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Transcript
The Chemical Basis of Life Basic Chemistry Matter: anything that has mass and takes up space Element: simple form of matter, a substance that cannot be broken down into two or more different substances 26 elements in the human body 11 major elements 15 trace elements Compound: atoms of two or more elements joined to form chemical combinations 96% of the human body is made up of 1. Carbon 2. Oxygen 3. Hydrogen 4. Nitrogen ESSENTIAL ELEMENTS Element Symbol % by Mass Element Symbol % by Mass Oxygen O 65.0 Iron Fe Trace Carbon C 18.5 Zinc Zn Trace Hydrogen H 9.5 Copper Cu Trace Nitrogen N 3.3 Iodine I Trace Calcium Ca 1.5 Manganese Mn Trace Phosphorus P 1.0 Boron B Trace Potassium K 0.4 Chromium Cr Trace Sulfur S 0.3 Molybdenum Mo Trace Sodium Na 0.2 Cobalt Co Trace Chlorine Cl 0.2 Selenim Se Trace Magnesium Mg 0.1 Flourine F Trace Atoms Structure Protons: + Electrons: – Neutrons: no charge Atomic Number = proton number Atomic Mass = protons + neutrons Chemical Bonds 1. 2. 3. Ionic or electrovalent bond: formed by a transfer of electrons; electrostatic force binds positively and negatively charged ions together Covalent bond: formed by sharing of electron pairs between atoms Hydrogen bond: weak bond; results from unequal charge distribution on molecules Chemical Bonds Chemical Bonds Ionic Bond Chemical Bonds Covalent Bond Chemical Bonds Chemical Reactions There are 3 basic types of chemical reactions involved in physiology: 1. Synthesis reaction (dehydration synthesis): combining of two or more substances to form a more complex substance; A+B AB 2. Decomposition reaction (hydrolysis): breaking down of a substance into two or more substances; AB A+B 1. Exchange reaction: decomposition of two substances and, in exchange, synthesis of two new compounds; AB+CD AD+BC Metabolism Metabolism—all of the chemical reactions that occur in body cells Catabolism Ultimately, the end products of catabolism are carbon dioxide, water, and other waste products More than half the energy released is transferred to ATP, which is then used to do cellular work Chemical reactions that break down complex compounds into simpler ones and release energy; hydrolysis (decomposition) is a common catabolic reaction Metabolism Anabolism Chemical reactions that join simple molecules together to form more complex molecules Chemical reaction responsible for anabolism is dehydration synthesis Inorganic Compounds 1. 2. 3. 4. Water: Body’s most abundant compound Oxygen and Carbon Dioxide Electrolytes: acids, bases, and salts: dissociate in solutions to form ions Buffers: maintain the constancy of the pH Organic Compounds Organic molecules Have at least one carbon atom and at least one C–C or C–H bond in each molecule Often have functional groups attached to the carbon-containing core of the molecule Organic Compounds Sugars, starches and cellulose are carbohydrates. Sugars and starches serve as energy sources for cells; cellulose is the main structural component of the walls that surround plant cells. Carbohydrates contain carbon, hydrogen, and oxygen in a ratio of two hydrogen and one oxygen to every carbon atom. Typically contain 3 to 7 carbon atoms. Large numbers of polar hydroxyl groups, plus a carbonyl group, gives a monosaccharide hydrophilic properties. Glucose (C6H12O6), the most abundant monosaccharide, is used as an energy source in most organisms. Glucose is so important in metabolism that its concentration is carefully kept at a homeostatic level in the blood of humans and other complex animals. When dissolved in water, glucose undergoes a rearrangement of its atoms, forming one of two possible ring structures. When the hydroxyl group is on the plane of the ring as the –CH2OH side group, the glucose is designated beta-glucose. When its on the side opposite the -- CH2OH side group, the compound is designated alpha-glucose. A disaccharide contains two monosaccharide rings joined by a glycosidic linkage, consisting of a central oxygen covalently bonded to two carbons, one in each ring. The most abundant carbohydrates are polysaccharides. A group that includes starches, glycogen, and cellulose. A polysaccharide is a macromolecule consisting of repeating units of simple sugars, usually glucose. Thousands of units are typically present in a single molecule. Starch, the typical form of carbohydrate used for energy storage in plants, is a polymer consisting of a-glucose subunits. When energy is needed for cellular work, the plant can hydrolyze the starch, releasing the glucose subunits. Humans and other animals that eat plant foods have enzymes to hydrolyze starch. Glycogen (sometimes referred to as animal starch) is the form which glucose is stored as energy sources in animal tissues. It is more extensively branched and more water soluble. Glycogen is stored mainly in the liver and muscle cells. Cellulose is the most abundant carbohydrate; it accounts for 50% or more of all the carbon in plants. Cellulose is a structural carbohydrate. Cellulose is an insoluble polysaccharide composed of many glucose molecules joined together. Humans do not have the enzymes needed to break down cellulose. Carbohydrates may also be combined with proteins to form glycoproteins, compounds present on the outer surface of cells other than bacteria. Some of these carbohydrate chains allow cells to adhere to one another, while others provide protection Most proteins secreted by cells are glycoproteins. These include the major components of mucus. Carbohydrates can also combine with lipids to form glycolipids, compounds present on the surface of animal cells that are thought to allow cells to recognize and interact with one another. The most abundant lipids in living organisms are triacyglycerols, also known as triglycerides. These compounds commonly known as fats, are an economical form of reserve fuel storage because, when metabolized, they yield more than twice as much energy per gram as do carbohydrates Saturated fatty acids contain the maximum possible number of hydrogen atoms. Fats high in saturated fatty acids, such as animal fat and solid vegetable shortening, tend to be solid at room temperature Unsaturated fatty acids include one or more adjacent pairs of carbon atoms joined by a double bond. They tend to be liquid at room temperature. Fatty acids with