Home Work Multiple Choice 1) Which is an α-amino acid? CH3 NH2 O a) CH3 CH CH C OH CH3 CH3 C O CH C OH NH2 b) NH2 CH3 c) H2C H2N d) O CH CH C OH CH2 O CH3 CH CH C OH 2) At physiological pH, most amino acids carry both a 1+ and 1- charge. This form is known as a ___. a) zwitterion b) anion c) cation d) isoelectric ion 3) Shown here is the amino acid glycine at a pH of ___. a) 1 b) 7 c) 14 d) both 1 and 14 4) Stereoisomers exist for most of the amino acids found in nature. Which statement below is correct? a) Both the D-amino acids and the L- amino acids are used by living things. b) Only the L-amino acids are incorporated in proteins. c) A common conversion is from the D-amino acid to the L-amino acid. d) L-amino acids are toxic. 5) If an amino acid is in a neutral solution, the form the carboxyl group takes is ___. a) —CO2– b) —CO2H+ c) —CO2– d) —CO2H 6) The side chain of the amino acid phenylalanine is shown here. -H2C The side chain is classified as ___. a) nonpolar b) polar-acidic c) polar-basic d) polar-neutral 7) The side chain of the amino acid tyrosine is shown here. The side chain is classified as ___. -H2C OH a) nonpolar b) polar-acidic c) polar-basic d) polar-neutral 8) The side chain of the amino acid histidine is shown here. The side chain is classified as ___. a) nonpolar b) polar-acidic c) polar-basic d) polar-neutral H N -H2C + N 9) The structure of the amino acid glutamine is shown below. Glutamine can be classified as H O + H3 N CH C O CH2 CH2 C NH2 O a) polar-neutral b) polar –acidic c) polar basic d) nonpolar 10) Shown here is the amino acid glycine at a pH of ___. a) 1 b) 7 c) 14 d) both 1 and 14 11) The structures of the amino acids proline and glycine are shown below. Which of the following statements is true? COO N C H CH2 H2C CH2 Proline COO H3 N+ C H H Glycine a) glycine is an α-amino acid, but proline is not b) both proline and glycine are chiral molecules c) glycine is achiral and proline is chiral d) proline exists as four enantiomers 12) The peptide bond that connects amino acids in proteins is actually an ___ linkage. a) amine b) amide c) ether d) ester 13) The term commonly used for a chain of amino acids 100 units long is ___. a) peptide b) oligopeptide c) polypeptide d) centapeptide 14) Which reaction is capable of breaking polypeptides into their component amino acids? a) hydrogenation (adding hydrogen) b) hydrolysis (adding water) c) dehydrogenation (removing hydrogen) d) dehydration (removing water) 15) Leucine-enkephalin, a pentapeptide, is a naturally occurring pain reliever found in the brain. How many peptide bonds are there in leucine-enkephalin? a) 5 b) 4 c) 6 d) 3 16) A tetrapeptide is given as: Ser-Lys-Ala-Pro. Which of the following statements is true? a) The serine provided a nitrogen for the peptide bond. b) The N-terminus is serine (Ser). c) There are four peptide bonds because there are four amino acids. d) The listing should be in alphabetical order. 17) The form of dipeptide aspatylserine (Asp-Ser) obtained from two amino acids, aspartic acid and serine, whose structures are shown here, is O H3 N+ CH C CH2 O O H3N+ CH C CH2OH COO aspartic acid serine O A O O H3N+ CH C O N CH C O H CH2OH CH2 COO B O O H3N+ CH C O CH C O CH2OH CH2 COO C O O H3N+ CH C N CH C O H CH2OH CH2 COO D O O H3N+ CH C CH C CH2 O CH2OH COO 18) Where is the peptide bond located in this dipeptide? O H2N CH CH2 OH serine C O NH CH H 3C CH C OH CH3 valine a) the CO—NH joining serine and the valine b) the doubly bonded oxygen just left of center between the amino acids c) the CH—CO on the top of the serine going to the right d) the NH—CH between the serine and valine 19) The sequence of the amino acids in a protein is known as the ___ structure. a) primary b) secondary c) tertiary d) quaternary 20) The α-helix and β-pleated sheet are both forms of the ___ structure of proteins. a) primary b) secondary c) tertiary d) quaternary 21) A biologically active protein referred to as a simple protein contains a) very few hydrogen bonds. b) only one heme group. c) less than three different amino acids. d) no prosthetic groups. 22) The element found in the center of the heme prosthetic group is ___. a) iron b) sulfur c) nitrogen d) carbon 23) Which interactions are involved in establishing and holding the three-dimensional structure of a protein? a) salt bridge and disulfide bonds b) hydrogen bonds c) hydrophobic effects d) all of these choices 24) The most abundant protein in the human body is a) collagen b) enzymes c) globular protein d) α-keratin 25) Proteins tend to assume a specific overall three-dimensional shape. This is referred to as the protein's ___. a) primary structure b) secondary structure c) tertiary structure d) quaternary structure 26) A contributing factor to the tertiary structure of a protein is a covalent bond between two atoms of ___. a) sulfur b) hydrogen c) carbon d) nitrogen 27) Which of the following sentences is true? a) Rearranging the amino acid residues in a peptide or protein changes its function. b) In an α-helix form, portions of polypeptide chain line up side by side with hydrogen bonds holding neighboring strands of sheet together. c) The order of amino acid residues in a protein is referred to as its tertiary structure. d) The overall three-dimensional shape of a protein is referred to as its primary structure. 