200501M1 - Chem 237 Winter 2005 Midterm 1a ANSWERS Multiple...

Info icon This preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
Chem 237 Winter 2005 Midterm 1a ANSWERS Multiple Choice—ONE answer per question. 1.5 mark each. 1. Suppose you have the following solutions: 0.1 M acetic acid (solution A) and 0.1 M sodium acetate (solution B). If you mix 90 mL of solution A with 10 mL of solution B, what will the resulting pH be? ANSWER: the pH of the solution must be lower than the pKa of acetic acid since more HA form is used in making the solution than the A- form. You do not need the pKa of acetic acid to answer this question. 2. What is the relationship between the [H + ] at pH 6 and pH 7? ANSWER: the pH scale is a log scale, and the lower the pH value, the higher the [H + ]. So, at pH 6 the [H + ] is 10 times greater than the [H + ] at pH 7. 3. Which amino acid side chain can form an ionic bond at p H 7? ANSWER: the only amino acid in the group that can form an ionic bond is Glu or Asp, depending on the version of the exam you had. 4. Titration of Val by NaOH results in two p K a s. The second of these p K a s is the titration of which group? ANSWER: the second of the two p K a s is the titration of the amine function, or NH 3 + + OH - Æ NH 2 + H 2 O. 5. What is the pI of the peptide Gly-Arg? ANSWER: Gly-Arg has 3 titratable groups, the COOH, the NH 3 + and the Arg + side chain. Titration of the acid function gives a dipeptide with a charge of +1; titration of the NH 3 + gives a charge of 0, and titration of the Arg+ side chain gives a charge of -1. So averaging the NH 3 + and Arg + gives (8 + 12.5) /2 = 10.25, or about 10.2 6. Which statement is true about the peptide Met-Leu-Gly-Trp [Asn-Ala-Val-Trp]? ANSWER: for either version of the exam, the first amino acid is the N-terminal. 7. ATP hydrolysis (ATP + H 2 O Æ ADP + P i ) can not be coupled in a thermodynamically favorable way with which of the following reactions? ANSWER: the only reaction of the group that can not be coupled to ATP hydrolysis is the first one, since the G o is more than 31 kJ/mol. All of the other reactions could be coupled to ATP hydrolysis to result in a thermodynamically favorable reaction. 8. Which statement is consistent with the concept of ATP as “energy currency”? ANSWER: ATP has a G o of hydrolysis that is higher than some metabolites and lower than others. This illustrates energy currency in that ATP is formed from energy rich metabolites and is used to make other, less energetic metabolites. 9. Which statement does illustrate the hydrophobic effect? ANSWER: hydrophobic amino acids, such as Peu, Met and Phe are found in the interior of proteins. 10. Which of the following groups correctly shows the H-bonding in an α -helix? (“----“ = H-bond) ANSWER: the H-bonds in an α -helix are between the carbonyl group of the peptide bond and the - H N of another peptide bond, or - C=O ---- H N . Multiple Guess questions from the deferred midterm: 1. Suppose you have the following solutions: 0.1 M Tris base and 0.1 M Tris acetate. And suppose you mix these solutions in the following ratios: mL 0.1 M Tris base mL 0.1 M Tris acetate Buffer #1 10 90 Buffer #2 50 50 Buffer #3 90 10
Image of page 1

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
What is true about the resulting buffers: a.
Image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern