The Chemistry of Microbiology

Microbiology with Diseases The Chemistry of Microbiology 2.1 Multiple-Choice Questions 1) Which of the following is a particle that is found in the nucleus of an atom and has no electrical charge? A) electron B) neutron C) element D) proton E) isotope Answer: B 2) An atom of carbon that has six protons and seven neutrons is an example of a(n) A) isotope. B) radioactive isotope. C) molecule. D) compound. E) dalton. Answer: A 3) An atom is electrically neutral when A) the number of electrons equals the number of neutrons. B) the numbers of its protons, electrons, and neutrons are all equal. C) it has no extra electrons in its valence shell. D) the number of protons equals the number of neutrons. E) the number of electrons equals the number of protons. Answer: E 4) Which parts of the atoms interact in a chemical reaction? A) protons B) neutrons C) ions D) electrons E) isotopes Answer: D 5) All of the following are associated with atomic structure EXCEPT A) valence. B) dalton. C) monomer. D) electron shell. E) neutron. Answer: C 6) The valence of an atom represents its A) ability to interact with other atoms. B) electronegativity. C) radioactivity. D) ability to attract electrons. E) ability to interact with water. Answer: A 7) The type(s) of bond produced when atoms share electrons equally is/are A) a nonpolar covalent bond. B) a hydrogen bond. C) an ionic bond. D) a polar covalent bond. E) polar covalent and ionic bonds. Answer: A 8) The type(s) of bond produced when atoms with significantly different electronegativities share electrons is/are A) a nonpolar covalent bond. B) a polar covalent bond. C) an ionic bond. D) a hydrogen bond. E) nonpolar covalent and ionic bonds. Answer: B 9) Which of the following types of chemical bonds do carbon atoms generally NOT form? A) nonpolar covalent bonds B) polar covalent bonds C) ionic bonds D) hydrogen bonds E) both ionic and hydrogen bonds Answer: E 10) All of the following are associated with ionic bonds EXCEPT A) cations. B) radioactivity. C) electrolytes. D) salts. E) anions. Answer: B 11) Which of the following is an incorrect pairing? A) electrolytes: anions B) synthesis: endothermic C) hydrolysis: hydrogen bonds D) catabolism: exothermic E) dehydration: anabolism Answer: C 12) Compounds that readily dissociate in water are A) nonpolar. B) ionic. C) polar. D) either polar or ionic. E) never polar or ionic. Answer: D 13) Which of the following is a property of water? A) it has a high capacity for heat. B) it is not a common reactant in metabolic reactions. C) It is not a good solvent. D) it is liquid in a very narrow temperature range. E) it is a non-polar molecule. Answer: A 14) An acid dissociates in water to release A) hydrogen ion(s). B) cation(s). C) hydroxyl group(s). D) anion(s). E) both anions and hydrogen ions. Answer: E 15) The reverse of a dehydration synthesis reaction is a(n) __________ reaction. A) anabolic B) exchange C) hydrolytic D) endothermic E) metabolic Answer: C 16) Which pH would be alkaline? A) 7.0 B) 8.0 C) 4.0 D) 1.5 E) 6.5 Answer: B 17) Which of the following is NOT a characteristic of saturated fats? A) they are usually solid at room temperature. B) they contain at least one double bond. C) they are found in animals. D) their fatty acids pack tightly together. E) they are a form of stored energy. Answer: B 18) Which of the following is NOT a characteristic of phospholipids? A) they are found in cellular membranes. B) they can form micelles and bilayers. C) they contain fatty acids that associate with water. D) they contain a hydrophilic phosphate "head." E) they contain two fatty acids and a phosphate functional group. Answer: C 19) Organisms use carbohydrates in all of the following ways EXCEPT A) as a component of cell walls. B) as a long-term energy source. C) as a short-term energy source. D) to keep membranes flexible at low temperatures. E) as a building block of DNA and RNA molecules. Answer: D 20) Fats, proteins, and complex carbohydrates are all produced by A) hydrolytic reactions. B) dehydration synthesis. C) exchange reactions. D) hydrogen bonding. E) catabolic reactions. Answer: B 21) Which of the following is an example of a polysaccharide? A) glycogen B) glucose C) fructose D) deoxyribose E) sucrose Answer: A 22) Which of the following statements about proteins is FALSE? A) They are composed of amino acids. B) They have multiple levels of structural organization. C) They can be hydrophobic, hydrophilic, or both. D) Their primary function is energy storage. E) They are formed by dehydration synthesis reactions. Answer: D 23) All of the following are components of an amino acid EXCEPT A) a carboxyl group. B) a pentose group. C) an amino group. D) an ?-carbon. E) an R group. Answer: B 24) Which of the following is found in nucleic acids? A) ionic bonds B) peptide bonds C) purines D) ß-sheets E) disulfide bridges Answer: C 25) Hydrogen bonds are found in all of the following EXCEPT A) between phosphates in ATP. B) in ?