Chapter 2 Chemistry of Life

Chapter 2Chapter 2Chemistry of LifeChemistry of Life

Elsevier items and derived items © 2008, 2004 by Mosby, Inc., an affiliate of Elsevier Inc. Slide 2

LEVELS OF CHEMICAL LEVELS OF CHEMICAL ORGANIZATIONORGANIZATION

Atoms (Figure 2-1)Atoms (Figure 2-1) Nucleus—central core of atomNucleus—central core of atom

• Proton—positively charged particle in nucleusProton—positively charged particle in nucleus• Neutron—non-charged particle in nucleusNeutron—non-charged particle in nucleus• Atomic number—number of protons in the nucleus; Atomic number—number of protons in the nucleus;

determines the type of atomdetermines the type of atom• Atomic mass—number of protons and neutrons combinedAtomic mass—number of protons and neutrons combined

Energy levels—regions surrounding atomic nucleus that Energy levels—regions surrounding atomic nucleus that contain electronscontain electrons

• Electron—negatively charged particleElectron—negatively charged particle• May contain up to eight electrons in each levelMay contain up to eight electrons in each level• Energy increases with distance from nucleusEnergy increases with distance from nucleus



LEVELS OF CHEMICAL LEVELS OF CHEMICAL ORGANIZATIONORGANIZATION

Elements, molecules, and compounds Elements, molecules, and compounds (Figure 2-2)(Figure 2-2) Element—a pure substance; made up of only Element—a pure substance; made up of only

one kind of atomone kind of atom Molecule—a group of atoms bound together in Molecule—a group of atoms bound together in

a groupa group Compound—substances whose molecules Compound—substances whose molecules

have more than one kind of atomhave more than one kind of atom



CHEMICAL BONDINGCHEMICAL BONDING

Chemical bonds form to make atoms more Chemical bonds form to make atoms more stablestable Outermost energy level of each atom is fullOutermost energy level of each atom is full Atoms may share electrons or donate or Atoms may share electrons or donate or

borrow them to become stableborrow them to become stable



Ionic bondsIonic bonds Ions form when an atom gains or loses electrons in its Ions form when an atom gains or loses electrons in its

outer energy level to become stableouter energy level to become stable• Positive ion—has lost electrons; indicated by superscript Positive ion—has lost electrons; indicated by superscript

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

• Negative ion—has gained electrons; indicated by Negative ion—has gained electrons; indicated by superscript negative sign(s), as in Clsuperscript negative sign(s), as in Cl

Ionic bonds form when positive and negative ions attract Ionic bonds form when positive and negative ions attract each other because of electrical attraction each other because of electrical attraction

Electrolyte—molecule that dissociates (breaks apart) in Electrolyte—molecule that dissociates (breaks apart) in water to form individual ions; an ionic compoundwater to form individual ions; an ionic compound



Covalent bonds (Figure 2-3)Covalent bonds (Figure 2-3) Covalent bonds form when atoms share their Covalent bonds form when atoms share their

outer energy to fill up and thus become stableouter energy to fill up and thus become stable Covalent bonds do not ordinarily easily Covalent bonds do not ordinarily easily

dissociate in waterdissociate in water



INORGANIC CHEMISTRYINORGANIC CHEMISTRY

OrganicOrganic molecules contain carbon-carbon molecules contain carbon-carbon covalent bonds or carbon-hydrogen covalent bonds or carbon-hydrogen covalent bonds; covalent bonds; inorganicinorganic molecules do molecules do notnot

Examples of inorganic molecules: water Examples of inorganic molecules: water and some acids, bases, and saltsand some acids, bases, and salts



WaterWater Water is a solvent (liquid into which solutes are Water is a solvent (liquid into which solutes are

dissolved), forming aqueous solutions in the bodydissolved), forming aqueous solutions in the body Water is involved in chemical reactions (Figure 2-4)Water is involved in chemical reactions (Figure 2-4)

• Dehydration synthesis—chemical reaction in which water is Dehydration synthesis—chemical reaction in which water is removed from small molecules so they can be strung removed from small molecules so they can be strung together to form a larger moleculetogether to form a larger molecule

• Hydrolysis—chemical reaction in which water is added to Hydrolysis—chemical reaction in which water is added to the subunits of a large molecule to break it apart into the subunits of a large molecule to break it apart into smaller moleculessmaller molecules

• Chemical reactions always involve energy transfers, as Chemical reactions always involve energy transfers, as when energy is used to build ATP moleculeswhen energy is used to build ATP molecules

• Chemical equations show how reactants interact to form Chemical equations show how reactants interact to form products; arrows separate the reactants from the productsproducts; arrows separate the reactants from the products




Acids, bases, and saltsAcids, bases, and salts Water molecules dissociate to form equal Water molecules dissociate to form equal

amounts of Hamounts of H++ (hydrogen ion) and OH (hydrogen ion) and OH (hydroxide ion)(hydroxide ion)

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

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



Acids, bases, and salts (cont.)Acids, bases, and salts (cont.) pH—mathematical expression of relative HpH—mathematical expression of relative H++

concentration in an aqueous solution (Figure 2-5)concentration in an aqueous solution (Figure 2-5)• pH 7 is neutral (neither acid nor base)pH 7 is neutral (neither acid nor base)

