Biology II – Chapter 2 & 3 Key Terms
1. acid – a substance that releases hydrogen ions (H+) into solution; a solution with a pH less than
7.
2. adenosine triphosphate (ATP) – a molecule composed of the sugar ribose, the base adenine,
and three phosphate groups; the major energy carrier in cells. The last two phosphate groups are
attached by “high-energy” bonds.
3. amino acid – the individual subunit of which proteins are made, composed of a central carbon
atom bonded to an amino group (-NH2), a carboxyl group (-COOH), a hydrogen atom, and a
variable group of atoms denoted by the letter R.
4. base – (1) a substance capable of combining with and neutralizing H+ ions in a solution; a
solution with a pH of more than 7.
5. buffer – a compound that minimizes changes in pH by reversibly taking up or releasing H+
ions.
6. carbohydrate – a compound composed of carbon, hydrogen, and oxygen, with the approximate
chemical formula (CH2O)n; includes sugars and starches.
7. coenzyme – an organic molecule that is bound to certain enzymes and is required for the
enzymes’ proper functioning; typically, a nucleotide bound to a water-soluble vitamin.
8. deoxyribonucleic acid (DNA) – a molecule composed of deoxyribose nucleotides; contains the
genetic information of all living cells.
9. disaccharide – a carbohydrate formed by the covalent bonding of two monosaccharides.
10. enzyme – a protein catalyst that speeds up the rate of specific biological reactions.
11. fat – (molecular) – a lipid composed of three saturated fatty acids covalently bonded to
glycerol; solid at room temperature.
12. fatty acid – an organic molecule composed of a long chain of carbon atoms, with a carboxylic
acid (COOH) ground at one end; may be saturated (all single bonds between the carbon atoms)
or unsaturated (one or more double bonds between carbon atoms).
13. glucose – the most common monosaccharide; with the molecular formula C6H12O6; most
polysaccharides, including cellulose, starch, and glycogen, are mode of glucose subunits
covalently bonded together.
14. glycerol – a three-carbon alcohol to which fatty acids are covalently bonded to make fats and
oils
15. glycogen – a long, branched polymer of glucose that is stored by animals in the muscles and
liver and metabolized as a source of energy.
16. hydrophilic – pertaining to a substance that dissolves readily in water or to parts of a large
molecule that form hydrogen bonds with water.
17. hydrophobic – pertaining to a substance that does not dissolve in water.
18. inorganic – describing any molecule that does not contain both carbon and hydrogen.
19. lactose – a disaccharide composed of glucose and galactose; found in mammalian milk.
20. lipid – one of a number of organic molecules containing large nonpolar regions composed
solely of carbon and hydrogen, which make lipids hydrophobic and insoluble in water; includes
oils, fats, waxes, phospholipids, and steroids.
21. monomer – a small organic molecule, several of which may be bonded together to form a chain
called a polymer.
22. monosaccharide – the basic molecular unit of all carbohydrates, normally composed of a chain
of carbon atoms bonded to hydrogen and hydroxyl groups.
23. nucleic acid – an organic molecule composed of nucleotide subunits; the two common types of
nucleic acids are ribonucleic acid (RNA) and deoxyribonucleic acid (DNA).
24. nucleotide – a subunit of which nucleic acids are composed; a phosphate group bonded to a
sugar (deoxyribose in DNA), which is in turn bonded to a nitrogen-containing base (adenine,
guanine, cytosine, or thymine in DNA). Nucleotides are linked together, forming a strand of
nucleic acid, as follows: bonds between the phosphate of one nucleotide link to the sugar of the
next nucleotide.
25. oil – a lipid composed of three fatty acids, some of which are unsaturated, covalently bonded to
a molecule of glycerol; liquid at room temperature
26. organic – describing a molecule that contains both carbon and hydrogen.
27. peptide – a chain composed of two or more amino acids linked together by peptide bonds.
28. peptide bond – the covalent bond between the amino group’s nitrogen of one amino avid and
the carboxyl group’s carbon of a second amino acid, joining the two amino acids together in a
peptide or protein.
29. pH scale – a scale, with values from 0 to 14, used for measuring the relative acidity of a
solution; at pH 7 a solution is neutral, pH 0 to 7 is acidic, and pH 7 to 14 is basic; each unit on
the scale represents a tenfold change in H+ concentration.
30. phospholipid – a lipid consisting of glycerol bonded to two fatty acids and one phosphate
group, which bears another group of atoms, typically charged and containing nitrogen. A double
layer of phospholipids is a component of all cellular membranes.
31. polymer – a molecule composed of three or more (perhaps thousands) smaller subunits called
monomers, which may be identical (for example, the glucose monomers of starch) or different
(for example, the amino acids of proteins).
32. polysaccharide – a large carbohydrate molecule composed of branched or unbranched chains of
repeating monosaccharide subunits, normally glucose or modified glucose molecules; includes
starches, cellulose, and glycogen.
33. protein – polymer of amino acids joined by peptide bonds.
34. ribonucleic acid (RNA) – a molecule composed of ribose nucleotides, each of which consists
of a phosphate group, the sugar ribose, and one of the bases adenine, cytosine, guanine, or
uracil; transfers heredity instructions from the nucleus to the cytoplasm; also the genetic
material of some viruses.
35. starch – a polysaccharide that is composed of branched or unbranched chains or glucose
molecules; used by plants are a carbohydrate-storage molecule.
36. steroid – a class of hormone whose chemical structure (four fused carbon rings with various
functional groups) resembles cholesterol; steroids, which are lipids, are secreted by the ovaries
and placenta; the testes, and the adrenal cortex.
37. triglyceride – a lipid composed of three fatty-acid molecules bonded to a single glycerol
molecule.
38. wax – a lipid composed of fatty acids covalently bonded to long-chain alcohols.