Test Bank For Human Physiology: An Integrated Approach, 8th Edition

Exam Name___________________________________ MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question. 1) Stanley Miller set out to demonstrate an explanation for the origins of organic molecules using a combination of simple organic molecules, heat and periodic bursts of electricity through the mixture, ultimately producing which kind of molecules? A) nucleic acids B) carbohydrates C) glycoproteins D) lipids E) amino acids Answer: E 2) Glycosylated molecules are formed with A) cholesterol. B) carbohydrates. C) nucleic acids. D) DNA. E) lysosomes. Answer: B 3) Cells regulate their level of activity by regulating the amount of proteins in the cell at any given time, so an up-regulation of enzymes would be expected to A) increase the cell’s response produced by the reaction catalyzed by the enzyme. B) decrease the level of productivity of chemical reactions that rely on the enzyme and decrease the rate of reactions catalyzed by the enzyme. C) have no effect on the rate of reactions catalyzed by the enzyme. D) decrease the rate of reactions catalyzed by the enzyme. E) decrease the level of productivity of chemical reactions that rely on the enzyme. Answer: A 4) When an enzyme reaches its saturation point, the amount of A) product produced continues to increase. B) substrate for the enzyme to act upon is very low and the amount of product produced by the enzyme decreases. C) substrate for the enzyme to act upon is low. D) product produced by the enzyme decreases. E) substrate for the enzyme to act upon is high. Answer: E 5) Which element make up more than 90% of the body’s mass? A) Ca, C, O B) O, C, H C) O, H, Na Answer: B 1 D) O, Ca, H E) C, Na, K 6) Phospholipids are key components of cell membranes and made up of which molecules? A) nucleotides B) glycerol C) fatty acids D) glycerol and fatty acids E) amino acids Answer: D 7) Chromium is A) a protein. B) a dietary supplement with no natural role in the body. C) not an element in the periodic table. D) an essential element involved in glucose metabolism. Answer: D 8) Which is a way to recognize a carbohydrate by looking at its name? A) It begins with lipo-. B) It begins with proteo-. C) It ends in -ose. D) It ends in -ase. E) It begins with nucleo-. Answer: C 9) Which is NOT an essential element for a living organism? A) hydrogen B) nitrogen C) mercury D) carbon E) oxygen Answer: C 10) The largest carbohydrate molecules are called polysaccharides because they are made up of ________ molecules bonded together with one another. A) amino acid B) simple sugar C) nucleotide D) purine E) pyrimidine Answer: B 11) Essential amino acids that are used to build proteins A) exist in twenty six different forms. B) can be used medically for both diagnosis and treatment of diseases. C) are linked together by ionic chemical bonds in proteins. D) can only be made by cells within our bodies. E) must be derived from the foods we eat and digest. Answer: E 12) Which is an example of a cation? A) HCO3 B) Ca2+ C) Cl- D) HPO4 2- E) SO4 2- C) electron. D) cation. E) anion. Answer: B 13) A positively-charged ion is called a(n) A) proton. B) neutron. Answer: D 2 14) The most important polar molecule is ________ because it is a universal solvent in biological solutions. A) magnesium sulfate B) water C) nucleic acid D) bicarbonate E) sodium chloride Answer: B 15) A substance is highly soluble if it is A) not very likely to dissolve in water. B) called aqueous. C) not very likely to dissolve in water and is called aqueous. D) very likely to dissolve in water. E) very likely to dissolve in water and is called aqueous. Answer: D 16) A free radical is a A) charged particle. B) molecule with an extra neutron. C) molecule with an extra proton. D) molecule with an extra electron. E) molecule with an unpaired electron. Answer: E 17) The chemical bonding behavior of an atom is directly determined by the A) mass of the atom. B) number of protons. C) size of the atom. D) number of neutrons. E) number and arrangement of electrons. Answer: E 18) Atoms in a covalent molecule share electrons A) in double pairs. B) in single pairs. C) in triple pairs. D) singly, never in pairs. E) can share electrons in single pairs, double pairs, or triple pairs. Answer: E 19) The weak interactions between atoms that keep atoms near each other are called A) ionic bonds. B) hydrogen bonds. C) hydrogen bonds and van der Waals forces. D) van der Waals forces and ionic bonds. E) van der Waals forces. Answer: C 3 20) Which statement about carbohydrates is FALSE? A) Polysaccharides include cellulose and glycogen. B) Simple sugars include galactose, glucose, and ribose. C) Glycogen is important both for energy storage and to provide structure for cells. D) Polysaccharides are important both for energy storage and to provide structure to cells. E) Glycogen is a storage polysaccharide made by animal cells. Answer: C 21) In lipids, unsaturated refers to A) the ring structure of steroids. B) the absence of double bonds between adjacent carbon atoms in a fatty acid. C) fats, such as butter and lard, which come from animal sources. D) glycerol, which acts as an anchor for joined fatty acids. E) the presence of