Chapter 2: The Chemistry of Life

Chemical Reactions

A process leading to chemical changes in matter, involving the making and/or breaking of chemical bonds.

Chemistry

The scientific study of matter.

Compounds

A substance containing two or more elements in a fixed ratio.

Elements

A substance that cannot be broken down into other substances by chemical means.

Matter

Anything that occupies space and has mass.

Products

An ending material in a chemical reaction.

Reactants

A starting material in a chemical reaction.

Atomic Number

The number of protons in each atom of a particular element.

Atomic Weight

Also called the atomic mass; the total mass of an atom, which is the mass in grams of 1 mole of the atom.

Periodic Table of Elements

A listing of all the elements ordered by their atomic number (the number of protons found in one atom of the element). Each entry in the periodic table of the elements typically contains the element symbol, its atomic mass, and its atomic number.

Symbol

Also called the atomic symbol, an abbreviation for the name of an element found within the periodic table of the elements.

Trace Elements

An element that is essential for the survival of an organism but is needed in only minute quantities.

Electrons

A subatomic particle with a single unit of negative electrical charge. One or more electrons move around the nucleus of an atom.

Ions

An atom or molecule that has gained or lost one or more electrons, thus acquiring an electrical charge.

Isotopes

A variant form of an atom. An isotope of an element has the same number of protons and electrons but a different number of neutrons.

Neutrons

An electrically neutral particle (a particle having no electrical charge), found in the nucleus of an atom.

Nucleus

(1) An atom’s central core, containing protons and neutrons. (2) The genetic control center of a eukaryotic cell.

Protons

A subatomic particle with a single unit of positive electrical charge, found in the nucleus of an atom.

Subatomic Particles

Protons, neutrons, and electrons; particles smaller than an atom.

Chemical Bonds

An attraction between two atoms resulting from a sharing of outer-shell electrons or the presence of opposite charges on the atoms. The bonded atoms gain complete outer electron shells.

Covalent Bonds

An attraction between atoms that share one or more pairs of outer-shell electrons.

Double Bond

A double covalent bond; the sharing of two pairs of electrons by two atoms.

Hydrogen Bond

A type of weak chemical bond formed when a partially positive hydrogen atom from one polar molecule is attracted to the partially negative atom in another molecule (or in another part of the same molecule).

Ionic Bonds

An attraction between two ions with opposite electrical charges. The electrical attraction of the opposite charges holds the ions together.

Nonpolar Bond

Also called a nonpolar covalent bond; a covalent bond in which electrons are shared equally between two atoms of similar electronegativity; the resulting bond does not have a positive and negative pole; the opposite of a polar bond.

Polar Bond

Also called a polar covalent bond; a covalent bond between atoms that differ in their attraction to electrons. The shared electrons are pulled closer to one atom, making it slightly negative and the other atom slightly positive.

Single Bond

A single covalent bond; the sharing of one pair of electrons by two atoms.

Adhesion

The clinging of one substance to another, such as water to plant cell walls, by means of hydrogen bonds.

Cohesion

The attraction between molecules of the same kind.

Solution

A liquid consisting of a homogeneous mixture of two or more substances: a dissolving agent, the solvent, and a substance that is dissolved, the solute.

Solvent

The dissolving agent in a solution.

Acid

A substance that increases the hydrogen ion (H+) concentration in a solution.

Aqueous Solution

A solution in which water is the solvent.

Base

A substance that decreases the hydrogen ion (H+) concentration in a solution.

Buffers

A chemical substance that resists changes in pH by accepting hydrogen ions from or donating hydrogen ions to solutions.

pH Scale

A measure of the relative acidity of a solution, ranging in value from 0 (most acidic) to 14 (most basic). pH stands for potential hydrogen and refers to the concentration of hydrogen ions (H+).

Cellulose

A large polysaccharide composed of many glucose monomers linked into cable-like fibrils that provide structural support in plant cell walls. Because cellulose cannot be digested by animals, it acts as fiber, or roughage, in the diet.

Coconut Oil

A high-fat liquid extract of the coconut fruit.

Functional Groups

A group of atoms that form the chemically reactive part of an organic molecule. A particular functional group usually behaves similarly in different chemical reactions.

Glucose

A six-carbon monosaccharide that serves as a building block for many polysaccharides and whose oxidation in cellular respiration is a major source of ATP for cells.

Hexokinase

An example of an enzyme, a protein that promotes a chemical reaction.

Keratin

Any member of a family of fibrous proteins; keratin is a key component of human skin, nails, and hair.

Organic Compounds

A chemical compound containing the element carbon and usually synthesized by cells.

RNA

A type of nucleic acid consisting of nucleotide monomers, with a ribose sugar, a phosphate group, and the nitrogenous bases adenine (A), cytosine (C), guanine (G), and uracil (U); usually single-stranded; functions in protein synthesis and as the genome of some viruses.

Dehydration Synthesis Reaction

A chemical reaction in which a monomer is joined to another monomer or polymer, forming a larger molecule and releasing a molecule of water.

Hydrolysis Reactions

Chemical reaction in which macromolecules are broken down by the chemical addition of water molecules to the bonds linking their monomers. A hydrolysis reaction is the opposite of a dehydration synthesis reaction.

Macromolecules

A giant molecule formed by joining smaller molecules. Examples of macromolecules include proteins, polysaccharides, and nucleic acids.

