Molecular and Cell Biology For Dummies

Introduction

Molecular and cellular 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 cellular biology. Gaining an understanding of molecular and cellular 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 cellular 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 & Cellular Biology For Dummies is an overview of the fundamentals of molecular and cellular biology. 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 ten years of teaching this subject. These types of gimmicks help my students wrap their brains around the fundamental principles of molecular and cellular biology, and I hope these strategies will help you, too.

In Molecular & Cell Biology For Dummies, I emphasize the main concepts and fundamental processes that are at the heart of molecular and cellular 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 cellular 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 cellular biology is a challenge for most people. I hope that this book will help you succeed in that challenge.

Conventions Used in This Book

In order to explain things as clearly as possible, I keep scientific jargon to a minimum and present information in straightforward, linear style. I break dense information into main concepts and divide complicated processes into steps.

To help you find your way through the subjects in this book, I use the following style conventions:

Italic is used for emphasis and to highlight new words or terms that are defined in the text.

Boldface is used to indicate key words in bulleted lists or the action parts of numbered steps.

Web addresses are written in monofont so that you can easily recognize them.

What You’re Not to Read

Sidebars are shaded gray boxes that include stories or information related to the main topic, but not necessary to your understanding. You can skip the sidebars if you want, but they contain some pretty fun and interesting information so I’m guessing you’ll read them anyway.

You can also skip any information marked with a Technical Stuff icon (see Icons Used in This Book later in this Introduction) without hurting your understanding of the main concepts. For someone who wants or needs to pick up all the details of a process, the Technical Stuff provides a more in-depth explanation.

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 cellular 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 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.

How This Book Is Organized

This book is divided into seven parts, with each part containing related subjects. Like all For Dummies books, each chapter is self-contained, so you can pick up whenever you need it and jump into the topic you’re working on. Once I explain a subject, I use that information in later topics. So, if you don’t read the book in order, you may occasionally want to refer to another section for background information. In those cases, I refer you to the appropriate chapter.

Part I: The World of the Cell

All living things are made of cells. In this part, I introduce the fundamental structure and function of cells. I also introduce viruses, microscopic particles that attack and destroy cells.

Part II: Molecules: The Stuff of Life

Living things are made of cells and cells are made of molecules. In this part, I explain the fundamental cellular chemistry that is necessary to understand the molecular nature of cells.

Part III: The Working Cell

The cell is the fundamental unit of life and possesses all the characteristics of living things: Cells require food, reproduce themselves, respond to signals, and exchange materials. In this part, I describe how cells function, including how they communicate, obtain matter and energy, and reproduce.

Part IV: Genetics: From One Generation to the Next

In living things that reproduce sexually, including humans, parents pass the instructions for life to their offspring. In this part, I describe how parental cells organize their DNA during sexual reproduction and demonstrate how scientists can predict and analyze inheritance patterns using the principles of Mendelian genetics.

Part V: Molecular Genetics: Reading the Book of Life

The DNA code is the underlying programming for how cells function and develop. In this part, I explain the essential core of molecular biology, including how DNA is copied and read by cells, how it determines the traits of organisms, and how DNA is regulated by the cell.

Part VI: Tools of Molecular Biology: Harnessing the Power of DNA

Powerful tools have enabled scientists to explore and manipulate the DNA code, opening a new frontier in biological science. In this part, I describe how scientists can use the tools of molecular biology to explore genomes and apply biological knowledge to solve current world problems.

Part VII: The Part of Tens

Like all For Dummies books, this book contains a Part of Tens where I include lists of fun and interesting topics related to molecular and cellular biology. In this part, I include ten fundamental rules that govern the behavior of cells and ten tips for improving your grade!

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:

Remember.eps I use this icon to emphasize main ideas that you should definitely keep in mind.

Tip.eps I use this icon to present study tips or other information that can help you navigate through difficult material.

TechnicalStuff.eps 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.

Warning(bomb).eps 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.

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 I

The World of the Cell

In this part . . .

Molecular and cellular biology looks at life on the smallest level, from the microscopic cells that make up living things to the mysterious molecules within those cells that contain the programming for how life functions. Cells are the smallest living things and they have all the properties of life, including reproduction, response to environmental signals, a need for energy, and the release of waste products.

Viruses are very small parasites of cells that have the ability to attack cells and convert them into factories for viral reproduction. In this part, I explain the science of molecular and cellular biology and present 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

Reading the genetic code

Molecular and cellular 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 cellular biology and how it relates to your life. My goal is to illustrate the importance of molecular and cellular 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, hand-held 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.

Tip.eps 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 chemistry. 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 and 16). 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 17) 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 18).

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 19) 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 fingerprinting, the Human Genome Project, 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. Scientists can extract, snip, copy, read, modify, and place DNA from cells into different cells using recombinant DNA technology (see Chapter 20). New technologies developed in the last 20 years allow scientists to read the entire genetic code, or genome, of organisms (see Chapter 21), essentially opening up the book of life for everyone to read.

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 cellular 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 the neurons of giant squid to tiny bacteria. They differ in function, from free-living amoebae to muscle cells in an animal 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.)

Tip.eps 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 contains the plans for 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 — 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.

Remember.eps 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 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.

Remember.eps 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