H. Lodish - Molecular Cell Biology (5ed, Freeman, 2003)

1LIFE BEGINSWITH CELLSA single ~200 micrometer (m) cell, the human egg, withsperm, which are also single cells. From the union of an eggand sperm will arise the 10 trillion cells of a human body.[Photo Researchers, Inc.]Like ourselves, the individual cells that form our bodiescan grow, reproduce, process information, respond tostimuli, and carry out an amazing array of chemical reactions.

These abilities define life. We and other multicellularorganisms contain billions or trillions of cells organized intocomplex structures, but many organisms consist of a singlecell. Even simple unicellular organisms exhibit all the hallmark properties of life, indicating that the cell is the fundamental unit of life.

As the twenty-first century opens, we facean explosion of new data about the components of cells,what structures they contain, how they touch and influenceeach other. Still, an immense amount remains to be learned,particularly about how information flows through cells andhow they decide on the most appropriate ways to respond.Molecular cell biology is a rich, integrative science thatbrings together biochemistry, biophysics, molecular biology,microscopy, genetics, physiology, computer science, and developmental biology. Each of these fields has its own emphasis and style of experimentation. In the followingchapters, we will describe insights and experimental approaches drawn from all of these fields, gradually weavingthe multifaceted story of the birth, life, and death of cells.

Westart in this prologue chapter by introducing the diversity ofcells, their basic constituents and critical functions, and whatwe can learn from the various ways of studying cells.1.1 The Diversity and Commonalityof CellsCells come in an amazing variety of sizes and shapes (Figure1-1). Some move rapidly and have fast-changing structures, aswe can see in movies of amoebae and rotifers. Others arelargely stationary and structurally stable. Oxygen kills somecells but is an absolute requirement for others. Most cells inmulticellular organisms are intimately involved with othercells.

Although some unicellular organisms live in isolation,others form colonies or live in close association with othertypes of organisms, such as the bacteria that help plants to extract nitrogen from the air or the bacteria that live in our intestines and help us digest food. Despite these and numerousOUTLINE1.1 The Diversity and Commonality of Cells1.2 The Molecules of a Cell1.3 The Work of Cells1.4 Investigating Cells and Their Parts1.5 A Genome Perspective on Evolution12CHAPTER 1 • Life Begins with Cells(a)(b)(c)(d)(e)(f)(g)(h)▲ FIGURE 1-1 Cells come in an astounding assortment ofshapes and sizes.

Some of the morphological variety of cells isillustrated in these photographs. In addition to morphology, cellsdiffer in their ability to move, internal organization (prokaryoticversus eukaryotic cells), and metabolic activities. (a) Eubacteria;note dividing cells. These are Lactococcus lactis, which are usedto produce cheese such as Roquefort, Brie, and Camembert.(b) A mass of archaebacteria (Methanosarcina) that produce theirenergy by converting carbon dioxide and hydrogen gas tomethane. Some species that live in the rumen of cattle give riseto >150 liters of methane gas/day.

(c) Blood cells, shown in falsecolor. The red blood cells are oxygen-bearing erythrocytes, thewhite blood cells (leukocytes) are part of the immune systemand fight infection, and the green cells are platelets that providesubstances to make blood clot at a wound. (d) Large single cells:fossilized dinosaur eggs.

(e) A colonial single-celled green alga,Volvox aureus. The large spheres are made up of many individualcells, visible as blue or green dots. The yellow masses inside aredaughter colonies, each made up of many cells. (f) A singlePurkinje neuron of the cerebellum, which can form more than ahundred thousand connections with other cells through thebranched network of dendrites. The cell was made visible byintroduction of a fluorescent protein; the cell body is the bulb atthe bottom. (g) Cells can form an epithelial sheet, as in the slicethrough intestine shown here.

Each finger-like tower of cells, avillus, contains many cells in a continuous sheet. Nutrients aretransferred from digested food through the epithelial sheet to theblood for transport to other parts of the body. New cells formcontinuously near the bases of the villi, and old cells are shedfrom the top. (h) Plant cells are fixed firmly in place in vascularplants, supported by a rigid cellulose skeleton. Spaces betweenthe cells are joined into tubes for transport of water and food.other differences, all cells share certain structural features andcarry out many complicated processes in basically the sameway. As the story of cells unfolds throughout this book, wewill focus on the molecular basis of both the differences andsimilarities in the structure and function of various cells.gle closed compartment that is surrounded by the plasmamembrane, lacks a defined nucleus, and has a relatively simpleinternal organization (Figure 1-2a). All prokaryotes have cellsof this type.

