Chemical bases of lifeChemical bases of life

Matter, Mass, and Matter, Mass, and WeightWeight

All living and nonliving things are composed of All living and nonliving things are composed of matter, which is anything that occupies space matter, which is anything that occupies space and has mass.Mass is the amount of matter in and has mass.Mass is the amount of matter in an object, and weight is the gravitational force an object, and weight is the gravitational force acting on an object of a given mass. acting on an object of a given mass.

An element is the simplest type of matter with An element is the simplest type of matter with unique chemical properties. The unique chemical properties. The characteristics of living and nonliving matter characteristics of living and nonliving matter result from the structure, organization, and result from the structure, organization, and behavior of atoms. behavior of atoms.

Electrons and Chemical Electrons and Chemical BondingBonding

The outermost electrons of an atom determine its The outermost electrons of an atom determine its chemical behavior. When these outermost chemical behavior. When these outermost electrons are transferred or shared between electrons are transferred or shared between atoms, chemical bonding occurs. Two major types atoms, chemical bonding occurs. Two major types of chemical bonding are ionic and covalent of chemical bonding are ionic and covalent bonding. bonding.

An atom is electrically neutral because it has an An atom is electrically neutral because it has an equal number of protons and electrons. If an atom equal number of protons and electrons. If an atom loses or gains electrons, thenumber of protons and loses or gains electrons, thenumber of protons and electrons are no longer equal, and a charged electrons are no longer equal, and a charged particle called an ion is formed.particle called an ion is formed.

Covalent BondingCovalent Bonding

Covalent bonding results when atoms share one or Covalent bonding results when atoms share one or more pairs of electrons. The resulting combination of more pairs of electrons. The resulting combination of atoms is called a molecule. An example is the covalent atoms is called a molecule. An example is the covalent bond between two hydrogen atoms to form a hydrogen bond between two hydrogen atoms to form a hydrogen molecule. molecule.

Each hydrogen atom has one electron. As the two Each hydrogen atom has one electron. As the two hydrogen atoms get closer together, the positively hydrogen atoms get closer together, the positively charged nucleus of each atom begins to attract the charged nucleus of each atom begins to attract the electron of the other atom. At an optimal distance, the electron of the other atom. At an optimal distance, the two nuclei mutually attract the two electrons, and each two nuclei mutually attract the two electrons, and each electron is shared by both nuclei. The two hydrogen electron is shared by both nuclei. The two hydrogen atoms are now held together by a covalent bond.atoms are now held together by a covalent bond.

IIonsons

Positively charged ions are called cations, and negatively Positively charged ions are called cations, and negatively charged ions are called anions. Because oppositely charged ions are called anions. Because oppositely charged ions are attracted to each other, cations and charged ions are attracted to each other, cations and anions tend to remain close together, which is called ionic anions tend to remain close together, which is called ionic bonding. For example, sodium and chloride ions are held bonding. For example, sodium and chloride ions are held together by ionic bonding to form an array of ions called together by ionic bonding to form an array of ions called sodium chloride,or table salt. sodium chloride,or table salt.

A sodium atom loses an electron to become a smaller-A sodium atom loses an electron to become a smaller-sized positively charged ion, and a chlorine atom gains an sized positively charged ion, and a chlorine atom gains an electron to become a larger-sized negatively charged ion. electron to become a larger-sized negatively charged ion. The attraction between the oppositely charged ions results The attraction between the oppositely charged ions results in an ionic bond and the formation of sodium chloride.in an ionic bond and the formation of sodium chloride.

Intermolecular ForcesIntermolecular Forces Intermolecular forces result from the weak Intermolecular forces result from the weak

electrostatic attractions between the electrostatic attractions between the oppositely charged parts of molecules, or oppositely charged parts of molecules, or between ions and molecules. Intermolecular between ions and molecules. Intermolecular forces are much weakerthan the forces forces are much weakerthan the forces producing chemical bonding.producing chemical bonding.

The positive hydrogen part of one water The positive hydrogen part of one water molecule forms a hydrogen bond (red dotted molecule forms a hydrogen bond (red dotted line) with the negative oxygen part of another line) with the negative oxygen part of another water molecule. As aresult, hydrogen bonds water molecule. As aresult, hydrogen bonds hold the water molecules together.hold the water molecules together.

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

Chemical Reactions and Chemical Reactions and EnergyEnergy

In a chemical reaction, atoms, ions, In a chemical reaction, atoms, ions, molecules, or compounds interact either molecules, or compounds interact either to form or to break chemical bonds. to form or to break chemical bonds.

The substances that enter into a The substances that enter into a chemical reaction are called the chemical reaction are called the reactants, and the substances that reactants, and the substances that result from the chemical reaction are result from the chemical reaction are called the products.called the products.

TThreehree important points can be made important points can be made about chemical reactionsabout chemical reactions

First, in some reactions, less complex reactants are First, in some reactions, less complex reactants are combined to form a larger, more complex product. combined to form a larger, more complex product. An example is the synthesis of the complex An example is the synthesis of the complex molecules of the human body from basic “building molecules of the human body from basic “building blocks” obtained in food. blocks” obtained in food.