double bonds between adjacent carbon atoms in a fatty acid. Answer: E 22) Each amino acid differs from others in the A) number of peptide bonds in the molecule. B) number of central carbon atoms. C) chemical structure of the R group. D) number of carboxyl groups. E) size of the amino group. Answer: C 23) The alpha-helix and B-sheets are examples of the ________ structure of a protein. A) primary B) secondary C) tertiary D) quaternary E) pentanary Answer: B 24) Interactions between different globular or fibrous polypeptide chains result in which type of structure? A) primary B) secondary C) tertiary D) quaternary E) pentagonal Answer: D 25) The concentration of a solution expresses the amount of A) solvent per volume of solution. B) solvent per volume of solute. C) solute per volume of solvent. D) solute per volume of solution. E) None of the answers are correct. Answer: D 26) Nucleic acids are polymers of units called A) bases. B) nucleotides. C) amino acids. Answer: B 27) A nucleotide is made up of a A) five-carbon sugar and a nitrogenous base. B) five-carbon sugar and an amino acid. C) five-carbon sugar and phosphate group. D) phosphate group and a nitrogenous base. E) five-carbon sugar, a nitrogenous base, and a phosphate group. Answer: E 4 D) ribose. E) fatty acids. 28) A nucleotide containing the base cytosine would base pairs with a nucleotide containing the base A) guanine. B) uracil. C) adenine. D) thymine. E) cytosine. Answer: A 29) An energy-transferring compound in cells is a nucleotide known as A) deoxyribonucleic acid. B) glucose. C) protein. D) adenosine triphosphate. E) fructose. Answer: D 30) Which bases are purines? 1. adenine 2. cytosine 3. guanine 4. thymine 5. uracil A) 1 and 2 B) 2 and 3 C) 2, 4, and 5 D) 1 and 3 E) 1, 3, and 5 Answer: D 31) Biomolecule polymers are a typical formation of ________ molecules. A) inorganic B) organic C) either organic or inorganic Answer: B 32) Cholesterol is a A) precursor to steroid hormones. B) component of animal cell membranes. C) dangerous fat that is absent from a healthy body. D) A and B E) A, B, and C Answer: D 33) An important buffer in the human body is A) HCO3 -. B) H+ . C) HCl. D) NaCl. E) H2 O. C) a salt. D) a buffer. E) neutral. Answer: A 34) Which of the following is most alkaline? A) stomach secretions, pH = 1 B) white wine, pH = 3 C) lemon juice, pH = 2 D) urine, pH = 6 E) tomato juice, pH = 4 Answer: D 35) If a solution has a pH that is less than 7, it is A) acidic. B) alkaline. Answer: A 5 36) Protein specificity is the A) ability of a protein to bind a certain ligand or a group of related ligands. B) degree to which a protein is attracted to a ligand. C) activation of a specific protein that is needed to perform a particular function. D) degree to which a protein-ligand complex initiates a response. E) B and C Answer: A 37) Which is a common feature of soluble proteins? A) chemical modulation B) noncovalent interaction C) structural support D) receptor binding E) All of the answers are correct. Answer: B 38) An ion has gained or lost A) proton(s). B) neutron(s). C) electron(s). D) carbon atom(s). E) double bond(s). Answer: C 39) An isotope has gained or lose A) proton(s). B) neutron(s). C) electron(s). D) carbon atom(s). E) double bond(s). Answer: B 40) The number of ________ determines the element. A) protons B) neutrons C) electrons D) carbon atoms E) double bonds Answer: A 41) This subatomic particle has a positive charge. A) sodium chloride B) electron C) neutron D) proton E) molecular oxygen Answer: D 42) This subatomic particle has a negative charge. A) proton B) magnesium C) neutron Answer: D 6 D) electron E) hydrogen 43) This subatomic particle has a neutral charge. A) proton B) magnesium C) neutron D) electron E) hydrogen Answer: C 44) A change in pH value of one unit indicates a A) 10 fold change in [H+ ]. B) 1-fold change in [H+ ]. C) change of 10-1 in pH. D) change of 10-2 in pH. E) Cannot be determined. Answer: A 45) A blood pH of less than 7.00 and greater than 7.70 is incompatible with life. A) True B) False Answer: A 46) Which statement describes the relationship between pH and hydrogen ions? A) pH and hydrogen ions are independent and unrelated. B) pH and hydrogen ions are directly related. C) pH and hydrogen ions are inversely related. D) pH is always 100 times more than the number of hydrogen ions. E) pH and hydrogen ions are equivalent. Answer: C 47) HCl (hydrochloric acid) is an acid because A) in solution it decreases the concentration of free H+ . B) in solution it donates its H+ . C) it is similar to ammonia. D) in solution it increases the pH. E) it is able to form hydroxide ions. Answer: B 48) Molecular structure and function of large complex biomolecules result from which interactions? A) ionic bonds B) hydrogen bonds C) covalent bond angles D) van der Waals forces E) All of the choices can contribute. Answer: E 49) Which formula describes the relationship between pH and hydrogen ions? A) pH = -log [H+ ] B) [H+ ] = log pH C) [H+ ] = -log pH D) pH= [H+ ] + [OH- ] E) pH = log [H+ ] Answer: A 7 50) All organic molecules contain A) adenosine. B) lipids. C) calcium. D) oxygen. E) carbon. Answer: E 51) Molecules that contain carbon are known as A) protons. B) atoms. C) nonessential