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Chapter 2

The Chemical Basis of LifeThe Chemical Basis of Life

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Basic Chemistry• Matter, Mass, and Weight

– Matter: anything that occupies space and has mass– Mass: the amount of matter in an object– Weight: the gravitational force acting on an object

of a given mass• Elements and Atoms

– Element: the simplest type of matter with unique chemical properties; composed of atoms of only one kind

– Atom: smallest particle of an element that has chemical characteristics of that element

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Atomic Structure• Atoms: composed of

subatomic particles– Neutrons: no electrical

charge– Protons: one positive charge– Electrons: one negative

charge

• Nucleus: formed by protons and neutrons

• Most of the volume of an atom occupied by electrons

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Radioactive Isotopes

• Forms of atoms that emit radioactivity such as gamma rays, which can then be measured

• Used clinically and in research• Examples of uses

– Tracking hormone uptake– Treating cancer– Sterilization of materials to be used in surgery

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Electrons and Chemical Bonding• Intramolecular bonding occurs

when outermost electrons are either shared with or transferred to another atom– Ionic Bonding: atoms

exchange electrons – Covalent Bonding: two or

more atoms share electron pairs• Ion: an atom loses or gains

electrons and becomes charged– Cation: positively charged ion– Anion: negatively charged ion

• In an ionic bond, cations and anions are attracted to each other and remain close to each other

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Covalent BondingAtoms share one or more

pairs of electrons– Single covalent: two

atoms share one pair of electrons

– Double covalent: Two atoms share 4 electrons

– Nonpolar covalent: Electrons shared equallybecause nuclei attract the electrons equally

– Polar covalent: Electrons not shared equally because one nucleus attracts the electrons more than the other does

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Molecules and Compounds• Molecules: two or more atoms chemically

combine to form an independent unit– Example: a hydrogen molecule (H2)

• Compounds: a substance composed of two or more different types of atoms chemically combined– Example: water (H2O)

• Molecular Mass: determined by adding up atomic masses of its atoms or ions– Example: NaCl (22.99 + 35.45)

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Intermolecular Forces: Hydrogen Bonds

• Occur when the positively charged H of one molecule is attracted to the negatively charged O, N or F of another molecule – For example, in water the

positively charged hydrogen atoms of one water molecule bond with the negatively charged oxygen atoms of other water molecules

– Hydrogen bonds play an important role in determining the shape of complex molecules

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Intermolecular Forces:Solubility and Dissociation

• Solubility: ability of one substance to dissolve in another– For example, sugar or salt

dissolves in water• Dissociation or Separation: in

ionic compounds, cations are attracted to negative end and anions attracted to positive end of water molecules; the ions separate and each becomes surrounded by water molecules

• Electrolyte: dissociation of an ionic compound in water

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Chemical Reactions• Atoms, ions, molecules or compounds interact

to form or break chemical bonds– Reactants: substances that enter into a chemical

reaction.– Products: substances that result from the reaction

• Chemical bonds are made (synthesis; anabolism) and broken (decomposition; catabolism) during chemical reactions

• Metabolism: collective term used for the sum of all of the anabolic and catabolic reactions in the body

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Fig. 2.10

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Oxidation-Reduction Reactions

• Oxidation: loss of an electron by an atom• Reduction: gain of an electron by an atom• Oxidation-Reduction Reactions: the

complete or partial loss of an electron by one atom is accompanied by the gain of that electron by another atom– Synthetic/decomposition reactions can be

oxidative reduction reactions– Reactions can be described in more than one

way

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Energy: the capacity to do work

• Potential Energy: energy stored in chemical bonds; energy that could do work if it were released. Breaking chemical bonds releases energy.

• Kinetic Energy: does work and moves matter• Mechanical Energy: energy resulting from the

position or movement of objects• Chemical Energy: form of potential energy in the

chemical bonds of a substance• Heat Energy: energy that flows between objects of

different temperatures

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ATP and Potential Energy

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Speed of Chemical Reactions

• Temperature affects rate of reaction. – Increase in temperature means increase of kinetic energy. – Molecules move faster, collide harder and more frequently.

• Concentration of reactants. – As concentration of reactants increases, rate of reaction increases. – A decrease of O2 in cells can cause death as rate of aerobic

chemical reactions decreases.• Catalysts: substances that increase the rate of chemical

reactions without being permanently changed or depleted– Enzymes: proteinaceous catalysts that increase the rate of chemical

reactions by lowering the activation energy necessary for reaction to begin

• Activation Energy: minimum energy reactants must have to start a chemical reaction

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Activation Energy and Enzymes

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Water

• High specific heat: large amount of heat required to raise temperature of water– Stabilizes body temperature

• Protection– Lubricant, cushion

• Participates in chemical reactions– Many reactions take place in water– Dehydration and hydrolysis

• Serves as a mixing medium

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Mixtures, Solutions and Measures of Concentration• Mixture: substances physically but not chemically

combined– Suspension: materials separate unless stirred. Sand and

water.– Colloid: dispersal of tiny particles through a medium. Milk.

• Solution: mixture of liquids, gasses, or solids that are uniformly distributed and chemically combined– Solvent: that which dissolves the solute– Solute: that which dissolves in the solvent

• Concentration: measure of number of particles of solute per volume of solution– Unit used by physiologists is osmolality– Concentration of body fluids influences movement of fluid

into and out of cells.

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Acids and Bases; Salts and Buffers

• Acid: a proton donor or any substance that releases hydrogen ions

• Base: a proton acceptor or any substance that binds to or accepts hydrogen ions

• Salt: a compound consisting of a cation other than a hydrogen ion and an anion other than a hydroxide ion. Example: NaCl

• Buffer: a solution of a conjugate acid-base pair in which acid and base components occur in similar concentrations

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The pH Scale• Refers to the Hydrogen

ion concentration in a solution– Neutral: pH of 7 or equal

hydrogen and hydroxide ions

– Acidic: a greater concentration of hydrogen ions

– Alkaline or basic: a greater concentration of hydroxide ions

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Organic Chemistry: Biochemicals• Carbohydrates: composed of carbon, hydrogen, oxygen.

– Divided into monosaccharides, disaccharides, polysaccharides– Example: glucose– Energy sources and structure

• Lipids: composed mostly of carbon, hydrogen, oxygen.– Relatively insoluble in water. – Example: anabolic steroids– Functions: protection, insulation, physiological regulation, component of

cell membranes, energy source• Proteins: composed of carbon, hydrogen, oxygen, nitrogen,

sometimes iodine. – Example: insulin– Functions: regulate processes, aid transport, protection, muscle contraction,

structure, energy• Nucleic Acids: composed of carbon, hydrogen, oxygen, nitrogen,

phosphorus. – Examples: ATP, DNA, RNA

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Fig. 2.14

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Fig. 2.15

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Fig. 2.16

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Fig. 2.18

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Fig. 2.19

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Fig. 2.22ab

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Fig. 2.22cd

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Fig. 2.23

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Fig. 2.24

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Fig. 2.26

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Fig. 2.27