation with and without enzymes.
FIGURE 10-8: Redox reactions.
FIGURE 10-9: The electron carrier cycle.
FIGURE 10-10: The electron carrier NAD
+
/NADH + H
+
.
Chapter 11
FIGURE 11-1: A comparison of the direct burning of sugar with the breakdown of ...
FIGURE 11-2: Oxidation and reduction during cellular respiration.
FIGURE 11-3: Transfer of electrons and energy through an electron transport cha...
FIGURE 11-4: An overview of cellular respiration.
FIGURE 11-5: The steps of glycolysis.
FIGURE 11-6: Substrate-level phosphorylation.
FIGURE 11-7: A comparison between lactic acid fermentation and alcohol fermenta...
FIGURE 11-8: The Krebs cycle.
FIGURE 11-9: The electron transport chain in the inner membrane of the mitochon...
FIGURE 11-10: The breakdown of molecules other than glucose during cellular res...
FIGURE 11-11: Connections between catabolism and anabolism.
Chapter 12
FIGURE 12-1: Basic structures of a vascular plant.
FIGURE 12-2: The electro-magnetic spectrum.
FIGURE 12-3: Absorption spectra for photosynthetic pigments.
FIGURE 12-4: The two halves of photosynthesis, the light reactions and the Calv...
FIGURE 12-5: The light reactions of photosynthesis (noncyclic photophosphorylat...
FIGURE 12-6: Noncyclic photophosphorylation (the Z scheme).
FIGURE 12-7: Cyclic photophosphorylation.
FIGURE 12-8: The Calvin cycle.
Chapter 13
FIGURE 13-1: Binary fission.
FIGURE 13-2: The cell cycle.
FIGURE 13-3: The process of mitosis and interphase.
FIGURE 13-4: Cytokinesis.
FIGURE 13-5: Regulation of the cell cycle by cyclins and cyclin-dependent kinas...
FIGURE 13-6: The accumulation of multiple mutations can lead to the development...
Chapter 14
FIGURE 14-1: The human life cycle.
FIGURE 14-2: A human karyotype.
FIGURE 14-3: An overview of meiosis.
FIGURE 14-4: The phases of meiosis.
Chapter 15
FIGURE 15-1: A single gene cross with Punnett squares.
FIGURE 15-2: Human pedigrees.
FIGURE 15-3: A Punnett square of a dihybrid cross.
FIGURE 15-4: A Punnett square for incomplete dominance.
FIGURE 15-5: Human blood type.
FIGURE 15-6: Distribution of polygenic trait.
FIGURE 15-7: A cross involving linked genes.
FIGURE 15-8: A Punnett square for a sex-linked trait.
Chapter 16
FIGURE 16-1: Origins of replication.
FIGURE 16-2: DNA replication.
FIGURE 16-3: Leading and lagging strands.
Chapter 17
FIGURE 17-1: Structure of a gene.
FIGURE 17-2: Transcription.
FIGURE 17-3: RNA splicing.
FIGURE 17-4: The codon dictionary.
FIGURE 17-5: Transfer RNA.
FIGURE 17-6: The ribosome.
FIGURE 17-7: Initiation and elongation of translation.
FIGURE 17-8: Termination of translation.
Chapter 18
FIGURE 18-1: Regulation of the
lac
operon.
FIGURE 18-2: Gene regulation of eukaryotes.
FIGURE 18-3: DNA packing and epigenetics.
FIGURE 18-4: Transcription factors in eukaryotic cells.
Chapter 19
FIGURE 19-1: The polymerase chain reaction.
FIGURE 19-2: Gel electrophoresis.
FIGURE 19-3: Cycle sequencing (Sanger sequencing).
FIGURE 19-4: Cycle sequencing (Sanger sequencing) vs. Next-generation sequencin...
FIGURE 19-5: Shotgun sequencing.
Chapter 20
FIGURE 20-1: Restriction enzymes.
FIGURE 20-2: Making cDNA.
FIGURE 20-3: Cloning a gene.
FIGURE 20-4: Nucleic acids probes.
FIGURE 20-5: Genetic engineering.
FIGURE 20-6: Transgenic plants.
FIGURE 20-7: Gene therapy in humans.
FIGURE 20-8: CRISPR-cas in nature.
FIGURE 20-9: CRISPR in the lab.
Guide
Cover
Table of Contents
Begin Reading
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Introduction
Molecular and cell biology isn’t just something that happens in a lab; it reaches out and touches your life in many ways, seen and unseen. Genetically modified organisms, designer cancer drugs, forensic science, and even home pregnancy tests are all applications of the science and techniques of molecular and cell biology. Gaining an understanding of molecular and cell biology can help you make informed decisions about your lifestyle and health.
