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why does a mammal go to all the trouble of making urea from ammonia rather than simply excreting ammonia as many bacteria do? During starvation, more urea production occurs, why? Explain why one might provide high concentrations of the amino acid Arg to patients who have a deficiency in one of the first three enzymes of the urea cycle?

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Tod Thiel
Tod ThielLv2
28 Sep 2019

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Related questions

(BIOCHEMISTRY QUESTION)

A. Gluconeogenesis is not just the reverse of glycolysis. Briefly describe one of the steps catalyzed by different enzymes in glycolysis and gluconeogenesis.

B. Explain how a biochemist might dicover that a certain enzyme is allosterically regulated.

C. What are the regulatory implications for the cell with regard to ATP & AMP, given the relative concentrations of ATP & AMP in a cell?

D. Describe the function of fructose 2,6-bisphosphate in overriding the control of gycolysis and gluconeogenesis in liver cells in response to lowered blood glucose levels.

E. The human disease beriberi is caused by a deficiency of thiamine in the diet. People with severe beriberi have higher than normal levels of pyruvate in their blood & urine. Explain this observation in terms of specific enzymatic reaction(s).

My Responses: Could you tell me if these are correct? If not, could you provide the correct answer and explanation?

A. Its a cellular process in which glucose is produced from pyruvate, amino acids, lactate, and other biogenic precursors.

B. They might learn that an enzyme is allosterically regulated if that protein or enzyme undergoes a conformational change modulated by the binding of one or more modulators/effectors to alternate sites on the protein, resulting in a change in its activity. And they usually have more than one polypeptide chain.

C. The regulatory implications for the cell would be that all activity would increase and concentrations would go up unless bound to PFK-1 and then the overall activity would drop.

D. Low blood glucose is when glucagon signals the liver to produce and release more glucose (gluconeogenesis) and stop consumption. Fructose 2, 6-bisphosphate mediates rapid hormonal regulation of glycolysis and gluconeogenesis.

E. Pyruvate is the product of both carbohydrate and amino acid catabolism that enters cellular respiration in the mitochondria when converted to acetyl-CoA catalyzed by the PDH complex. The first step in the PDH complex reaction is a decarboxylation reaction that cannot be catalyzed without the enzyme thiamine pyrophosphate (TPP). This coenzyme is a derivative of thiamine or vitamin B1.

The people of Malaysia belong to three communities: the local people called Malays, immigrants from South India called Tamils, and immigrants from China. During the early 20th century, the Malays lived mainly in coastal villages, the Tamils worked on rubber estates, and the Chinese worked in tin mines. In general, the people were very poor and they consumed a limited variety of foods.[1] Rice was the staple diet of all three communities and therefore the key source of caloric and nutrient content. Malays typically grew their own rice and dehulled it before consuming it; dehulling partially removes the aleurone layer of the rice seed. Following their South Indian food habits, the Tamils ate parboiled rice, and the Chinese ate polished white rice imported from Thailand. It was found that among the three Malaysian communities, the Chinese community was much more prone to suffer from some degree of sub-optimal thiamin intake. Out of every 1,000 Chinese inhabitants, about 120 had mild thiamin deficiency, about 80 had severe thiamin deficiency, and about 16 people had died of it. Suboptimal intake of thiamin was rare in Malays and was not reported at all in Tamils.[1] Thiamin, also called Vitamin B1, is required for all tissues, and its deficiency causes the disease Beriberi. Less severe deficiency results in non-specific symptoms such as weight loss, malaise, irritability, and confusion. Although the origin of the word Beri-beri is disputed, it is believed to be a Philippine word meaning “I can’t, I can’t” and was probably coined to refer to the lack of neuromotor coordination in people afflicted with this disease.[2] Thiamin is water-soluble and is stable in the acidic medium. It is unstable to heat, oxygen, and UV light in neutral and alkaline medium. The active form of thiamin is thiamin pyrophosphate (TPP). This active form is a cofactor for pyruvate dehydrogenase and transketolase enzymes that are involved in the metabolism of carbohydrates. These enzymes play an important role in the biosynthesis of a number of cell constituents such as neurotransmitters, pentoses, and reduced equivalents, used in oxidant stress. The human body cannot store thiamin and therefore requires a continuous supply of the vitamin. The thiamin in an individual on a thiamin-free diet typically depletes in fewer than two weeks. Thiamin absorption is affected by compounds, called thiamin antagonists or anti-thiamin factors, that alter the structure of thiamin. These compounds include alcohols, polyphenols, flavonoids, and thiaminase, a heat labile enzyme found in certain foods.[2] In affluent countries, where the diet is rich in thiamin, the most common cause of thiamin deficiency is excessive alcohol consumption. Alcohol intake affects thiamin status in two ways. First, alcoholics get a significant percentage of their daily energy intake from alcoholic beverages, which are nutrient deficient. In other words, alcoholics replace their consumption of nutrient dense foods that are part of their normal diet with the consumption of nutrient deficient alcohol. Second, alcohol inhibits the intestinal ATPase involved in the absorption of thiamin.[4] Sub-clinical thiamin insufficiency associated with excessive alcohol consumption produces an encephalopathy called Wernicke-Korsafoff syndrome. Patients with this syndrome have a higher than normal incidence of abnormal transketolase, which has a very low binding affinity to TPP. This problem can be overcome by putting patients on high-dose thiamin therapy. Some patients, however, might have a form of abnormal transketolase that does not bind at all with TPP. Such people do not respond to high-dose thiamin therapy.[4] Thiamin deficiency is observed in individuals who have low thiamin intake and a diet rich in polished rice, especially if their diet also consists of anti-thiamin factors such as tea, coffee, raw fermented fish, and betel nuts. The minimum amount of thiamin needed by the body can increase because of increased physiological or metabolic demands arising from pregnancy and lactation, heavy physical exertion, illnesses like cancer, liver diseases, hyperthyroidism, and surgery. Since TPP is required for carbohydrate metabolism, the recommended dietary allowances for thiamin are based on the assumption that its intake is related to total energy intake. The recommended dietary allowance in the United States is 0.5 mg/1000 Kcal.

