203f01_e2_key

203f01_e2_key - Chemistry 203 Lg (Fall 2001) Exam #2...

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Unformatted text preview: Chemistry 203 Lg (Fall 2001) Exam #2 October 23, 2001: 11:00-12:00 Professor Charles E. McKenna INITIAL OF LAST NAME Please do not open this exam until you are told to do so. Write legibly to avoid confusion. GOOD LUCK ! ! Maximum Question # Points . Grader A I will observe the rules of Academic in grity while taking this exam. Studs; Signaturfl—‘w Circle the most nearly correct answer. (4 Pts.) (1) Not counting any unshared electron pairs, the number of electrons on a neon atom (Ne) available 0 for bonding is: - 0 In CH3—O—H, to complete its “octet’ the oxygen atom must use: @m bonding, four non—bonding electrons - two bonding, two non-bonding electrons — eight non—bonding electrons - eight bonding electrons (3) The compound Li+F has: — covalent bond only - hydrogen bond only — both covalent and ionic bonds fir ionic bond (4) Which among the following @ a polar covalent bond: - CH3-—C‘H3 @—CH3 — - N5 N .__._ . (5) The compound shown contains: 0 0 ll n Hz—N—C—CHg—C—O—CH3 9 both an amine and an ester group — both an amide and an acid group — both a ketone and an aldehyde group — both an ester and an alkene group (6) In a bond making process like 2H‘ 9 H—I—l - the reaction happens more slowly at higher temperatures — the product (H2) is less stable than the starting material- (ZH atoms) - energy must be supplied — gy is released \ \ . In the reaction H2 + HZC 2 CH2 (PdfC) 9 H3C—CH3 the total number of (old) bonds broken is: — 2 - 4 - 8 (8) Which one of the following molecules is chiral? (9) In the compound (carbon monoxide) shown to the figg$lpma S '— 30:0 3 If Jr - carbon has formal Charge 0, oxygen has formal charge 0 on has formal chage —1 , oxygen has formal charge +1 — both atoms have formal charge -1 é'f - both atoms have formal charge +1 10) How many different dipeptides HEN—aaI—aagaag—am—COZH are possible, assuming aaTl could be any of the common amino acids? w 4 - 400 ~ 8,000 -160,000 (1]) Myoglobin, the O2 storage protein of muscle, (shown to the right be10w): - has several extensive B-sheet re ions an embedded Fe atom which actually binds the O2 — has no extensive OL-helical regions - all of the above are true (12) Fri ary vs. teniarystructure of a protein: @5111“)! = amino acid sequence, tertiary = overall conformation in space - primary = coils or sheets, tertiary = random structure - primary = overall conformation in space, tertiary = coils or sheets - primary = overall conformation in space, tertiary = amino acid sequence Transition 51m: (13] The reaction diagram above shows the change in energy when a starting material is converted to a product P, with (B) and without (A) a catalyst. According to the diagram: - the catalyst raises the reaction energy barrier. slowing down the reaction — higher temperature will slow down the reaction - adding the catalyst has no effect on the reaction rate constant (transition state) - ad g the catalyst has no effect on the net amount of energy released but speeds up the reaction [14) Protein folding in H20 solutions: — cr tes the protein tertiary structure - places non-polar R groups like ~—CH3, ~CH(CH3)2 on the surface of the protein in contact with water molecules ~ places polar —C(O)NH2, —OH, and charged groups in the interior of the protein - has no role in creating the active site of enzymes Hyena—coz- - NHZ-CHR-COJJI — CH4 - 'NH3~Cl-IR—C0; fin water at neutral pH, the predominant structure of an amino acid would be (16) The figure below shows a pyruvate molecule binding to the active site of enzyme lactate - like-charge repulsion forces only ~ weak (van der Waals) forces, H-bonding and ionic bonding — H—bonding and ionic bonding only weak forces. H-bonding and covalent (disulfide) bonds (1'?) The rate of an enzyme-catalyzed reaction depends on two steps, E + S -> E*S followed by ES -> E + P where E = enzyme, S : substrate, E*S is an intermediate complex and P is product. If the second step is much slower than the first step, then the overall rate of formation of P depends on: - the rate of the first step 0 the rate of the second step — equally on the two steps - the rate of neither step (18 The electronegativity of atoms tends to - : increase from left to right — increase from right to left peak in mid-row (C) — be constant from left to right (no change) (19) Difference between drugs acting competitively vs. non-competitively: to inhibit an enzyme - competitive drug binds at a site remote from the active site ~ competitive drug causes irreversible inactivation of the enzyme — non—competitive drug binds to the active site of the enzyme 0 non-competitive drug binds at a site remote from the active site (20) The pictures above show, within a protein: - formation of a peptide bond - a Van der Waals (weak like-like) bond formation 6 formation of a covalent Cys-Cys bond - rupture of a peptide bond (21). A typical compound of Li is: - LiH4 — LiH3 - Lin (22') Why do we need to have some amino acids in our diet, but not others?: @276 but not all amino acids are synthesized in the body — none of the amino acids are synthesized in the body - essential amino acids are needed as vitamins — dietary amino acids provide more energy (23) Thermodynamics is concerned with. . .. kinetics with. the amount of heat produced in a reaction. . ...the rate of a reaction (one does not necessarily — _ the amount of heat produced in a reaction. . ..the rate of a reaction (one depends on the other) & depend on the other) - the periodic table rows. . ..the periodic table columns - none of the above 7 The alpha helix and beta-sheet substructures found in most proteins are largely due to - internal H—bonding from one amino acid to another in the same protein - external H—bonding to H20 - Van der Waals (like~like) forces - Ionic charge attractionfrepulsion forces (25) Reason why starch is edible by humans, cellulose (paper) is not even though both are chains of glucose molecules? @ack an enzyme that cleaves the linkage between the glucoses - paper doesn t taste as good as starch — paper is explosive ~ we have an enzyme that converts starch into protein MULTIPLE BONUS QUESTIONS! (plus 4 x 2 points) (3) Write the names for these amino acids: l H N—CHficfl—OH 1 2 | S” w we, THE OH 0 ll HzN—i:2—-C——OH 2 g ‘JLI. £4: we“, La (b) Write the symbols for these amino acids: / (i) Arginine Ark 3/ fl (ii) Alanine M / / §S Periodic: £2113“ at 5th: Elements I? Is - “mm-km .13 :6 as my _ I’Wfi. VA. WA -;.,,z 3' Is 3" It " 1 3 E C N 0 'F 1 Ne 2 193;; .1191! _1§-.9!l_l tam; i 31m: i ...
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203f01_e2_key - Chemistry 203 Lg (Fall 2001) Exam #2...

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