Which of the following statements are TRUE for respiration? P. The conversion of one molecule of pyruvate to three molecules of $CO_2$ generates four molecules of NADH Q. Fructose 6-phospate is the principal substrate for glycolysis R. The oxidation of glucose 6-phosphate to 6-phosphogluconate is the first step in the oxidative pentose phosphate pathway S. The mitochondrial 'alternative oxidase' provides an alternative pathway for transfer of electrons from ubiquinone to oxygen utilizing proton pumping complex of the respiratory chain
To determine which statements about respiration are TRUE, let's evaluate each statement provided in the question.
Statement P: The conversion of one molecule of pyruvate to three molecules of \(CO_2\) generates four molecules of NADH.
In cellular respiration, pyruvate enters the mitochondria where it is converted to acetyl-CoA. This acetyl-CoA enters the citric acid cycle (Kreb’s cycle) where one molecule of pyruvate generates three \(CO_2\) molecules. During this conversion, four molecules of NADH are produced: two from the conversion of pyruvate to acetyl-CoA and two during the citric acid cycle. Hence, this statement is TRUE.
Statement Q: Fructose 6-phosphate is the principal substrate for glycolysis.
In glycolysis, glucose is initially converted to glucose 6-phosphate and then to fructose 6-phosphate. While fructose 6-phosphate is an intermediate in glycolysis, the principal substrate for glycolysis is actually glucose, which is phosphorylated in the initial step. Therefore, this statement is FALSE.
Statement R: The oxidation of glucose 6-phosphate to 6-phosphogluconate is the first step in the oxidative pentose phosphate pathway.
The oxidative pentose phosphate pathway begins with the oxidation of glucose 6-phosphate to 6-phosphogluconate, which produces NADPH. This makes the statement TRUE.
Statement S: The mitochondrial 'alternative oxidase' provides an alternative pathway for transfer of electrons from ubiquinone to oxygen utilizing proton pumping complex of the respiratory chain.
Alternative oxidase provides a bypass of complexes III and IV of the electron transport chain, but it does not utilize the proton pumping mechanism of these complexes. Hence, the statement is FALSE.
By evaluation, the TRUE statements are P and R. Therefore, the correct answer is the option: P, R.
Important Questions from Metabolism Glycolysis Nucleotide
- The oxidative phase of the hexose monophosphate pathway generates ________ moles of NADPH per mole of glucose 6-phosphate (answer in integer).
- Which one of the following enzymes is NOT inhibited by glucose-6-phosphate?
- Assume that in the oxidative branch of the pentose phosphate pathway, each glucose-6-phosphate molecule generates the following products: 2 molecules of NADPH, 1 molecule of $\text{CO}_2$ and 1 molecule of ribulose-5-phosphate.
If 30 molecules of glucose-6-phosphate enter this pathway, and you randomly draw one molecule from the products of the pathway, the probability that this molecule is NADPH is __________ (round off to one decimal place). - Match the hormones in Group I with their metabolic precursor in Group II
Group I Group II P. 17-$\beta$ estradiol 1. Arachidonic acid Q. Thromboxane A2 2. Tyrosine R. Epinephrine 3. $\beta$-carotene S. Retinoic acid 4. Cholesterol - Phosphoglucose isomerase was incubated with 0.2 M of glucose 6-phosphate. On reaching equilibrium, 55% of glucose 6-phosphate was converted to fructose 6-phosphate. The equilibrium constant for this reaction is ________.