Understanding cells and how they function is fundamental to all other fields of biology, including medicine. All living things are made of cells, and scientists can trace every response, every function of larger organisms back to the structure and function of cells. Genetic diseases are a dramatic example of how important one cell type, one protein, and one gene can be to an organism. Exploring this connection between genes, proteins, and cellular function is at the heart of molecular and cell biology.
As you take your own journey into the inner space of the cell, I hope this book will act as your guidebook, pointing out landmarks and signposts, and translating the sometimes complicated language of the local inhabitants!
About This Book
Molecular & Cell Biology For Dummies, 2nd Edition is an overview of the fundamentals of molecular and cell biology that’s been updated with recent advances in the science. My goal is to explain each topic in a clear and straightforward fashion, keeping scientific jargon to a minimum. I want this book to be understandable by anyone who picks it up, even if they don’t have a science background. To help you understand what is sometimes a complex science, I share every analogy, funny story, and memory trick that I’ve gathered in my 20 years of teaching this subject. These types of gimmicks help my students wrap their brains around the fundamental principles of molecular and cell biology, and I hope these strategies will help you, too.
Molecular & Cell Biology For Dummies, 2nd Edition emphasizes the main concepts and fundamental processes that are at the heart of molecular and cell biology. When I had to make a choice between getting the main idea across or including every molecular detail of a process, I chose the main idea. I think that once you understand the main concept or the big events of a process, you can later add in details fairly easily. However, if you try to tackle a complicated process and every little detail at the same time, you can hit information overload and not really understand anything at all. My emphasis on main ideas and events will make the subject of molecular and cell biology easier, but that doesn’t mean the topic will be easy. The world of the cell is complex and busy with detailed processes, so understanding molecular and cell biology is a challenge for most people. I hope that this book will help you succeed in that challenge.
Foolish Assumptions
As I wrote this book, I tried to imagine who you might be and what you may need in order to understand molecular and cellular biology. Here’s who I pictured:
You’re a student in a molecular and cell biology class who is having trouble understanding everything and keeping up with the pace of the class. For you, I present the topics in a straightforward way with an emphasis on the most important concepts and processes. By reading this book before you go to lecture, you may have an easier time understanding what your professor is talking about.
You’re a student in a molecular and cellular biology class who is determined to get an
A,
and you want to gather all possible resources to help you in your goal. For you, I make studying more efficient by presenting the core concepts of molecular and cellular biology in straightforward bulleted lists. These lists can supplement your own notes, making sure that you’ve nailed the big ideas.
You’re someone who wants to know more about the science behind the stories you hear in the news and see on TV. Maybe you’re interested in forensic science and want a better understanding of what they’re talking about on
CSI
and the Discovery Channel. Or maybe you’re worried about the potential impacts of gene editing, genetically modified organisms, or genetic screening on our society, and you want to know more about the science behind these topics. For you, I try to keep terminology to a minimum and include lots of analogies to help you relate the science to your everyday life.
Icons Used in This Book
All For Dummies books use icons to help identify particular types of information. Here’s the list of icons I use in this book and what they all mean:
I use this icon to emphasize main ideas that you should definitely keep in mind.
I use this icon to present study tips or other information that can help you navigate through difficult material.
I use this icon to flag detailed information that isn’t essential to the main concept or process being presented. If you’re not a student in a molecular and cellular biology class, you can definitely skip this material.
I use this icon to flag potentially confusing ideas or common wrong ideas that people typically have about how something works. I know about these danger spots from my years of teaching, and I’ve flagged them to help you avoid these pitfalls.
Beyond the Book
In addition to what you’re reading right now, this product also comes with a free access-anywhere Cheat Sheet that tells you about plate tectonics and the geologic timescale. To get this Cheat Sheet, simply go to www.dummies.com and type Molecular & Cell Biology For Dummies Cheat Sheet in the Search box.
Where to Go from Here
With Molecular & Cell Biology For Dummies, you can start anywhere in the book that you want. If you’re reading this book for general interest, you’ll probably find it best to begin at the beginning with the chapter on cells and then move to whatever interests you next from there. If you’re currently having trouble in a molecular and cellular biology class, jump right into the subject that’s confusing you. If you’re using the book as a companion to a molecular and cellular biology class that is just beginning, the book follows the organization of most college classes with one exception — most college classes work from the smallest to the largest, beginning with molecules then moving on to cells. I prefer to start with cells to give you a sense of context, an idea of where everything is happening, and then move on to the molecules.
