Chemical bases of life

Matter, Mass, and Weight All living and nonliving things are composed of matter, which is anything that occupies space and has mass.Mass is the amount of matter in an object, and weight is the gravitational force acting on an object of a given mass. All living and nonliving things are composed of matter, which is anything that occupies space and has mass.Mass is the amount of matter in an object, and weight is the gravitational force acting on an object of a given mass. An element is the simplest type of matter with unique chemical properties. The characteristics of living and nonliving matter result from the structure, organization, and behavior of atoms. An element is the simplest type of matter with unique chemical properties. The characteristics of living and nonliving matter result from the structure, organization, and behavior of atoms.

Electrons and Chemical Bonding The outermost electrons of an atom determine its chemical behavior. When these outermost electrons are transferred or shared between atoms, chemical bonding occurs. Two major types of chemical bonding are ionic and covalent bonding. The outermost electrons of an atom determine its chemical behavior. When these outermost electrons are transferred or shared between atoms, chemical bonding occurs. Two major types of chemical bonding are ionic and covalent bonding. An atom is electrically neutral because it has an equal number of protons and electrons. If an atom loses or gains electrons, thenumber of protons and electrons are no longer equal, and a charged particle called an ion is formed. An atom is electrically neutral because it has an equal number of protons and electrons. If an atom loses or gains electrons, thenumber of protons and electrons are no longer equal, and a charged particle called an ion is formed.

Covalent Bonding Covalent bonding results when atoms share one or more pairs of electrons. The resulting combination of atoms is called a molecule. An example is the covalent bond between two hydrogen atoms to form a hydrogen molecule. Covalent bonding results when atoms share one or more pairs of electrons. The resulting combination of atoms is called a molecule. An example is the covalent bond between two hydrogen atoms to form a hydrogen molecule. Each hydrogen atom has one electron. As the two hydrogen atoms get closer together, the positively charged nucleus of each atom begins to attract the electron of the other atom. At an optimal distance, the two nuclei mutually attract the two electrons, and each electron is shared by both nuclei. The two hydrogen atoms are now held together by a covalent bond. Each hydrogen atom has one electron. As the two hydrogen atoms get closer together, the positively charged nucleus of each atom begins to attract the electron of the other atom. At an optimal distance, the two nuclei mutually attract the two electrons, and each electron is shared by both nuclei. The two hydrogen atoms are now held together by a covalent bond.

Ions Positively charged ions are called cations, and negatively charged ions are called anions. Because oppositely charged ions are attracted to each other, cations and anions tend to remain close together, which is called ionic bonding. For example, sodium and chloride ions are held together by ionic bonding to form an array of ions called sodium chloride,or table salt. Positively charged ions are called cations, and negatively charged ions are called anions. Because oppositely charged ions are attracted to each other, cations and anions tend to remain close together, which is called ionic bonding. For example, sodium and chloride ions are held together by ionic bonding to form an array of ions called sodium chloride,or table salt. A sodium atom loses an electron to become a smaller- sized positively charged ion, and a chlorine atom gains an electron to become a larger-sized negatively charged ion. The attraction between the oppositely charged ions results in an ionic bond and the formation of sodium chloride. A sodium atom loses an electron to become a smaller- sized positively charged ion, and a chlorine atom gains an electron to become a larger-sized negatively charged ion. The attraction between the oppositely charged ions results in an ionic bond and the formation of sodium chloride.

Intermolecular Forces Intermolecular forces result from the weak electrostatic attractions between the oppositely charged parts of molecules, or between ions and molecules. Intermolecular forces are much weakerthan the forces producing chemical bonding. Intermolecular forces result from the weak electrostatic attractions between the oppositely charged parts of molecules, or between ions and molecules. Intermolecular forces are much weakerthan the forces producing chemical bonding. The positive hydrogen part of one water molecule forms a hydrogen bond (red dotted line) with the negative oxygen part of another water molecule. As aresult, hydrogen bonds hold the water molecules together. The positive hydrogen part of one water molecule forms a hydrogen bond (red dotted line) with the negative oxygen part of another water molecule. As aresult, hydrogen bonds hold the water molecules together.

In water, amphipathic molecules aggregate into spherical clusters. Their polar regions form hydrogen bonds with water molecules at the surface of the cluster. In water, amphipathic molecules aggregate into spherical clusters. Their polar regions form hydrogen bonds with water molecules at the surface of the cluster.

Chemical Reactions and Energy In a chemical reaction, atoms, ions, molecules, or compounds interact either to form or to break chemical bonds. In a chemical reaction, atoms, ions, molecules, or compounds interact either to form or to break chemical bonds. The substances that enter into a chemical reaction are called the reactants, and the substances that result from the chemical reaction are called the products. The substances that enter into a chemical reaction are called the reactants, and the substances that result from the chemical reaction are called the products.

