What Is The Function Of Cells In The Human Body – Basic questions • What are the main cellular structures and their functions? •How do cells get and use energy? • How are substances transported through the cell membrane? •Why can some cells generate action potentials and others cannot? • How do the cells of a multicellular organism communicate with each other? •What are the normal mechanisms of cell growth control? evolve.elsevier.com/Copstead/ •Review questions and answers •Glossary (with audio pronunciations for selected terms) •Animations •Case analysis •Review of key ideas A fundamental principle of biology states that the cell is the basic unit of life. Because most diseases are understood at the cellular and molecular level, the cell is also the basic unit of disease. Currently, the fields of cell and molecular biology are experiencing an explosion of knowledge leading to a better understanding of the cellular aspects of human physiology and disease. Detailed knowledge of cellular dysfunction has led to the development of specific and appropriate methods of prevention and treatment of many diseases. Thus, an understanding of cellular mechanisms is critical for health care professionals and is fundamental to the discussion of pathophysiological processes presented in the remainder of this text. Cells are complex, Membrane-bound entities composed of many chemicals and macromolecules. They are able to multiply and thus form new cells and organisms. The earliest cells on Earth probably arose about 3.5 billion years ago from the spontaneous assembly of organic (carbon-containing) and inorganic molecules.1 Over billions of years, the random association of self-replicating molecules now called deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) and is believed to have arisen as a result of natural selection. The evolution of the cell membrane created a closed compartment that provided a selective advantage for the cell and made the first separation between life (inside) and life (outside). In this protected environment, the early cells developed and continued to develop. Today there are a large number of different cell types, but many of the basic biochemical mechanisms of these cells are very similar. Scientists believe that all modern cells, from bacteria to human neurons, evolved from simple progenitor cells.2 Therefore, many mysteries of human cellular physiology can be unlocked by studying cells that grow easily and multiply rapidly, such as yeast and bacteria. Much of our knowledge of cell physiology comes from studying a class of cells called prokaryotes, which includes bacteria and archaea. Prokaryotic cells are smaller and simpler than eukaryotic cells, lacking a nucleus or cytoplasmic organelles. Fungi, plants, and animals belong to the eukaryotic class of cells with a membrane-bound nucleus and numerous cytoplasmic organelles (Figure 3-1). This chapter covers the basics of eukaryotic cell structure, physiology, metabolism, and communication. FIGURE 3-1 Structure of a typical eukaryotic cell showing intracellular organelles. Plasma membrane Membrane structure All cells are surrounded by a barrier called plasma membrane (plasmalemma) consisting mainly of lipids and proteins. This cell membrane is a highly selective filter that protects the internal cell contents from the external environment. The plasma membrane performs a variety of functions, including transport of nutrients and waste products, generation of membrane potentials, and regulation of cell recognition, communication, and growth. The cell membrane is a sensor of signals and allows the cell to respond and adapt to changes in the environment. According to the fluid mosaic model first described by Singer and Nicholson in the 1960s, 3 the plasma membrane is a dynamic assembly of lipid and protein molecules. Most lipids and proteins move rapidly in the fluid structure of the membrane. As shown in Figure 3-2, lipid molecules are arranged in a bilayer, or lipid bilayer, which is highly impermeable to many water-soluble molecules, including ions, glucose, and proteins. Various proteins embedded or “solvated” in the lipid bilayer perform most of the membrane’s functions. Some membrane proteins are involved in the transport of certain molecules into and out of the cell; others function as enzymes or respond to external signals; and some serve as a structural link connecting the plasma membrane with neighboring cells. The lipid structure of the plasma membrane is similar to the structure of the membrane surrounding cell organelles (for example, the nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, lysosomes). FIGURE 3-2 Section of cell membrane showing lipid bilayer structure and integral membrane proteins.

