4: In yeast pyruvate is normally metabolised to ethanol. Why is this metabolic o

Question

4: In yeast pyruvate is normally metabolised to ethanol. Why is this metabolic option more beneficial for the yeast cells than conversion of pyruvate to lactate? a) Conversion to ethanol releases more NAD per mole than the conversion to lactate. b) The carbon atoms are more oxidized in ethanol than in lactate c) Increased levels of lactate increase the cellular osmotic pressure, which disrupts the oxygen gradient and flow of oxygen into cells and their mitochondria. Ethanol has a neutral pH, but lactate (lactic acid) production is accompanied by a detrimental decrease in pH. Ethanol production is not more beneficial. Yeast normally produces ethanol and lactate in equimolar amounts. d) e) 5: Yeasts are unicellular eukaryotic microorganisms and many species of yeast can be classified as facultative anaerobes. Which option below provides a correct definition for the term facultative anaerobe? a) b) c) d) An organism that can grow with or without oxygen, because it can make ATP by aerobic respiration if oxygen is present, but is capable of switching to fermentation or anaerobic respiration if oxygen is absent. An organism that lives and grows in the absence of molecular axygen and, hence will die in the presence of oxygen. An organism that needs oxygen because it cannot make ATP in the absence of oxygen. Hence, it cannot ferment or respire anaerobically. An organism that does not require oxygen as it metabolises energy anaerobically e) An organism that needs oxygen because it cannot ferment or respire anaerobicaly. However, it will be poisoned by high concentrations of oxygen. Which of the following options provides a correct definition for the Pasteur effect? a) b) c) 6: It is the inhibition of oxygen consumption on the addition of glucose to tissues or microorganisms having a high rate of aerobic glycolysis It is the phenomenon that occurs in facultatively anaerobic cells whereby oxygen inhibits glycolysis or fermentation It is the process that involves heat-treating milk or similar fluids to improve storage qualities and destroy pathogenic bacteria, without radically altering taste and nutritional characteristics. If a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium shifts to counteract the change to reestablish an equilibrium. d) e) It describes the metabolism of cancer cells (and many ceils grown in vitro) that involves high levels of glucose fermentation to lactate even when an adequate level of oxygen is present for aerobic respiration.

Explanation / Answer

4. In yeast, puryate is normally oxidized to ethanol rather than lactate because it lead to generation of more NAD+ that can generate more electrons that can be used in electron transport chain and ultimately releases morning energy. Hence, option a is correct

5. Facultative anaerobes are those which are able to survive both in presence or absence of oxygen .It normaly grow in presence of oxygen but when no oxygen is present it can perform anaerobic respiration. Hence, option a is correct.

6. Pasteur effect is a phenomenon that occurs in facultative anaerobe where oxygen inhibits glycolysis and fermentation. Hence, option b is correct.

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