BIOL Ch. 2 Test Bank

2-31 Although covalent bonds are 10-100 times stronger than noncovalent interactions, many biological processes depend upon the number and type of noncovalent interactions between molecules. Which of the noncovalent interactions below will contribute most to the strong and specific binding of two molecules, such as a pair of proteins? (a) electrostatic attractions (b) hydrogen bonds (c) hydrophobic interactions (d) Van der Waals attractions

(a) electrostatic attractions

2-13 The first task you are assigned in your summer laboratory job is to prepare a concentrated NaOH stock solution. The molecular weight of NaOH is 40. How many grams of solid NaOH will you need to weigh out to obtain a 500 mL solution that has a concentration of 10 M? (a) 800 g (b) 200 g (c) 400 g (d) 160 g

(b) 200 g

2-63 Because there are four different monomer building blocks that can be used to assemble RNA polymers, the number of possible sequence combinations that can be created for an RNA molecule made of 100 nucleotides is _______. (a) 100^4 (b) 4^100 (c) 4 × 100 (d) 100/4

(b) 4^100

2-30 Which combination of answers best completes the following statement: When atoms are held together by ___________ __________, they are typically referred to as _________. (a) hydrogen bonds, molecules. (b) ionic interactions, salts. (c) ionic interactions, molecules. (d) double bonds, nonpolar.

(b) ionic interactions, salts

2-7 Carbon 14 is an unstable isotope of carbon that decays very slowly. Compared to the common, stable carbon 12 isotope, carbon 14 has two additional ______________. (a) electrons. (b) neutrons. (c) protons. (d) ions.

(b) neutrons

2-4 Which subatomic particles contribute to the atomic mass for any given element? (a) protons (b) protons and neutrons (c) neutrons (d) protons and electrons

(b) protons and neutrons

2-26 Double covalent bonds are both shorter and stronger than single covalent bonds, but they also limit the geometry of the molecule because they ____________________. (a) create a new arrangement of electron shells. (b) change the reactivity of the bonded atoms. (c) limit the rotation of the bonded atoms. (d) prevent additional bonds from being formed with the bonded atoms.

(c) limit the rotation of the bonded atoms

2-5 Which subatomic particles can vary between isotopes of the same element, without changing the observed chemical properties? (a) electrons (b) protons and neutrons (c) neutrons (d) neutrons and electrons

(c) neutrons

2-27 Polar covalent bonds are formed when the electrons in the bond are not shared equally between the two nuclei. Which one of these molecules contains polar bonds? (a) molecular oxygen (b) methane (c) propane (d) water

(d) water

2-12 Avogadro's number, calculated from the atomic weight of hydrogen, tells us how many atoms or molecules are in a mole. The resulting base for all calculations of moles and molarity (how many molecules are present when you weigh out a substance or measure from a stock solution) is the following: 1 g of hydrogen atoms = 6 × 1023 hydrogen atoms = 1 mole of hydrogen. Sulfur has a molecular weight of 32. How many moles and atoms are there in 120 grams of sulfur? (a) 3.75 and 6 × 1023 (b) 32 and 6 × 1023 (c) 1.75 and 1.05 ×1024 (d) 3.75 and 2.25 × 1024

d) 3.75 and 2.25 × 1024

2-2 Indicate whether the statements below are true or false. If a statement is false, explain why it is false. A. The chemistry of life is carried out and coordinated primarily by the action of small molecules. B. Carbon-based compounds make up the vast majority of molecules found in cells. C. The chemical reactions in living systems are loosely regulated, allowing for a wide range of products and more rapid evolution.

A. False. Although small molecules are important in many processes, the chemical reactions in living systems are regulated by the coordinated action of large polymeric molecules. B. True. C. False. The chemical reactions in living systems are very tightly controlled, ensuring that events occur at the proper time and at the proper location inside the cell.

2-62 Each nucleotide in DNA and RNA has an aromatic base. What is the principal force that keeps the bases in a polymer from interacting with water? (a) hydrophobic interactions (b) hydrogen bonds (c) covalent bonds (d) van der Waals interactions

(a) hydrophobic interactions

2-32 Which of the following expressions accurately describes the calculation of pH? (a) pH = -log10[H+] (b) pH = log10[H+] (c) pH = -log2[H+] (d) pH = -log10[OH-]

(a) pH = -log10[H+]

2-3 Which subatomic particles contribute to the atomic number for any given element? (a) protons (b) protons and neutrons (c) neutrons (d) protons and electrons

(a) protons

2-39 Aromatic carbon compounds such as benzene are planar and very stable. Double bond character extends around the entire ring, which is why it is often drawn as a hexagon with a circle inside. This characteristic is caused by electron __________. (a) resonance. (b) pairing. (c) partial charge. (d) stacking.