elements. D) minerals. E) organic molecules. Answer: E 52) Which elements make up 90% of the body’s mass? A) carbon dioxide, oxygen, and sodium B) sodium, potassium, and calcium C) oxygen, carbon, and nucleic acids D) hydrogen, nitrogen, and oxygen E) oxygen, carbon, and hydrogen Answer: E 53) Which results when an atom has such a strong attraction for electrons that it pulls one or more electrons completely away from another atom? A) hydrogen bond B) ionic bond C) Van der Waals attraction D) weak bond E) covalent bond Answer: B 54) These are weak attractive forces that are responsible for the surface tension of water. A) Van der Waals attractions B) ionic bonds C) hydrogen bonds D) potassium bonds E) covalent bonds Answer: C 55) These result when the carbon atoms in phospholipids share a pair of electrons. A) hydrogen bonds B) covalent bonds C) Van der Waals attractions D) ionic bonds E) potassium bonds Answer: B 56) Van der Waals forces are weak attractive forces between the nucleus of one atom and the electrons of another atom close by. A) True B) False Answer: A 8 57) Glycogen is an example of a A) carbohydrate. B) nucleotide. C) lipid and protein. D) protein. E) lipid. Answer: A 58) Nucleotides perform which function(s)? A) They transfer energy and are part of genetic material. B) They store glucose as fat. C) They are the building blocks of proteins like cell receptors. D) They are the starting material for steroid hormones. E) They form structural elements in the cell membrane. Answer: A 59) Which biological molecules exhibit saturation, specificity and competition? A) lipids B) lipids and proteins C) proteins D) nucleotides E) carbohydrates Answer: C 60) Triglycerides and steroids are examples of A) nucleotides. B) lipids. C) proteins. D) lipids and proteins. E) carbohydrates. Answer: B 61) Potassium channels are usually made up of several subunits. This is an example of which level of protein structure? A) primary B) secondary C) tertiary D) quaternary E) alpha helix Answer: D 62) The sequence of amino acids in the chain is an example of which level of protein structure? A) primary B) secondary C) tertiary D) quaternary E) alpha helix Answer: A 63) Hemoglobin molecules are made from four globular protein subunits. The three-dimensional shape of these globular subunits is an example of which level of protein structure? A) primary B) secondary C) tertiary D) quaternary E) alpha helix Answer: C 64) -strands are an example of a flat arrow arrangement of amino acids. A) True B) False Answer: A 9 65) Which level of protein structure occurs from spontaneous folding that results from covalent bonds and noncovalent interactions? A) quaternary B) tertiary C) secondary D) triangular E) primary Answer: B 66) The protein keratin which is found in hair and nails is categorized as which protein shape? A) acidic B) triangular C) hexavalent D) fibrous E) globular Answer: D 67) Which types of bonds between amino acids plays an important role in the shape of globular proteins? A) sodium bonds B) metallic bonds C) secondary bonds D) collagen bonds E) disulfide bonds Answer: E 68) Which would be disrupted by changes in free hydrogen ions in solution, thus disrupting the molecule’s shape and function? A) hydrogen bonds B) double bonds C) covalent bonds D) disulfide bonds E) sodium bonds Answer: A 69) During intense exercise our muscles produce lactate and hydrogen ions. Which molecules would be affected by the accumulation of hydrogen ions? A) the proteins actin and myosin B) DNA in the nucleus C) glucose molecules in the adipose tissue D) phospholipids in the membrane E) cholesterol in the plasma membrane Answer: A 70) Which best describes an irreversible antagonist? A) reversible agonist B) allosteric enhancer C) involved in activation via phosphorylation D) binds to proteins away from the active site E) cannot be displaced by competition Answer: E 71) Protein kinase A is a molecule inside our cells that can activate enzymes within the cell. Protein kinase A does this by adding phosphates to the enzymes. This is which type of modulation? A) allosteric modulator B) reversible antagonist C) covalent modulator D) competitive inhibitor E) irreversible agonist Answer: C 10 72) A reaction is stopped by substance X but can recover when more of the customary ligand is supplied. Substance X is an example of a A) allosteric modulator. B) covalent modulator. C) irreversible antagonist. D) competitive inhibitor. E) phosphatase. Answer: D 73) Which is an allosteric modulator? A) A substance involved in activation via phosphorylation. B) A substance that binds to proteins away from the active site. C) A substance that binds irreversibly. D) A substance that has no effect on the affinity of the ligand. E) A substance that can be displaced by competition at the active site. Answer: B 74) The smallest organizational level is a(n) A) molecule. B) atom. C) tissue. D) element. E) nucleus. D) molecule. E) element. Answer: B 75) When two or more atoms are chemically linked, they form a(n) A) tissue. B) nucleus. C) atom. Answer: D 76) Oxygen, carbon, and hydrogen, along with eight other elements are considered A) minor essential elements. B) major essential elements. C) atoms. D) compounds. E) molecules. Answer: B 77) The center of an atom is called the A) molecule. B) electron. C) proton. D) nucleus. E) element. Answer: D 78) Electrons travel around the center of the atom at high speed forming a(n) A) shell. B) element. C) nucleus. D) atom. Answer: A 79) An element’s ability to bind other elements is determined by A) its state of glycosylation. B) the number of enzymes required. C) the arrangement of electrons in the outer shell of an atom. D) the amount of folding in its subunits. E) its amino acid composition. Answer: C 11 E) molecule. 