T hree important points can be made about chemical reactions First, in some reactions, less complex reactants are combined to form a larger, more complex product. An example is the synthesis of the complex molecules of the human body from basic “building blocks” obtained in food. First, in some reactions, less complex reactants are combined to form a larger, more complex product. An example is the synthesis of the complex molecules of the human body from basic “building blocks” obtained in food. Second, in other reactions, a reactant can be broken down, or decomposed, into simpler, less complex products. An example is the breakdown of food molecules into basic building blocks. Second, in other reactions, a reactant can be broken down, or decomposed, into simpler, less complex products. An example is the breakdown of food molecules into basic building blocks. Third, atoms are generally associated with other atoms through chemical bonding or intermolecular forces; therefore, to synthesize new products or break down reactants it is necessary to change the relationship between atoms. Third, atoms are generally associated with other atoms through chemical bonding or intermolecular forces; therefore, to synthesize new products or break down reactants it is necessary to change the relationship between atoms.

Synthesis Reactions When two or more reactants chemically combine to form a new and larger product, the process is called a synthesis reaction. An example of a synthesis reaction is the combination of two amino acids to form a dipeptide. In this particular synthesis reaction, water is removed from the amino acids as they are bound together. When two or more reactants chemically combine to form a new and larger product, the process is called a synthesis reaction. An example of a synthesis reaction is the combination of two amino acids to form a dipeptide. In this particular synthesis reaction, water is removed from the amino acids as they are bound together. Synthesis reactions in which water is a product are called dehydration (water out) reactions. Note that old chemical bonds are broken and new chemical bonds are formed as the atoms rearrange as a result of a synthesis reaction. Synthesis reactions in which water is a product are called dehydration (water out) reactions. Note that old chemical bonds are broken and new chemical bonds are formed as the atoms rearrange as a result of a synthesis reaction.

Decomposition Reactions The term decompose means to break down into smaller parts. A decomposition reaction is the reverse of a synthesis reaction— a larger reactant is chemically broken down into two or more smaller products. The term decompose means to break down into smaller parts. A decomposition reaction is the reverse of a synthesis reaction— a larger reactant is chemically broken down into two or more smaller products. The breakdown of a disaccharide (a type of carbohydrate) into glucose molecules is an example. Note that this particular reaction requires that water be split into two parts and that each part be contributed to one of the new glucose molecules. Reactions that use water in this manner are called hydrolysis reactions. The breakdown of a disaccharide (a type of carbohydrate) into glucose molecules is an example. Note that this particular reaction requires that water be split into two parts and that each part be contributed to one of the new glucose molecules. Reactions that use water in this manner are called hydrolysis reactions.

Reversible Reactions A reversible reaction is a chemical reaction in which the reaction can proceed from reactants to products or from products to reactants. When the rate of product formation is equal to the rate of the reverse reaction, the reaction system is said to be at equilibrium. A reversible reaction is a chemical reaction in which the reaction can proceed from reactants to products or from products to reactants. When the rate of product formation is equal to the rate of the reverse reaction, the reaction system is said to be at equilibrium. At equilibrium the amount of reactants relative to the amount of products remains constant. An important reversible reaction in the human body involves carbon dioxide and hydrogen ions. At equilibrium the amount of reactants relative to the amount of products remains constant. An important reversible reaction in the human body involves carbon dioxide and hydrogen ions.

Major Categories of Organic Molecules in the Body

Adenosine Triphosphate Adenosine triphosphate (ATP) is an especially important organic molecule found in all living organisms. It consists of adenosine and three phosphate groups. Adenosine triphosphate (ATP) is an especially important organic molecule found in all living organisms. It consists of adenosine and three phosphate groups. Adenosine is the sugar ribose with the organic base adenine. The potential energy stored in the covalent bond between the second and third phosphate groups is important to living organisms because it provides the energy used in nearly all of the chemical reactions within cells. Adenosine is the sugar ribose with the organic base adenine. The potential energy stored in the covalent bond between the second and third phosphate groups is important to living organisms because it provides the energy used in nearly all of the chemical reactions within cells.

Sucrose (table sugar) is a disaccharide formed by the linking together of two monosaccharides, glucose and fructose. Sucrose (table sugar) is a disaccharide formed by the linking together of two monosaccharides, glucose and fructose. Many molecules of glucose linked end-to- end and at branch points form the branched-chain polysaccharide glycogen, shown in diagrammatic form in (a). The four red subunits in (b) correspond to the four glucose subunits in (a). Many molecules of glucose linked end-to- end and at branch points form the branched-chain polysaccharide glycogen, shown in diagrammatic form in (a). The four red subunits in (b) correspond to the four glucose subunits in (a).

(a) Steroid ring structure, shown with all the carbon and hydrogen atoms in the rings and again without these atoms to (a) Steroid ring structure, shown with all the carbon and hydrogen atoms in the rings and again without these atoms to emphasize the overall ring structure of this class of lipids. (b) Different steroids have different types and numbers of chemical emphasize the overall ring structure of this class of lipids. (b) Different steroids have different types and numbers of chemical groups attached at various locations on the steroid ring, as shown by the structure of cholesterol. groups attached at various locations on the steroid ring, as shown by the structure of cholesterol.

Structures of 8 of the 20 amino acids found in proteins. Note that proline does not have a free amino group, but it can still Structures of 8 of the 20 amino acids found in proteins. Note that proline does not have a free amino group, but it can still form a peptide bond. form a peptide bond.