Whatever your circumstance, the Table of Contents and Index can help you find the information you need. Best wishes from me to you as you begin your journey into the marvelous world of the cell.
Part 1
The World of the Cell
IN THIS PART …
Discover the science of molecular and cellular biology.
Take a guided tour of the inside of a cell.
Explore the basic structure and function of cells and viruses.
Chapter 1
Exploring the World of the Cell
IN THIS CHAPTER
Discovering the microscopic world
Getting matter and energy
Researching the genetic code
Molecular and cell biology is about studying cell structure and function down to the level of the individual molecules that make up the cell. The most famous molecule in cells is DNA, and much of molecular biology focuses on this molecule — reading DNA, working with DNA, and understanding how cells use DNA.
In this chapter, I present an overview of molecular and cell biology and how it relates to your life. My goal is to illustrate the importance of molecular and cell biology and to give you a preview of the topics I explore in more depth in the later chapters of this book.
Cells and Viruses: Discovering the Inhabitants of the Microscopic World
If you were alive just 400 years ago, you would’ve had no idea that germs can spread diseases, that your blood contains cells that carry oxygen around your body, or that new people are made when sperm cells join with egg cells. Four hundred years ago, no one had any idea that there was an entire world just beyond the power of the human eye. A Dutch cloth merchant named Antony van Leeuwenhoek changed all that when he used small, handheld microscopes to peer beyond the known world into the world of the cell.
In 1676, van Leeuwenhoek used his microscopes to look into a drop of lake water — water that appeared clear to his eyes — and was astounded to see tiny creatures swimming around in it. van Leeuwenhoek was the first to see bacteria, blood cells, and sperm cells fertilizing an egg. Along with Robert Hooke, who observed the first plant cells, van Leeuwenhoek laid the foundation for the development of cell biology and microbiology and began new chapters in the sciences of anatomy, physiology, botany, and zoology.
You: On the cellular level
Imagine your eyes have super powers, and you’re staring at your own skin, revealing a patchwork of thin, flaky cells. These skin cells are just one type of more than 200 types of cells found in your body — cells that make up your tissues, organs, and organ systems (see Figure 1-1). Increase the power of your eyes, and you can zoom in on your chromosomes, which are made of DNA (see Chapter 7) and contain the instructions for your traits (see Chapter 15).
FIGURE 1-1: The organization of living things.
Them: Bacteria and viruses
If you looked at your body with super-powered eyes, your cells aren’t the only cells you’d see. All over your body and, in fact, everywhere on Earth you look, you can see another type of cell — the prokaryotic cell (see Chapter 2). Prokaryotic cells come in two types:
Bacteria
are probably most familiar to you because they can make you sick, but bacteria do many good things, too. The bacteria that live all over your body actually help keep you from getting sick, and many of the foods you eat, such as yogurt, owe their flavors to bacteria.
Archaea
are just as common as bacteria but are usually less familiar to people because they aren’t known for causing human disease, and they’re still being studied by scientists. On a microscope (or with super-powered eyes), archaea look just like bacteria, so scientists didn’t realize archaea existed until around 40 years ago when improvements in molecular biology made their discovery possible.
Your super-powered eyes could also show you another type of alien creature, even smaller than the cells of bacteria and archaea — viruses (see Chapter 3). Viruses really are like little alien ships that land on your cells and take them over, enslaving the molecules within your cells and making them work to build more viruses. Your cells don’t work for you anymore, and you feel the effects — your throat gets sore, your nose runs, or you ache all over. Fortunately, your immune system comes to the rescue, sending in white blood cells to fight off the invading viruses.
Because bacteria and viruses both make people sick, they often get confused — even in the news media! However, bacteria and viruses have very different structures — bacteria are cells, and viruses are not — which makes a big difference when it comes to medicine. Antibiotics target bacterial cells, and they don’t work on viruses!
SPEAKING THE LANGUAGE OF CELLS
If you want to learn about cells, you need to speak their chemical language. Cells are made of molecules, they communicate through molecules, and they respond to signals by changing existing molecules or making new ones. The DNA code (see Chapter 7), written in the chemical letters A, T, C, and G, is used by your body to create cellular workers like proteins (see Chapter 6) that control how your cells function. DNA and proteins, along with carbohydrates (see Chapter 5) and lipids (see Chapter 8), are the fundamental building blocks that make up your cells and thus your entire body.
The Life of a Cell: How Cells Get What They Need to Survive and Reproduce
Your cells are the smallest piece of you that is alive. All the things that you can think of that you need to do to keep your body alive — get energy from food, take in oxygen, and release wastes — are also true for your cells:
When you eat food, you take in a source of energy and matter for your cells that you process with your cellular metabolism (see
Chapter 10
).
