Ringkasan

THE ORIGIN AND EVOLUTION OF CELLS

The First Cell:

All present-day cells, both prokaryotes and eukaryotes, are descended from a single ancestor. The first cell is thought to have arisen at least 3.8 billion years ago as a result of enclosure of self-replicating RNA in a phospholipid membrane.

KEY TERMS: prokaryotic cell, eukaryotic cell, RNA world, phospholipid, amphipathic, hydrophobic, hydrophilictop link

The Evolution of Metabolism:

The earliest reactions for the generation of metabolic energy were a form of anaerobic glycolysis. Photosynthesis then evolved, followed by oxidative metabolism.

KEY TERMS: adenosine 5′-triphosphate (ATP), glycolysis, photosynthesis, oxidative metabolismtop link

Present-Day Prokaryotes:

Present-day prokaryotes are divided into two groups, the archaebacteria and the eubacteria, which diverged early in evolution.

KEY TERMS:archaebacteria, eubacteria, cyanobacteria, Escherichia coli (E. coli), cell wall, plasma membrane, ribosometop link

Eukaryotic Cells:

Eukaryotic cells, which are larger and more complex than prokaryotic cells, contain a nucleus, cytoplasmic organelles, and a cytoskeleton. They are thought to have evolved from symbiotic associations of prokaryotes.

KEY TERMS:nucleus, mitochondrion, chloroplast, lysosome, peroxisome, vacuole, endoplasmic reticulum, Golgi apparatus, cytoskeleton, endosymbiosistop link

The Development of Multicellular Organisms:

The simplest eukaryotes are unicellular organisms, such as yeasts and amoebas. Multicellular organisms evolved from associations between such unicellular eukaryotes, and division of labor led to the development of the many kinds of specialized cells that make up present-day plants and animals.

KEY TERMS: yeast, Saccharomyces cerevisiae, pseudopodium, parenchyma cell, collenchyma cell, schlerenchyma cell, epidermal cell, epithelial cell, fibroblast, erythrocyte, granulocyte, monocyte, macrophage, lymphocyte, neurontop link

CELLS AS EXPERIMENTAL MODELS

E. coli:

Because of their genetic simplicity and ease of study, bacteria such as E. coli are particularly useful for investigation of fundamental aspects of biochemistry and molecular biology.top link

Yeasts:

As the simplest eukaryotic cells, yeasts are an important model for studying various aspects of eukaryotic cell biology.top link

Dictyostelium discoideum:

The unicellular eukaryote Dictyostelium is widely used for experimental analysis of cell movement.

KEY TERMS:Dictyostelium discoideumtop link

Caenorhabditis elegans:

The nematode C. elegans is a simple multicellular organism that serves as an important model in developmental biology.

KEY TERMS:Caenorhabditis elegans, somatic cell, germ celltop link

Drosophila melanogaster:

Because of extensive genetic analysis, studies of the fruit fly Drosophila have led to major advances in understanding animal development.

KEY TERMS:Drosophila melanogastertop link

Arabidopsis thaliana:

The small flowering plant Arabidopsis is widely used as a model for studies of plant molecular biology and development.

KEY TERMS:Arabidopsis thalianatop link

Vertebrates:

Many kinds of vertebrate cells can be grown in culture, where they can be studied under controlled laboratory conditions. Specialized cell types, such as neurons and muscle cells, provide useful models for investigating particular aspects of cell biology. The frog Xenopus laevis and zebrafish are important models for studies of early vertebrate development, and the mouse is a mammalian species suitable for genetic analysis.

KEY TERMS:Xenopus laevis, zebrafish, transgenic mousetop link

TOOLS OF CELL BIOLOGY

Light Microscopy:

A variety of methods are used to visualize cells and subcellular structures and to determine the intracellular localization of specific molecules using the light microscope.

KEY TERMS: resolution, bright-field microscopy, phase-contrast microscopy, differential interference-contrast microscopy, video-enhanced differential interference-contrast microscopy, fluorescence microscopy, green fluorescent protein (GFP), confocal microscopy, two-photon excitation microscopytop link

Electron Microscopy:

Electron microscopy, with a resolution that is approximately a hundredfold greater than that of light microscopy, is used to analyze details of cell structure.

KEY TERMS:transmission electron microscopy, metal shadowing, freeze fracture, freeze etching, scanning electron microscopytop link

Subcellular Fractionation:

The organelles of eukaryotic cells can be isolated for biochemical analysis by differential centrifugation.

KEY TERMS: differential centrifugation, ultracentrifuge, density-gradient centrifugation, velocity centrifugation, equilibrium centrifugationtop link

Growth of Animal Cells in Culture:

The propagation of animal cells in culture has allowed studies of the mechanisms that control cell growth and differentiation.

KEY TERMS: primary culture, immortal cell linetop link

Culture of Plant Cells:

Cultured plant cells can differentiate to form specialized cell types and, in some cases, can regenerate entire plants.

KEY TERMS: totipotencytop link

Viruses:

Viruses provide simple models for studies of cell function.

KEY TERMS:bacteriophage, retrovirus

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