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Chapter 1 Our Biological Heritage and Cell 主讲人 黄 文 英 It is assumed that our solar system was created some 4,600 million years ago. At that time the atmosphere surrounding our planet did not contain oxygen. This was a prerequisite for the evolution of life from nonliving organic matter, for without atmospheric oxygen and thus without high-altitude ozone, the ultraviolet radiation from the sun could reach the surface of the earth. Content Section 1 Section 2 Section 3 Development of Primitive Organisms Mammals The Cell and its Regulatory Mechanisms Section 1 Development of Primitive Organisms A new milestone in biological evolution occurred about 1,500 million years ago, when the unicellular organism with a nucleus (the eukaryote) developed (Vidal 1984). Section 2 Mammals 1 Microcosmic Mechanism of Animal Evolution 2 Appearance of Mammals 3 Emergence of Primates 4 Modern Human Evolution Microcosmic Mechanism of Animal Evolution Evolution was then ready for the next major step, the development of larger animals, probably beginning some 700 million years ago (Valentine 1978) the evolution of larger organisms . In the evolution of larger animals, the individual cell retained its original size, that is, the same size as the unicellular organism living more than 1,000 million years ago. However, more of these single cells were piled together as a means of increasing the size of the organism. Special structures in the cell, the genes, were encoded with detailed instructions about the proliferation of the cell mass, guiding specialization in shape, structure, and function. Appearance of Mammals In the course of diversification of multicellular organisms that took place over the last 700 million years, new types of organisms appeared and divergence occurred within already established groups. The earliest fossil traces of animal life are burrows that begin to appear in rocks younger than 700 million years (Valentine 1978). Evolution is a consequence of the gradual accumulation of genetic difference due to point mutation and rearrangements in the chromosomes. Emergence of Primates Maybe only 10 million or as much as 20 million years ago, the family tree of primates developed a branch called the hominids, which finally resulted in Homo sapiens sapiens, the only surviving hominid. Somewhere along the line a prototypic anthropoid ape abandoned life in the trees and started to forge and hunt on the ground. A species related to these creatures may have been Ramapithecus. Modern Human Evolution 1 2 Most likely, a human being living 50,000 years ago had the same potential for physical and intellectual performance, such as playing a piano or constructing a computer, as anyone living today. Humans, like all higher animals, are basically designed for mobility. Consequently, our locomotive apparatus and service organs constitute the majority of our total body mass. SECTION 3 The Cell and its Regulatory Mechanisms 1 2 The Structure of Cell The Regulatory Mechanism of Cell Activity The Cell Membrane The Structure of Cell Membrane The structural framework of the cell membrane, approximately 5 nm thick, is a double layer of lipid molecules. The individual lipid molecule has a head and two tails. Polar (i.e., hydrophilic, or soluble in water) heads form the outer and inner membrane surfaces, while apolar (i.e., hydrophobic, or insoluble in water) tails meet in the membrane interior. This structure serves as an anchor for other components of the membrane, such as proteins and glycoproteins (figure 1.4). The Cell Membrane Transport Mechanisms Through the Cell Membrane The Active Transport and Pssive Transport Transport through cell membranes can be active or passive, depending on whether it consumes energy or not (figure 1.6). Exocytosis and Endocytosis The Intracellular Structure 3 Cytoplasmic Vesicles 3 The Endoplasmic Reticulum 3 The Intracellular Vesicle 3 The Mitochondria 3 The Nucleus and Enzymes Summary The cell interior consists of organelles, small structures of different shapes and functions, suspended in the cytosol. The cytosol is a viscous solution of proteins, carbohydrates, ions, and nutrients suspended in water. The various organelles serve different functions in the cell, much like the different organs in our body. The Regulatory Mechanism of Cell Activity 1 2 3 4 The Intracellular Signal Conduction and Communication Sensitivity of the Cell Adapts to the Level of the Stimulus Common Cellular Strategies for Adaptation to New Demands Control of Gene Expression Summary The purpose of this brief review of our biological heritage is to provide some basic facts that may be useful in understanding the complicated interplay between all the biological processes that form the basis for our existence and performance. Humans are made to be physically active. This chapter also provides an overview of cell biology as a basis for understanding how cells and organs of the body react to different challenges in connection with work and physical activity.