• pH values above 7 are basic; pH values below 7 are acidicpH values above 7 are basic; pH values below 7 are acidic Neutralization occurs when acids and bases mix and Neutralization occurs when acids and bases mix and

form saltsform salts Buffers are chemical systems that absorb excess acids Buffers are chemical systems that absorb excess acids

or bases and thus maintain a relatively stable pHor bases and thus maintain a relatively stable pH



ORGANIC CHEMISTRYORGANIC CHEMISTRY

Carbohydrates—sugars and complex Carbohydrates—sugars and complex carbohydrates (Figure 2-6)carbohydrates (Figure 2-6) Contain carbon (C), hydrogen (H), oxygen (O)Contain carbon (C), hydrogen (H), oxygen (O) Made up of six-carbon subunits called Made up of six-carbon subunits called monosaccharidesmonosaccharides

or single sugars (e.g., glucose)or single sugars (e.g., glucose) Disaccharide—double sugar made up of two Disaccharide—double sugar made up of two

monosaccharide units (e.g., sucrose, lactose)monosaccharide units (e.g., sucrose, lactose) Polysaccharide—complex carbohydrate made up of Polysaccharide—complex carbohydrate made up of

many monosaccharide units (e.g., glycogen made up of many monosaccharide units (e.g., glycogen made up of many glucose units)many glucose units)

Function of carbohydrates is to store energy for later useFunction of carbohydrates is to store energy for later use




Lipids—fats and oilsLipids—fats and oils Triglycerides (Figure 2-7)Triglycerides (Figure 2-7)

• Made up of one glycerol unit and three fatty acidsMade up of one glycerol unit and three fatty acids• Store energy for later useStore energy for later use

Phospholipids (Figure 2-8)Phospholipids (Figure 2-8)• Similar to triglyceride structure, except with only two fatty acids, Similar to triglyceride structure, except with only two fatty acids,

and with a phosphorus-containing group attached to glyceroland with a phosphorus-containing group attached to glycerol• The head attracts water and the double tail does not, thus The head attracts water and the double tail does not, thus

forming stable double layers (bilayers) in waterforming stable double layers (bilayers) in water• Form membranes of cellsForm membranes of cells

CholesterolCholesterol• Molecules have a steroid structure made up of multiple ringsMolecules have a steroid structure made up of multiple rings• Cholesterol stabilizes the phospholipid tails in cellular Cholesterol stabilizes the phospholipid tails in cellular

membranes and is also converted into steroid hormones by the membranes and is also converted into steroid hormones by the bodybody






Proteins (Figure 2-9)Proteins (Figure 2-9) Very large molecules made up of amino acids Very large molecules made up of amino acids

held together in long, folded chains by peptide held together in long, folded chains by peptide bondsbonds

Structural proteinsStructural proteins• Form structures of the bodyForm structures of the body

• Collagen is a fibrous protein that holds many tissues Collagen is a fibrous protein that holds many tissues togethertogether

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




Proteins (cont.)Proteins (cont.) Functional proteinsFunctional proteins

• Participate in chemical processesParticipate in chemical processes

• Examples: hormones, cell membrane channels and Examples: hormones, cell membrane channels and receptors, enzymesreceptors, enzymes

• Enzymes (Figure 2-10)Enzymes (Figure 2-10) Catalysts—help chemical reactions occurCatalysts—help chemical reactions occur Lock-and-key model—each enzyme fits a particular Lock-and-key model—each enzyme fits a particular

molecule that it acts on as a key fits into a lockmolecule that it acts on as a key fits into a lock

Proteins can combine with other organic Proteins can combine with other organic molecules to form glycoproteins or lipoproteinsmolecules to form glycoproteins or lipoproteins




Nucleic acidsNucleic acids Made up of nucleotide unitsMade up of nucleotide units Sugar (ribose or deoxyribose)Sugar (ribose or deoxyribose) PhosphatePhosphate

• Nitrogen base (adenine, thymine or uracil, guanine, Nitrogen base (adenine, thymine or uracil, guanine, cytosine)cytosine)



Nucleic acids (cont.)Nucleic acids (cont.) DNA (deoxyribonucleic acid) (Figure 2-11)DNA (deoxyribonucleic acid) (Figure 2-11)

• Used as the cell’s “master code” for assembling proteinsUsed as the cell’s “master code” for assembling proteins• Uses deoxyribose as the sugar and A, T (not U), C, and G Uses deoxyribose as the sugar and A, T (not U), C, and G

as basesas bases• Forms a double helix shapeForms a double helix shape

RNA (ribonucleic acid)RNA (ribonucleic acid)• Used as a temporary “working copy” of a gene (portion of Used as a temporary “working copy” of a gene (portion of

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

basesbases By directing the formation of structural and functional By directing the formation of structural and functional

proteins, nucleic acids ultimately direct overall body proteins, nucleic acids ultimately direct overall body structure and functionstructure and function


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Chapter 2 Chemistry of Life