Foundations of Biology I Fall 2015 Dr Lesley Ashmore Midterm Exam 1 Directions Before beginning first mark your NAME and PEOPLESOFT ID on the scantron sheet Record your answers here and on the scantron sheet Turn in the scantron answers before you leave but keep this exam booklet Reach each question carefully Some answers may be partially correct you must select the BEST ANSWER You have 50 minutes to complete the exam Ensure that you leave enough time to enter all answers on your scantron sheet MULTIPLE CHOICE Choose the one alternative that best completes the statement or answers the question 1 Many researchers who study the origin of life propose that the first life form capable of templating its own replication and catalyzing self replication was made of surrounded by a A protein phospholipid bilayer B DNA protein coat C RNA phospholipid bilayer D DNA phospholipid bilayer E RNA protein coat 1 2 How would water molecules interact with an amino functional group A the oxygen molecules in water will form hydrogen bonds with the hydrogen s of the amino group B the hydrogen molecules in water will form hydrogen bonds with the hydrogen s of the amino group C water will tend to pull protons away from the nitrogen of the amino group leaving it negatively charged D the amino group will tend to pull protons away from water leaving it positively charged E A and D are both correct 2 3 This is from your textbook Heat shock proteins recognize denatured proteins by binding to hydrophobic patches that would not normally be exposed What can you conclude from this sentence A Heat shock proteins probably recognize and bind to nonpolar amino acids B Proteins are inflexible and heat shock proteins are essential when they break due to heat C Heat shock proteins are probably involved in rebuilding protein primary structure D Normal proteins do not have hydrophobic regions in their primary structure E High temperatures cause chemical reactions that transform hydrophilic amino acids to hydrophobic amino acids 3 4 The ability of atoms to combine with other atoms is determined by A the atom s nucleus B the atom s atomic weight C the atom s ability to form isomers D the number and distribution of electrons in the outer shell 4 1 Scenario Pepsin is a digestive enzyme secreted into gastric juice in the stomach along with a large amount of hydrochloric acid Pepsin binds to proteins in food and breaks peptide bonds to cut amino acids free Pepsin is optimized to perform most efficiently at the pH of the gastric juice in the stomach Pepsin only has 4 basic amino acids out of 327 total 43 out of 327 amino acids are classified as acidic The rest fall into the polar 170 or nonpolar 110 categories This graph shows the rate of reactions catalyzed by pepsin at different pHs Use this information to answer the following THREE questions 5 What is the specific chemical reaction catalyzed by pepsin A cannot be determined without knowing the specific substrate of this enzyme B dehydration of a polymer C peptidoglycan D hydrolysis of a polymer E peptidogenesis 5 6 What can you tell me about the net charge of pepsin in the stomach assume all amino acids are in the configuration they tend to have in a very strong acid Ignore the contribution of the backbone A slightly positive 4 B totally neutral C negative 39 D very negative 43 E very very negative 213 6 7 Uuuugh you feel queasy so you take an antacid Your friend warns you that if you alter the pH of your stomach you will be unable to digest proteins You determine that the dosage of the antacid will increase the concentration of hydroxide ions in your stomach by 100 fold According to the information in the graph will pepsin still be able to digest proteins at the adjusted pH A yes though it will be about 30 less efficient B no the enzyme will denature at the adjusted pH and cease to digest proteins C you cannot alter the pH by this amount it s off the pH scale D yes the antacid will not alter the efficiency of the enzyme E no because the reaction is exergonic at that pH 7 2 8 Imagine what might change if water was a linear molecule with the same chemical formula H O H Which of the following statements would be true A Hydrogen bonding between water molecules would be much weaker B Water would be a better solvent for polar and charged molecules C The bonds between O and H would no longer be polar D Ice would still be less dense than liquid water but the specific heat of liquid water would be higher E Water would be unable to form hydrogen bonds with partial negative charges on other molecules 8 The following three questions relate to the demonstration in recitation 3 testing the effects of different household chemicals on a superabsorbent organic polymer sodium polyacrylate 9 Out of the four chemicals salt sugar vinegar and oil which denatured our polymer A salt vinegar and sugar B salt vinegar C vinegar only D salt only E all of them 9 10 Which statement best explains the results when the chemical s from answer A was were added to the polymer A The chemical s broke the ionic bonds that kept the polymer neutralized forcing it to release water and contract B The chemical s disrupted the hydrogen bonds and neutralized the negative charges that held the polymer in its superabsorbent tertiary structure C The chemical s formed covalent bonds with the polymer and altered its structure D The chemical s disrupted the ability of water to hydrogen bond with itself making the water less dense and unable to hold a gel form E The chemical s broke the covalent bonds holding the polymer together breaking it into component monomers 10 11 Which statement best relates the purpose of the demonstration A to test the hypothesis that cells use buffers to protect cells from pH changes and how pH changes affect organic polymers B To visualize a denaturation reaction by showing that conditions that denature proteins in cells also denature organic molecules that have tertiary structures held by hydrogen ionic bonds C to demonstrate the process of the exergonic hydrolysis reaction that breaks down polymers into component monomers D to show how the electronegativity of organic molecules affects their tertiary structures in different solvents E to visualize and explain how water s hydrogen bonding gives water its unique properties 11 3 The following questions refer to these five amino acids 12 Which of the following answer choices is an amino acid classified as basic and why A Aspartate because the R