28) Some proteins require more than one polypeptide chain to be biologically active. The level of protein structure involved is the ___ of a protein. a) primary b) secondary c) tertiary d) quaternary 29) The overall three-dimensional shape of a protein is determined by its ___ and is known as the ___ structure of a protein. a) amino acid residues/primary b) amino acid residues/tertiary c) isoelectric point/secondary d) hydrogen bonding/secondary 30) Which of the following is an example of a protein that exhibits a quaternary structure? a) insulin b) hemoglobin c) collagen d) keratin 31) Which of the following do not contribute to the overall stability of a tertiary structure of proteins? a) salt bridges b) hydrogen bonding c) hydrophobic effect d) hormones 32) Globular proteins in water typically assume their specific shapes because a) they are water-soluble due to the polar points located along the length of the protein molecules. b) the nonpolar portion of the molecule is inside and the polar portion is outside, as stated by the folding rule. c) they can assume the β–sheet form, which stretches along the surface of the solution. d) all of the polar side chains in the molecular structure fold inward to be protected from the effects of the polarity of water. 33) The hydrophobic portions of a protein tend to a) form chemical bonds between them so that the structure of the protein is rigid. b) be attracted to each other by means of strong interatomic forces. c) be strongly attracted to the water in the surroundings, pulling portions of the molecule away from its center. d) fold into the interior of the three-dimensional shape away from water. 34) In which of the following levels of protein structure can hydrogen bonding NOT play a role? a) primary b) secondary c) tertiary d) quaternary 35) Proteins can contain prosthetic groups, which are a) polypeptide chains that contain only one kind of amino acid. b) polypeptide chains that come off the main chain to form a branch. c) groups containing nonpeptide components. d) groups of amino acids that form accessory structures to the protein. 36) What kind of noncovalent interaction occurs between the –NH3+ ending of one side chain of an amino acid with the –COO– ending of sidechain of another amino acid in tertiary structure of a protein? a) salt bridge b) hydrogen bonding c) covalent disulfide bond d) hydrophobic effect 37) Which of the following substances recognized by immune system evoke production of one or more antibodies? a) secondary proteins b) antigens c) globular proteins d) glycolipids 38) Which is a means of denaturing a protein? a) changes in temperature b) changes in pH c) use of detergents or soaps d) all of these choices 39) What level of protein structure is not disturbed by denaturing? a) tertiary structure b) primary structure c) secondary structure d) quaternary structure 40) The ___ is the location on the protein molecule where enzyme catalyzed reactions take place. a) substrate b) zymogen c) active site d) coenzyme 41) An enzyme displays ___ when the enzyme accepts only one specific substrate. a) absolute specificity b) relative specificity c) stereospecificity d) no specificity 42) Catalysts, including enzymes, have the role of a) changing a nonspontaneous chemical reaction to spontaneous. b) lowering the activation energy of a reaction. c) heating up the reactants to make the reaction progress faster. d) changing the pH to a favorable pH for the reaction to progress. 43) The enzyme known as alcohol dehydrogenase is capable of oxidizing ethanol, methanol and other hydroxyl group containing organic compounds into their corresponding aldehydes. Such an enzyme with ___ catalyzes the reaction of structurally related substances. a). absolute specificity b) relative specificity c) stereospecificity d) no specificity 44) Organic compounds that are not polypeptides but are necessary for enzymes to properly function are called ___. a) substrates b) zymogens c) active sites d) coenzymes 45) A change in pH usually produces a change in enzyme activity because a) pH of the environment changes the conformation of the enzyme. b) enzyme activity increases at extreme pH values (either acidic or basic). c) enzyme activity is usually least active below its optimum pH. d) enzyme activity is most active above its optimum temperature. 46) Many of the chemical reactions of living things involve enzymes, which are a) proteins that are in the form of parallel sheets. b) proteins that catalyze reactions. c) small DNA molecules. d) denatured proteins. 47) A certain enzyme's name is glucose-6-phosphorylase. This enzyme most likely catalyzes a reaction that a) converts glucose into six phosphorous atoms. b) synthesizes six glucose molecules. c) joins six glucose molecules to a phosphate. d) places a phosphate on the sixth carbon of glucose. 48) ___ are inactive enzyme precursors that are synthesized, stored and may be activated where needed. a) Substrates b) Zymogens c) Active sites d) Coenzymes 49) An inhibitor is a substance that affects an enzyme by a) reducing the ability to act as a catalyst. b) removing the prosthetic group from an enzyme. c) reacting with the enzyme so there is less effect of the chemical reaction’s surroundings on the rate of reaction. d) stopping the separation of the enzyme from the product keeping the reaction from going to completion. 50) The function of feedback inhibition is to a) affect the polarity of a substrate so that it will not be picked up by an enzyme. b) provide a stimulus to the enzyme that makes it active during a reaction. c) provide a way of keeping the wrong substrate from coming in contact with an enzyme. d) control an enzyme reaction so that there isn’t an overproduction of the product.
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