Questions
1. Thiamin deficiency was observed only in the Chinese community even though all three
communities had the same staple (rice) diet. Explain.
2. On packages of enriched rice sold in supermarkets, the rice preparation directions state that the
rice should not be washed before cooking. Explain.
3. Severe metabolic acidosis caused by high levels of lactate is often associated with thiamin
deficiency. Explain.
4. Provide two plausible explanations for what might cause above normal levels of pyruvate in blood
and urine. How can one determine which of the two explanations is correct?
5. Why does thiamin utilization increase among cancer patients?
6. A negative correlation exists between the need for thiamin and the amount of fat in the diet.
Explain.

1. C6H12O6 + 6O2 Ã 6CO2 + 6H2O Glucose is being _____ to _____ and oxygen is being _____ to _____. a. oxidized; carbon dioxide; reduced; water b. oxidized; water; reduced; carbon dioxide Incorrect c. reduced; water; oxidized; carbon dioxide d. reduced; carbon dioxide; oxidized; water

2. Which of the following stages in the breakdown of the piece of toast you had for breakfast generates the most ATP? a. the citric acid cycle Incorrect b. glycolysis c. the digestion of starch to glucose d. oxidative phosphorylation

3. Which of the following is a catabolic pathway? a. gluconeogenesis b. production of starch Incorrect c. glycolysis d. production of glycogen

4. Per molecule, the oxidation of a fatty acid results in _____ energy storage than the oxidation of glucose. a. the same b. less Incorrect c. more d. None of the above; fatty acids cannot be oxidized.

5. Of the eight reactions in the citric acid cycle, how many are oxidation-reduction reactions? a. one b. two c. three d. four e. five

6. The process of glycolysis transfers the energy in sugar molecules into the stored energy of activated carriers such as ATP and NADH. Which statement is true about glycolysis? a. Only eukaryotic organisms do glycolysis. b. The ten reactions of glycolysis are identical in all eukaryotic cells, but are different in prokaryotic cells due to their diverse metabolic strategies. Incorrect c. The ten reactions of glycolysis are identical in almost all living organisms on the planet. d. There are many ways to oxidize glucose and transfer energy into activated carriers; the diversity of organisms on the planet is reflected in the diversity of their mechanisms of glycolysis.

7. Referring to the sentence completed in #13 above, the purpose of the latter reaction (in active muscle cells) is to _____. a. accumulate lactic acid in the cell, which provides additional energy for the production of ATP Incorrect b. slow down glycolysis until oxygen becomes available again c. accelerate the Krebs cycle, which will restore the oxygen supply d. regenerate NAD+ so that glycolysis can continue in the absence of oxygen

8. What are the products of the citric acid cycle? a. carbon dioxide, NADH, FADH2 and GTP b. carbon dioxide, NAD+, FAD and GTP c. NADH, FADH2, and acetyl CoA Incorrect d. carbon dioxide and water

9. Which statement is true about enzymes? a. Enzymes catalyze chemical reactions because they make inherently endergonic reactions exergonic. b. Each enzyme in a cell can catalyze many different chemical reactions involving chemically different substrates. Incorrect c. Enzymes can only catalyze reactions in one direction. d. After catalyzing a reaction, an enzyme is permanently altered and can no longer bind substrate. e. None of the above is true. 1

10. ∆G measures the change in free energy in a system as it converts reactant (Y) into product (X). When [X] = [Y], ∆G is equal to _____. a. RT b. ΔG° + RT c. ΔG° d. ln [X]/[Y]

11. The ∆G° for the hydrolysis of ATP is -7.3 kcal/mol. What conditions in the cell would lead to a ∆G for ATP hydrolysis of -11 kcal/mol? a. An increase in the ATP/ADP ratio b. An increase in anabolic activity in the cell c. Transport of ATP out of the compartment where the reaction is occurring Incorrect d. A decrease in the ATP/ADP ratio

12. In the first reaction of glycolysis, a phosphate transferred from ATP to a glucose molecule to produce glucose-6-phosphate and ADP. Under conditions existing in the cell, the free energy change for this reaction is -8.0 kcal/mole. Which of the following statements is true? Recall that the ∆G° for the hydrolysis of ATP is -7.3 kcal/mol. a. Glucose concentrations in the cell are always low, making this reaction more favorable than would be expected. b. This reaction is less favorable than would be expected, given the ∆G° of ATP hydrolysis. c. Glucose-6-P concentrations in the cell are very low relative to glucose concentrations, making the reaction more favorable than would be expected. d. The ∆G° for the addition of a phosphate to glucose must be -0.7 kcal/mole.

13. Protein E can bind to two different proteins, S and I. The binding reactions are described by the following equations and values: E + S --> ES Keq for ES = 10 E + I> EI Keq for EI = 2 Given the equilibrium constant values, which one of the following statements is true? a. When S is present in excess, no I molecules will bind to E. b. E binds I more tightly than S. c. The binding energy of the ES interaction is greater than that of the EI interaction. d. Changing an amino acid on the binding surface of I from a basic amino acid to an acidic one will probably make the free energy of association with E more negative.

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