(A) Urea cycle (B) TCA cycle (C) Glycolysis (D) Pyruvate oxidation (E) Respiratory chain

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Quentin Simpson
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1 Biochemistry - Problem Drill 15: Citric Acid Cycle No. 1 of Which of the following statements is not a metabolic pathway involved in carbohydrate catabolism and ATP production. (A) Urea cycle (B) TCA cycle (C) Glycolysis (D) Pyruvate oxidation (E) Respiratory chain A. Correct! Yes, the urea cycle is not involved in the breakdown of carbohydrate and involved in of ATP production. No, this does involve the catabolism of carbohydrate and ATP production. No, this does involve the catabolism of carbohydrate and ATP production. No, this does involve the catabolism of carbohydrate and ATP production. No, this does involve the catabolism of carbohydrate and ATP production. The urea cycle takes place in the liver and functions to convert ammonia to another substance like urea or uric acid which is less toxic to the organism. The correct answer is (A).

No. 2 of 10 2. There are three stages of cellular respiration. Which of the series presented below correctly represents these three stages in the correct order?

glycolysis (D) acetyl-coa production acetyl-coa oxidation TCA cycle (E) acetyl-coa production acetyl-coa oxidation electron transfer No, this is not the correct sequence. B.

2 No. 2 of There are three stages of cellular respiration. Which of the series presented below correctly represents these three stages in the correct order? (A) acetyl-coa oxidation electron transfer acetyl-coa production (B) electron transfer acetyl-coa production acetyl-coa oxidation (C) acetyl-coa production acetyl-coa oxidation glycolysis (D) acetyl-coa production acetyl-coa oxidation TCA cycle (E) acetyl-coa production acetyl-coa oxidation electron transfer No, this is not the correct sequence. B. Incorrect No, this is not the correct sequence. No, this is not the correct sequence. No, this is not the correct sequence. E. Correct! Yes, this is the correct sequence. The correct answer is (E).

3 No. 3 of Which of the following is not characteristic of the TCA cycle? (A) The cycle starts with acetyl-coa transferring acetyl groups to oxaloacetate. (B) Citrate loses two carboxyl groups as CO 2. (C) Most of the energy is made available via ATP. (D) For every acetyl group that enters the TCA cycle 3 molecules of NADH are made. (E) At the end of the TCA cycle oxaloacetate is regenerated. No, this statement is correct so this is not the best selection. No, this statement is correct so this is not the best selection. C. Correct! Yes, most of the energy is made available by transferring electrons to NAD + making NADH. No, this statement is correct so this is not the best selection. No, this statement is correct so this is not the best selection. Most of the energy in the TCA cycle is made available by transferring electrons to NAD + making NADH. The correct answer is (C).

4 No. 4 of Which of the following is incorrect characteristic of the TCA cycle? (A) In prokaryotes the TCA cycle occurs in the cytoplasm. (B) In eukaryotes the TCA cycle occurs in the cytoplasm. (C) Intermediates in the TCA cycle are frequent precursors to other biosynthetic pathways. (D) The TCA cycle requires the presence of oxygen. (E) Lost intermediates in prokaryotes are replenished by anaplerotic reactions. No, this is a correct statement with respect to the TCA cycle. B. Correct! Yes, this statement is not correct with respect to the TCA cycle in eukaryotes. In eukaryotes the TCA cycle occurs in the mitochondria. No, this is a correct statement with respect to the TCA cycle. No, this is a correct statement with respect to the TCA cycle. No, this is a correct statement with respect to the TCA cycle. In eukaryotes the TCA cycle occurs in the mitochondria. The correct answer is (B).

5 No. 5 of What does this chemical reaction show? Select the best response. (A) (B) (C) (D) (E) The carboxylate group is removed forming carbon dioxide. This is an example of oxidative decarboxylation. Pyruvate decarboxylation reaction. Enzyme mediated decarboxylation. All of the above No, this statement is correct but is not the best response. No, this statement is correct but is not the best response. No, this statement is correct but is not the best response. No, this statement is correct but is not the best response. E. Correct! Yes, all of these statements are correct. The equation shown is in fact pyruvate decarboxylation also known as oxidative decarboxylation. It is often referred to by all of these statements. The purpose of this question is to demonstrate that you need to not only know these reactions but understand what they are doing. So that when unexpected phrases are used to describe them you still know the answer. The correct answer is (E).

