ACS_Biochemistry_Exam_Review- LATEST UPDATES 2022 (DETAILED SOLUTIONS)

ACS Biochemistry 360 Review 1. Which of the following statements about collagen is correct? a) Collagen contains a high proportion of hydroxylated proline residues. b) Collagen is a globular, intracellular protein. c) Post-translational modification of collagen involves vitamin A. d) The structure of collagen consists of a superhelix of three α helices twisted together Explanation – collagen has α chains, NOT helices. Each of the polypeptides in the triple superhelix of procollagen is an unusual left-handed helix not the right-handed α helix seen in globular proteins. However, the three polypeptides are twisted around each other in a righthanded manner to form the triple helix. All α helices are right-handed and get broken from high amounts of proline, hydroxylated proline, and glycine; but, these triplets of amino acids strength collagen. Glycine-X-Y. 2. Which of the following polypeptides is expected to be a globular protein? a) KFSCCKDVVDG b) IPVDSEDKHWY c) AFSCKHEDGML d) RDGLIVFYWSC e) DEHRKICLRRG Explanation – Utilize the one letter codes for all amino acids and know their charge and polarity. Globular proteins are usually seen in aqueous environments and will fold to have nonpolar amino acids on its interior. Based on that information, the polypeptide needs to have outside amino acids that are charged or polar while the interior will have nonpolar/hydrophobic amino acids. D is correct because (RDGLIVFYWSC) arginine, aspartate, serine, and cysteine are polar/charged. 3. Select answers that match with the amino acid. Some answers will have more than one answer. 1. acidic side chain 2. non-chiral amino acid 3. basic side chain 4. side chain can be modified by adding phosphates 5. involved in disulfide cross links 6. often found in the turns of proteins 7. is converted to tyrosine by hydroxylation ____________leucine 11 ____________aspartate 1 ____________serine 4, 12 ____________lysine 3, 8, 9 ____________phenylalanine 7, 13 ____________asparagine 9, 12 ____________glycine 2, 6 ____________tyrosine 4, 12, 13 8. important in the structure in collagen 9. has more than one amino group 10. has overall net charge of -2 at pH 7.4 11. only straight or branched hydrocarbons in side chain 12. polar, non-charged side chain 13. aromatic side chain ____________proline 6, 8 ____________cysteine 5, 12 Explanation – 6: Follow-up question: Where are Pro & Glycine seen in proteins? Ans: Beta sheets (for turns) and collagen. Can these AA be used for α-helices? Ans: No. Due to Proline’s N involved in the ring, it is too rigid for a N-Cα bond (makes kink) & N doesn’t have hydrogen bond. For Glycine, too much flexibility; more likely to be seen in a coiled-coil structure (collagen) 8: Lys increases tensile strength by cross-linking between α chains. This may not be common knowledge about Lys. During the ACS Review, I did not go over this. 10. There are amino acids that have a -2 charge at physiological pH. If it said -1, then the acidic amino acids would be correct. 12. Technically tyrosine is a polar, non-charged side chain, but through GCU we are taught that it is aromatic. During ACS Review, this was not added to the list. 4. The amino acid most likely to yield the above titration curve above would be: a) Arginine b) Glutamic acid c) Glycine d) Methionine e) Tyrosine Explanation – Based on the location where pI is, the amino acid is basic (due to it having a basic pH). The only possible answer that is a basic amino acid is arginine. Know the properties of all amino acids and how to calculate pI from a titration curve. From pI, you should be able figure out the amino acid the titration curve corresponds with. 5. An enzyme has Vmax of 50 mol product formed (minute x mg protein)-1 and a Km of 10for the substrate. When a reaction mixture contains the enzyme and 5 substrate, which of the following percentages of the maximum velocity will be closest to the initial reaction rate? a) 5% b) 15% c) 33% d) 50% e) 66% Explanation Km = 10  Vmax = 50 1/2Vmax = 25 S Option 1: Rearrange Michaelis-Menten equation to find the ratio between the new velocity (Vo) and Vmax. The original equation was