Your cells do cellular respiration (see
Chapter 11
), using oxygen to transfer energy out of food into a form that they can use to do work.
Cells can also use the energy and molecules from food to grow and make new cells (see
Chapter 13
).
Ultimately, you can trace all the food that you eat back to cells, like those of plants, that make food through photosynthesis (see Chapter 12). In fact, life on Earth couldn’t even exist without the organisms that make food, because they capture the energy and matter that all cells need to survive.
Sexual Reproduction: Shuffling the Genetic Deck for the Next Generation
You began life as a single cell, when a sperm cell from your dad combined with an egg cell from your mom. Your parents made these special reproductive cells through a special type of cell division called meiosis (see Chapter 14). Each cell from your parents donated half of your genetic information — 23 chromosomes from Mom and 23 from Dad — for a total of 46 chromosomes in each of your cells. What you look like and much of how you behave is a result of the interaction between the genes you got from Mom and the genes you got from Dad.
Tracking the inheritance of genes and how they interact to determine traits is part of the science of genetics (see Chapters 15). Through genetics, you can understand things like why your eyes are a certain color or why some traits seem to run in families.
DNA to Protein: Following the Instructions in the Genetic Code
The instructions for your traits, from the level of the cell to the level of the whole you, are encoded in your DNA. Whenever your cells divide to make new cells, they must copy your DNA through DNA replication (see Chapter 16) so that each new cell gets a set of instructions. The working cells of your body are constantly reading the DNA code and using the instructions to build molecules, such as proteins, that they need to do their jobs for the body. Proteins are constructed by the combined efforts of two processes, called transcription and translation (see Chapter 17).
Signals, such as hormones, can tell your working cells that they need to change their behavior. To change their behavior, your cells may need to change their tools. Gene regulation (see Chapter 18) allows your cells to turn off some genes for proteins and turn others on. In fact, how your cells use your DNA is just as important as what your code actually says!
DNA Technology: Tackling the World’s Problems
You’ve probably heard a lot about the impacts of biotechnology — genetically modified organisms (GMOs), DNA testing, genome editing, and gene therapy are just some of the topics that regularly appear in the news.
A revolution in biology has occurred over the past 50 years or so, a revolution based on scientists’ ability to read and manipulate the genetic code of life. New technologies developed in the last 30 years allow scientists to rapidly copy and read genes (see Chapter 19), essentially opening up the book of life for everyone to read. Scientists can extract, snip, copy, read, modify, and place DNA from cells into different cells using recombinant DNA technology and genome editing (see Chapter 20).
New branches of biology are growing to study all this new information and present many opportunities for future careers:
Bioinformatics
is a science that blends computing, biology, and information technology to organize and analyze the large amounts of information that are being generated by biologists all around the world.
Genomics
is the study of entire genomes of organisms. By studying all of the DNA sequence of a cell, scientists are discovering new proteins and new understandings of how DNA is regulated in cells.
Proteomics
is the study of the entire body of proteins in a cell and how they interact with each other. The types of proteins found in different cells are compared in order to look for patterns common to certain cell types.
Molecular biology has spread throughout the older branches of biology as well. Botany, zoology, ecology, physiology — every “ology” you can think of, really — now has a molecular component. Living things are studied down to the level of the cell and the molecules, such as DNA and proteins, that make up the cell.
Even medicine is becoming increasingly molecular — Departments of Molecular Medicine are popping up all over — as doctors and scientists seek to understand and treat disease at the level of the cell and molecule. Designer drugs that specifically target the molecular defect of a particular disease are already in the works.
Molecular and cell biology already impacts your life in many ways and will almost certainly become more important in your future.
Chapter 2
Take a Tour inside the Cell
IN THIS CHAPTER
Comparing life on Earth
Exploring the eukaryotic cells of plants, animals, and fungi
Getting to know bacteria and other prokaryotic cells
All living things are made of cells. All cells are built out of the same materials and function in similar ways, showing the relationship of all life on Earth. Eukaryotic cells, such as those of plants and animals, are structurally complex. Prokaryotic cells, such as those of bacteria, have a simpler organization. In this chapter, I present cell structures and their functions for both eukaryotic and prokaryotic cells.
Admiring the Unity and Diversity of Cells
The unity among cells on Earth is truly amazing. All cells have DNA as the genetic material, use the same processes to make proteins, and follow the same basic metabolic principles as other cells. So, on the most fundamental level, cells on Earth show their unity and their relationship to each other.
