Cellular Respiration

Cellular Respiration

The action of oxidation of organic materials occurring in all living cells is called internal or cellular respiration. It gets carbon dioxide, water, and energy.

C6H12O6 + 6O2 = 6CO2 + 6H2O + 673 Kilocalorie energy

Cellular respiration is a long process, so to understand it easily it is divided into the following three steps –

1: Glycolysis, 2: Krebs Cycle, and 3: The Electron Transport System

1: Glycolysis or Embden Meyerhof Parnas pathway- EMP pathway

GlycolysisIt was discovered by Gustav Embden, Otto Meyerhof, and Jakub Karol Parnas. So it is called the EMP pathway too. This process occurs in the cytoplasm and does not require oxygen. Therefore, it is equally present in both oxy and anoxic respiration. It consists of a series of coordinated reactions that result in the formation of two molecules of Pyruvic acid from one molecule of glucose. A total of 4 ATP molecule is formed in it and the energy of two ATP molecule is used in various chemical reactions. Additionally, two independent hydrogen ions are also obtained which react with NAD or NADP to form NADH2 or NADHP2 respectively. These later form 6 ATP molecules. Thus a total of 8 ATP molecules benefit from glycolysis. This entire process can be better understood by the following diagram-

2: Krebs Cycle

cellular respirationIt was discovered by Hans Adolf Kreb, this action is called Krebs cycle after him. This action of cellular respiration occurs in the matrix of mitochondria. In this, Pyruvic acid derived from glycolysis is converted into Acetyl CoA before entering the Krebs cycle, which gives the advantage of 6 ATP molecules. 24 ATP molecules have the advantage. It is a complex process that can be easily understood by the following diagram-

3: Electron Transport System (ETS)Electron transportation system

This system is the most important part of internal respiration and is formed by various electron receptor protein molecules (NAD, NADP, and FAD) in Cristie of mitochondria. When electrons pass through these molecules, the energy is released, which the ADP molecules accept and transform themselves into ATP molecules. H+ generated in the glycolysis and Krebs cycle generates molecules of NADH2 and FADH2 by down-regulating NAD and FAD, respectively. These molecules oxidize on entering the electron transport system and convert ADP to ATP. Three ATP from each NADH2 and 2 ATP molecules from FADH2 are formed.
Thus one molecule of glucose under cellular respiration yields a total of 38 ATP (8 ATP from Glycolysis + 6 ATP from Acetyl CoA + 24 ATP from Krebs Cycle).

        Steps     Reduced Coenzymes         ATP Through ETS         Direct ATP                   Total ATP
Glycolysis 2 NADH2 2 NADH2 × 3 6 ATP    2 ATP 8 ATP
Acetylation 2 NADH2 2 NADH2 × 3  6 ATP       6 ATP
Krebs cycle 6 NADH2 6 NADH2 × 3  18 ATP    2 ATP 24 ATP
         − 2 FADH2 2 FADH2 × 2 4 ATP
         −         C6H12O6 + 6O2  =  6CO2 + 6H2O + 38ATP                                     Total 38 ATP                                  

ATP (Adenosine Tri Phosphate)

The chemical energy released from the oxidation of food substances is stored in ATP, which is used for all biological and muscular activities in the body. ATP is converted to ADP after releasing energy. The ADP recaptures and converts into ATP. That is why ATP is called the energy coin of the metabolic world. In this process, ATP is obtained by contracting the energy in molecules of ADP as specific energy bonds. Three phosphate molecules are present in the ATP molecule, with one phosphate radical leaving ADP and two phosphate radicals forming either AMP or Adenosine Mono Phosphate. A total of 12 kcal of energy is required to produce ATP from one molecule ADP. This implies that a total of 456 kcal of energy is contracted in 38 ATP molecules, the remaining energy (because after full oxidation of a glucose molecule released 673 K.Cl energy) is released as heat. . ATP is also called the energy coin or energy currency of the cell.

Respiratory Quotient (RQ)

In respiration, the volume of carbon d-oxide that exits and the amount of oxygen absorbed is called respiratory quotient (RQ). It varies for different substances. It is 1.00 for carbohydrates, 0.8- 0.9 for proteins, and 0.7 for fats.

Full form of biomolecules

FAD = Flavin Adenine Dinucleotide
NADP = Nicotinamide Adenine Dinucleotide Phosphate
NAD = Nicotinamide Adenine Dinucleotide
ATP = Adenosine Tri Phosphate
ADP = Adenosine Di Phosphate
AMP = Adenosine Mono Phosphate

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