Week 3 Practice Quiz

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Apr 3, 2024

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9/15/22, 5:42 PM Quiz: Week 3 Practice Quiz F22 https://canvas.ou.edu/courses/249882/quizzes/357868/take 1/15 Week 3 Practice Quiz F22 Started: Sep 15 at 5:42pm Quiz Instructions 1 pts Question 1 essentially all PO essentially all HPO none of the above 50:50 H PO and HPO essentially all H PO 50:50 H PO and H PO essentially all H PO 50:50 HPO and PO Consider the titration curve of phosphate (PO ) ion shown below. When 1.5 equivalents of H has been added to a solution of phosphate ion, what species predominates? 4 3− + 4 3− 4 2− 2 4 − 4 2− 2 4 − 3 4 2 4 − 3 4 4 2− 4 3−

9/15/22, 5:42 PM Quiz: Week 3 Practice Quiz F22 https://canvas.ou.edu/courses/249882/quizzes/357868/take 2/15 1 pts Question 2 75:25 H PO to HPO 25:75 H PO to H PO essentially all HPO essentially all H PO none of the above 25:75 H PO to HPO 50:50 H PO and HPO 75:25 H PO to H PO essentially all H PO essentially all PO 50:50 H PO and H PO 50:50 HPO and PO Consider the titration curve of phosphoric acid (H PO ) shown below. What species will be present when 0.25 equivalents of OH has been added? 3 4 − 2 4 − 4 2− 3 4 2 4 − 4 2− 2 4 − 2 4 − 4 2− 2 4 − 4 2− 3 4 2 4 − 3 4 4 3− 3 4 2 4 − 4 2− 4 3−

9/15/22, 5:42 PM Quiz: Week 3 Practice Quiz F22 https://canvas.ou.edu/courses/249882/quizzes/357868/take 3/15 1 pts Question 3 L D The structure below is that of a generalized amino acid. Assuming that the R group is not H, then what is the relative configuration (D or L) of the structure that is shown? Note that the alpha-carbon is at the intersection of the two lines, the horizontal bonds are projecting out of the plane of the paper (or screen), and the vertical bonds are projecting behind the plane of the paper (or screen). 1 pts Question 4 The structure below is that of a generalized amino acid. Assuming that the R group is not H and that it has lower priority than the alpha-amino and alpha-carboxyl groups, what is the absolute configuration ( R or S ) of the structure that is shown? Note that the alpha carbon is at the intersection of the two lines, the horizontal bonds are projecting out of the plane of the paper (or screen), and the vertical bonds are projecting behind the plane of the paper (or screen).

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9/15/22, 5:42 PM Quiz: Week 3 Practice Quiz F22 https://canvas.ou.edu/courses/249882/quizzes/357868/take 4/15 R S 1 pts Question 5 7.6 8.2 3.9 9.3 8.8 6.1 10.4 A compound used to make a buffer is known to have two aminium functional groups and a carboxyl functional group. The respective p K s of the groups are 8.2, 10.4, and 3.9. A biochemist has 100.0 mL of a 0.25 M solution of this compound at an initial pH of 8.2. She adds 50.0 mL of a 0.15 M solution of HCl to the solution. What will be the final pH of this solution after the addition of the HCl? a 1 pts Question 6 3.4 4.4 A compound used to make a buffer is known to have two aminium functional groups and a carboxyl functional group. The respective p K s of the groups are 8.2, 10.4, and 3.9. A biochemist has 100.0 mL of a 0.10 M solution of this compound at an initial pH of 8.2. She adds 50.0 mL of a 0.15 M solution of HCl to the solution. What will be the final pH of this solution after the addition of the HCl? a

9/15/22, 5:42 PM Quiz: Week 3 Practice Quiz F22 https://canvas.ou.edu/courses/249882/quizzes/357868/take 5/15 3.9 8.2 10.4 9.3 6.1 1 pts Question 7 Yes, the statement is true. No, the statement is false. In a normal alpha-helix, there are 3.6 residues per turn, and the pitch is 5.4 angstroms. 1 pts Question 8 Yes, the statement is true. No, the statement is false. Intra-helix hydrogen-bonding in an alpha-helix occurs between the amide (carbonyl) oxygen of one residue (call it the n residue) and the hydrogen that is bonded to the amide nitrogen of the residue that occurs four residues beyond (call it the n +4 residue). (Assuming that there is an amino acid residue in the alpha helix four residues ahead of the n one.) th th th 1 pts Question 9