(a) resonance

2-16 A covalent bond between two atoms is formed as a result of the ______________. (a) sharing of electrons. (b) loss of electrons from both atoms. (c) loss of a proton from one atom. (d) transfer of electrons from one atom to the other.

(a) sharing of electrons

2-10 Which of the following elements is least abundant in living organisms? (a) sulfur (b) carbon (c) oxygen (d) nitrogen

(a) sulfur

2-25 Which of the following factors do not influence the length of a covalent bond? (a) the tendency of atoms to fill the outer electron shells (b) the attractive forces between negatively charged electrons and positively charged nuclei (c) the repulsive forces between the positively charged nuclei (d) the minimization of repulsive forces between the two nuclei by the cloud of shared electrons

(a) the tendency of atoms to fill the outer electron shells

2-57 DNA and RNA are different types of nucleic acid polymer. Which of the following is true of DNA but not true of RNA? (a) It contains uracil. (b) It contains thymine. (c) It is single-stranded. (d) It has 5′-to-3′ directionality.

(b) It contains thymine

2-44 Which of the following monomer building blocks is necessary to assemble selectively permeable boundaries around and inside cells? (a) sugars (b) fatty acids (c) amino acids (d) nucleotides

(b) fatty acids

2-61 Both DNA and RNA are synthesized by covalently linking a nucleoside triphosphate to the previous nucleotide, constantly adding to a growing chain. In the case of DNA, the new strand becomes part of a stable helix. The two strands are complementary in sequence and antiparallel in directionality. What is the principal force that holds these two strands together? (a) ionic interactions (b) hydrogen bonds (c) covalent bonds (d) van der Waals interactions

(b) hydrogen bonds

2-8 If the isotope 32S has 16 protons and 16 neutrons, how many protons, neutrons, and electrons will the isotope 35S have, respectively? (a) 16, 20, 15 (b) 16, 19, 15 (c) 16, 19, 16 (d) 16, 19, 17

(c) 16, 19, 16

2-14 You have a concentrated stock solution of 10 M NaOH and want to use it to produce a 150 mL solution of 3 M NaOH. What volume of water and stock solutions will you measure out to make this new solution? (a) 135 mL of water, 15 mL of NaOH stock (b) 115 mL of water, 35 mL of NaOH stock (c) 100 mL of water, 50 mL of NaOH stock (d) 105 mL of water, 45 mL of NaOH stock

(d) 105 mL of water, 45 mL of NaOH stock

2-55 Choose the answer that best fits the following statement: Cholesterol is an essential component of biological membranes. Although it is much smaller than the typical phospholipids and glycolipids in the membrane, it is a(n) _________________ molecule, having both hydrophilic and hydrophobic regions. (a) polar (b) oxygen-containing (c) hydrophobic (d) amphipathic

(d) amphipathic

2-1 Select the answer that best completes the following statement: Chemical reactions in living systems occur in an ____________ environment, within a narrow range of temperatures. (a) optimal (b) organic (c) extracellular (d) aqueous

(d) aqueous

2-33 The pH of an aqueous solution is an indication of the concentration of available protons. However, you should not expect to find lone protons in solution; rather, the proton is added to a water molecule to form a(n) ______________ ion. (a) hydroxide (b) ammonium (c) chloride (d) hydronium

(d) hydronium

2-47 Cells require one particular monosaccharide as a starting material to synthesize nucleotide building blocks. Which of the monosaccharides below fills this important role? (a) glucose (b) fructose (c) ribulose (d) ribose

(d) ribose

2-66 Macromolecules in the cell can often interact transiently as a result of noncovalent interactions. These weak interactions also produce stable, highly specific interactions between molecules. Which of the factors below is the most significant in determining whether the interaction will be transient or stable? (a) the size of each molecule (b) the concentration of each molecule (c) the rate of synthesis (d) surface complementarity between molecules

(d) surface complementarity between molecules

2-17 An ionic bond between two atoms is formed as a result of the ______________. (a) sharing of electrons. (b) loss of electrons from both atoms. (c) loss of a proton from one atom. (d) transfer of electrons from one atom to the other.

(d) transfer of electrons from one atom to the other.

2-54 Many types of cells have stores of lipids in their cytoplasm, usually seen as fat droplets. What is the lipid most commonly found in these droplets? (a) cholesterol (b) palmitic acid (c) isoprene (d) triacylglycerol

(d) triacylglycerol

2-9 A. If 0.5 mole of glucose weighs 90 g, what is the molecular mass of glucose? B. What is the concentration, in grams per liter (g/L), of a 0.25 M solution of glucose? C. How many molecules are there in 1 mole of glucose?

