1/4 Chemistry and Biochemistry 153A Spring 2009, Lecture 1 Midterm Exam 1, ID: A Instructions:  You will have 50 minutes to complete this exam.  You may use a pencil (recommended) or blue or black ink pen to write your answers. Other color inks will not be graded.  Only answers on the answer sheet, in the indicated space, will be graded; writing anywhere else will be ignored. Be sure to write your name on the answer sheet.  Do not write in the score boxes on your answer sheet; you will be docked points if you do.  For answers with a word or sentence limit, words beyond this limit will not be read or graded.  For short- or multi-answer questions, including irrelevant or wrong information or selections in your answer will cause you to lose points.  Write legibly. If the grader cannot read your answer, you won’t get credit.  Items you may have on your desk: - non-programmable scientific calculator, without its case or cover - writing utensil(s) - student ID ALL other items must be placed into a bag, which must be zipped up or closed and pushed completely under your chair.  No hats, hoods or earphones allowed. (Head scarves are fine.)  If you continue to write after ‘time’ is called, your exam will be taken and docked 10 points.  Questions are printed front and back – don’t miss any!Chem 153A, Spring 2009, Lecture 1 Midterm 1, ID: A 2/4 1. (1 pt) Write your exam ID (A) in the blank at the upper right of your answer sheet. Do not write in the score box. 2. (20 pts) True or False? a. Water is an amphipathic molecule. b. The stronger an acid, the higher its pKa. c. Similarities in primary or tertiary structure (or both) can reveal that proteins have related functions. d. There is no rotation about the bonds that sit in a peptide plane. e. The Henderson-Hasselbalch equation relates the protonation state of a buffer to the pH of the buffer solution. f. Phosphorylation is a reversible modification of proteins. g. In an α-helix, the backbone carbonyl groups point toward the helix’s amino-terminal end. h. Circular dichroism is a spectroscopic technique that can be used to measure protein secondary structure. i. Single chains of collagen and keratin both form right-handed helices. j. Glycosaminoglycan, a structural polysaccharide, provides stability to the bacterial cell wall. 3. (4 pts) Multiple Choice. Which one of the following statements is correct? a. A reducing sugar becomes reduced in the presence of Cu2+. b. All reducing sugars are mutarotatory. c. A polysaccharide can be simultaneously reducing and non-reducing. d. The following disaccharide is a non-reducing sugar: e. None of the above. 4. (4 pts) Multiple Choice. Which one of the following statements is correct? a. The melting point of linoleic acid is higher than that of oleic acid. b. Peripheral membrane proteins can be identified by stretches of hydrophobic amino acids in their sequence. c. A membrane’s fluidity increases with increasing saturation of its lipids. d. Phosphatidylcholines are a type of membrane glycerolipids. e. None of the above.Chem 153A, Spring 2009, Lecture 1 Midterm 1, ID: A 3/4 5. (8 pts) Given a solution of alanine at pH 5: A. 1:1000 B. 1:100 C. 1:10 D. 1:1 E. 10:1 F. 100:1 G. 1000:1 H. None of the above b. Is alanine a good general buffer at pH 5.0? Explain why or why not. If you answered no, include in your explanation the pH(s) at which alanine would be a good buffer. (30 words or less.) 6. (30 pts) Consider the 20 protein amino acids: a. Which have side chains that can: (Circle all that apply.) A. participate in an ion pair at pH 7? B. participate in a disulfide bond at pH 7? C. participate in a hydrogen bond at pH 7? D. participate in a van der Waals contact at pH 7? E. ionize (i.e. lose or gain a proton) in the range of pH 1-14? b. The pH titration of a dipeptide gives the curve shown below. How many different dipeptides could give rise to this curve? Show your reasoning. c. Calculate the pI of this dipeptide (from part b). Show your work.Chem 153A, Spring 2009, Lecture 1 Midterm 1, ID: A 4/4 7. (3 pts) Briefly define ‘dihedral angle.’ (10 words or less.) 8. (30 pts) Given the following molecule: a. To what class of compounds does this molecule belong? Be as specific as possible. b. Give the common names of the individual components of this molecule (as indicated by the brackets labeled A-D). c. Name the types of linkages in this molecule (as indicated by the numbers 1-4). Be as specific as possible. d. What is the function of this type of molecule? e. Where in the cell would you expect to find this type of molecule? Be as specific as possible. (15 words or less) f. True or False? This molecule is a glycoconjugate. g. Would you expect concentrations of this type of molecule to be higher in animals living in the arctic or in the tropics? Explain why in 40 words or