80) Ions with a positive charge are called A) electrons. B) anions. C) tissues. D) cations. E) neurons. C) cations. D) electrons. E) anions. 82) A ________ is a made up of solutes dissolved in a solvent. A) cocktail B) compound C) molecule D) solution E) nucleus D) glucose. E) lactose. Answer: D 81) Ions with a negative charge are called A) tissues. B) neurons. Answer: E Answer: D 83) Substances that easily dissolve in water are A) nonpolar. B) lipids. C) isotonic. D) hydrophobic. E) hydrophilic. Answer: E 84) Substances that do not dissolve well in water are A) salts. B) hydrophobic. C) hydrophilic. D) polar. E) isotonic. Answer: B 85) A(n) ________ is any molecule or ion that binds to a receptor protein. A) vitamin B) ligand C) cofactor D) enzyme E) phospholipid Answer: B 86) Two methods of protein activation include ________ and ________. A) homeostatic, osmotic B) enzymatic, glycolytic C) exergonic, endogonic D) proteolytic, cofactor binding E) mechanistic, covalent bonding Answer: D 87) DNA contains the five-carbon sugar A) ribose. B) uracil. C) deoxyribose. Answer: C 12 88) RNA contains the five-carbon sugar A) uracil. B) ribose. C) glucose. D) lactose. E) deoxyribose. Answer: B 89) The purines found in DNA are ________ and ________. A) deoxyribose, guanine B) cytosine, uracil C) cytosine, thymine D) guanine, cytosine E) adenine, guanine Answer: E 90) The pyrimidines found in DNA are ________ and ________. A) deoxyribose, guanine B) cytosine, uracil C) cytosine, thymine D) adenine, guanine E) guanine, cytosine Answer: C 91) In a chemical reaction, ________ between atoms are broken as atoms are rearranged in new combinations to form different chemical substances. A) electron shells B) homeostatic interactions C) nuclei D) chemical bonds E) protons Answer: D 92) The reaction rate of many chemical reactions that occur in the body are controlled by molecules called A) enzymes. B) neurotransmitters. C) purines. D) nucleic acids. E) intermediates. Answer: A ESSAY. Write your answer in the space provided or on a separate sheet of paper. 93) How many milliequivalents are represented by a mole of bicarbonate ions (HCO3 – )? Answer: 1000 milliequivalents. This is calculated by taking the equivalent value of the molecule, which equals the molarity of the molecule (1 in this case) times the number of charges the molecule carries (in this case, the minus symbol indicates a charge of negative one, i.e., -1), so 1 × 1 = 1 equivalent. 1 equivalent = 1000 milliequivalents. 94) List and define the seven categories of soluble proteins. Answer: The seven categories: enzymes, membrane transporters, signal molecules, receptors, binding proteins, regulatory proteins, and immunoglobulins. See the “Protein Interactions” section of the chapter. 13 MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question. 95) Which elements combine to form nonpolar covalent bonds? A) nitrogen and hydrogen B) sodium and chlorine C) carbon and hydrogen D) hydrogen and oxygen E) carbon and chlorine Answer: C 96) The symbol Ca2+ means calcium has A) gained two protons. C) lost two electrons. B) lost two protons. D) gained two electrons. Answer: C 97) In a 5% NaCl solution, A) the solute is water. B) there are 5 grams of sodium chloride for every 100 mL of total solution. C) there are 5 grams of sodium chloride for every 100 mL of water. D) A and B E) A and C Answer: B SHORT ANSWER. Write the word or phrase that best completes each statement or answers the question. 98) A molecule of sucrose has a molecular weight of 342 Daltons. How many grams of sucrose would be required to make one liter of a 2.5 Molar solution of sucrose? Answer: 805 grams (per liter). This is calculated by multiplying the amount of sucrose in one liter of a 1 molar solution (342 grams) times the molar concentration (2.5). 342 × 2.5 = 805 grams MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question. 99) A covalent double bond is formed when atoms A) swap two pairs of electrons. B) transfer a pair of electrons from one atom to the other. C) transfer two pairs of electrons from one atom to the other. D) share one pair of electrons (a total of two). E) share two pairs of electrons (a total of four). Answer: E 100) The term polar is used to describe molecules because A) there are at least two distinct ends of the molecule regarding electron position and the resulting charge. B) such molecules are always linear in shape. C) polar covalent molecules were first discovered in polar bears. D) polar covalent molecules are found in colder climates. E) there are at least two distinct ends of the molecule regarding hydrogen placement. Answer: A 14 ESSAY. Write your answer in the space provided or on a separate sheet of paper. 