one double bond are called monounsaturated fatty acids. Those with more than one double bond are polyunsaturated fatty acids. At least two unsaturated fatty acids (linoleic acid and arachidonic acid) are essential nutrients that must be obtained from food because the human body cannot make them. Phospholipids belong to a group of lipids, called amphipathic lipids, in which one end of each molecule is hydrophobic and the other end is hydrophilic. The properties of these lipid molecules cause them to form lipid bilayers in aqueous solution, making them uniquely suited to function as the functional components of cell membranes. linoleic acid Name% LA†ref.Safflower oil78%Grape seed oil73%Poppyseed oil70%Sunflower oil68%Hemp oil60%Corn oil59%Wheat germ oil55%Cottonseed oil54%Soybean oil51%Walnut oil51%Sesame oil45%Rice bran oil39%Pistachio oil32.7%Peanut oil32%[17]Canola oil21%Chicken fat1823%[18]Egg yolk16%Linseed oil15%Lard10%Olive oil10%Palm oil10%Cocoa butter3%Macadamia oil2%Butter2%Coconut oil2% arachidonic acid Meat, eggs and dairy Synthesized from linoleic acid Lipids are a group of compounds that are defined, not by their structure, but rather by the fact that they are soluble in nonpolar solvents (ether and chloroform) and are relatively insoluble in water (hydrophobic). They consists mainly of carbon and hydrogen, with few oxygencontaining functional groups. Groups of lipids are fats, phospholipids, caratenoids, steroids, and waxes. The orange and yellow plant pigments called carotenoids are classified with lipids because they are insoluble in water and have an oily consistency. Most animals can convert carotenoids to vitamin A, which can then be converted to the visual pigment retinal. A steriod consists of carbon atoms arranged in four attached rings; three of the rings contain six carbon atoms, and the fourth contains five The length and structure of the side chains that extend from these rings distinguish one steroid from another. Among the steroids of biological importance are cholesterol, bile salts, reproductive hormones, and cortisol and other hormones secreted by the adrenal cortex Cholesterol is an essential structural component of animal cell membranes, but when there is excess cholesterol in the blood it forms plaques on artery walls. Leading to an increased risk of heart attack. Plant cell membranes contain molecules similar to cholesterol. Some of these plant steroids are able to block the absorption of cholesterol by the intestines. Bile salts emulsify fats in the intestine so that they can be enzymatically hydrolyzed. Steroid hormones regulate certain aspects of metabolism in a variety of animals. Most genetic information is used to specify the structure of proteins. Proteins are involved in virtually all aspects of metabolism because most enzymes (molecules that regulate the thousands of different chemical reactions that take place in an organism) are proteins. Proteins can be assembled into a variety of shapes, allowing them to serve as major structural components of cells and tissues. For this reason, growth and repair, as well as maintenance of the organism, depend on these compounds. The protein constituents of a cell are the clues to its lifestyle. Each cell type contains characteristic forms, distributions, and amounts of protein that largely determine what the cell looks like and how it functions. Amino acids, the constituents of proteins, have an amino group (--NH2) and a carboxyl group (--COOH) bonded to the same asymmetrical carbon atom, know as the alpha carbon. There are about 20 amino acids commonly found in proteins, each uniquely identified by the variable side chain (R group) bonded to the a-carbon Amino acids classified as having nonpolar side chains tend to have hydrophobic properties, whereas those classified as polar are more hydrophilic. With some exceptions, bacteria and plants can synthesize all their needed amino acids from simpler substances. If the proper raw materials are available, the cells of humans and animals can manufacture some, but not all, of the biologically significant amino acids. Those that animals cannot synthesize and so must obtain from the diet are known as essential amino acids. Polar Amino Acids Nonpolar Amino Acids Electrically Charged Amino Acids Acidic Basic Amino acids combine chemically with one another by a condensation reaction that bonds the carboxyl carbon of one molecule with the amino nitrogen of another. The covalent carbon-to-nitrogen bond linking two amino acids together is called a peptide bond. When two amino acids combine, a dipeptide is formed; a long chain of amino acids is a polypeptide. An almost infinite variety of protein molecules is possible, differing from one another in the number, types, and sequences of amino acids they contain. The overall structure of a protein helps determine its biological activity. The biological activity of a protein can be disrupted by a change in conformation. When a protein is heated, subjected to significant pH changes, or treated with a number of chemicals, its structure can become disordered and the coiled peptide chains can unfold to give a more random conformation. Such changes in shape and the accompanying loss of biological activity are termed denaturation of the protein. Denaturation generally cannot be reversed (you can’t “unfry” an egg). Nucleic acids transmit hereditary information and determine what proteins a cell manufactures. Ribonucleic acids (RNAs) Deoxyribonucleic Acids (DNAs) DNA comprises the genes, the hereditary material of the cell, and contains all the instructions for making proteins, as well as all the RNA, needed by the organism. RNA is required as a direct participant in the complex process in which amino acids are linked to form polypeptides. Nucleic acids are polymers of nucleotides, molecular units that consist of: 1. A five carbon sugar, either ribose (in RNA) or deoxyribose (in DNA) 2. One or more phosphate groups, which make the molecule acidic 3. A nitrogenous base, a ring compound that contains nitrogen. The base may either be a double-ringed purine or a single-ringed pyrimidine Adenosine triphosphate (ATP), composed of adenine, ribose, and three phosphates , is a major importance as the primary energy currency of all cells. The two terminal phosphate groups are joined to the nucleotide by covalent bonds.