2 the Structure and Ultrastructure of the Cell Gunther Neuhaus Institut Fu¨R Zellbiologie, Freiburg, Germany
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2 The Structure and Ultrastructure of the Cell Gunther Neuhaus Institut fu¨r Zellbiologie, Freiburg, Germany 2.1 Cell Biology . .........................40 2.2.7.6 Isolating Secondary Walls . 107 2.1.1 Light Microscopy . 43 2.2.8 Mitochondria . 109 2.1.2 Electron Microscopy . 45 2.2.8.1 Shape Dynamics and Reproduction . 110 2.2.8.2 Membranes and Compartmentalization in 2.2 The Plant Cell . .........................46 Mitochondria . 112 2.2.1 Overview . 46 2.2.9 Plastids . 113 2.2.2 The Cytoplasm . 50 2.2.9.1 Form and Ultrastructure of 2.2.2.1 The Cytoskeleton . 51 Chloroplasts . 114 2.2.2.2 Motor Proteins and Cellular Kinetic 2.2.9.2 Other Plastid Types, Starches . 116 Processes . 55 2.2.2.3 Flagella and Centrioles . 57 2.3 Cell Structure in Prokaryotes ............. 119 2.2.3 The Cell Nucleus . 59 2.3.1 Reproduction and Genetic Apparatus . 122 2.2.3.1 Chromatin . 60 2.3.2 Bacterial Flagella . 124 2.2.3.2 Chromosomes and Karyotype . 63 2.3.3 Wall Structures . 125 2.2.3.3 Nucleoli and Preribosomes . 64 2.2.3.4 Nuclear Matrix and Nuclear Membrane . 65 2.4 The Endosymbiotic Theory and the 2.2.3.5 Mitosis and the Cell Cycle . 66 Hydrogen Hypothesis . ............. 125 2.2.3.6 Cell Division . 73 2.4.1 Endocytobiosis . 126 2.2.3.7 Meiosis . 73 2.4.2 Origin of Plastids and Mitochondria by 2.2.3.8 Crossing-Over . 79 Symbiogenesis . 127 2.2.3.9 Syngamy . 79 2.2.4 Ribosomes . 79 2.2.5 Membranes . 82 The structure and living manifestation of cells are the 2.2.5.1 Molecular Components . 82 realm of cell biology. This discipline unites ultrastructure 2.2.5.2 The Fluid Mosaic Model . 83 (microstructure, fine structure) research, biochemistry, 2.2.5.3 Membranes as Compartment Boundaries . 83 and molecular biology, as well as many aspects of physi- 2.2.6 Cellular Membranes and Compartments . 85 ology. Before 1950, before the modern methods of cell 2.2.6.1 The Cell Membrane . 85 research had been established, the study of cells was called 2.2.6.2 The Endoplasmic Reticulum . 86 cytology (Greek ky´tos, bubble, cell). It was mainly 2.2.6.3 Dictyosomes and the Golgi Apparatus . 87 restricted to the light microscopy of cells. 2.2.6.4 Membrane Traffic, Exocytosis, and Cell research is hugely significant because all forms Endocytosis . 90 of life are organized in cells. Many organisms are uni- 2.2.6.5 Coated Vesicles . 92 cellular, where a single cell represents the individual. 2.2.6.6 Peroxisomes and Glycoxysomes . 93 This is true for most prokaryotes and, according to 2.2.6.7 Vacuoles and Tonoplast . 93 definition, also for all eukaryotic protists, including 2.2.7 Cell Walls . 96 flagellates from various algal divisions and diatoms. 2.2.7.1 Development and Differentiation . 97 Eukaryotes are mostly multicellular. As the cells are 2.2.7.2 The Primary Cell Wall . 97 generally microscopically small, large multicellular 2.2.7.3 Plasmodesmata and Pit Fields . 102 organisms have achieved unbelievably high numbers of 2.2.7.4 Secondary Walls of Fiber and Wood cells. A tree can be made up of more than ten trillion Cells . 104 cells. Even a medium-sized leaf is made up of about 2.2.7.5 Pits . 107 20 million cells. A. Bresinsky et al., Strasburger’s Plant Sciences, DOI 10.1007/978-3-642-15518-5_2, # Springer-Verlag Berlin Heidelberg 2013 40 2 The Structure and Ultrastructure of the Cell recombination and syngamy (cell and nucleus fusion of genetically different gametes of the same species) (see > Sects. 2.2.3.7–2.2.3.9). Cells can only arise from like cells by division or fusion: ‘‘omnis cellula e cellula’’ (R. Virchow 1858). The characteristics of living systems listed in the Introduc- tion are only manifested at the cell level, not below. Thus, a cell is the smallest unit capable of life – an elementary organism. That this is also true for multicellular organisms can be seen in the sexual pro- cesses; it is also proven by the fact that it is possible to culture cells (> Fig. 2.1). Fig. 2.1 2.1 Cell Biology One-week-old autotrophic suspension culture of Glycine max (soybean) cells (Â120). Some cells have already divided The development of cell research is a good example of the once or more times. This can be used for ‘‘cloning’’ or dependency of advancements in natural sciences on meth- artificial production of genetically uniform (identical) plant odological possibilities. Most cells are microscopically small. material The first descriptions of cells date from the seventeenth century after the invention of the microscope. The funda- Multicellular organisms are phylogenetically younger mental similarity of plant, animal, and protist cells was only than unicellular organisms. During the evolution of discovered after microscopes had undergone significant multicellular organisms, a number of significant vital improvements at the start of the nineteenth century. functions have remained fixed at the single-cell level. Once the cell