Question

Redraw the flow-chart with corrections. Explain in brief the process of obtaining energy through oxidation of carbohydrates, lipids & proteins.

How energy is formed from oxidation of carbohydrates, fats and proteins? Correct the diagram given below.

Answer 1

Corrected flow-chart:

Process of obtaining the energy:

1. Carbohydrates: Carbohydrates such as glucose are broken down into pyruvic acid through glycolysis. Pyruvic acid is then converted into acetyl-Coenzyme A (Acetyl-CoA), which enters the Krebs cycle and is oxidised. The NADH₂ and FADH₂ produced during this process are oxidised in the electron transport chain, releasing energy as ATP.
2. Proteins: Proteins are digested into amino acids. These amino acids are converted into intermediates that enter the Krebs cycle, often through acetyl-CoA. During the Krebs cycle, NADH₂ and FADH₂ are formed, which are oxidised in the electron transport chain to produce ATP.
3. Lipids: Lipids are broken down into fatty acids and glycerol. Fatty acids are converted into acetyl-CoA, which enters the Krebs cycle and is oxidised. The NADH₂ and FADH₂ produced are then oxidised through the electron transport chain, resulting in the release of energy as ATP.

Answer 2

1. Dietary carbohydrates are digested by enzymes and transformed into glucose. Proteins and lipids are metabolised into amino acids and glycerol, respectively.
2. Carbohydrates are oxidised during cellular respiration. Aerobic respiration involves three processes for glucose oxidation: glycolysis, the tricarboxylic acid cycle (Krebs cycle), and the electron transfer chain.
3. During glycolysis, one molecule of glucose yields two molecules of pyruvic acid, ATP, NADH₂, and water. The process converts pyruvic acid into Acetyl-Coenzyme-A, releasing two molecules of NADH₂ and CO₂.
4. In the TCA cycle, molecules of Acetyl-CoA enter mitochondria and undergo a series of cyclic events. The acetyl portion of Acetyl-CoA is totally oxidised throughout this cyclical phase. This reaction releases chemicals such as CO₂, H₂O, NADH₂, and FADH₂.
5. In the third step of the ETC reaction, NADH₂ and FADH₂ from the first two steps are used to produce ATP molecules. Each NADH₂ molecule yields 3 ATP molecules, while FADH₂ yields 2 ATP molecules.
6. When one molecule of glucose is completely oxidised in the presence of oxygen, it produces 38 molecules of ATP, which is how carbohydrates are converted into energy.
7. Insufficient carbohydrates in the diet might lead to the use of protein or lipids for energy. Acetyl-CoA is produced by the conversion of fatty acids from lipids and amino acids from proteins. Acetyl-CoA can be oxidised through the TCA cycle to produce energy.