9/15/22, 5:42 PM Quiz: Week 3 Practice Quiz F22 https://canvas.ou.edu/courses/249882/quizzes/357868/take 6/15 The statement is false. The statement is true. The hydrogen bonding pattern between adjacent beta-strands that run antiparallel in a beta sheet tend to be off-axis such that the amide nitrogen (to which the hydrogen is covalently bonded) is not in line with the amide oxygen (hydrogen bond acceptor) of the neighboring beta-strand. 1 pts Question 10 10.3 7.0 What is the isoelectric point (pI) of the following peptide? To facilitate answering this question, assume that the N-terminal aminium group has a p K of 8, the C-terminal carboxyl group has a p K of 3.5, and that the ionizable side chains have p K s as follows: Asp = 4.0, Glu = 4.0, His = 6, Cys = 8.4, Tyr = 10, Lys = 10, and Arg = 12.5. Also, assume that if the pH is at least two units above or below the p K of a particular group, then that group is completely unprotonated or protonated, as the case may be. Hint: you might want to imagine what the net charge is at pH 7, and then if the net charge is positive you know that the pI will be greater than 7; if the net charge is negative at pH 7, you know that the pI is less than 7. What you should find is that there will be two groups that bracket the point at which the net charge is zero. The pI will be the average of the p K s of these two groups. a a a a a

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9/15/22, 5:42 PM Quiz: Week 3 Practice Quiz F22 https://canvas.ou.edu/courses/249882/quizzes/357868/take 7/15 none of the other answers is reasonably close. 6.0 3.8 1 pts Question 11 NAR DAR NGAR DGAR KAGD What is the name of the peptide (shown below) using the one-letter code for amino acids? (Please note that the protonation state of this peptide – as shown – is unusual.) 1 pts Question 12 Consider the peptide shown below. What is the amino acid sequence of this peptide? Use the one-letter code to express your answer.

9/15/22, 5:42 PM Quiz: Week 3 Practice Quiz F22 https://canvas.ou.edu/courses/249882/quizzes/357868/take 8/15 1 pts Question 13 −1 −0.5 +1 What would be the approximate net charge of the peptide shown below at pH = 1? To facilitate answering this question, assume that the N-terminal aminium group has a p K of 8, the C-terminal carboxyl group has a p K of 3.5, and that the ionizable side chains have p K s as follows: Asp = 4.0, Glu = 4.0, His = 6, Cys = 8.4, Tyr = 10, Lys = 10, and Arg = 12.5. Also, if the pH is at least two units above or below the p K of a particular group, then assume that the group is completely unprotonated or protonated, as the case may be. a a a a

9/15/22, 5:42 PM Quiz: Week 3 Practice Quiz F22 https://canvas.ou.edu/courses/249882/quizzes/357868/take 9/15 0 +1.5 −2.5 −1.5 +3 −2 +0.5 −3 +2.5 +2 1 pts Question 14 ether ketone imine amide ester alcohol The peptide bond represents what type of functional group? 1 pts Question 15

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9/15/22, 5:42 PM Quiz: Week 3 Practice Quiz F22 https://canvas.ou.edu/courses/249882/quizzes/357868/take 10/15 2 3 5 no cleavage would occur 4 If the peptide DGLWRK was incubated with the protease chymotrypsin, how many fragments (i.e., smaller peptides or free amino acids) would result? 1 pts Question 16 GGHAW GGHWA GWAGH GGWAH AWGGH A pentapeptide that contains histidine, two glycines, tryptophan, and alanine is incubated with the protease chymotrypsin. A dipeptide and a tripeptide result, and the dipeptide contains tryptophan while the tripeptide contains histidine and two glycines. Brief treatment with carboxypeptidase A yields free histidine. What is the sequence of the peptapeptide? 1 pts Question 17 The strong attractive forces that nonpolar molecules have for each other is the primary reason that oil separates from water.

