Chapter 2 Glossary, Summary, and Practice Questions

KEY TERMS

acid a substance that donates hydrogen ions and therefore lowers pH

adhesion the attraction between water molecules and molecules of a different substance

amino acid a monomer of a protein

anion a negative ion formed by gaining electrons

atomic number the number of protons in an atom

base a substance that absorbs hydrogen ions and therefore raises pH

buffer a solution that resists a change in pH by absorbing or releasing hydrogen or hydroxide ions

carbohydrate a biological macromolecule in which the ratio of carbon to hydrogen to oxygen is 1:2:1; carbohydrates serve as energy sources and structural support in cells

cation a positive ion formed by losing electrons

cellulose a polysaccharide that makes up the cell walls of plants and provides structural support to the cell

chemical bond an interaction between two or more of the same or different elements that results in the formation of molecules

chitin a type of carbohydrate that forms the outer skeleton of arthropods, such as insects and crustaceans, and the cell walls of fungi

cohesion the intermolecular forces between water molecules caused by the polar nature of water; creates surface tension

covalent bond a type of strong bond between two or more of the same or different elements; forms when electrons are shared between elements

denaturation the loss of shape in a protein as a result of changes in temperature, pH, or exposure to chemicals

deoxyribonucleic acid (DNA)

cell

a double-stranded polymer of nucleotides that carries the hereditary information of the

disaccharide two sugar monomers that are linked together by a peptide bond

electron a negatively charged particle that resides outside of the nucleus in the electron orbital; lacks functional mass and has a charge of –1

electron transfer the movement of electrons from one element to another

element one of 118 unique substances that cannot be broken down into smaller substances and retain the characteristic of that substance; each element has a specified number of protons and unique properties

enzyme a catalyst in a biochemical reaction that is usually a complex or conjugated protein

evaporation the release of water molecules from liquid water to form water vapor

fat

a lipid molecule composed of three fatty acids and a glycerol (triglyceride) that typically exists in a solid form at room temperature

glycogen a storage carbohydrate in animals

hormone a chemical signaling molecule, usually a protein or steroid, secreted by an endocrine gland or group of endocrine cells; acts to control or regulate specific physiological processes

hydrogen bond a weak bond between partially positively charged hydrogen atoms and partially negatively charged elements or molecules

hydrophilic describes a substance that dissolves in water; water-loving

hydrophobic describes a substance that does not dissolve in water; water-fearing

ion an atom or compound that does not contain equal numbers of protons and electrons, and therefore has a net charge

ionic bond a chemical bond that forms between ions of opposite charges isotope one or more forms of an element that have different numbers of neutrons lipids a class of macromolecules that are nonpolar and insoluble in water

litmus paper filter paper that has been treated with a natural water-soluble dye so it can be used as a pH indicator

macromolecule a large molecule, often formed by polymerization of smaller monomers

mass number the number of protons plus neutrons in an atom matter anything that has mass and occupies space monosaccharide a single unit or monomer of carbohydrates

neutron a particle with no charge that resides in the nucleus of an atom; has a mass of 1

nonpolar covalent bond a type of covalent bond that forms between atoms when electrons are shared equally between atoms, resulting in no regions with partial charges as in polar covalent bonds

nucleic acid a biological macromolecule that carries the genetic information of a cell and carries instructions for the functioning of the cell

nucleotide a monomer of nucleic acids; contains a pentose sugar, a phosphate group, and a nitrogenous base

nucleus (chemistry) the dense center of an atom made up of protons and (except in the case of a hydrogen atom) neutrons

octet rule states that the outermost shell of an element with a low atomic number can hold eight electrons

oilan unsaturated fat that is a liquid at room temperature

periodic table of elements an organizational chart of elements, indicating the atomic number and mass number of each element; also provides key information about the properties of elements

pH scale a scale ranging from 0 to 14 that measures the approximate concentration of hydrogen ions of a substance

phospholipid a major constituent of the membranes of cells; composed of two fatty acids and a phosphate group attached to the glycerol backbone

polar covalent bond a type of covalent bond in which electrons are pulled toward one atom and away from another, resulting in slightly positive and slightly negative charged regions of the molecule

polypeptide a long chain of amino acids linked by peptide bonds polysaccharide a long chain of monosaccharides; may be branched or unbranched protein a biological macromolecule composed of one or more chains of amino acids

proton a positively charged particle that resides in the nucleus of an atom; has a mass of 1 and a charge of +1 radioactive isotope an isotope that spontaneously emits particles or energy to form a more stable element ribonucleic acid (RNA) a single-stranded polymer of nucleotides that is involved in protein synthesis

saturated fatty acid a long-chain hydrocarbon with single covalent bonds in the carbon chain; the number of hydrogen atoms attached to the carbon skeleton is maximized

solvent a substance capable of dissolving another substance

starch a storage carbohydrate in plants

steroid a type of lipid composed of four fused hydrocarbon rings

surface tension the cohesive force at the surface of a body of liquid that prevents the molecules from separating

temperature a measure of molecular motion

trans-fat a form of unsaturated fat with the hydrogen atoms neighboring the double bond across from each other rather than on the same side of the double bond

triglyceride a fat molecule; consists of three fatty acids linked to a glycerol molecule

unsaturated fatty acid a long-chain hydrocarbon that has one or more than one double bonds in the hydrocarbon chain

van der Waals interaction a weak attraction or interaction between molecules caused by slightly positively charged or slightly negatively charged atoms

CHAPTER SUMMARY

The Building Blocks of Molecules

Matter is anything that occupies space and has mass. It is made up of atoms of different elements. All of the 92 elements that occur naturally have unique qualities that allow them to combine in various ways to create compounds or molecules. Atoms, which consist of protons, neutrons, and electrons, are the smallest units of an element that retain all of the properties of that element. Electrons can be donated or shared between atoms to create bonds, including ionic, covalent, and hydrogen bonds, as well as van der Waals interactions.