-helices. C) between water molecules. D) in the DNA double helix between nucleotides. E) between the R groups of amino acids in proteins. Answer: A 26) Tertiary and quaternary structure of proteins involves __________ bonds. A) hydrogen B) ionic C) polar covalent D) nonpolar covalent E) ionic, hydrogen, polar, and nonpolar covalent Answer: E 27) Which of the following are examples of pyrimidines? A) uracil and adenine B) cytosine and guanine C) thymine and adenine D) thymine and guanine E) cytosine and thymine Answer: E 28) All of the following bases are found in RNA molecules EXCEPT A) adenine. B) thymine. C) uracil. D) cytosine. E) guanine. Answer: B 29) The "spine" of the DNA molecule is composed of A) amino acids. B) pentoses. C) phosphates. D) nitrogenous bases. E) alternating phosphates and pentoses. Answer: E 30) Which of the following would NOT normally be found as a component of a cell's nucleic acids? A) adenine deoxyribonucleotides B) thymine deoxyribonucleotides C) uracil deoxyribonucleotides D) cytosine ribonucleotides E) adenine ribonucleotides Answer: C 31) All of the following are associated with ATP molecules EXCEPT A) a long-term energy supply. B) high-energy bonds. C) a recyclable energy supply. D) formation of coenzymes. E) three phosphate groups. Answer: A 32) Which of the following statements concerning nucleic acids is FALSE? A) Nucleic acid strands are held together by hydrogen bonds between complementary bases. B) Not all DNA is double stranded. C) Some viruses have DNA as their genomes. D) The nucleic acid polymer is composed of peptide bonds. E) Cytosine is found in all nucleic acid molecules. Answer: D 33) Which of the following is an incorrect pairing? A) primary structure: amino acid sequence B) secondary structure: disulfide bridges C) tertiary structure: covalent bonds D) quaternary structure: two or more polypeptides E) secondary structure: ?-pleated sheets Answer: B 34) Proteins contain both acidic and basic R groups, and can therefore function as A) energy storage macromolecules. B) structural macromolecules. C) buffers. D) catalysts. E) genetic material. Answer: C 35) An increase in the pH of a solution by 2 whole numbers represents a change in the number of hydrogen ions by what factor? A) 2 B) 20 C) 1000 D) 10 E) 100 Answer: E 36) Plant cell walls are composed of __________ held together by __________. A) polysaccharides, hydrogen bonds B) amino acids, peptide bonds C) disaccharides, hydrophobic interactions D) fatty acids, polar covalent bonds E) peptidoglycan, ionic bonds Answer: A 37) The presence of __________ in the cell wall of a microbe causes it to be resistant to drying. A) fats B) phospholipids C) sterols D) glycolipids E) waxes Answer: E 38) Some __________ are used as hormones. A) phospholipids B) waxes C) steroids D) ions E) polyunsaturated fats Answer: C 39) Lipids found in the membranes of all eukaryotic cells are A) polyunsaturated fats. B) phospholipids. C) steroids. D) waxes. E) triglycerides. Answer: B 40) A protein is a __________ of amino acids. A) monomer B) polymer C) bilayer D) solution E) decomposition product Answer: B 41) DNA is composed of repeating units of sugars, phosphates, and nucleic acids. This is an example of a A) polymer. B) monomer. C) salt. D) micelle. E) lipid. Answer: A 42) A polymer composed of simple sugars is a(n) A) protein. B) triglyceride. C) starch. D) glycoprotein. E) amino acid. Answer: C 43) An amino acid is an example of a A) monomer. B) base. C) micelle. D) polymer. E) salt. Answer: A 44) Glucose is an example of what type of carbohydrate? A) a disaccharide B) a monomer C) a pentose D) a pentose polymer E) a hexose monomer Answer: E 45) Adenosine triphosphate (ATP) is a A) monomer. B) polymer. C) simple carbohydrate. D) lipid. E) bilayer. Answer: A 46) Amylose is a(n) __________ carbohydrate. A) simple B) monomer C) polymer D) nucleotide E) ionic Answer: C 2.2 True/False Questions 1) The smallest chemical units of matter are elements. Answer: FALSE 2) The side groups of amino acids can interact with each other and with other molecules. Answer: TRUE Section: Organic Molecules 3) Monosaccharides are usually found in cyclic forms. Answer: TRUE Section: Organic Molecules 4) The electron shells of atoms hold eight electrons each. Answer: FALSE 5) Hydrogen bonds are stronger then covalent bonds. Answer: FALSE 6) Carbohydrates are composed of carbon, hydrogen, and oxygen. Answer: TRUE 7) Denaturation of a protein is always permanent. Answer: FALSE 8) The long-term chemical energy storage molecules in plants are triglycerides. Answer: FALSE 9) One of the products of dehydration synthesis reactions is water. Answer: TRUE 10) Salts are produced from exchange reactions in which acids and bases neutralize each other. Answer: TRUE 2.3 Short Answer Questions 1) Another name for a unit of atomic mass is a(n) __________. Answer: dalton 2) Prokaryotes that grow best under acidic conditions are called __________. Answer: acidophiles 3) Cell