9/15/22, 5:42 PM Quiz: Week 3 Practice Quiz F22 https://canvas.ou.edu/courses/249882/quizzes/357868/take 11/15 The statement is false The statement is true 1 pts Question 18 Yes, it will bind to the resin. No, it will not bind to the resin. An anion-exchange resin has functional groups that are positively charged so that anions will bind to the resin if the pH is right. A scientist wants to run an ion-exchange chromatography experiment with an anion-exchange resin. The protein she wants to purify is known to have an isoelectric point (pI) of 8.1. A sample that contains the target protein has been equilibrated in a buffer at pH 7.0. When the biochemist adds the sample to the anion-exchange column, will the protein of interest bind to the resin? 1 pts Question 19 This statement is true. This statement is false. When Christian Anfinsen studied the reversible denaturation/renaturation of RNase, he found that removal of urea followed by oxidation led to a large proportion of improperly folded and inactive RNase molecules whereas oxidation followed by removal of urea led to a large proportion of properly folded and active RNase molecules. 1 pts Question 20

9/15/22, 5:42 PM Quiz: Week 3 Practice Quiz F22 https://canvas.ou.edu/courses/249882/quizzes/357868/take 12/15 This statement is not true. This statement is true. In X-ray crystallography, a higher resolution corresponds to a lower numerical value that represents the resolution. 1 pts Question 21 This statement is true. This statement is not true. In macromolecular X-ray crystallography, a suitable crystal of the macromolecule in question is mounted on a goniometer, and a beam of X-rays is shone through the crystal. The resulting diffraction pattern is a Fourier transform of the electron density of the macromolecules in the crystal lattice. 1 pts Question 22 -R-O-P(O)(OH) -P(O)OH-O-P(O)OH- -CO-NH- >C=NH- R-O-P(O)OH-O-R Which of the following represents a phosphoanhydride group? 2

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9/15/22, 5:42 PM Quiz: Week 3 Practice Quiz F22 https://canvas.ou.edu/courses/249882/quizzes/357868/take 13/15 1 pts Question 23 No, the above-described sequence would not properly enter the desired number. Yes, the above-described sequence would properly enter the desired number. You wish to enter the number 1.2 × 10 into your calculator. If you entered 1.2 and then pressed the y key (or possibly the x key, depending on the model of calculator) followed by a 3, would this be correct? 3 x y 1 pts Question 24 No, the above-described sequence would not properly enter the desired number. Yes, the above-described sequence would properly enter the desired number. A person wants to enter 10 into their calculator. If they entered 10 and then pressed the Exp key, or possibly, the EE key (depending on the model of calculator), and then entered 3 would this sequence of steps allow them to successfully enter the desired number? 3 1 pts Question 25 No, the two expressions are not equivalent. Yes, the two expressions are equivalent given the properties of logarithms. A person is working a problem and ends up with the following expression: log( xy ) = z . The person rewrites this expression as log x + log y = z . Is this correct? In other words, does log( xy ) = log x + log y ?

9/15/22, 5:42 PM Quiz: Week 3 Practice Quiz F22 https://canvas.ou.edu/courses/249882/quizzes/357868/take 14/15 1 pts Question 26 60% metal A and 40% metal B 70% metal A and 30% metal B 30% metal A and 70% metal B 40% metal A and 60% metal B 50% metal A and 50% metal B A particular alloy is made of two metals. The density of one of the metals (call it metal A) is 3.0 g/cm . The density of the other metal (call it metal B) is 5.0 g/cm . If the density of the alloy is 4.0 g/cm , what must be the percent composition of the alloy in terms of metal A and metal B? 3 3 3 1 pts Question 27 alpha plus beta mainly alpha few secondary structures Type MT How would the protein structure shown below be categorized?

9/15/22, 5:42 PM Quiz: Week 3 Practice Quiz F22 https://canvas.ou.edu/courses/249882/quizzes/357868/take 15/15 Quiz saved at 5:42pm mainly beta 1 pts carboxyl carbon [ Choose ] methyl carbon [ Choose ] methylene carbon [ Choose ] Question 28 In the figure below, match the type of carbon to the correct arrow. Submit Quiz

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