Exam 2: Cell Chemistry and Bioenergetics

The citric acid cycle is summarized in the following figure. Answer the following question(s) about this cycle. -Aconitase catalyzes an isomerization reaction in the citric acid cycle shown above, in which H?O is first removed and then added back to the substrate. Which step is catalyzed by this enzyme? Write down the step number as your answer, e.g. 5.

Under anaerobic conditions, glycolysis provides most of the ATP that the cell needs. In animal cells, pyruvate, the end product of glycolysis, is converted to lactic acid by lactate dehydrogenase, as shown below: CH₃(CO)COO- + X ?CH₃(CHOH)COO- + Y What is the correct carrier pair (in place of X and Y) in this reaction?

Sort the following from a low to a high contribution to the total mass of an E. coli bacterium. Your answer would be a four-letter string composed of letters A to D only, e.g. DCBA. (A) Water (B) Sugars (C) Proteins (D) Nucleic acids

The free-energy change (?G) for a simple reaction, A ? B, is 0 kJ/mole at 37°C when the concentrations of A and B are 10 M and 0.1 M, respectively. What is the free-energy change for the reaction when the concentrations of A and B are instead 0.01 M and 1 M, respectively? Recall that ?G° = -5.9 × log(K?q). Write down your answer as a number with the appropriate sign (+ or -) and in kJ/mole, e.g. +11.8 kJ/mole.

What are the molecules that normally supply carbon and oxygen atoms, respectively, for the citric acid cycle?

The substrate for the glycolytic enzyme glyceraldehyde 3-phosphate dehydrogenase is glyceraldehyde 3-phosphate (with one phosphate group) while its product is 1,3-bisphosphoglycerate (with two phosphate groups). Where does the extra phosphate group come from?

Arsenate is a toxic ion that can interfere with both glycolysis and oxidative phosphorylation. Arsenate resembles Pᵢ (inorganic phosphate) and can replace it in many enzymatic reactions. One such reaction is catalyzed by glyceraldehyde 3-phosphate dehydrogenase in step 6 of glycolysis. Upon completion of the reaction, instead of the normal product, 1,3-bisphosphoglycerate, the mixed anhydride 1-arsenato-3-phosphoglycerate is formed; this undergoes rapid spontaneous hydrolysis into arsenate plus 3-phosphoglycerate, the latter being a normal product of step 7 in glycolysis. What would be the effect of arsenate poisoning in glycolysis?

The three families of cellular macromolecules are polymerized and depolymerized by a general mechanism involving water. Each of them has a set of monomers whose polymerization changes the total free energy of the system. Which of the following statements is true regarding these macromolecules?

The citric acid cycle is summarized in the following figure. Answer the following question(s) about this cycle. -In step 1 of the citric acid cycle drawn above, what is the molecule indicated with a question mark?

Indicate true (T) and false (F) statements below regarding fatty acid metabolism. Your answer would be a four-letter string composed of letters T and F only, e.g. TTTT. ( ) Most animals derive their energy from fatty acids between meals. ( ) Fatty acids are converted to acetyl CoA in the cytosol, which is then transported into mitochondria for further oxidation. ( ) Fatty acids are stored in fat droplets in the form of triacylglycerols. ( ) The breakdown of fatty acids into each acetyl CoA unit requires the hydrolysis of two ATP molecules.

What is the reaction performed on the molecule labeled as substrate in the following diagram? What is the name of the activated carrier?

In the first reaction of the glycolytic pathway, the enzyme hexokinase uses ATP to catalyze the phosphorylation of glucose, yielding glucose 6-phosphate and ADP. The ΔG° value for this reaction is -17 kJ/mole. The enzyme glucose 6-phosphatase catalyzes a "reverse" reaction, in which glucose 6-phosphate is converted back to glucose, and a phosphate is released. The ΔG° value for this reaction is -14 kJ/mole. What is the ΔG° value for the following reaction? ATP + H₂O → ADP + Pᵢ

The amino acid serine has an amino group, a carboxyl group, and a hydroxyl group. Which of the following better represents the structure of this amino acid at neutral pH?

Indicate true (T) and false (F) statements below regarding the cellular metabolism of nucleotides and amino acids. Your answer would be a four-letter string composed of letters T and F only, e.g. TTTT. ( ) Nitrogen fixation occurs in the mitochondria in most animal cells to generate amino acids. ( ) All 20 natural amino acids must be provided in our diet and are therefore "essential." ( ) There are NO essential nucleotides that must be provided in the diet. ( ) Catabolism of amino acids in our body leads to the production of urea which is excreted. Answers

Weak noncovalent attractions in the cell can be very strong in a nonaqueous environment. Some of these attractions are as strong as covalent interactions in a vacuum (their bond energy is approximately 340 kJ/mole), but become more than twenty-five times weaker (their bond energy becomes approximately 13 kJ/mole) in water. What type of attraction shows this phenomenon?

ATP is the main energy currency in cells, and it can especially be used to drive condensation reactions that produce macromolecular polymers. How does ATP normally catalyze the condensation reaction, which by itself is energetically unfavorable?

Which of the following is true regarding a fatty acid molecule in water?

Which of the following statements is true regarding cellular metabolism?

Sort the following molecules from a low to high rate of diffusion inside the cytosol. Your answer would be a four-letter string composed of letters A to D only, e.g. ADCB. (A) Myoglobin (a protein) (B) Glycine (an amino acid) (C) Ribosome (a protein-RNA complex) (D) CO?

Imagine the reaction A → B with a negative ΔG value under experimental conditions. Which of the following statements is true about this reaction?