Question

The energy from compounds like glucose can be harvested to generate ATP in aerobic respiration. This is a complex process that involves many chemical conversions.

Describe the main processes that occur. Include all critical concepts in your answer, and where in the cell they occur. You do not need to describe the individual chemical reactions, but do describe the most important elements of each part of aerobic respiration.

Make sure it is clear from your description that you understand how the different processes interconnect, and how ATP eventually is generated. Your answer should be approximately 200 words. In the answer terms like glucose, pyruvate, cyclical behavior of the citrate cycle, NAD+, OXPHOS complexes, proton motive force etc. should be included/ discussed.

Essay answers are limited to about 500 words

Answer 1

Ans : Aerobic respiration is the process of generation ATP, the energy currency of the cell, by breaking down complex biomolecules like carbohydrates, lipids and amino acids.

Glucose is coverted to CO₂ with the release of free energy. A glucose molecule is  broken down into Pyruvate through the process of Glycolysis in the cytosol. Pyruvate is coverted to Acetyl CoA which enters the mitochondria, where it undergoes a cyclic process called the Citric Acid Cycle by which it is coverted to citrate and through a series of reactions and recycled by forming oxaloacetate. During both glycolysis and Citric acid cycle, the free energy released is retained in the reduced coenzymes NADH and FADH2, which undergo redox reactions in an Electron Transport Chain, transporting electrons from NADH and FADH2 to two molecules of Oxygen which combines with H+ to form water.

This process also pumps out Hydrogen ions from the mitochondrial matrix to the intermembrane space of mitochondrial membrane. This causes a higher cocentration of H+ in the intermembrane space than in the mitochondrial matrix, creating an electrochemical proton gradient across the inner mitochondrial membrane.

There is a proton motive force (pmf) genrated across the membrane. It can be defined as the electrochemical potential difference between protons in the aqueous phases on different sides of a membrane. Inorder to balance the resulting difference in pH on both sides of the membrane, the H+ ions flow back to the mitochondrial matrix, which dissipates some energy. This energy is utilized by ATP synthase, a transmembrane protein on the inner mitochondrial membrane to generate ATP molecules. This process is called Chemiosmosis.

Both Electron Transport Chain and Chemiosmosis is combinely called Oxydative Phosphorylation. It takes place via 5 complexes (Complex 1 - Complex 5) on the inner mitochondrial membrane and the ATP synthase enzyme. 4 ATP molecules are generated from the oxidation of one molecule of Glucose.