Beyond the fundamentals, however, cells have fantastic variations. Cells differ in size, from squid neurons that are several feet in length to invisible bacteria. They differ in function, from free-living amoebae to muscle cells in your heart to sperm cells inside the pollen grain of a plant. Cells also differ in their role in the environment, from food makers to predators to decomposers that eat the dead.
Based on their basic chemistry, structure, and hereditary material, all cells on Earth fall into one of three groups, as if the family tree of life on Earth split into three main branches, called domains:
Eucarya:
Plants, animals, fungi, and protists
Bacteria:
Familiar, single-celled microorganisms, some of which are useful to humans and some of which cause human diseases
Archaea:
Single-celled microorganisms found in all types of environments, but first discovered in extreme environments, such as hot springs
Cells of the Eucarya are structurally distinct from cells of the Bacteria and the Archaea. Cells of Eukarya are eukaryotic, while cells of the Bacteria and Archaea are prokaryotic.
Eukaryotic cells
have a
nucleus,
a chamber within the cell that is separated by a membrane and contains the DNA. They also have
organelles,
membrane-enclosed structures inside the cell that perform various functions for the cell. Finally, eukaryotic cells are typically much larger than prokaryotic cells, on average about ten times larger. (For more on these cells, see the section “
Your Body, Your Cells: Eukaryotic Cells
,” later in this chapter.)
Prokaryotic cells
don’t have a nucleus; their DNA is contained within the cytoplasm of the cell. They also don’t have any membrane-enclosed organelles, and they’re typically much smaller than eukaryotic cells. (See the upcoming section “
Tiny but Mighty: Prokaryotic Cells
” for more on prokaryotic cells.)
The root eu means true and karyon means seed, so eukaryotic cells are true-seeded cells because the nucleus looks a little bit like a seed inside the cell. On the other hand, pro means before, so prokaryotes are before seed cells because they don’t have a nucleus.
Finding Common Ground: Structures in All Cells
Every living thing on Earth, including animals, plants, bacteria, yeast, and mold, is made of cells. Some living things, such as animals and plants, are multicellular; their bodies are made of many cells. Other living things, such as bacteria and yeast, are unicellular — made of just one cell. But whether a cell is one of many or the only one making up a living thing, all cells have certain things in common:
Just like you have skin that covers your body, all cells have a boundary that separates them from their environment. The boundary of a cell is called the
plasma membrane
(or
cytoplasmic membrane
).
The area inside all cells is called the
cytoplasm
.
All cells contain
deoxyribonucleic acid
(DNA), which determines how the cell is built and how it functions.
All cells make proteins to help them function. Proteins are built on structures called
ribosomes
, so all cells have ribosomes.
The following sections describe these four items.
Customs: Plasma membrane
The plasma membrane, shown in Figure 2-1, separates the cell from its environment and is selectively permeable, which means it chooses what enters and exits the cell. You can think of the plasma membrane as an international boundary where customs officers inspect the traffic and determine what is allowed to cross back and forth. The molecules that act like customs officers are proteins. Proteins called receptors detect signals from the environment of the cell, and transport proteins help some molecules get across the membrane. (For more details on how molecules cross the plasma membrane, see Chapter 9.)
FIGURE 2-1: The fluid-mosaic model of plasma membranes.
The plasma membrane is made up of two layers of phospholipids along with proteins, sterols, and carbohydrates:
Phospholipids
are molecules that are similar in structure to fat molecules. Like fat molecules, part of the phospholipids — the
hydrophobic tails
part
—
doesn’t mix well with water. Phospholipids also have a hydrophilic head that is attracted to water. Phospholipids make up almost 50 percent of the plasma membrane.
Proteins
are stuck in the membrane and associated with the edges of the membrane. Proteins make up almost 50 percent of the plasma membrane.
Sterols
are also embedded in plasma membranes. The type of sterol depends on the type of cell. Animal cells have cholesterol in their plasma membranes. Sterols are present in small amounts in the plasma membrane.
Carbohydrates
are attached to receptors on the outside of the plasma membrane. They’re present in small amounts in the plasma membrane.
The components of the plasma membrane are organized into a phospholipid bilayer. Because the hydrophobic tails of the phospholipids don’t mix well in water, the two layers of phospholipids make a “fat sandwich” with their two rows of hydrophilic heads pointed toward the water and the hydrophobic tails sandwiched between them and away from the water. Transport proteins and sterols are embedded within the phospholipid bilayer, and carbohydrates are attached to receptors on the outside of the cell.
The structure and behavior of the plasma membrane are described by a theory called the fluid mosaic model of the plasma membrane, which basically says that membranes are made of several components and that these components can move within the membrane.
