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Chapter 2Chapter 2
Chemistry of Life
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Learning ObjectivesLearning Objectives
• 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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Learning Objectives (cont’d.)Learning Objectives (cont’d.)
• 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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Chapter 2Lesson 2.1Chapter 2Lesson 2.1
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Levels of Chemical OrganizationLevels 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
to form a larger chemical unit Compound—substances whose molecules
have more than one kind of element
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Important Elements in the Human Body
Important Elements in the Human Body
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Levels of Chemical OrganizationLevels of Chemical Organization
• Atoms Nucleus—central core of atom
Proton—positively charged particle in nucleus Neutron—noncharged particle in nucleus Atomic number—number of protons in the
nucleus; determines the type of atom
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A Model of the AtomA Model of the Atom
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Levels of Chemical Organization (cont’d.)
Levels of Chemical Organization (cont’d.)
Energy levels—regions surrounding atomic nucleus that contain electrons
electron—negatively charged particle may contain up to two electrons in the level
closest to the nucleus may contain up to eight electrons in the
remaining levels energy increases with distance from the
nucleus
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Chemical BondingChemical Bonding
• Chemical bonds form to make atoms more stable. Outermost energy level of each atom is full. Atoms may share electrons, or donate or
borrow them to become stable.
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Chemical Bonding (cont’d.)Chemical Bonding (cont’d.)
• 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 (cont’d.)Chemical Bonding (cont’d.)
Ionic bonds form when positive and negative ions attract each other because of electrical attraction.
Electrolyte—molecule that dissociates (breaks apart) in water to form individual ions; an ionic compound
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Ionic BondingIonic Bonding
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Chemical BondingChemical Bonding
• Covalent bonds Covalent bonds form when atoms that share
their outer energy fill up and thus become stable.
Covalent bonds do not ordinarily dissociate in water.
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Covalent BondingCovalent Bonding
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Chapter 2Lesson 2.2Chapter 2Lesson 2.2
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Inorganic ChemistryInorganic Chemistry
• Organic molecules contain carbon–carbon covalent bonds and/or carbon-hydrogen covalent bonds; inorganic molecules do not.
• Examples of inorganic molecules: water and some acids, bases, and salts.
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Inorganic Chemistry (cont’d.)Inorganic Chemistry (cont’d.)
• Water Water is a solvent (liquid into which solutes are
dissolved), forming aqueous solutions in the body
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
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Water-Based ChemistryWater-Based Chemistry
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Acids, bases, and saltsAcids, 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 Inorganic Chemistry
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. Neutralization occurs when acids and bases
mix and form salts. Buffers are chemical systems that absorb
excess acids or bases and thus maintain a relatively stable pH.
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The pH ScaleThe pH Scale
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Chapter 2Lesson 2.3Chapter 2Lesson 2.3
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Organic ChemistryOrganic Chemistry
• Carbohydrates—sugars and complex carbohydrates Contain carbon (C), hydrogen (H), oxygen
(O) Made up of six carbon subunits called
monosaccharides or single sugars (e.g., glucose)
Disaccharide—double sugar made up of two monosaccharide units (e.g., sucrose, lactose)
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Organic Chemistry (cont’d.)Organic Chemistry (cont’d.)
Polysaccharide—complex carbohydrate made up of many monosaccharide units (e.g., glycogen made up of many glucose units)
The function of carbohydrates is to store energy for later use.
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CarbohydratesCarbohydrates
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Organic Chemistry (cont’d.)Organic Chemistry (cont’d.)
• Lipids—fats and oils Trigylcerides
Made up of one glycerol unit and three fatty acids
Store energy for later use
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TriglycerideTriglyceride
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Organic Chemistry (cont’d.)Organic Chemistry (cont’d.)
Phospholipids Similar to triglyceride structure, except with
only two fatty acids, and with a phosphorus-containing group attached to glycerol
The head attracts water and the double tail repels water, thus forming stable double layers (bilayers) in water
Form membranes of cells
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Phospholipids Phospholipids
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Organic Chemistry (cont’d.)Organic Chemistry (cont’d.)
Cholesterol Cholesterol molecules have a steroid
structure made up of multiple rings. Cholesterol stabilizes the phospholipid tails in
cellular membranes. It is converted into steroid hormones, such as
estrogen, testosterone, and cortisone by the body.
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Organic Chemistry (cont’d.)Organic Chemistry (cont’d.)
• Proteins very large molecules made up of amino
acids held together in long folded chains by peptide bonds
Structural proteins form 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 (cont’d.)Organic Chemistry (cont’d.)
Functional proteins Participate in chemical processes (examples:
hormones, cell membrane channels and receptors, enzymes)
Enzymeso Catalysts help chemical reactions occur.o Lock-and-key—each enzyme fits a particular
molecule that it acts on as a key fits into a lock Proteins can combine with other organic molecules
to form glycoproteins or lipoproteins.
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ProteinProtein
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Organic Chemistry (cont’d.)Organic Chemistry (cont’d.)
• Nucleic acids Made up of nucleotide units
sugar (ribose or deoxyribose) phosphate nitrogen base (adenine, thymine or uracil,
guanine, cytosine)
• By directing the formation of structural and functional proteins, nucleic acids ultimately direct overall body structure and function
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Organic Chemistry (cont’d.)Organic Chemistry (cont’d.)
DNA (deoxyribonucleic acid) used as the cell’s “master code” for
assembling proteins composed of deoxyribose (the sugar),
phosphate, and four bases: cytosine, guanine, adenine, and thymine
forms a double helix
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Organic Chemistry (cont’d.)Organic Chemistry (cont’d.)
RNA (ribonucleic acid) Used as a temporary “working copy” of a
gene (portion of the DNA code) Composed of ribose (the sugar), phosphate,
and four bases: adenine, uracil, cytosine, and guanine