Bilayer of lipids The bilayer structure of all biological membranes is due to the special properties of lipid molecules, which lead to their self-assembly into bilayers. The three main types of membrane lipids are cholesterol, phospholipids, and glycolipids. All three have a molecular structure that is amphipathic; that is, they have a hydrophilic (water-loving) charged or polar end and a hydrophobic (water-fearing) nonpolar end.1 This amphipathic nature causes lipids to form bilayers in aqueous solution. A typical phospholipid molecule is shown in Figure 3-3. Hydrophobic non-polar tails tend to bond with other hydrophobic non-polar tail groups to avoid contact with polar water molecules. Hydrophilic polar head groups interact better with the surrounding aqueous environment. Bilayers with tails in the middle allow chemical “satisfaction” of both parts of lipid molecules. In addition, lipid bilayers tend to close themselves, forming compact, spherical compartments (Figure 3-4). If the membrane is punctured or torn, it reseals itself to prevent the hydrophobic tails from contacting water. FIGURE 3-3 Schematic drawing of a typical membrane phospholipid molecule showing the amphipathic nature of the structure. FIGURE 3-4 The amphipathic nature of membrane lipids results in bilayer structures that tend to form spheres. Often, individual molecules of lipids and proteins can freely and rapidly diffuse in the plane of the bilayer. The degree of fluidity of the membrane depends on the composition of lipids. Saturated lipids have straight tails that stack together to stiffen the membrane, while lipids with bent, unsaturated hydrocarbon tails increase fluidity. About 50% of the lipids in the eukaryotic cell membrane are cholesterol, which reduces the permeability of the membrane and prevents the leakage of small water-soluble molecules. Membrane-dwelling phospholipids differ in the size, shape, and charge of polar head groups, as well as affecting fluidity by the degree of saturation of tail groups. Figure 3-5 shows the structures of the four most common membrane phospholipids: phosphatidylethanolamine, phosphatidylserine, phosphatidylcholine, and sphingomyelin. Some membrane-bound proteins require specific phospholipid headgroups to function properly. Some lipids—sphingolipids and especially cholesterol—can bind together temporarily to form rafts in a sea of ​​moving lipids. These rafts may help to fold and organize membrane proteins into functional units. For example, a membrane receptor and its intracellular target proteins may associate in a raft to facilitate the transfer of information across the membrane.4 FIGURE 3-5 Chemical structures of the four most common membrane phospholipids. Glycolipids have one or more sugar (i.e. carbohydrates) molecules in the polar head region. Glycolipids and glycoproteins are found only in the outer half of the lipid bilayer, with sugar groups exposed on the cell surface (Figure 3-6). Membrane glycolipids are involved in cell recognition and cell-cell interactions.5 FIGURE 3-6 A section of a cell membrane showing the orientation of membrane glycoproteins toward the outer surface of the cell. Membrane proteins About 50% of the mass of a normal cell membrane is protein. The specific types of membrane proteins vary depending on the cell type and environmental conditions. Some membrane proteins, called transmembrane proteins, span across the membrane bilayer and interact with extracellular and intracellular fluids. Transmembrane proteins perform a variety of functions, including the transport of charged and polar molecules into and out of cells and the transduction of extracellular signals into intracellular messages. Other peripheral membrane proteins are less membrane-anchored. General structural orientations of membrane proteins are shown in Figure 3-7. The amino acid structure of membrane proteins determines their location in the membrane. Non-polar amino acids are located in the hydrophobic environment of the membrane, and charged and polar amino acids are released into the aqueous liquid or bind to the head groups of polar lipids. Many membrane proteins have a complex three-dimensional structure, with many twists and turns through the lipid bilayer. FIGURE 3-7 Structural orientation of some proteins in the cell membrane. A, a membrane-associated protein with a noncovalent attachment to plasma lipids. B, a membrane protein with a non-covalent attachment to another membrane protein. C, a transmembrane protein that diffuses across the lipid bilayer. D, covalently bound peripheral membrane protein. The type of membrane proteins in a particular cell depends on the basic functions of the cell. For example, the renal tubule cell contains many of the transmembrane proteins necessary for the kidney’s function of electrolyte and nutrient reabsorption. In contrast, human erythrocytes (erythrocytes) contain peripheral proteins that are mainly attached to the inner surface of the membrane.6 One of these proteins is a spectrum of long, thin, flexible rod-like structures that form a support network or cytoskeleton for the cell. cell. This is it

What Is The Function Of Cells In The Human Body

What is the function of liver in human body, what is the function of appendix in human body, function of human cells, what is the function of pancreas in human body, function of cells in the human body, what is the function of magnesium in the human body, what is the function of kidney in human body, what is the function of gallbladder in human body, what is the function of white cells, what is the function of mast cells, what is the function of potassium in the human body, what is the function of stem cells