The phospholipids and proteins move back and forth within the plasma membrane, making the plasma membrane a fluid structure. Thus, the plasma membrane is flexible and able to fuse with other membranes. For example, small membranes may carry proteins up to the surface of the cell so that the protein can leave the cell. The membranes carrying the proteins simply melt into the plasma membrane, just like two soap bubbles merge with each other.
A happenin’ place: The cytoplasm
The fluid-filled interior of the cell is called the cytoplasm. The cytoplasm is filled with molecules, structures, and activity, like a crowded party packed with people and conversations. Many of the chemical reactions that make up the metabolism of the cell happen in the cytoplasm, including important reactions that build proteins. Molecules and cellular components, including organelles, are constantly moving around in cells, being transported from one place to another by proteins or just moving randomly around due to their own kinetic energy (energy of motion) and attraction to other molecules.
The library: DNA-containing region
All cells contain DNA as their genetic material. (For more on DNA, see Chapter 7.) However, the location of the DNA is different in the two structural types of cells:
In eukaryotic cells, the DNA is separated from the cytoplasm by membranes inside the cell, forming a structure called the
nucleus.
(For more information on the nucleus, see the section “
Home office: The nucleus
,” later in this chapter.)
In prokaryotic cells, the DNA is located within the cytoplasm in a region of the cell called the
nucleoid.
Workbenches: Ribosomes
All cells need to be able to make proteins because proteins are the main worker molecules of the cell. Proteins are made on structures called ribosomes. All ribosomes have certain things in common:
Ribosomes are made of two types of molecules:
ribosomal RNA
(rRNA) and proteins. (For more on rRNA, see
Chapter 7
.)
The molecules that make up ribosomes are twisted together to form two components: the large subunit and the small subunit. These subunits are built separately from each other and come together to form a completed ribosome when protein synthesis begins.
The ribosomes of prokaryotic cells are different from those of eukaryotic cells. Although both types of ribosomes are made of rRNA and protein, the exact composition of those molecules is different.
Ribosome size is measured in Svedberg units (S), a unit that describes how fast particles fall out of solution during centrifugation. As a centrifuge spins things around really fast, larger, more dense particles fall to the bottom of the centrifuge tube (“spin out” of solution) faster than smaller, less dense particles. So, centrifugation, and Svedberg units, can tell you the relative size of particles, such as prokaryotic and eukaryotic ribosomes:
Prokaryotic ribosomes are smaller than eukaryotic ribosomes
. They’re called
70S
ribosomes because complete ribosomal spin out at 70S. If you spin the ribosomal subunits separately, the large subunit spins out at 50S, and the small subunit spins out at 30S. Only in biology does 50+30=70! This answer is because when the two subunits join together to make a completed ribosome, they pack together into a tight package.
Eukaryotic ribosomes are larger than prokaryotic ribosomes
and spin out at 80S. The large subunit alone spins out at 60S, and the small subunit at 40S. More strange biological math: 60+40=80! Again, the two subunits pack together to form the complete ribosome.
In eukaryotic cells, ribosomes that are located in different places in the cell have slightly different functions:
Free ribosomes
are located in the cytoplasm of the cell. They make proteins that will function in the cytoplasm of the cell.
Membrane-bound ribosomes
attach themselves to the membrane of the
rough endoplasmic reticulum,
which is located inside cells. Membrane-bound ribosomes produce proteins that will either be part of membranes or that will be released from the cell.
Your Body, Your Cells: Eukaryotic Cells
The eukaryotic cells of animals, plants, fungi, and microscopic creatures called protists have many similarities in structure and function. They have the structures common to all cells: a plasma membrane, cytoplasm, and ribosomes.
All eukaryotic organisms contain cells that have a nucleus, organelles, and many internal membranes.
With all the wonderful diversity of life on Earth, however, you’re probably not surprised to discover that eukaryotic cells have many differences. By comparing the structure of a typical animal cell, shown in Figure 2-2, with that of a typical plant cell, shown in Figure 2-3, you can see some of the differences among eukaryotic cells.
Cell walls,
additional reinforcing layers outside the plasma membrane, are present in the cells of plants, fungi, and some protists, but not in animal cells.
Chloroplasts,
which are needed for photosynthesis, are found in the cells of plants and algae, but not animals.
Large, central vacuoles,
which contain fluid and are separated from the cytoplasm with a membrane, are found in the cells of plants and algae, but not animals.
Centrioles,
small protein structures that appear during cell division, are found in the cells of animals, but not plants.
FIGURE 2-2: Structures in a typical animal cell.
