Question

Which of the following statements regarding metabolic pathways is incorrect?
A) Many of the steps of glycolysis can run in reverse
B) Starch, sucrose or glycogen must be hydrolyzed before it can enter the glycolysis.
C) After fats are digested glycerol enters glycolysis by forming DHAP.
D) After fat digestion, fatty acids can no longer participate in cellular respiration

Answer 1

Hint: In eukaryotes metabolism occurs through a variety of pathways. The first mechanism involved is known as Glycolysis which occurs in the cytoplasm. Which is followed by oxidative phosphorylation in the mitochondria. Followed by Kreb’s cycle occurring in the mitochondrial matrix.

Complete answer:
The end products of fat digestion are fatty acids and glycerol. Glycerol enters into the respiratory pathway by changing into one of the intermediates of glycolysis. And fatty acids undergo a process called beta-oxidation to form acetyl coenzyme A and enter the Krebs cycle to take part in cellular respiration. Thus option D is incorrect.

Considering the other given options:
Out of the 10 steps in glycolysis seven are reversible in nature. The reversible steps are:
Step 2: Isomerization between Glucose-6-Phosphate and Fructose-6-Phosphate.
Step 4: Cleavage of Fructose-1,6,-bisphosphate to form G3P and DHAP.
Step 5: G3P to 1,3-bisphosphoglycerate.
Step 6: 1,3-bisphosphoglycerate to 3-phosphoglycerate
Step 7: 3-phosphoglycerate to 2-phosphoglycerate
Step 8: 2-phosphoglycerate to 2-phosphoenol pyruvate
Step 10: Pyruvate to lactate.
Thus statement A is correct.

Bigger polysaccharides such as starch, sucrose and glycogen must be hydrolyzed before it can enter the glycolysis pathway. Thus the statement is correct.

After fat digestion, the products formed are fatty acids and glycerol. Out of which glycerol enters glycolysis after being converted into DHAP. Thus it is a correct statement.

Thus the most appropriate answer is option D. That is, the incorrect statement is: After fat digestion, fatty acids can no longer participate in cellular respiration.

Note: The process of aerobic respiration occurs in the mitochondrial matrix and is known as Kreb’s cycle or the Citric acid cycle. For one molecule of glucose two cycles are required. The end products are ATP, water and carbon dioxide.