Second, in other reactions, a reactant can be broken Second, in other reactions, a reactant can be broken down, or decomposed, into simpler, less complex down, or decomposed, into simpler, less complex products. An example is the breakdown of food products. An example is the breakdown of food molecules into basic building blocks. molecules into basic building blocks.

Third, atoms are generally associated with other Third, atoms are generally associated with other atoms through chemical bonding or intermolecular atoms through chemical bonding or intermolecular forces; therefore, to synthesize new products or forces; therefore, to synthesize new products or break down reactants it is necessary to change the break down reactants it is necessary to change the relationship between atoms.relationship between atoms.

Synthesis ReactionsSynthesis Reactions

When two or more reactants chemically combine to When two or more reactants chemically combine to form a new and larger product, the process is called a form a new and larger product, the process is called a synthesis reaction. An example of a synthesis reaction synthesis reaction. An example of a synthesis reaction is the combination of two amino acids to form a is the combination of two amino acids to form a dipeptide. In this particular synthesis reaction, water dipeptide. In this particular synthesis reaction, water is removed from the amino acids as they are bound is removed from the amino acids as they are bound together. together.

Synthesis reactions in which water is a product are Synthesis reactions in which water is a product are called dehydration (water out) reactions. Note that old called dehydration (water out) reactions. Note that old chemical bonds are broken and new chemical bonds chemical bonds are broken and new chemical bonds are formed as the atoms rearrange as a result of a are formed as the atoms rearrange as a result of a synthesis reaction.synthesis reaction.

Decomposition ReactionsDecomposition Reactions

The term decompose means to break down into The term decompose means to break down into smaller parts. A decomposition reaction is the reverse smaller parts. A decomposition reaction is the reverse of a synthesis reaction— a larger reactant is of a synthesis reaction— a larger reactant is chemically broken down into two or more smaller chemically broken down into two or more smaller products. products.

The breakdown of a disaccharide (a type of The breakdown of a disaccharide (a type of carbohydrate) into glucose molecules is an example. carbohydrate) into glucose molecules is an example. Note that this particular reaction requires that water Note that this particular reaction requires that water be split into two parts and that each part be be split into two parts and that each part be contributed to one of the new glucose molecules. contributed to one of the new glucose molecules. Reactions that use water in this manner are called Reactions that use water in this manner are called hydrolysis reactions.hydrolysis reactions.

Reversible ReactionsReversible Reactions

A reversible reaction is a chemical reaction in A reversible reaction is a chemical reaction in which the reaction can proceed from reactants to which the reaction can proceed from reactants to products or from products to reactants. When the products or from products to reactants. When the rate of product formation is equal to the rate of rate of product formation is equal to the rate of the reverse reaction, the reaction system is said the reverse reaction, the reaction system is said to be at equilibrium. to be at equilibrium.

At equilibrium the amount of reactants relative to At equilibrium the amount of reactants relative to the amount of products remains constant. An the amount of products remains constant. An important reversible reaction in the human body important reversible reaction in the human body involves carbon dioxide and hydrogen ions.involves carbon dioxide and hydrogen ions.

Major Categories of Organic Major Categories of Organic Molecules in the BodyMolecules in the Body

Adenosine TriphosphateAdenosine Triphosphate Adenosine triphosphate (ATP) is an Adenosine triphosphate (ATP) is an

especially important organic molecule especially important organic molecule found in all living organisms. It consists of found in all living organisms. It consists of adenosine and three phosphate groups. adenosine and three phosphate groups.

Adenosine is the sugar ribose with the Adenosine is the sugar ribose with the organic base adenine. The potential energy organic base adenine. The potential energy stored in the covalent bond between the stored in the covalent bond between the second and third phosphate groups is second and third phosphate groups is important to living organisms because it important to living organisms because it provides the energy used in nearly all of the provides the energy used in nearly all of the chemical reactions within cells.chemical reactions within cells.

Sucrose (table sugar) Sucrose (table sugar) is a disaccharide is a disaccharide formed by the linking formed by the linking together of two together of two monosaccharides, monosaccharides, glucose and fructose.glucose and fructose.

Many molecules of Many molecules of glucose linked end-to-glucose linked end-to-end and at branch end and at branch points form the points form the branched-chain branched-chain polysaccharide polysaccharide glycogen, shown in glycogen, shown in diagrammatic form in diagrammatic form in (a). The four red (a). The four red subunits in (b) subunits in (b) correspond to the four correspond to the four glucose subunits in (a).glucose subunits in (a).

(a) Steroid ring (a) Steroid ring structure, shown with structure, shown with all the carbon and all the carbon and hydrogen atoms in hydrogen atoms in the rings and again the rings and again without these atoms without these atoms toto

emphasize the overall emphasize the overall ring structure of this ring structure of this class of lipids. (b) class of lipids. (b) Different steroids Different steroids have different types have different types and numbers of and numbers of chemicalchemical

groups attached at groups attached at various locations on various locations on the steroid ring, as the steroid ring, as shown by the shown by the structure of structure of cholesterol.cholesterol.

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

form a form a peptide peptide bond.bond.