FIGURE 2-3: Structures in a typical plant cell.
Home office: The nucleus
The nucleus, shown in Figure 2-4, houses and protects the cell’s DNA, which contains all the instructions necessary for the cell to function. The DNA is like a set of blueprints for the cell, so you can think of the nucleus as the office where the blueprints are kept. If information from the blueprints is required, the information is copied into RNA molecules and moved out of the nucleus. The DNA plans stay safely locked away.
The boundary of the nucleus is the nuclear envelope, which is made of two phospholipid bilayers similar to those that make up the plasma membrane.
The phospholipids bilayers of the nuclear envelope are supported by a scaffold of protein cables, called the nuclear lamina, on the inner surface of the nucleus. The nuclear envelope separates the contents of the nucleus from the cytoplasm. The structures within the nucleus are
FIGURE 2-4: The nucleus.
DNA in the form of chromosomes or chromatin:
When a cell is about to divide to make a copy of itself, it copies its DNA and bundles the DNA up tightly so that the cell can move the DNA around more easily. The tightly bundled DNA molecules are visible through a microscope as little structures in the nucleus called
chromosomes.
Most of the time, however, when a cell is just functioning and not about to divide, the DNA is very loose within the nucleus, like a bunch of long, very thin spaghetti noodles. When the DNA is in this form, it is called
chromatin.
Nucleoli where ribosomal subunits are made:
Information in the DNA needs to be read in order to make the small and large subunits needed to build ribosomes. The cell builds the ribosomal subunits in areas of the nucleus called nucleoli. Then, the cell ships the subunits out of the nucleus to the cytoplasm, where they join together for protein synthesis. When you stain cells and look at them under the microscope, nucleoli look like large spots within the nucleus.
The DNA plans for the cell are kept in the nucleus, but most of the activity of the cell occurs in the cytoplasm. Because the DNA is separate from the rest of the cell, a lot of traffic crosses back and forth between the nucleus and the cytoplasm. Molecules enter and exit the nucleus through small holes, called nuclear pores, that pass through the nuclear membrane. Groups of proteins organize into little rings that penetrate through the nuclear envelope to form the nuclear pores. The traffic in and out of the nuclear pores include the following:
RNA molecules
and
ribosomal subunits
made in the nucleus must exit to the cytoplasm.
Proteins
made in the cytoplasm but needed for certain processes, such as copying the DNA, must cross into the nucleus.
Nucleotides,
building blocks for DNA and RNA, must cross into the nucleus so that the cell can make new DNA and RNA molecules.
ATP
molecules that provide energy for processes inside the nucleus like assembly of DNA molecules (see
Chapter 10
for more on ATP).
Traffic through the nuclear pores is controlled by proteins called importins and exportins. Proteins that are to be moved into or out of the nucleus have specific chemical tags on them that act like zip codes, telling the importins and exportins which way to move the protein with the tag. The movement of molecules into and out of the cell requires the input of energy from the cell in the form of adenosine triphosphate (ATP).
Post office: The endomembrane system
The endomembrane system, shown in Figure 2-5, of the eukaryotic cell constructs proteins and lipids and then ships them where they need to go. Because this system is like a large package-shipping company, you can think of it as the post office of the cell.
FIGURE 2-5: The endomembrane system.
The endomembrane system has several components:
The
endoplasmic reticulum
is a set of folded membranes that begins at the nucleus and extends into the cytoplasm. It begins with the outer membrane of the nuclear envelope and then twists back and forth like switchbacks on a steep mountain trail. The endoplasmic reticulum comes in two types:
Rough endoplasmic reticulum
(RER) is called rough because it’s studded with ribosomes. Ribosomes that begin to make a protein that has a special destination, such as a particular organelle or membrane, will attach themselves to the rough endoplasmic reticulum while they make the protein. As the protein is made, it’s pushed into the middle of the rough ER, which is called the
lumen.
Once inside the lumen, the protein is folded and tagged with carbohydrates. It will then get pushed into a little membrane bubble, called a
transport vesicle
, to travel to the Golgi apparatus for further processing.
Smooth endoplasmic reticulum
(SER) doesn’t have attached ribosomes. It makes lipids — for example, phospholipids for cell membranes. Lipids from the SER may also travel to the Golgi apparatus.
The
Golgi apparatus
looks a little bit like a stack of pancakes because it’s made of a stack of flattened membrane sacs, called
cisternae
. The side of the stack closest to the nucleus is called the
cis
face of the Golgi, whereas the side farthest from the nucleus is called the
trans
face. Molecules arrive at the cis face of the Golgi and incorporate into the nearest cisterna. Lipids become part of the membrane itself, while proteins get pushed into the middle, or lumen, of the cisterna. The Golgi apparatus constantly changes as new cisternae form at the cis face, and old cisternae are removed from the trans face. As molecules make their journey through this flowing system, they’re modified and marked with chemical tags, so that they’ll get shipped to their proper destination.
Vesicles
are little bubbles of membrane in the cell and come in several types:
Transport vesicles
carry molecules around the cell. They’re like the large envelopes that you put your letters in. Transport vesicles travel from the ER to the Golgi and then to the plasma membrane to bring molecules where they need to go. They travel by gliding along protein cables that are part of the cytoskeleton. (For more information on the cytoskeleton, see the section “
Scaffolding and railroad tracks: The cytoskeleton
,” later in this chapter.)
Lysosomes
are the garbage disposals of the cell. They contain digestive enzymes that can break down large molecules, organelles, and even bacterial cells.
Secretory vesicles
bring materials to the plasma membrane so that the cell can release, or secrete, the materials.
Peroxisomes
are small organelles encircled by a single membrane. Often, they help break down lipids, such as fatty acids. Also, depending on the type of cell they are in, peroxisomes may be specialists in breaking down particular molecules. For example, peroxisomes in liver cells break down toxins, such as the ethanol from alcoholic beverages. In plants cells,
glyoxisomes,
a special kind of peroxisome, help convert stored oils into molecules that plants can easily use for energy.
Altogether, the endomembrane system works as a sophisticated manufacturing, processing, and shipping plant. This system is particularly important in specialized cells that make lots of a particular protein and then ship them out to other cells. These types of cells actually have more endoplasmic reticulum than other cells so that they can efficiently produce and export large amounts of protein.
As an example of how the endomembrane system functions, follow the pathway of synthesis and transport for an exported protein:
A ribosome begins to build a protein, such as insulin, that will be exported from the cell.
At the beginning of the protein is a recognizable marker that causes the ribosome to dock at the surface of the rough endoplasmic reticulum.
The ribosome continues to make the protein, and the protein is pushed into the lumen of the RER.
Inside the lumen, the protein folds up, and carbohydrates are attached to it.
The protein is pushed into the membrane of the RER, which pinches around and seals to form a vesicle, and the vesicle carries the protein from the RER to the Golgi.
The vesicle fuses with the cis face of the Golgi apparatus, and the protein is delivered to the lumen of the Golgi, where the protein is modified.
The protein eventually leaves in a vesicle formed at the trans face,
which travels to the plasma membrane, fuses with the membrane, and releases the protein to the outside of the cell.
The fireplace: Mitochondria
The mitochondrion (see Figure 2-6) is the organelle where eukaryotes extract energy from their food by cellular respiration (see Chapter 11).
Mitochondria are like the power plants of the cell because they transfer energy from food to ATP. ATP is an easy form of energy for cells to use, so mitochondria help cells get usable energy.
FIGURE 2-6: The mitochondrion.
Part of the process that extracts the energy from food requires a membrane, so mitochondria have lots of internal folded membrane to give them more area to run this process. Mitochondria actually have two membranes, the outer membrane and the inner membrane. The inner membrane is the one that is folded back and forth to create more area for energy extraction; the folds of this membrane are called cristae. The outer membrane separates the interior of the mitochondrion from the cytoplasm of the cell.
The two membranes of the mitochondrion create different compartments within the mitochondrion:
The space between the two membranes of the mitochondrion is the
intermembrane space.
The inside of the mitochondrion is the
matrix.
Mitochondria also contain ribosomes for protein synthesis and a small, circular piece of DNA that contains the code for some mitochondrial proteins. The ribosomes and DNA of mitochondria resemble those found in bacterial cells. (To learn why, see the sidebar “Where do little organelles come from?”)
In the kitchen: Chloroplasts
Chloroplasts, shown in Figure 2-7, are the place where eukaryotes make food molecules by the process of photosynthesis (see Chapter 12). Chloroplasts are found in the cells of plants and algae.
FIGURE 2-7: The chloroplast.
Like mitochondria, chloroplasts have two membranes, an inner membrane and an outer membrane. In addition, they have little sacs of membranes called thylakoids stacked up in towers called grana.
The multiple membranes of the chloroplast divide it into several different spaces:
The
intermembrane space
is between the inner and outer membranes.
The central, fluid-filled part of the chloroplast is called the
stroma.
The interior of the thylakoid is another fluid-filled space.
Like mitochondria, chloroplasts contain their own ribosomes for protein synthesis and a small, circular piece of DNA that contains the code for some chloroplast proteins.
