Question

1. Louis Pasteur noted that microbes (which can grow either anaerobically or aerobically) consumed large amounts of glucose when grown without oxygen, forming lactic acid. However, when an excess of oxygen was supplied, the concentration of lactic acid decreased as well as the consumption of glucose. Known as the “Pasteur Effect,” explain this phenomenon

2.DPN is used as a drug to treat obesity, working as a proton uncoupler to diminish the proton gradient needed for ATP synthesis because of oxidative phosphorylation.

a.) Why would this drug be effective in weight loss?

b.) Why would its use be dangerous to your health? Note that there are two questions being asked here.

Answer 1

Question 1

Pasteur Effect Phenomenon

The Pasteur effect is an inhibiting effect of oxygen on the fermentation process. This phenomenon occurs when a sudden change from anaerobic to aerobic process.

Explanation :

Facultative anaerobes ( grows anaerobically and aerobically) can produce energy using two different metabolic pathways (Glycolysis and Kreb's Cycle). When the oxygen concentration is low, they use the metobolic pathway of glycolysis, that converts glucose into pyruvate which is turned into ethanol and carbon dioxide releasing H+ ion, and the free energy is used to produce ATP, but production efficiency is low (2 moles of ATP). This is because, under anaerobic conditions, pyruvate derived from the conversion of glucose cannot enter the Krebs cycle via Acetyl Coa to produce energy. Instead, pyruvate is converted into lactate, known as the Pasteur effect. Therefore, the rate of glucose metabolism is faster, but the amount of ATP produced is smaller.

When oxygen concentration increases, facultative microbes use the Kreb's cycle(Citric acid cycle) metabolic pathway in which, pyruvate is converted to acetyl CoA which increases the efficiency upto 31 moles of ATP. This is because, under aerobic conditions, the ATP and citrate production increases and the rate of glycolysis slows down, because the ATP and citrate produced act as allosteric inhibitors for phosphofructokinase 1, an enzyme in the glycolysis pathway. This means that, about 15 times as much glucose must be consumed anaerobically as aerobically to yield the same amount of ATP.

Question 2

a) Why would this drug be effective in weight loss?

Ans : ATP (adenosinetriphosphate) is energy rich phosphate bonds which are produced during the final oxidative phosphorylation process. During this final phase of process, ATP synthetase converts adenosinediphosphate(ADP) to ATP(adenosinetriphosphate) with the addition of an inorganic phosphate molecule (Pi). DNP interferes with the final energy production pathway by preventing the uptake of inorganic phosphate molecules into the mitochondria which decreases the formation of high-energy phosphate bonds in mitochondria. But at the same time stimulates systemic oxygen consumption. This dissociative effect is known as uncoupling of oxidative phosphorylation. Thus DNP that acts as an uncoupling agent making the inner mitochondrial membrane leaky to protons stopping the final energy conversion. This shift in the proton electrochemical gradient then results in potential energy dissipating as heat, instead of being converted to ATP. This causes the rapid carbohydrate (glucose) consumption or burning of calories which results in the rapid weight loss.

b) Why would its use be dangerous to your health?

Ans : DNP works by uncoupling oxidative phosphorylation in mitochondria. Energy is therefore released as heat, which means that adenosine triphosphate (ATP), which provides energy for cell processes is not made. This means, DNP might cause loss of body mass as the body breaks down fat to compensate for the lack of ATP. Due to this breakdown of body fat coupled with overheating and a lack of ATP can lead to death. There is no effective treatment for who takes DNP too much and the side effects are severe and sometimes fatal.