Water

Water has many properties that are critical to maintaining life. It is polar, allowing for the formation of hydrogen bonds, which allow ions and other polar molecules to dissolve in water. Therefore, water is an excellent solvent. The hydrogen bonds between water molecules give water the ability to hold heat better than many other substances. As the temperature rises, the hydrogen bonds between water continually break and reform, allowing for the overall temperature to remain stable, although increased energy is added to the system. Water’s cohesive forces allow for the property of surface tension. All of these unique properties of water are important in the chemistry of living organisms.

The pH of a solution is a measure of the concentration of hydrogen ions in the solution. A solution with a high number of hydrogen ions is acidic and has a low pH value. A solution with a high number of hydroxide ions is basic and has a high pH value. The pH scale ranges from 0 to 14, with a pH of 7 being neutral. Buffers are solutions that moderate pH changes when an acid or base is added to the buffer system. Buffers are important in biological systems because of their ability to maintain constant pH conditions.

Biological Molecules

Living things are carbon-based because carbon plays such a prominent role in the chemistry of living things. The four covalent bonding positions of the carbon atom can give rise to a wide diversity of compounds with many functions, accounting for the importance of carbon in living things. Carbohydrates are a group of macromolecules that are a vital energy source for the cell, provide structural support to many organisms, and can be found on the surface of the cell as receptors or for cell recognition. Carbohydrates are classified as monosaccharides, disaccharides, and polysaccharides, depending on the number of monomers in the molecule.

Lipids are a class of macromolecules that are nonpolar and hydrophobic in nature. Major types include fats and oils, waxes, phospholipids, and steroids. Fats and oils are a stored form of energy and can include triglycerides. Fats and oils are usually made up of fatty acids and glycerol.

Proteins are a class of macromolecules that can perform a diverse range of functions for the cell. They help in metabolism by providing structural support and by acting as enzymes, carriers or as hormones. The building blocks of proteins are amino acids. Proteins are organized at four levels: primary, secondary, tertiary, and quaternary. Protein shape and function are intricately linked; any change in shape caused by changes in temperature, pH, or chemical exposure may lead to protein denaturation and a loss of function.

Nucleic acids are molecules made up of repeating units of nucleotides that direct cellular activities such as cell division and protein synthesis. Each nucleotide is made up of a pentose sugar, a nitrogenous base, and a phosphate group. There are two types of nucleic acids: DNA and RNA.

ART CONNECTION QUESTIONS

• Figure 2.3 How many neutrons do (K) potassium-39 and potassium-40 have, respectively?

REVIEW QUESTIONS

• Magnesium has an atomic number of 12. Which of the following statements is true of a neutral magnesium atom?

• It has 12 protons, 12 electrons, and 12 neutrons.
• It has 12 protons, 12 electrons, and six neutrons.
• It has six protons, six electrons, and no neutrons.
• It has six protons, six electrons, and six neutrons.
• Which type of bond represents a weak chemical bond?

• hydrogen bond
• ionic bond
• covalent bond
• polar covalent bond
• An isotope of sodium (Na) has a mass number of 22. How many neutrons does it have?
• 11
• 12
• 22
• 44
• Which of the following statements is not true?

• Water is polar.
• Water stabilizes temperature.
• Water is essential for life.
• Water is the most abundant atom in Earth’s atmosphere.
• Using a pH meter, you find the pH of an unknown solution to be 8.0. How would you describe this solution?

• weakly acidic
• strongly acidic
• weakly basic
• strongly basic

CRITICAL THINKING QUESTIONS

• Why are hydrogen bonds and van der Waals interactions necessary for cells?
• Why can some insects walk on water?
• Explain why water is an excellent solvent.
• 
  The pH of lemon juice is about 2.0, whereas tomato juice’s pH is about 4.0. Approximately how much of an increase in hydrogen ion concentration is there between tomato juice and lemon juice?
• 2 times
• 10 times
• 100 times
• 1000 times
• An example of a monosaccharide is .

• fructose
• glucose
• galactose
• all of the above
• Cellulose and starch are examples of .

• monosaccharides
• disaccharides
• lipids
• polysaccharides
• Phospholipids are important components of

.

• the plasma membrane of cells
• the ring structure of steroids
• the waxy covering on leaves
• the double bond in hydrocarbon chains
• The monomers that make up proteins are called

.

• nucleotides
• disaccharides
• amino acids
• chaperones

• Explain at least three functions that lipids serve in plants and/or animals.
• Explain what happens if even one amino acid is substituted for another in a polypeptide chain. Provide a specific example.