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

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
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 .
Background image of page 1

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

View Full DocumentRight Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 12/02/2010 for the course CHEM 233 taught by Professor Daub during the Fall '09 term at Waterloo.

Page1 / 6

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

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online