A. 180 daltons. A mole of a substance has a mass equivalent to its molecular weight expressed in grams. B. 45 g/L C. 6 × 1023 molecules

2-52 Indicate whether the statements below are true or false. If a statement is false, explain why it is false. A. A disaccharide consists of a sugar covalently linked to another molecule such as an amino acid or a nucleotide. B. The hydroxyl groups on monosaccharides are reaction hot spots and can be replaced by other functional groups to produce derivatives of the original sugar. C. The presence of double bonds in the hydrocarbon tail of a fatty acid does not greatly influence its structure.

A. False. A disaccharide consists of two sugar molecules that undergo a condensation reaction to form a covalent bond (known as a glycosidic linkage). B. True. C. False. The presence of a double bond in the hydrocarbon chain of a fatty acid causes a kink in the chain, decreasing its flexibility and packing with neighboring hydrocarbon chains

2-35 Indicate whether the statements below are true or false. If a statement is false, explain why it is false. A. Any covalently bonded H atom can participate in a hydrogen bond if it comes in close proximity with an oxygen atom that forms part of a water molecule. B. Protons are constantly moving between water molecules, which means there is an overall equilibrium between hydroxyl ions and hydronium ions in aqueous solutions. C. A strong base is defined as a molecule that can readily remove protons from water.

A. False. Hydrogen atoms that are covalently bonded to carbon atoms do not participate in hydrogen bonds because these hydrogens have almost no net positive charge. B. True. C. True

2-65 Indicate whether the statements below are true or false. If a statement is false, explain why it is false. A. "Nonpolar interactions" is simply another way of saying "van der Waals attractions." B. Condensation reactions occur in the synthesis of all the macromolecules found in cells. C. All proteins and RNAs pass through many unstable conformations as they are folded, finally settling on one single, preferred conformation.

A. False. Van der Waals attractions describe the general attractive forces between all atoms. The contact distance between any two nonbonded atoms is the sum of the van der Waals radii. Nonpolar interactions are based on the exclusion of hydrophobic molecules from a hydrophilic environment. B. True. C. True.

2-43 Indicate whether the molecules below are inorganic (I) or organic (O). A. glucose B. ethanol C. sodium chloride D. water E. cholesterol F. adenosine G. calcium H. glycine I. oxygen J. iron K. phospholipid

A. O B. O C. I D. I E. O F. O G. I H. O I. I J. I K. O

2-24 Indicate whether the statements below are true or false. If a statement is false, explain why it is false. A. There are four elements that constitute 99% of all the atoms found in the human body. B. Copper, zinc, and manganese are among 11 nonessential trace elements that contribute less than 0.1% of all the atoms in the human body. C. Approximately 0.9% of the atoms in the human body come from seven essential elements—Na, Mg, K, Ca, P, S, and Cl—all of which form stable ions in aqueous solution.

A. True. B. False. Cu, Zn, and Mn are essential trace elements in the human body. C. False. Na, Mg, K, Ca, and Cl form ions in aqueous solution, but P and S form covalent bonds in order to fill their outer electron shells.

2-15 Indicate whether the statements below are true or false. If a statement is false, explain why it is false. A. Electron shells fill discrete regions around the nucleus of the atom and limit the number of electrons that can occupy a specific orbit. B. H, C, O, and N are the most common elements in biological molecules because they are the most stable. C. Some atoms are more stable when they lose one or two electrons, even though this means they will have a net positive charge.

A. True. B. False. H, C, N, and O are the most common elements in biological molecules because their outer shells are unfilled, making them highly reactive. C. True.

2-19 Indicate whether the statements below are true or false. If a statement is false, explain why it is false. A. Electrons are constantly moving around the nucleus of the atom, but they can move only in discrete regions. B. There is no limit to the number of electrons that can occupy the fourth electron shell. C. Atoms with unfilled outer electron shells are especially stable and are therefore less reactive.

A. True. B. False. The fourth electron shell has the capacity to hold 18 electrons. C. False. Atoms that have their outer electron shells filled are the most stable and least reactive. Atoms with unfilled outer shells are more reactive because they tend to share or transfer electrons to fill and therefore stabilize the outer shell.

2-69 A protein chain folds into its stable and unique three-dimensional structure, or conformation, by making many noncovalent bonds between different parts of the chain. Such noncovalent bonds are also critical for interactions with other proteins and cellular molecules. From the list provided, choose the class(es) of amino acids that are most important for the interactions detailed below. A. forming ionic bonds with negatively charged DNA B. forming hydrogen bonds to aid solubility in water C. binding to another water-soluble protein D. localizing an "integral membrane" protein that spans a lipid bilayer E. tightly packing the hydrophobic interior core of a globular protein acidic nonpolar basic uncharged polar

A. basic B. uncharged polar C. uncharged polar, basic, and acidic D. nonpolar E. nonpolar

2-28 A. In which scientific unit is the strength of a chemical bond usually expressed? B. If 0.5 kilocalories of energy are required to break 6 × 1023 bonds of a particular type, what is the strength of this bond?

A. kilocalories per mole (or kilojoules per mole) B. 0.5 kcal/mole

2-38 A. What is the pH of pure water? B. What concentration of hydronium ions does a solution of pH 8 contain? C. Complete the following reaction: CH3COOH + H2O ↔ __________. D. Will the reaction in (C) occur more readily (be driven to the right) if the pH of the solution is high?

A. pH 7 B. 10-8 M C. CH3COO- + H3O+ D. Yes. If the pH is high, then the concentration of hydronium ions will be low. Therefore the rightward reaction, which produces hydronium ions, will be favored

2-59 A. Write out the sequence of amino acids in the following peptide, using the full names of the amino acids. Pro-Val-Thr-Gly-Lys-Cys-Glu B. Write the same sequence with the single-letter code for amino acids. C. According to the conventional way of writing the sequence of a peptide or a protein, which is the C-terminal amino acid and which is the N-terminal amino acid in the above peptide?

A. proline-valine-threonine-glycine-lysine-cysteine-glutamic acid (or glutamate) B. PVTGKCE C. C-terminal is glutamic acid (or glutamate); N-terminal is proline

2-58 Match each term related to the structure of nucleic acids (A-I) with one of the descriptions provided. A. base B. glycosidic bond C. nucleoside D. nucleotide E. phosphoanhydride bond F. phosphoester bond G. ribose H. phosphodiester bond I. deoxyribose; ____ the linkage between two nucleotides ____ the linkage between the 5′ sugar hydroxyl and a phosphate group ____ the nitrogen-containing aromatic ring ____ five-carbon sugar found in DNA ____ sugar unit linked to a base ____ linkage between the sugar and the base ____ linkages between phosphate groups ____ sugar linked to a base and a phosphate ____ five-carbon sugar found in RNA

H—the linkage between two nucleotides F—the linkage between the 5′ sugar hydroxyl and a phosphate group A—the nitrogen-containing aromatic ring I—five-carbon sugar found in DNA C—sugar unit linked to a base B—linkage between the sugar and the base E—linkages between phosphate groups D—sugar linked to a base and a phosphate G—five-carbon sugar found in RNA

2-64 There are 20100 different possible sequence combinations for a protein chain with 100 amino acids. In addition to the amino acid sequence of the protein, what other factors increase the potential for diversity in these macromolecules? (a) free rotation around single bonds during synthesis (b) noncovalent interactions sampled as protein folds (c) the directionality of amino acids being added (d) the planar nature of the peptide bond

(a) free rotation around single bonds during synthesis

2-49 Which of the following are examples of isomers? (a) glucose and galactose (b) alanine and glycine (c) adenine and guanine (d) glycogen and cellulose

(a) glucose and galactose

2-56 For each of the following sentences, fill in the blanks with the best word or phrase selected from the list below. Not all words or phrases will be used; each word or phrase should be used only once. Proteins are ______________ built from amino acids, which each have an amino group and a _____________ group attached to the central _______________. There are twenty possible _______________ that differ in structure and are generally referred to as "R." In solutions of neutral pH, amino acids are _______________, carrying both a positive and negative charge. When a protein is made, amino acids are linked together through _______________, which are formed by condensation reactions between the carboxyl end of the last amino acid and the ___________________ end of the next amino acid to be added to the growing chain.

polypeptides, carboxyl, a-carbon, side chains, ionized, peptide bonds, amino

2-18 For each of the following sentences, fill in the blanks with the best word or phrase selected from the list below. Not all words or phrases will be used; each word or phrase should be used only once. Whereas ionic bonds form a(n) __________________, covalent bonds between atoms form a(n) __________________. These covalent bonds have a characteristic bond __________________ and become stronger and more rigid when two electrons are shared in a(n) __________________. Equal sharing of electrons yields a(n) __________________ covalent bond. If one atom participating in the bond has a stronger affinity for the electron, this produces a partial negative charge on one atom and a partial positive charge on the other. These __________________ covalent bonds should not be confused with the weaker __________________ bonds that are critical for the three-dimensional structure of biological molecules and for interactions between these molecules.

salt, molecule, length, double bond, nonpolar, polar, non covalent