nucleus had been observed in plant tissue This is especially true for the storage, replication, realiza- and then also in animal and human cells, T. Schwann tion, and recombination of genetic information. Nearly published his epochal work Microscopic Investigations on every cell in a body contains a cell nucleus with the com- the Accordance in the Structure and Growth of Plants and plete, often usually diploid, gene or chromosome comple- Animals in 1839. Thus, the first pillar of general biology ment. The cell can double this gene complement by DNA was established. Further observations based on the consis- replication and distribute identical copies to daughter cells tent application of microscopic techniques and the first (mitosis; see > Sect. 2.2.3.5). All the body cells of cell physiology investigations (e.g., osmosis) followed rap- a multicellular organism generally share the same gene idly. During the second half of the nineteenth century, complement, making them part of a cell clone. It seems three main principles of cytology began to crystallize: therefore paradoxical that during their individual devel- 1. All living organisms are made up of cells. opment (ontogeny) cells nevertheless differentiate in 2. Cells are the basic building units of life. a regular fashion, taking on different forms and functions. 3. The individual development of the multicellular organism This differentiation or determination problem has begins – at least with regard to sexual reproduction – with basically been resolved since it is understood that each a unicellular stage. stage of differentiation is a result of the activation of a characteristic part of the gene complement and the Around 1880, after E. Abbe had made improvements repression of the remaining genes. Activation and repres- to microscope optics, the theoretical seeing limit of 0.2 mm sion of genes are controlled by integration signals that, as was reached. At the same time, the preparation techniques long as they do not have an environmental origin had also undergone important advances. By 1900, all cell causing individual adaptation, come from certain cells organelles visible with a light microscope had been (in a multicellular system) and are reacted to by other described (> Fig. 2.2). After the rediscovery of Mendel’s specialized cells. inheritance laws at the start of the twentieth century, the Sexual processes can only occur in the single-cell emphasis of research for the following four decades was state. Special gametes are formed in this case. The most mainly on cell nuclei and chromosomes (karyology, biologically significant sexual processes are meiosis with cytogenetics). The Structure and Ultrastructure of the Cell 2 41 a b Cell wall Vacuole c Nuclear envelope Chromatin Nucleolus d Mitochondrion Oleosome Plastid (Chloroplast) . Fig. 2.2 The plant cell under the light microscope (LM). (a) A photosynthetic parenchyma cell of a deciduous leaf. (b) Chloroplasts in the cells of a leaf (Katharina ondulata, Â300). (c) Cells in a suspension culture (tobacco; BY2) (Â350): the large cells are almost filled with the central vacuole; the cell nuclei and nucleoli are in the parietal cytoplasm tube that thickens at the cell corners; numerous other cytoplasm tubes running through the cell can also be seen. (d) Nuclear region of an Allium cell, phase contrast (Â3,100); chromatin and a nucleolus are in the nucleus, leucoplasts (two with pale starch-like inclusions), sausage- shaped mitochondria, and spherical oleosomes are in the cytoplasm (a After D. von Denffer; b, c interference microscope images from P. Sitte; d phase contrast microscope image from P. Sitte) 42 2 The Structure and Ultrastructure of the Cell The explosive development of cell research after biomacromolecules. Recently, novel and quite diverse 1945 – the ultrastructural, biochemical, and molecular observation and preparation techniques have greatly phase – was again paralleled by technological advance- expanded the potential for studying living cells. This is ments: electron microscopy, cell fractionation using an especially important in the transition from genomics to ultracentrifuge (> Box 2.1), X-ray structure analysis of proteonomics. Box 2.1: Cell Fractionation The ultracentrifuge enables the harvesting of uniform frac- tions of subcellular particles for biochemical or analytical study (> Fig. B2.1). The cell structure is lost in the process. Large quantities of uniform cells are carefully broken down into a suitable isolation medium, e.g., by mixing, crumbling, or using ultrasound. The resulting homogenized matrix ide- ally has no more entire cells but still has unbroken cell nuclei, plastids, and so on. The individual cell components can then be separated from the homogenized matrix. Differential centrifugation is when the homogenized matrix is submitted to a series of centrifuge episodes of increasing acceleration (100–50,000 rpm; at high speeds, the centrifugal force can exceed that of Earth’s acceleration due to gravity g by over 100,000 times).