Bacteria, the most numerous prokaryotes, aresingle-celled organisms; the cyanobacteria, or blue-green algae,can be unicellular or filamentous chains of cells. Although bacterial cells do not have membrane-bounded compartments,many proteins are precisely localized in their aqueous interior,or cytosol, indicating the presence of internal organization. Asingle Escherichia coli bacterium has a dry weight of aboutAll Cells Are Prokaryotic or EukaryoticThe biological universe consists of two types of cells—prokaryotic and eukaryotic.

Prokaryotic cells consist of a sin-[Part (a) Gary Gaugler/ Photo Researchers, Inc. Part (b) Ralph Robinson/Visuals Inlimited, Inc. Part (c) NIH/Photo Researchers, Inc. Part (d)John D. Cunningham/Visuals Unlimited, Inc. Part (e) CarolinaBiological/Visuals Unlimited, Inc. Part (f) Helen M. Blau, StanfordUniversity. Part (g) Jeff Gordon, Washington University School ofMedicine.

Part (h) Richard Kessel and C. Shih/Visuals Unlimited, Inc.]1.1 • The Diversity and Commonality of Cells(a) Prokaryotic cell3(b) Eukaryotic cellNucleusPeriplasmic spaceand cell wallGolgi vesiclesLysosomeOuter membraneInner (plasma)membraneNucleoidMitochondrion0.5 mEndoplasmic reticulumNucleoid1 mNuclear membranePlasma membraneGolgi vesiclesNucleusMitochondrionPeroxisomeLysosomeInner (plasma) membraneCell wallPeriplasmic spaceOuter membraneRough endoplasmicreticulumSecretory vesicle▲ FIGURE 1-2 Prokaryotic cells have a simpler internalorganization than eukaryotic cells. (a) Electron micrograph of athin section of Escherichia coli, a common intestinal bacterium.The nucleoid, consisting of the bacterial DNA, is not enclosedwithin a membrane.

E. coli and some other bacteria aresurrounded by two membranes separated by the periplasmicspace. The thin cell wall is adjacent to the inner membrane.(b) Electron micrograph of a plasma cell, a type of white bloodcell that secretes antibodies. Only a single membrane (the plasmamembrane) surrounds the cell, but the interior contains manymembrane-limited compartments, or organelles. The definingcharacteristic of eukaryotic cells is segregation of the cellular DNAwithin a defined nucleus, which is bounded by a doublemembrane. The outer nuclear membrane is continuous with therough endoplasmic reticulum, a factory for assembling proteins.Golgi vesicles process and modify proteins, mitochondria generateenergy, lysosomes digest cell materials to recycle them,peroxisomes process molecules using oxygen, and secretoryvesicles carry cell materials to the surface to release them.25 1014 g.

Bacteria account for an estimated 1–1.5 kg ofthe average human’s weight. The estimated number of bacteria on earth is 5 1030, weighing a total of about 1012 kg.Prokaryotic cells have been found 7 miles deep in the oceanand 40 miles up in the atmosphere; they are quite adaptable!The carbon stored in bacteria is nearly as much as the carbonstored in plants.Eukaryotic cells, unlike prokaryotic cells, contain a defined membrane-bound nucleus and extensive internal mem-branes that enclose other compartments, the organelles (Figure 1-2b). The region of the cell lying between the plasmamembrane and the nucleus is the cytoplasm, comprising thecytosol (aqueous phase) and the organelles.

Eukaryotes comprise all members of the plant and animal kingdoms, including the fungi, which exist in both multicellular forms (molds)and unicellular forms (yeasts), and the protozoans (proto,primitive; zoan, animal), which are exclusively unicellular.Eukaryotic cells are commonly about 10–100 m across,[Part (a) courtesy of I. D. J. Burdett and R. G. E. Murray. Part (b) fromP.