surface markers composed of both carbohydrate and lipid molecules are known as __________. Answer: glycolipids 4) Molecules such as amino acids that have identical atoms and functional groups, but are mirror images of each other, are __________. Answer: stereoisomers 5) A chemical reaction in which a water molecule is a reactant is known as a(n) __________ reaction. Answer: hydrolysis 6) A(n) __________ is a molecule that binds with hydrogen ions when it is dissolved in water. Answer: base 7) The folding of a polypeptide into a three-dimensional shape is its __________ structure. Answer: tertiary 8) The DNA double helix is held together by __________ bonds. Answer: hydrogen 9) A six-carbon sugar is called a(n) __________. Answer: hexose 10) A(n) __________ is any molecule that speeds up a chemical reaction. Answer: catalyst 11) The monomer of a nucleic acid is called a(n) __________. Answer: nucleotide 12) A chemical reaction that traps energy within newly formed chemical bonds is a(n) __________ reaction. Answer: endothermic 13) A(n) __________ is a substance that maintains the pH even when the amounts of acid and/or base are changing. Answer: buffer 14) The sum of all the chemical reactions within an organism is referred to as its __________. Answer: metabolism 15) The __________ of an element vary in the number of neutrons in the nucleus. Answer: isotopes 2.4 Essay Questions 1) Compare and contrast synthesis reactions with decomposition reactions. Answer: Synthesis and decomposition reactions are often the reverse of each other. Synthesis reactions consume energy (are endothermic), whereas decomposition reactions release energy (are exothermic). Synthesis reactions often release water molecules in a process called dehydration synthesis, whereas decomposition reactions often consume water molecules in a process called hydrolysis. Finally, decomposition reactions break large macromolecules into their component monomers, which can then be used in synthesis reactions to build new macromolecules for use by the cell, whereas synthesis reactions utilize component monomers to build larger molecules. 2) Discuss the importance of hydrogen bonds in the chemistry of the cell. Answer: The chemistry of the cell would basically be impossible without hydrogen bonds. Water, which is required by all cellular reactions, would not have its unique properties of cohesiveness and polarity without hydrogen bonds. Hydrogen bonds hold the double helix of DNA together and contribute to the overall shape of protein molecules. However, unlike covalent bonds, hydrogen bonds are not permanent bonds, so they can easily and temporarily be broken, a characteristic that is important at certain points in the cell's life cycle (such as during DNA replication). 3) Define and discuss the importance and impact of pH on living organisms. Answer: pH is the measurement of the hydrogen ion concentration of a solution or within a cell. The relationship between pH and hydrogen ions is an inverse one: as the number of hydrogen ions increases, the pH drops (acid), and as the number of ions decreases, the pH rises (basic). Changes in pH can have drastic consequences for important cellular molecules such as proteins, which in turn can have a disastrous effect on the metabolism and structure of the cell; for this reason, organisms can exist only in a fairly narrow range of pH. Although the range of pH that is compatible with life is narrow, that range can vary widely among organisms: some organisms prefer highly acidic pH levels, whereas others can function only at alkaline pH levels. 4) Describe the chemical properties of phospholipids that account for their behavior in water. Answer: Phospholipids have polar phosphate "heads" and nonpolar fatty acid "tails," which interact in different ways with water molecules. The phospholipid heads are attracted to polar water molecules, but the nonpolar tails of the phospholipid are repelled by water. As the tails are driven away from the water molecules, they congregate together, either in the interior of a ball of lipid (called a micelle) or within the interior of a double layer of phospholipids (called a bilayer). This leaves the phosphate heads "outside," where they can easily interact with the water molecules. 5) Nitrogen is an essential element for living things, as demonstrated by the fact that nearly all fertilizers contain nitrogenous compounds. Discuss why nitrogen is essential. Answer: Nitrogen is a component in the structure of two of the four types of organic macromolecules. The amino group of an amino acid is a key reactant in the formation of peptide bonds, or primary structure, of proteins. Nitrogen also participates in hydrogen bonding and thereby contributes to the secondary, tertiary, and quaternary structure of proteins. Nitrogen is a key structural component of the bases in nucleic acids, and its participation in hydrogen bonding results in the formation of the base pairs and therefore the double helix of DNA.