Chapter 2

Chemistry of Life

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Objectives:

What you need to know

• Define the terms atom, element,

molecule, and compound

• Describe the structure of an atom

• Compare and contrast ionic and

covalent types of chemical bonding

• Distinguish between organic and

inorganic chemical compounds

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Objectives:

What you need to know

• Discuss the chemical characteristics of

water

• Explain the concept of pH

• Discuss the structure and function of the

following types of organic molecules:

carbohydrate, lipid, protein, and nucleic

acid

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Levels of Chemical Organization

• Atoms

– Nucleus—central core of atom

• Proton—positively charged particle in nucleus

• Neutron—uncharged particle in nucleus

• Atomic number—number of protons in nucleus

• Atomic mass—number of protons and neutrons

combined

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Levels of Chemical Organization

• Atoms

– Energy levels—orbital regions surrounding

atomic nucleus that contain electrons

• Electron—negatively charged particle

• May contain up to 8 electrons in each level

• Energy level increases the farther away it is

from the nucleus

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Levels of Chemical Organization

• Elements, molecules, and compounds

– Element—a pure substance; made up of

only one kind of atom

– Molecule—a group of atoms bound

together in a group

– Compound—substances whose molecules

have more than one kind of atom

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Chemical Bonding

• Chemical bonds form to make atoms

more stable

– Atoms react with one another in ways that

make their outermost energy level full

– Atoms may share electrons or donate or

borrow them to become stable

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Chemical Bonding

• Ionic bonds

– Ions form when an atom gains or loses

electrons in its outer energy level to

become stable

• Positive ion—has lost electrons; indicated by

superscript positive sign(s), as in Na+ or Ca++

• Negative ion—has gained electrons; indicated

by superscript negative sign(s), as in Cl–

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Chemical Bonding

• Ionic bonds

– Ionic bonds form when positive and

negative (oppositely charged) ions attract

each other

– Electrolyte—molecule that dissociates

(breaks apart) in water to form individual

ions; an ionic compound

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Chemical Bonding

• Covalent bonds

– Covalent bonds form when atoms share their outer energy ions to complete the energy level and thus become stable

– Covalent bonds do not ordinarily easily dissociate in water

– Covalent bonding is used to form all of the major organic compounds found in the body

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Chemical Bonding

• Hydrogen bonds

– Hydrogen bonds do not create new

molecules

– Hydrogen bonds weakly bond to

neighboring molecules

– Hydrogen bonds are present in water,

DNA, and proteins

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Inorganic Chemistry

• Organic molecules contain carbon-

carbon covalent bonds and/or carbon-

hydrogen covalent bonds; inorganic

molecules do not

• Organic molecules are generally larger

and more complex than inorganic

molecules

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Inorganic Chemistry

• Water

– Water is an inorganic compound essential

to life

– Water is a solvent (liquid into which solutes

are dissolved), forming aqueous solutions

in the body

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Inorganic Chemistry

– Water is involved in chemical reactions

• Dehydration synthesis—chemical reaction in which water

is removed from small molecules so they can be strung

together to form a larger molecule

• Hydrolysis—chemical reaction in which water is added to

the subunits of a large molecule to break it apart into

smaller molecules

• Chemical reactions always involve energy transfers, as

when energy is used to build ATP molecules

• Chemical equations show how reactants interact to form

products; arrows separate the reactants from the

products

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Inorganic Chemistry

• Acids, bases, and salts

– Water molecules dissociate to form equal amounts of H+ (hydrogen ion) and OH–(hydroxide ion)

– Acid—substance that shifts the H+/OH–balance in favor of H+; opposite of base

– Base—substance that shifts the H+/OH–balance against H+; also known as an alkaline; opposite of acid

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Inorganic Chemistry

• Acids, bases, and salts

– pH—Mathematical expression of relative

H+ concentration in an aqueous solution

• 7 is neutral (neither acid nor base)

• pH values above 7 are basic; pH values below

7 are acidic

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Inorganic Chemistry

• Acids, bases, and salts

– Neutralization occurs when acids and

bases mix and form salts

– Buffers form chemical systems that absorb

excess acids or bases and thus maintain a

relatively stable pH

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Organic Chemistry

• Carbohydrates—sugars and complex carbohydrates

– Contain carbon (C), hydrogen (H), oxygen (O)

– Monosaccharides— basic unit of carbohydrate molecules (e.g., glucose)

– Disaccharide—double sugar made up of two monosaccharide units (e.g., sucrose, lactose)

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Organic Chemistry

• Carbohydrates—sugars and complex

carbohydrates

– Polysaccharide—complex carbohydrate

made up of many monosaccharide units

(e.g., glycogen; stored by the body)

– Function of carbohydrates is to store

energy for later use

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Organic Chemistry

• Lipids—fats and oils

– Triglycerides

• Formed by a glycerol unit and joined to three

fatty acids

• Store energy for later use

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Organic Chemistry

• Lipids—fats and oils

– Phospholipids

• Similar to triglyceride structure, but have

phosphorus-containing units—each with a head

and two tails

• The head attracts water and the double tail

does not, thus forming stable double layers

(bilayers) in water

• Form membranes of cells

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Organic Chemistry

• Lipids—fats and oils

– Cholesterol

• Molecules have a steroid structure made up of

multiple rings

• Cholesterol stabilizes the phospholipid tails in

cellular membranes and is also converted into

steroid hormones by the body

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Organic Chemistry

• Proteins

– Very large molecules made up of amino acids held together in long, folded chains by peptide bonds

– Structural proteins• Form essential structures of the body

• Collagen is a fibrous protein that holds many tissues together

• Keratin forms tough, waterproof fibers in the outer layer of the skin

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Organic Chemistry

• Proteins

– Functional proteins

• Participate in chemical processes of the body

• Examples include hormones, cell membrane

channels and receptors, and enzymes

• Enzymes—chemical catalysts

– Help chemical reactions occur

– Enzyme action sometimes called lock-and-key model

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Organic Chemistry

• Nucleic acids

– Made up of nucleotides

• A phosphate unit

• A sugar (ribose or deoxyribose)

• A nitrogen base (adenine, thymine or uracil,

guanine, cytosine)

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Organic Chemistry

• Nucleic acids

– DNA (deoxyribonucleic acid)

• Used as the cell’s ―master code‖ for assembling

proteins

• Uses deoxyribose as the sugar and A, T (not

U), C, and G as bases

• Forms a double helix shape

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Organic Chemistry

• Nucleic acids

– RNA (ribonucleic acid)

• Used as a temporary ―working copy‖ of a gene

(portion of the DNA code)

• Uses ribose as the sugar and A, U (not T), C,

and G as bases

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Organic Chemistry

• Nucleic acids

– By directing the formation of structural and

functional proteins, nucleic acids ultimately

direct overall body structure and function