101) The more likely a fat is to be solid at room temperature, the more it potentially can contribute to cardiovascular disease. With this in mind, which fats will be the most dangerous? Answer: The more saturated or the higher the number of hydrogens a fat contains, the more likely it will be solid at room temperature. Therefore, saturated animal fats are the most associated with cardiovascular disease. MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question. 102) Lipids are hydrophobic, and do not usually dissolve in water. Because blood is water-based, the lipid cholesterol is combined with ________ so it can be transported by blood. A) hydrophobic molecules B) cations C) nothing; cholesterol is not transported in blood D) anions E) hydrophilic molecules Answer: E 103) Only free H+ contributes to the hydrogen ion concentration. A) True B) False Answer: A 104) In the equation CO2 + H2 O H2 CO3 A) HCO3 B) H2 O H+ + HCO3 – , which of these is an acid? C) H2 CO3 D) H+ E) CO2 Answer: C 105) Chemical reactions that occur in the human body proceed at a faster rate due to special catalytic molecules called A) proteins. B) enzymes. C) cytozymes. D) antibodies. E) antagonists. Answer: B 106) The fuel molecule cells use to run all their activities is A) protein. B) starch. C) vitamins. D) glucose. Answer: D 107) A fatty acid that contains three double bonds in its carbon chain is said to be A) polyunsaturated. B) saturated. C) carboxylated. D) monounsaturated. E) hydrogenated. Answer: A 108) Most of the lipid found in the human body is in the form of A) monoglycerides. B) phospholipids. C) triglycerides. D) steroids. E) prostaglandins. Answer: C 15 E) sucrose. 109) Each of the following is a function of proteins EXCEPT A) transport. B) storage of genetic information. C) binding to ligands. D) signaling. E) catalyst. Answer: B 110) If a polypeptide contains 10 peptide bonds, how many amino acids does it contain? A) 0 B) 11 C) 5 D) 10 E) 12 Answer: B 111) Glycoprotein molecules A) allow atoms to pack closely together and occupy minimum space. B) aid in the formation of chemical bonds between carbon atoms. C) create a coat on the cell surface that assists in cell aggregation and adhesion. D) act as buffers in body fluids. E) increase the solubility of lipids. Answer: C ESSAY. Write your answer in the space provided or on a separate sheet of paper. 112) Compare and contrast the role of up-regulation and down-regulation of proteins. Answer: These terms refer to the net change in the amount of a functional protein present in a cell in response to a signal. Up-regulation is an increase in the amount of the protein, whereas down-regulation is a decrease. 113) What is the induced-fit model? List the types of bonds involved and classify them as strong or weak. Answer: The interaction between a protein binding site and a ligand that are in close proximity results in a conformational change of the protein to fit more closely to the ligand. The bonds involved are hydrogen (weak), ionic (strong), and van der Waals (weak). SHORT ANSWER. Write the word or phrase that best completes each statement or answers the question. 114) The ________ of a solution is the negative logarithm of the hydrogen ion concentration, expressed in moles per liter of solution. Answer: pH 115) When a nitrogenous base is bonded to a pentose sugar and a phosphate, a ________ is formed. Answer: nucleotide 116) Solutions are formed with water and ________ solutes which dissolve in them. Answer: hydrophilic 117) The ________ molecules which form the bilayer region of the cell membrane have hydrophilic regions on the outer surface and hydrophobic regions on the inner surface. Answer: phospholipid 16 ESSAY. Write your answer in the space provided or on a separate sheet of paper. 118) Compare and contrast the chemical bonds between adjacent monomers in DNA, and between two strands of DNA. Answer: The bonds holding monomers together are covalent bonds, between sugar and phosphate molecules. The bonds holding neighboring strands together at the complementary bases are hydrogen bonds. 119) Compare and contrast the general chemical structures of monosaccharides and amino acids. Answer: Monosaccharides consist of carbon, hydrogen, and oxygen, in the ratio C:H:O of 1:2:1. Amino acids consist of a central carbon (CH), a carboxylic acid (COOH), an amine (NH2 ), and an organic side chain of variable structure (mainly a hydrocarbon chain, designated as R). 120) What are functional groups? List the common functional groups in biological molecules. Answer: Several combinations of atoms that occur repeatedly in biological molecules. See Table 2.1 in the main text. 121) True or False? Lipids are hydrophobic because they easily dissolve in water. If true what allows them to dissolve in water or if false, what is it about their molecular structure that makes them less likely to dissolve in water? Answer: False. Lipids are considered hydrophobic because they have an even distribution of electrons and no positive or negative poles. Thus, nonpolar molecules have no regions of partial charge, and therefore tend to repel water molecules. 