exam 1a 2018 key - georgia institute of technology€¦ · exam 1a chem 4511/6501 spring february...

Exam 1a Chem 4511/6501 Spring February 1, 2018 Name_________KEY_________________

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[3 points each] _E__1. Which of the following best describes the hydrophobic effect?

A) It is caused by an affinity of hydrophobic groups for each other. B) It is caused by an affinity of water for hydrophobic groups. C) It is caused by a tendency of hydrophobic groups to decrease in entropy when in contact with other hydrophobic groups. D) It is caused by a tendency of hydrophobic groups to increase in entropy when in contact with other hydrophobic groups. E) It is caused by a tendency of water to lose entropy when in contact with hydrophobic groups.

_C__2. Which of the following statements are true? A) Eukaryotes and bacteria contain DNA in a nucleus. B) Archaea and bacteria contain DNA in a nucleus C) Eukaryotes contain membrane bound organelles (e.g. mitochondria, Golgi

complexes). D) Archaea and bacteria are multicellular. E) All of the above are true. F) None of the above are true.

_D__3. Living organisms are:

A) thermally isolated. B) closed systems. C) isolated systems. D) open systems. E) none of the above.

_C__4. Glycolysis is the process by which energy is harvested from glucose by living

things. Several reactions of glycolysis are thermodynamically unfavorable (non-spontaneous), but proceed because they are coupled with other reactions. Which reaction(s) is (are) spontaneous?

A) Pi + glucose à glucose-6-phosphate + H2O DG = 13.8 kJ/mol

B) Pi + fructose-6-phosphate à fructose-1,6-bisphosphate + H2O DG = 16.3 kJ/mol

C) ATP + H2O à ADP + Pi DG = -30.5 kJ/mol

D) None are spontaneous. E) All are spontaneous.

5. Which of the above pair(s) of reactions can be coupled so that the overall reaction is favorable? (check one or more).

___A and B _X_A and C _X_B and C ___None of them

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_B__6. For a reaction with DH = 22 kJ/mol and DS = -22 J/K•mol, at 10°C, the reaction is:

A) spontaneous B) nonspontaneous C) at equilibrium D) exergonic E) impossible to determine

_D__7. Standard free energy of a reaction can be used to determine Keq using the equation

A) Keq = ln e−DG°/TDS B) Keq = e−DH°/RT C) Keq = eDG°/RT D) Keq = e−(DH° - TDS°)/RT E) Keq = e−DG°/TDS F) Keq = log e−DG°/RT

__E_8. The Ka values for several acids are given below. Which acid (with its conjugate

base) would be the best buffer at pH = 7.5? A) Tris, Ka = 6.3 x 10-9 B) MES, Ka = 7.9 x 10-7. C) Acetic Acid, Ka = 1.8 x 10-5

D) Formic Acid, Ka = 1.8 x 10-4 E) HEPES, Ka = 3.2 x 10-8

__B_9. Phosphoric acid, a polyprotic acid, has pKa values of 2.14, 6.86, and 12.38. What is the primary ionic form pH 3?

A) H3PO4 B) H2PO41− C) HPO42− D) PO43− E) none of the above _B_10. Kw, the ionization constant of water, is _____ at _____.

A) 1014; 25°C. B) 10–14; 25°C. C) 10-7; 25°C. D) 107; 25K. E) 10–14; 0°C __C_11. You have a 1 mM solution of NaOH. What is the pH of the solution?

A) 3 B) 10.2 C) 11.0 D) 0.1 E) 14.1 _C__12. Which of these is true about amphiphilic molecules?

A) They have both oxidizing and reducing groups. B) They both polar and charged groups. C) They have both hydrophilic and hydrophobic groups. D) They have both cationic and anionic groups. E) None of these.

_G__13. Which of the following amino acids are optically active? A) Pro B) Phe C) His D) Trp E) Tyr F) A and C G) all are optically active. _D__14. Proteins can be quantified using UV absorbance (~ 280 nm). This is due to the absorptivity of which type of amino acids?

A) basic B) hydrophobic C) neutral D) aromatic E) charged

15. For the following pairs of liquids, indicate which has the greater boiling temperature. Circle one symbol. H2O < = > NH3 Ar < = > Ne CH4 < = > NH3 /30,45

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16. Imagine two point charges of opposite sign separated by 5 Å in solution. In which solvent would the attractive force between then be the greatest (circle one)? Solvent e Acetone 21 Methanol 33 Glycerol 43 17. (4 points) A bacterial cell with a diameter of about 2 microns has 30 copies of a given protein.

A) What is the concentration of this protein within the cell? (30 molecules/6.02 x 1023 molecules/mole) [4/3 x 3.14 x (1x10-6)3/1000]= B) How many copies of the protein would be required for the concentration of the protein to be 5 uM? Omit this question

18. (4 points) Draw a circle around each asymmetric atom (chiral center) in the chemical structure below: [all four carbons within the ribose ring]

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19. (6 points) Imagine an a-helix that is 36 amino acids in length. What is the end-to-end length of the helix?

(5.4 Å/turn x 36 aa)/(3.6 aa/turn)=54Å How many helical turns would the helix make? (36 aa x 100°/aa)/(360°/turn) = 10 turns What is the approximate width of the helix? Around 7-12 Å (points for as low as 5)

20. (10 points) Draw a two-strand parallel b-sheet with three amino acids in each strand. All the amino acids are alanine. Show stereo chemistry at each Ca. Show the hydrogen bonds between the two strands.

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21. (6 points) Below are two a-helices from a-keritin.

True or False _F_ Residue a is generally charged _F_ Residue c is generally charged _T_ Residue e is generally charged _T_ Residue a is generally hydrophobic _F_ Residue c is generally hydrophobic _F_ Residue e is generally hydrophobic _F_ Coiled coils contain a tetrad repeat _F_ Coiled coils contain a pentad repeat _F_ Coiled coils contain a hexad repeat _T_ Coiled coils contain a heptad repeat _F_ Coiled coils contain a octad repeat T/F Proteins do not form coiled coils (coiled coils are fake news) 22) [6 points] Circle each the molecular interactions in Ne (liq). Short-range repulsion Dipole-dipole interactions Dipole-charge interactions Charge-charge interactions Dipole-induced dipole interactions Charge-induced dipole Hydrogen bonding interactions Fluctuating dipole interactions (London interactions, Dispersive interactions) /12,84


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23) [8 points] Draw the peptide CRQPWKV a) indicate stereochemistry of all the Ca-positions, b) indicate the predominant ionization states of the sidechains at pH 5.5, c) draw boxes around the first 2 sets of six co-planer atoms, d) Label f and j on the 4th and 5th amino acids,

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25) [6 points] Identify the species/parameters indicated on the reaction coordinate below

Test Version A i reactants ii intermediate iii (second) transition state iv (first) transition state v products Test Version B 1 The standard free energy of the reaction 2 The activation free energy for the second reverse step of the reaction 3 The activation free energy for the first forward step of the reaction 4 The activation free energy for the second forward step of the reaction 5 The activation free energy for the first reverse step of the reaction /8,100

exam 1a 2018 key - georgia institute of technology€¦ · exam 1a chem 4511/6501 spring february...

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