Metabolism

The total of all the chemical reactions in an organism.

Monomers

A chemical subunit that serves as a building block of a polymer.

Polymers

A large molecule consisting of many identical or similar molecular units, called monomers, covalently joined together in a chain.

Carbohydrates

A biological molecule consisting of a simple sugar (a monosaccharide), two monosaccharides joined into a double sugar (a disaccharide), or a chain of monosaccharides (a polysaccharide).

Chitin

A structural polysaccharide found in many fungal cell walls and in the exoskeletons of arthropods.

Disaccharide

A sugar molecule consisting of two monosaccharides linked by a dehydration synthesis reaction.

Fructose

A monosaccharide with the chemical formula C6H12O6 found in many fruits; also called fruit sugar.

Glycogen

A complex, extensively branched polysaccharide made up of many glucose monomers; serves as an energy-storage molecule in liver and muscle cells.

Isomers

One of two or more molecules with the same molecular formula but different structures and thus different properties.

Lactose

A disaccharide (double sugar) made by combining a molecule of glucose with a molecule of galactose; commonly called “milk sugar.”

Maltose

A disaccharide (double sugar) made by combining two molecules of glucose.

Monosaccharides

The smallest kind of sugar molecule; a single-unit sugar; also known as a simple sugar. Monosaccharides are the building blocks of more complex sugars and polysaccharides.

Polysaccharide

A carbohydrate polymer consisting of many monosaccharides (sugars) linked by covalent bonds.

Starch

A storage polysaccharide found in the roots of plants and certain other cells; a polymer of glucose.

Sucrose

A disaccharide (double sugar) made by combining a molecule of glucose with a molecule of fructose; sucrose is common table sugar.

Adipose Tissue

A type of connective tissue in which the cells contain fat.

Anabolic Steroids

A synthetic variant of the male hormone testosterone that mimics some of its effects.

Cholesterol

A steroid that is an important component of animal cell membranes and that acts as a precursor molecule for the synthesis of other steroids, such as hormones.

Fatty Acid

A carboxylic acid with a long carbon chain. Fatty acids vary in length and in the number and location of double bonds; three fatty acids linked to a glycerol molecule form a fat molecule, also known as a triglyceride.

Hydrophobic

“Water-fearing”; pertaining to nonpolar molecules (or parts of molecules), which do not dissolve in water.

Lipids

An organic compound consisting mainly of carbon and hydrogen atoms linked by nonpolar covalent bonds and therefore mostly hydrophobic and insoluble in water. Lipids include fats, waxes, phospholipids, and steroids.

Phospholipid

A molecule that is a constituent of the inner bilayer of biological membranes, having a hydrophilic head and a hydrophobic tail.

Phospholipid Bilayers

A double layer of phospholipid molecules (each molecule consisting of a phosphate group bonded to two fatty acids) that is the primary component of all cellular membranes.

Steroids

A type of lipid whose carbon skeleton is in the form of four fused rings: three 6-sided rings and one 5-sided ring. Examples are cholesterol, testosterone, and estrogen.

Triglyceride

A dietary fat that consists of a molecule of glycerol linked to three molecules of fatty acids.

Hydrogenation

The process of converting unsaturated fats to saturated fats by adding hydrogen.

Omega-3 Fatty Acids

A group of essential fatty acids, consumption of which in the diet is required for proper health.

Saturated Fats

A fat molecule in which all carbons in the hydrocarbon tails are connected by single bonds and the maximum number of hydrogen atoms are attached to the carbon skeleton. Saturated fats solidify at room temperature and are more commonly found in animal products.

Trans Fat

Unsaturated fatty acids produced by the partial hydrogenation of vegetable oils and present in hardened vegetable oils, most margarines, many commercial baked foods, and many fried foods.

Unsaturated Fats

Fat with hydrocarbon chains that lack the maximum number of hydrogen atoms and therefore have one or more double covalent bonds. Because of their bent shape, unsaturated fats and fatty acids tend to stay liquid at room temperature.

Amino Acid

An organic molecule containing a carboxyl group, an amino group, a hydrogen atom, and a variable side group (also called a radical group or R group); serves as the monomer of proteins.

Peptide Bonds

The covalent linkage between two amino acid units in a polypeptide, formed by a dehydration synthesis reaction between two amino acids.

Polypeptide

A chain of amino acids linked by peptide bonds.

Proteins

A biological polymer constructed from amino acid monomers.

Activation Energy

The amount of energy that reactants must absorb before a chemical reaction will start.

Active Site

The part of an enzyme molecule where a substrate molecule attaches (by means of weak chemical bonds); typically, a pocket or groove on the enzyme’s surface.

Competitive Inhibitors

A substance that reduces the activity of an enzyme by binding to the active site, preventing the actual substrate from binding there.

Enzyme

A protein that serves as a biological catalyst, changing the rate of a chemical reaction without itself being changed in the process.

Inhibitors

A substance that reduces the activity of an enzyme by binding to it.

Noncompetitive Inhibitors

A substance that reduces the activity of an enzyme by binding to a site other than the active site. This binding of the noncompetitive inhibitor changes the shape of the active site, preventing the actual substrate from binding.

Substrate

(1) A specific substance (reactant) on which an enzyme acts. Each enzyme recognizes only the specific substrate of the reaction it catalyzes. (2) A surface in or on which an organism lives.