122) Explain the polar character of an ammonia molecule (NH3 ). What is the cause of the partial charges? What is the overall charge for NH3 ? Answer: When chemically bonded with each other, the nitrogen atom is partially negative whereas the hydrogen atoms are partially positive. The nitrogen atom in a molecule of ammonia has a stronger attraction for the electrons participating in the covalent bonds than the hydrogen atoms. The net charge on the molecule is still zero, however. 123) Water striders are insects that literally walk on water. These insects are frequently found living on ponds. If hydrogen bonds did not exist, how would this affect the life of water striders? Answer: Hydrogen bonds are responsible for the surface tension of water, the attractive force between water molecules that can make it difficult to separate them. The surface tension is strong enough to support the weight of water striders, thus allowing them to walk on water. If water molecules could not form hydrogen bonds, the water striders would not be able to walk on water because there would be no surface tension to support their weight. Therefore, these insects would have to adapt to terrestrial conditions near ponds or lakes rather than living on them. 124) If the dissociation constant of a protein is less than one (Kd < 1), what can you conclude about the affinity of the protein for the ligand? Answer: Since Kd < 1, you know that [P][L] < [PL]. Therefore, at equilibrium, there is a higher concentration of protein-ligand complex suggesting that the protein has a relatively high binding affinity for the ligand. 125) Noncovalent molecular interactions occur between many different biomolecules and often involve proteins. Give an example of such an interaction and what the function might be. Answer: Examples of such interactions would be the interactions between carbohydrates, proteins, and lipids. These interactions form molecules like glycolipids and glycoproteins. These molecules are usually used as signaling molecules on the surfaces of cells. 17 126) Tenzin is assigned a project regarding ions, isotopes, and free radicals. Her teacher tells her that she has to describe what is similar between them, and how they are different. Tenzin is having some trouble, and calls you in for help. Assuming she has learned and understood some basic chemistry, help her organize her thoughts by making a table or flow chart. Answer: All of these terms are similar in that they describe a structure that has either gained or lost something but different in their overall function. An ion is an atom that has gained or lost one or more electrons and thus bears an electrical charge. Ions form when salts dissolve in water and are required for normal cell function. An ion's charge affects both its behavior in solution and its chemical reactivity. An isotope is an atom that has gained or lost one or more neutrons; as neutrons lack a charge, isotopes remain neutral. Some isotopes emit radiation, a type of energy, rendering them both useful and dangerous; compared to ions, they are rare in nature. A free radical is an atom or molecule that has at least one unpaired electron (an electron is more stable if paired with another electron). Free radicals can be either electrically charged (e.g., superoxide) or neutral (e.g., hydroxy), depending upon the total number of protons and electrons present. Because free radicals are unstable, they are highly reactive and disruptive to cell function; compared to ions, they are rare in the body. Neither isotopes nor free radicals are known to be required for normal cell function. 127) Ahmed is trying to memorize chemical structures of every compound his professor has indicated are important to the human body. Explain to him that an easier way is to memorize a few rules of chemical bonding and then figure out the structure of the important compounds, especially the simpler compounds. Answer: Elements combine to form molecules in predictable ways because of how the outer shell electrons combine between atoms. In most cases, the outer shell will be most stable with a total of eight electrons. This information is easily discernible from the periodic table. Therefore an atom with seven outer shell electrons, such as K, combines very readily with an atom with one outer shell electron, such as Cl; an atom with six outer shell electrons, such as Ca will combine with an atom with two outer shell electrons or with two atoms with one outer shell electron each, and so on. Examples: KCl, CaCl2 , CH4 . 