BIOCHEMISTRY ACTUAL EXAM ALL

BIOCHEMISTRY ACTUAL EXAM ALL

CHAPTERS

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CHAPTERS 1, 2, 3, 4 AND 7 LATEST

Which will show the greater degree of dissociation: formic acid (pKa = 3.75) or

acetic acid (pKa = 4.76) if dissolved in water at 0.1 M concentrations?

• Formic acid C. Within the accuracy of measurement they will be equally

dissociated. B. Acetic acid D. Cannot tell from data given. - ANSWER- A. Formic acid

Which will show the greater degree of dissociation: formic acid (pKa = 3.75) or

acetic acid (pKa = 4.76) if dissolved at 0.1 M concentrations in solutions whose pH is 11.0?

• Formic acid C. Within the accuracy of measurement they will be equally

dissociated. B. Acetic acid D. Cannot tell from data given. - ANSWER- C. Within the accuracy of measurement they will be equally dissociated.

Which of the following experimental observations disproved the vitalist claim that the substances of which living matter is composed are qualitatively different from those which compose the non-living world?

• the demonstration by the Buchner brothers that broken and therefore dead yeast

cells could convert sugar into ethanol B. the crystallization by Sumner of the enzyme urease C. Pasteur's proof that living organisms arise only from other living 1 / 4

organisms rather than by spontaneous generation caused by the "vital force" D.Wöhler's synthesis of urea from ammonium cyanate E. none of the above - ANSWER- D. Wöhler's synthesis of urea from ammonium cyanate

At pH 6.5 ribonuclease-A has a net charge of +4. At pH 2 the protein has a net charge of +19. If the protein is dissolved in 0.1 M KCl at both pHs, and if the solution contains no other solutes, in which case will the protein molecules have a larger number of chloride ions in their immediate vicinity?

• pH 2 C. a pH midway between 2 and 6.5 B. pH 6.5 D. It will have the same

number of chlorides at the two pHs. E. cannot tell from data given. - ANSWER- A.PH 2

The free energy of a reaction which is not at equilibrium, such as is the case in

nearly all cellular reactions, involves two terms: the standard free energy at

equilibrium and a term expressing the deviation of the actual conditions from equilibrium. In the Henderson-Hasselbalch equation governing buffers, the equivalent of the standard free energy term occurs at the pH at which

• the weak acid is fully dissociated. D. half the weak acid is dissociated. B. the

weak acid is fully in the undissociated form. E. none of the above. C. the pH = the pI. - ANSWER- D. the weak acid is fully in the undissociated form

Which of the following is best described as an entropy driven reaction?

• H = -82 kJ/mol, -TS = -136 kJ/mol D. none of the above is entropy driven B. H

= -1367 kJ/mol, -TS = +41 kJ/mol E. all the above are entropy driven. C. H = +110 kJ/mol, -TS = -140 kJ/mol - ANSWER- C. delta H= +110 kJ/mol

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Rank the following vitalist statements in order of decreasing breadth of their claims about the living world.

• Living matter may be composed of the same materials as non-living matter, but

organisms arise from non-living matter by spontaneous generation by intervention of the "vital force." 2. The substances composing living mater are qualitatively different from those of the non-living world. 3. The structure of enzymes is too complex to be described in chemical terms, and the nature of biological catalysis is not comprehensible. 4. We may be able to make some of the substances of living matter, but the reactions which constitute life occur only in living cells.

• 1,2,3,4 B. 4,3,2,1 C. 2,1,4,3 D. 3,2,4,1 E. none of these - ANSWER- C. 2, 1, 4,

3

"Salting out" is a phenomenon in which addition of high concentrations of salt ions decreases the solubility of a protein, causing it to precipitate. The precipitate contains many salt ions. Which of the following is most likely to explain salting out?

• The salt ions form "ion atmospheres" around the protein charges, thus

screening the repulsion of one protein molecule from another and allowing them to come into contact with one another, forming the precipitate. B. The salt ions cause the protein molecules to unfold. C. Rapid diffusional motion of the salt ions causes them to bombard the dissolved protein molecules, driving them into colliding with one another. D. The salt ions cause the protein molecules to fold. E. None of the above is a good explanation. - ANSWER- A. The salt Ions form "ion atmospheres" around the protein charges, thus screening the repulsion of one protein molecule from another and allowing them to come into contact with one another, forming the precipitate

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In biochemistry we often study "model systems" because they illustrate principles which are broadly applicable. Why is formic acid a useful model system for studying buffering in biochemical systems?

• It is a simple compound which shows all the buffering properties of a weak

acid. B. It is cheap and easy to work with in the laboratory. C. Its multiple carboxyl groups are a good model for proteins. D. Its pKa, 3.75, is in the physiological range very near neutrality. E. It is toxic to baboons. - ANSWER- A. It is a simple compount which shows all the buffering properites of a weak acid

• The protein myoglobin acts as an oxygen storage protein in muscle tissue. It

contains 152 amino acids. If the side chains of asparagine and glutamine are ignored, how many water molecules would be required to hydrolyze myoglobin completely to its constituent amino acids?

• None. Proteins are not hydrolyzable. D. 204 B. 152 E. 202 C. 151 - ANSWER-

C. 151

Which of the bonds listed below would be the weakest?

• a simple carbon-carbon double bond D. a carbon-oxygen double bond B. a

carbon-carbon bond in an aromatic ring E. a hydrogen bond C. a carbon-carbon single bond - ANSWER- E. a Hydrogen Bond

On comparing the molecular weight of a free amino acid in solution with that of the same amino acid as a nonterminal residue in a protein, one finds that

• the free amino acid exceeds the residue weight by 18 daltons. B. the residue's

weight exceeds that of the free amino acid by 18 daltons. C. the difference depends on which amino acid one considers. D. the free amino acid and the residue have the

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