Homework 1 1 Which three cellular components are present in both prokaryotes and eukaryotes A ribosomes chloroplasts mitochondria B nucleus ribosomes RNA C RNA DNA ribosomes D endoplasmic reticulum DNA RNA E mitochondria DNA RNA A Keq e G RT B Keq ln e G TS C Keq e H RT D Keq e G TS Explanation pro do not have a nucleus or membrane bound organelles 2 Keq can be determined from the change in standard free energy using the equation 3 Sheets composed of two layers of amphipathic molecules arranged with the hydrophilic groups on the surface and the hydrophobic groups buried in the center that form in water are E Keq log e G RT called A micelles B liposomes C vacuoles D bilayer membranes E none of the above Explanation in our cell membrane lipid head are hydrophilic and their tails are hydrophobic 4 Consider the reaction A B C D After reaching equilibrium at 25 C the following concentrations of reactants and products were measured A 10M B 15M C 10M D 10M Calculate G for this reaction A 1000 J mol B 10kJ mol C 1 J mol D insufficient data to determine answer E none of the above A 37 kJ mol B 3 7 kJ mol C 0 kJ mol Explanation Keq products reactants 10 10 10 15 100 150p G RTlnKeq 0 008314 298 ln 100 150 1000J mol multiply by 1000 to get to J 5 The G for the conversion of glucose 6 phosphate G6P to fructose 6 phosphate F6P is 1 7 kJ mole In a particular human cell the concentration G6P is 8 0 M and the concentration F6P is 1 0 M Calculate the G of the reaction as it occurs in this cell at 37 C D 7 1 kJ mol E 0 6 kJ mol Explanation G G RTln products reactants G 1700 J mol 8 314 310 ln 1 8 3695 J mol 3 7kJ mol 6 For a reaction with H 23 kJ mol and S 22 J K mol at 2 C the reaction is A spontaneous B nonspontaneous C at equilibrium D impossible to determine reactivity E none of the above Explanation G H TS G 23000 J mol 275 22 J mol 16950 Since G is positive the rxn will be nonspontaneous 7 Phosphoric acid is a polyprotic acid with pK values of 2 14 6 86 and 12 38 Which ionic form predominates at pH 9 3 A H3PO4 B H2PO41 C HPO42 D PO43 E none of the above A 10 1 B 1 1 C 1 10 Explanation the ionization of phosphoric acid takes place in steps Triprotic phosphoric acid gives Hydrogens away in 3 steps From pKa 0 2 12 and from 2 12 7 21 mostly H3PO4 dihydrogen phosphate From pKa 7 21 12 67 mostly HPO42 why it is the answer since it falls w in that level 8 The pK1 of citric acid is 3 09 What is the citric acid monosodium citrate ratio in a 1 0 M citric acid solution with a pH of 2 09 D 10 11 E 1 11 Explanation buffer citric acid monosodium citrate Hendersons equation pH pKa log salt citrate acid citric acid pH buffer 2 09 pKa citric acid 3 09 2 09 3 09 log salt acid 1 log salt acid 1 log salt acid 1 log citric acid log10 log citric acid 10 1 citric acid 9 A graduate student at TAMU wants to measure the activity of a particular enzyme at pH 4 0 To buffer her reaction she will use a buffer system based on one of the acids listed below which acid is most appropriate for the experiment A Formic acid Ka1 78 10 4 B MES Ka8 13 10 7 C PIPES Ka1 74 10 7 D Tris Ka8 32 10 9 E Piperidine Ka7 58 10 12 Explanation 1st find pKa of all acids and see which has the closest pKa to the given pH pKa logKa Formic acid pKa log 1 78x10 4 pKa 3 7496 MES pKa log 8 13x10 7 pKa 6 0899 PIPES pKa log 1 74x10 7 Pka 6 7595 Tris pKa log 8 32x10 7 pKa 8 0799 Piperidine pKa log 7 58x10 7 pKa 11 1203 Formic acid has the closest pKa value so that is the answer 10 The capacity of a buffer to resist changes in pH upon addition of protons or hydroxide ions depends on A the pKa of the weak acid in the buffer B the pH of the buffer D all of the above E none of the above QUIZ 1 C the total concentration of the weak acid and its conjugate base in the buffer 1 What are the four most abundant elements in a human body A C N O H B C N O P C C S O H D C Na O H E none of the above 2 Using phylogeny all living organisms can be divided into the following domains A bacteria eukarya and vertebrate B archaea and eukarya C bacteria eukarya and archaea D eukarya and bacteria E none of the above 3 A reaction with a H and a S will never be spontaneous A positive positive B positive negative C negative positive D negative negative E none of the above Explanation the reaction is both enthalpically and entropically opposed It will be nonspontaneous endergonic at all temperatures 4 Which of the following statements about water is not true A It has a high dielectric constant B It dissolves salts and polar substances C It can form two hydrogen bonds per water molecule D It packs in a hexagonal honeycomb shaped lattice when the temperature falls below 0 C E In the liquid state it is only 15 less hydrogen bonded than in the solid state at 0 C 5 Amphiphilic molecules A have both oxidizing and reducing groups B are micelles C have chromophores in two different wavelength regions D have both acidic and basic groups E have both hydrophilic and hydrophobic groups 6 Physical properties that depend on the amounts of various species rather than the identities of those species are called A osmotic properties B hydrophobic properties C London dispersion forces D aggregate properties E colligative properties HOMEWORK 2 1 Which amino acid does not have a primary alpha amino group 2 Which of the following amino acids is the least abundant in proteins A glutamine B arginine C lysine D proline E glutamate A V B W C G D F E A 3 Which of the following tripeptides carries a net positive charge at pH 7 0 A Ala Thr Asn B Gln Val Ser C Arg Glu Met D Pro Ile Leu E Leu Lys Gly Explanations Options A B and D can be ruled out because they do not contain any basic AA Although option C Arg Glu Met has basic amino acid arginine with additional amine group charge it gets neutralised by the negative charge conferred by the additional carboxylic acid group of Glutamate Hence option C can also …