Aerobic Respiration

Respiration is the metabolic process through which food molecules of glucose are converted into ATP, which is then used by the cell. Photosynthesis, in which plants employ sunlight and carbon dioxide to produce food molecules while releasing oxygen as a waste product, is the antithesis of respiration.

During aerobic respiration, oxygen is present, which aids the process inefficiently in producing energy. Anaerobic respiration is a type of metabolism in which oxygen is not present and a less effective way of metabolism is used. Aerobic respiration occurs in the cytoplasm or gooey inner cell space, and mitochondria of all eukaryotic cells, while photosynthesis occurs in the chloroplasts of plant and algae cells.

Aerobic Respiration

Aerobic respiration is the conversion of nutrients to the water, carbon dioxide, and energy via an electron transport system in which the molecular oxygen serves as the final electron acceptor. To give energy from glucose, most of the eukaryotes and prokaryotes use aerobic respiration. The overall reaction is:

C6H12O6+6O2→6CO2+6H2O

It’s important to note that glucose (C6H12O6) is oxidised to produce CO2 and oxygen (O2) is reduced to make water (H2O). This is a high-powered reaction that “releases” energy in the form of ATP molecules. Aerobes and facultative anaerobes both produce ATP in this way. Obligate aerobes require molecular oxygen since they can only make ATP through aerobic respiration. In contrast, facultative anaerobes are capable of aerobic respiration but can switch to fermentation, an anaerobic ATP-producing process, if oxygen is unavailable.

Aerobic respiration includes four stages:

• glycolysis,
• Oxidative decarboxylation of Pyruvate
• Citric Acid Cycle
• Oxidative Phosphorylation

Glycolysis

Glycolysis is the initial stage of aerobic respiration, and it takes place in the cell’s cytoplasm. One six-carbon sugar molecule is divided into two three-carbon pyruvate molecules in this process. Two ATP molecules are produced as a result of this action.

The overall equation is as follows:

C6H12O6 + 2 ADP + 2 PI + 2 NAD+ → 2 Pyruvate + 2 ATP + 2 NADH + 2 H+ + 2 H2O

The cofactor NAD+ is reduced to NADH in this mechanism. This is significant because NADH will power the creation of significantly more ATP through the mitochondria’s electron transport chain later in the cellular respiration process.

Using the oxidative decarboxylation mechanism, pyruvate is converted into fuel for the citric acid cycle in the next step.

Oxidative decarboxylation of pyruvate

2 (Pyruvate– + Coenzyme A + NAD+ → Acetyl CoA + CO2 + NADH)

The link between glycolysis and the citric acid cycle is oxidative decarboxylation, often known as the link reaction of the transition reaction. The Pyruvate is transported into the mitochondrial matrix by the pyruvate translocase, the protein. Pyruvate is coupled with Coenzyme A to produce acetyl-CoA and release a carbon dioxide molecule.

This transition reaction is significant because acetyl-CoA is an excellent fuel for the citric acid cycle, which can then power the oxidative phosphorylation process in the mitochondria, which generates a significant quantity of ATP.

This process also produces more NADH. This means there will be more fuel available to make additional ATP later in the cellular respiration process.

Citric Acid Cycle

The citric acid cycle, also known as the tricarboxylic acid cycle or the Krebs cycle, is a set of redox processes that starts with Acetyl CoA. These processes take place in the matrix of eukaryotic cells’ mitochondria. It occurs in the cytoplasm of prokaryotic cells.

2 (ACETYL COA + 3 NAD+ + FAD + ADP + PI → CO2 + 3 NADH + FADH2 + ATP + H+ + COENZYME A)

Because there are two pyruvates and hence two molecules of Acetyl CoA created to join the citric acid cycle for each molecule of glucose, the reaction occurs twice.

NADH and FADH2, another electron carrier for the electron transport chain, are both produced. All of the NADH and FADH2 produced in the previous phases are now used in the oxidative phosphorylation process.

In summary, two carbons enter the reaction in the form of Acetyl CoA for each round of the cycle. Two carbon dioxide molecules are produced as a result of this process. Three molecules of NADH and one molecule of FADH are produced by the processes. A single molecule of ATP is created.

Oxidative phosphorylation

The major energy-producing stage of aerobic respiration is oxidative phosphorylation. It generates massive amounts of ATP by folding the membranes within the cell’s mitochondria.

34 (ADP + PI+ NADH + 1/2 O2 + 2H+ → ATP + NAD+ + 2 H2O)

NADH and FADH2 transfer electrons to the electron transport chain in the mitochondrial membrane during this process, which they get from glucose during the preceding steps of cellular respiration.

Complex I, Q, complex III, cytochrome C, and complex IV are among the protein complexes embedded in the mitochondrial membrane that make up the electron transport chain.

All of this works together to pass electrons from higher to lower energy levels while harvesting the energy generated. This energy is used to fuel proton pumps, which in turn fuel the production of ATP. The proton pumps of the mitochondrial membrane, like the sodium-potassium pumps of the cell membrane, generate a concentration gradient that can be used to power other activities.

The protons that are carried across the membrane utilise the energy extracted from NADH and FADH2 “want” to move through channel proteins from their high to low concentration areas. Channel proteins in question are ATP synthesis, which is the ATP-producing enzyme. Protons cause the production of ATP when they pass through ATP synthase. Mitochondria are known as the “powerhouses of the cell” because of this process. The electron transport system in the mitochondria produces roughly 90% of the ATP produced by the cell by breaking down food.

This is also the stage that necessitates the use of oxygen. The electrons would back up if oxygen molecules were not present to take the depleted electrons at the end of the electron transport chain, and the process of ATP synthesis would be halted.

This is also the stage that necessitates the use of oxygen. The electrons would back up if oxygen molecules were not present to take the depleted electrons at the end of the electron transport chain, and the process of ATP synthesis would be halted.