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Chapter: Anatomy and Physiology for Health Professionals: Levels of Organization : Chemical Basics of Life

Chemistry describes the composition of substances and how chemicals react with each other.


Chemistry describes the composition of substances and how chemicals react with each other. The human body is made up of chemicals. Matter is composed of elements, some of which occur in a pure form. There are various states of matter, including gaseous, liquid, and solid states. Energy is different from matter, taking up space, having no mass, and only being measured by how it affects matter. Energy is the capacity to put matter into motion or to perform “work.”

Many elements are combined with other elements. They are composed of atoms, which are the smallest complete units that still have the properties of the elements they form. Atoms of different elements have characteristic sizes, weights, and ways of interacting. An atom consists of one or more electrons surround-ing a nucleus, which contains one or more protons and usually one or more neutrons. Electrons are negative, protons are positive, and neutrons are uncharged. When atoms combine, they gain, lose, or share elec-trons. Atoms of the same element may bond to form amolecule of that element. Compounds that release ions when they dissolve in water are known as electrolytes. A molecule is any chemical structure that consists of atoms held together by covalent bonds. Compounds are chemically pure, with identical molecules.

Mixtures are substances containing two or more components that are physically intermixed, and include colloids, solutions, and suspensions. Chemical bonds are energy exchanges between electrons of reacting atoms, and include ionic, covalent, and hydrogen bonds. Ionic bonds form between ions. Covalent bonds are formed when electrons are shared, producing molecules in which the shared electrons are located in a single orbital common to both atoms. When the positive hydrogen end of a polar molecule is attracted to the negative nitrogen or oxygen end of another polar molecule, the attraction is called a hydrogen bond. A chemical reaction occurs when a chemical bond is formed, broken, or rearranged. The four types of chemical reactions are synthesis, decomposition, exchange, and reversible reactions. Catalysts can increase the rate of chemical reactions without becoming chemically changed themselves or without becoming a part of the product.

Acids are electrolytes that release hydrogen ions in water. Bases are electrolytes that release ions that bond with hydrogen ions. Hydrogen ion ­concentrations can be measured by a value called pH. Biochemistry (biologic chemistry) is the study of chemical processes within and relating to living organisms. Organic chemicals are those that contain the elements carbon and hydrogen and generally oxygen as well. Inorganic chemicals do not contain these elements. Inorganic substances include water, oxygen, carbon dioxide, and salts. Organic substances include carbohydrates, lip-ids, and proteins. Carbohydrates provide much of the energy required by the body’s cells and help to build cell structures. They contain various types of sugars, including monosaccharides, disaccharides, and poly-saccharides. Lipids are insoluble in water, but may dis-solve in other lipids, oils, ether, chloroform, or alcohol. Fats are the most common type of lipids. Unsaturatefats are safer than saturated or trans fats. Proteins are the most abundant organic components of the human body and are the basic structural materials of the body. Nucleic acids are large organic molecules that carry genetic information or form structures within cells. They include DNA and RNA.

In the body, enzymes promote chemical reactions by acting as catalysts to accelerate these reactions without themselves being permanently changed or consumed. Some enzymes are only made of protein, whereas others have a protein portion (apoenzyme)and a cofactor. Most organic cofactors are derived from B complex (or other) vitamins and are known as coenzymes. ATP pairs with catabolized glucose topower the body. ATP is the main molecule in cells that transfer energy and provides a type of energy that all body cells can use immediately.

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