128) Define polar covalent, nonpolar covalent, ionic, and hydrogen bonding. Which of these bonds involves more than one molecule? Which of these bonds is/are important in determining the properties of water? Explain. Answer: Polar covalent bonds occur within a single molecule that shares electrons unequally; i.e., the constantly orbiting electrons spend more time at some locations and less at others. Nonpolar covalent bonds occur within a single molecule that shares electrons equally; i.e., the probability of an electron occupying a particular location is the same at all locations. Ionic bonds occur within a single molecule in which one atom completely loses an electron to another, causing each to develop an opposite charge; it is this electrical attraction that holds the molecule together. Hydrogen bonding occurs between separate molecules that contain polar covalent bonds; where electrons spend more time the molecule is partially negative, and where electrons spend less time the molecule is partially positive. The ends of different molecules are thus electrically attracted to each other. Water is a polar covalent molecule, with the oxygen end being partially negative and attracted to the partially positive hydrogen portions of other water molecules. Hydrogen-bonding between water molecules is responsible for surface tension and the crystalline structure of ice. 129) Ionic bonds are considered to be strong chemical bonds. Yet, ions dissociate in water. Explain how both can be true. Answer: Molecules such as sodium chloride are bonded by ionic bonds. So much energy would be required to separate a molecule of NaCl into Na+ and Cl- that it is practically impossible. That is, if the sodium chloride is DRY. Because water molecules have partial charges resulting from their polar covalent bonds, sodium chloride dissociates in water. This means that the ions separate and function relatively independently. An attraction between sodium and chloride still exists, however, and the dissociation can be described as an increase in bond length rather than a loss of the bond. Evaporate the water, though, and the sodium chloride crystals reform. 18 130) Your swimming buddy, Mario, jumped into a pool parallel to the water surface. When he stood up, he yelled "ouch," and you noticed that the skin on his chest and belly looked red and irritated. How would you describe the properties of water to explain to Mario why this happened? Why doesn't it hurt when pool water is penetrated perpendicular to the surface, as with a hands-first or feet-first dive? Answer: Because Mario was parallel to the water surface, the force of his mass was spread out over a relatively large area of the water, making the force per unit water lower than in a typical dive. The surface tension of water, while not strong enough to keep Mario from penetrating the water surface, was strong enough to momentarily resist him. The force of the water pushing back on Mario, however briefly, was enough to cause pain. In a typical dive position, the force of Mario's entire mass is spread only over a tiny area of the water, and thus the force per unit water surface is greater. This higher force is sufficient to immediately break the hydrogen bonds and overcome the surface tension. 131) You are helping your dad prepare food in the kitchen. Dad has a tablespoon of water in one hand and a tablespoon of vegetable oil in the other, when he trips over the rug and spills both spoons on the countertop. Dad notices that the oil forms a thin film on the countertop, whereas spilled water forms smaller, taller beads. How should you explain the different behavior of these liquids to your dad? Answer: Water forms beads when it strikes a nonabsorptive surface because of surface tension resulting from the hydrogen bonds between neighboring water molecules. Vegetable oil molecules are nonpolar covalent, therefore, there is no hydrogen bonding between the lipid molecules and no bead formation. 132) Mahamoud is confused on the similarities and differences between proteins and nucleic acids. Assuming he has learned and understood the basic chemistry, what is the likely source of his confusion? To help him sort this out, make a table or flow chart to explain the structure of these molecules and their relationship to each other. Answer: His confusion probably stems from the fact that both proteins and nucleic acids are classified as macromolecules, and both are assembled by covalently bonding certain monomers in a particular order. Also, nucleic acids contain the information necessary for manufacturing proteins, the term acid is used in describing the structure of both nucleic acids and proteins, and both nucleic acids and proteins must contain nitrogen. The monomer of protein is the amino acid, which has a central carbon, a variable chain denoted as R, and a nitrogen-containing amino group. There are 20 naturally occurring amino acids. The monomer of the nucleic acid is the nucleotide, which has a sugar attached to a nitrogen-containing base, and a phosphate. There are five different bases and two different sugars. The sequence of bases in a DNA or RNA molecule determines the sequence of amino acids in the protein. 133) Proteins are described as having different levels of structure. List and distinguish between the level(s) that produce a linear shape vs. a globular shape, and explain why one of those levels can result in either a linear or globular shape. Answer: Linear shapes: primary, secondary, quaternary. Primary structure is simply the sequence of covalently bonded amino acids in a peptide chain. Secondary structure is further bonding between nearby amino acids in a peptide chain, with the molecule still retaining a strand-like shape. Quaternary structure can involve separate linear polypeptide chains held together in a strand. Globular shapes: tertiary and quaternary. Tertiary structure involves bonding between distant amino acids, which causes the molecule to be wadded. Quaternary structure occurs when more than one globular peptide chain bonds together. 