Respiration can be of two types:

1. When there is no oxygen present (Anaerobic)
2. When there is the presence of oxygen (Aerobic)

In Anaerobic respiration, the final electron acceptor isn’t O₂ whereas in aerobic respiration the final electron acceptor is O₂ that gets converted to a water molecule.

Fermentation is a good example of anaerobic respiration.

C₆H₁₂O₆        Fermentation         2C₂H₃OH + CO₂ + Energy

 

What is cellular respiration?

Cellular respiration is a complex metabolic pathway in which the glucose is broke down and get converted into an energy molecule (ATP).Cellular respiration is the process by which we can understand how a carbohydrate molecule is converted into an energy molecule in the form of ATP (Adenosine triphosphate) inside our body.

In cellular respiration, the glucose molecule is converted into CO₂ and H₂O with the production of ATP molecules.

A-P~P~P (ATP) = A-P~P (ADP) + Pi +7300 calories

Oxidation of carbohydrates

Carbohydrates enter in cells in the form of monosaccharides (Glucose or glycogen). Then these monosaccharides get converted into pyruvic acid which is a 3 Carbon compound by a different reaction and by the help of various enzymes. The process of conversion, of monosaccharides into pyruvic acid is known as Glycolysis (Embden-Meyerhof pathway). Glycolysis takes place in the cytoplasm of the cell. The product of Glycolysis then enters in the mitochondria for its oxidation known as metabolic pathways:

• Glycolysis (Embden-Meyerhof pathway)
• Oxidative Decarboxylation
• Krebs cycle, TCA (tricarboxylic acid cycle)
• Oxidative phosphorylation

Glycolysis:

Conversion of glucose into pyruvic acid in by the help of various enzymes, and it didn’t require oxygen.

Steps:

• Activation: in initial reactions (1-3) the molecule of glucose, converted to fructose 1-6-diphosphate and this requires 2 molecules of ATP.
• Cleavage: in intermediate reactions (4,5) fructose 1-6-diphosphate splits into two end products.
• Oxidation: in reactions 6-10 two molecules of glyceraldehyde 3-phosphate are oxidized and eventually converted to pyruvic acid.

In the case of anaerobic respiration, the product of glycolysis is converted to ethanol. The reaction for anaerobic respiration is:

C₆H₁₂O₆        >        CH₃CO.COOH                  >                 CH₃CHO        >            CH₃CH₂OH

Glucose                       pyruvic acid                                       acetaldehyde                       ethyl alcohol

The product of glycolysis which is pyruvic acid contains a large amount of energy, it needs further degradation, and this is done in three consecutive steps:

Oxidative Decarboxylation, Krebs cycle, and oxidative phosphorylation

Oxidative Decarboxylation

After the glycolysis pyruvic acid directly enters the mitochondrial matrix and gets converted to acetyl-CoA.

Steps:

Krebs cycle

Two molecules of acetyl CoA from oxidation passes through a series of the reaction of the Krebs cycle which is also known as TCA (tricarboxylic acid cycle)

Steps:

 

Oxidative phosphorylation

Two molecules of FADH₂ and six molecules of NADH produced from the Krebs cycle are oxidized by O₂ in ETS (electron transport system)

Compound occur in ETS

• Pyridine linkage dehydrogenase: Requires as their coenzyme either NAD⁺ or NADP⁺ both can accept two electrons at a time.
• Flavin-linked dehydrogenase (flavoproteins) as FAD or FMN

• Ubiquinone’s (coenzymes)

• Cytochromes are the proteins containing iron-porphyrin groups.
• Iron-sulfur proteins FeS are electron carriers of mitochondria.

 

Three complexes of the ETS

• The NADH-dehydrogenase complex largest of all the complexes, with about 800,000 Daltons mass and more than 22 polypeptide chains.
• The b-c1 complex contains 8 different polypeptide chains and it is a dimer of about 500,000 Daltons.

• The cytochrome oxidase complex comprises of eight different polypeptide chains and isolated as a dimer of 300,000 Daltons approx.

 

F₀F₁ complex

It is the one of most important and main proteins in the inner mitochondrial membrane.

It helps in ATP synthesis and known as a proton pump.

F₀ complex is an integral membrane complex composed of hydrophobic proteins

F₁ complex attached to he F₀ complex F1 particles a complex of five distinct polypeptides alpha(α), beta (β), gamma (γ), delta(𝛿), epsilon (€).