6 No. 6 of Complete the equation shown below by selecting the correct response from A E. For every molecule of pyruvate entering the TCA cycle: Acetyl-CoA + 2H 2 O + 3NAD + + FAD + GDP + Pi (A) CO 2 + 2NADH + FADH 2 + Co-ASH + GTP (B) 2CO 2 +NADH + FADH 2 + Co-ASH + GTP (C) CO 2 + NADH + 2FADH 2 + Co-ASH + GTP (D) 2CO 2 + 2NADH + FADH 2 + Co-ASH + GTP (E) None of the above D. Correct! Yes, this is the correct equation. No, there is a correct answer listed. For every molecule of pyruvate entering the TCA cycle: Acetyl-CoA + 2H 2 O + 3NAD + + FAD + GDP + Pi 2CO 2 + 2NADH + FADH 2 + Co- ASH + GTP It is very important to memorize and understand what these kinds of equations are telling you. By knowing these equations you will be able to figure out most questions with respect to the energetic of metabolic cycles. The correct answer is (D).

7 No. 7 of Complete the equation shown below by selecting the correct response from A E. For every molecule of glucose entering the TCA cycle: Glucose +2H 2 O + 10 NAD + + 2FAD + 4ADP + 4Pi (A) 6CO NADH + 6H + + 2FADH 2 + 4ATP (B) 6CO NADH + 10H + + 2FADH 2 + 4ATP (C) 6CO NADH + 6H + + 2FADH 2 + 8ATP (D) 6CO NADH + 6H + + 2FAD + 4ATP (E) None of the above A. Correct! Yes, this is the correct net equation for one molecule of glucose entering the TCA cycle. For every molecule of glucose entering the TCA cycle: Glucose +2H 2 O + 10 NAD + + 2FAD + 4ADP + 4Pi 6CO NADH + 6H + + 2FADH 2 + 4ATP As mentioned previously it is important to understand what these kinds of equations are telling you. By knowing these equations you will be able to figure out most questions with respect to the energetic of metabolic cycles. Also from this and the previous question you now know that pyruvate and glucose are important in the TCA cycle. The correct answer is (A).

8 No. 8 of Which of the following reactions are anapleurotic within the TCA cycle? (A) Pyruvate oxaloacetate (B) Beta-oxidation of fatty acids succinyl-coa (C) Aspartate oxaloacetate (D) Glutamate alph-ketoglutarate (E) All of the above No, this statement is correct however not the best selection. No, this statement is correct however not the best selection. No, this statement is correct however not the best selection. No, this statement is correct however not the best selection. E. Correct! Yes, while all the reactions shown are anaplerotic reactions within the TCA cycle this is the best response. Anaplerotic reactions are those that make intermediates of the TCA cycle. Formation of any of the intermediates can be used to replenish the whole cycle. There are four reactions classed as anapleurotic in the TCA cycle. The pyruvate going to oxaloacetate is considered the most important physiologically. The correct answer is (E).

9 No. 9 of For every acetyl a group that enters the TCA cycle molecules of NADH is produced. (A) 1 (B) 2 (C) 3 (D) 4 (E) 5 No, this is not the correct answer. Review the equations on TCA cycle. No, this is not the correct answer. Review the equations on TCA cycle. C. Correct! Yes, for every acetyl group that enters the TCA cycle 3 molecules of NADH are made. No, this is not the correct answer. Review the equations on TCA cycle. No, this is not the correct answer. Review the equations on TCA cycle. For every acetyl group that enters the TCA cycle 3 molecules of NADH are made. The correct answer is (C).

10 No. 10 of At the end of each turn of the TCA cycle is regenerated. (A) Isocitrate (B) Succinyl CoA (C) Fumerate (D) Malate (E) Oxaloacetate No, this is not the correct answer. Review the TCA cycle schematic. No, this is not the correct answer. Review the TCA cycle schematic. No, this is not the correct answer. Review the TCA cycle schematic. No, this is not the correct answer. Review the TCA cycle schematic. E. Correct! Yes, this is the correct answer to the question. At the end of each turn of the TCA cycle oxaloacetate is regenerated. Review the schematic for the cycle shown below. The correct answer is (E).

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