134) While every level of a protein's structure is important to the function of that protein, which level of structure is most important to the function of enzymes, and why? Answer: Enzymes and other globular proteins depend upon the three-dimensional shape resulting from the globular folding. Under conditions in which this shape is altered by denaturing agents such as heat, the protein ceases to function, though the primary and secondary structure may be unchanged. 19 135) You are a student intern in the research and development department of a pharmaceutical company. You have discovered a compound that destroys the common cold virus in cultured human cells. Chemical characterization reveals that carbon, hydrogen, and oxygen are present, in a 20:40:4 ratio of C:H:O. Experiments in rats show that neither oral nor injectable treatment with the compound was effective in destroying the virus. Discuss some possible reasons for this lack of effectiveness. Answer: The relatively low amount of oxygen and high carbon and hydrogen indicate that this compound is probably a lipid. Oral administration may result in digestion of the compound so that none is absorbed into the blood. Lipids are not highly soluble in water, and because blood is a watery medium, the injected lipid may not transport well in the blood. Also, human cells as well as the viruses may behave differently in culture compared to in a real patient. 136) Describe what happens to NaCl when placed in water. Answer: Water molecules break the ionic bonds holding Na+ and Cl- together. Each sodium ion becomes surrounded by polar water molecules, with the electronegative ends of water molecules interacting with the ion. Each chloride ion also becomes surrounded by polar water molecules, but in this case it is the electropositive ends of the water molecules that bind to the ion. A consequence is that sodium and chloride ions can function relatively independently of each other when in solution. MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question. 137) How many grams of glucose, molecular mass = 180 Daltons, is necessary to make 1 liter of a 1.0 molar solution? A) 360 B) 180 C) 1.0 D) 6.02 × 1023 E) 90 Answer: B 138) A 5 M solution of 100 mL of glucose contains how many grams of glucose, molecular mass = 180 Daltons? A) 6.02 × 1023 B) 1.0 C) 180 D) 90 E) 360 Answer: D 139) If 100 mL of water contains 5 grams of NaCl, molecular mass = 58.5 Daltons, what is the molarity of the solution in moles/L? A) 0.05 B) 0.085 C) 2.92 D) 0.85 E) 0.25 Answer: D 140) How many grams of NaCl, molecular mass = 58.5 Daltons, are the molar equivalent to 90 g of glucose (molecular mass = 180 daltons)? A) 29.25 B) 0.25 C) 117 D) 14.6 E) 0.5 Answer: A 141) How many grams of NaCl, molecular mass = 58.5 Daltons, are necessary to make 1 liter of 5% saline? A) 58.5 B) 2.9 C) 1 D) 6.02 × 1023 E) 50 Answer: E 142) A typical blood concentration of glucose is 100 mg/dL. The molecular weight of glucose is approximately 180 Daltons. What is the molarity of this solution in millimoles? A) 5.6 B) 0.56 C) 100 D) 18 E) 10 Answer: A 20 143) If in an acid-base reaction H2 SO4 2- donates two H+ , one mole of H2 SO4 2- would equal how many equivalents? A) 1 B) 4 C) 2 D) 0.75 E) 0.5 Answer: C ESSAY. Write your answer in the space provided or on a separate sheet of paper. 144) What is the difference between atomic mass and molecular mass. Answer: The atomic mass is the actual mass of an atom, expressed in atomic mass units (amu) or Daltons (Da), where 1 amu = 1.6 × 10-27 kg. However, molecular mass is the sum of the atomic mass of each element × the number of atoms of each atom that make up the molecule. 145) A. Distinguish between the mass of a molecule and the mass of a mole, using NaCl in your example. B. Calculate the mass of a mole of NaCl in g, using the mass of one Da (amu). C. Calculate the mass of a dozen NaCl molecules, a dozen donuts, and a mole of donuts, assuming a 30 gram donut. Answer: A. The mass of a molecule is determined by the mass of its component atoms. From the periodic table, the mass of Na is 23 amu and of Cl is nearly 36 amu, so the mass of one molecule of NaCl is 59 Da. A mole is like a dozen, i.e., it is a particular number of items, specifically 6.02 × 1023. B. A mole of NaCl = 59 Da × 6.02 × 1023 = 3.55 × 1025 Da. 1 Da = 1.66 × 10-27 kg, so 3.55 × 1025 Da × 1.66 × 10-27 kg/Da × 1000 g/kg = 59 g. C. A dozen NaCl molecules: 12 × 59 Da × 1.66 × 10-27 kg/Da × 1000 g/kg = 1.2 × 10-21 g. A dozen donuts: 12 × 30 g = 360 g. A mole of donuts: 6.02 × 1023 × 30 g = 1.8 × 1025 g. 146) Write the chemical formula for the molecule drawn below. Which class of organic molecule does it belong to? Is it most likely polar or nonpolar? Answer: C11H12N2 O2 . The presence of the carboxylic acid (COOH) and amine (NH2 ) indicates this is an amino acid. Because of the R group structure, it is relatively nonpolar (this amino acid is tryptophan). 147) What is the pH of a 0.005 M HCl solution? Assume complete dissociation. Answer: pH = 2.3. If pH = – log [H+ ] and HCl is a strong acid, we can assume complete dissociation will occur in solution. 21