Respiration & Energy Transfer (Anaerobic Respiration) - NEET

RESPIRATION & ENERGY TRANSFER

Respiration & Energy Transfer (Anaerobic Respiration) : 

• Maintenance of life requires a continuous supply of energy.

• Respiration fulfills the continuous need for energy.

• Respiration is a catabolic process wherein complex organic substrate is oxidized to simple components to generate biological energy.

Cellular respiration occurs in two different ways like 1.) anaerobic and 2.) aerobic respiration.

A. ANAEROBIC RESPIRATION:

• It is cellular respiration that does not involve oxygen at all.

• It is also called "Fermentation".

• It is completed through steps like glycolysis and conversion of glycolytic product to any suitable product like lactic acid, ethanol, etc.

A.) GLYCOLYSIS:

• Occurs: Cytoplasm of a cell.

• It involves the breakdown of a glucose molecule into two pyruvic acid molecules.

• This is a common step in anaerobic as well as aerobic respiration.

• It is completed in two phases as preparatory phase and the pay-off phase.

• The overall process of glycolysis is completed in ten steps.

1.) Preparatory phase:

• The first five steps constitute the preparatory phase through which glucose is phosphorylated twice at the cost of two ATP molecules and a fructose 1,6-biphosphate is formed.

• This molecule is split to form: 1.) a molecule of glyceraldehyde 3-phosphate & 2.) a molecule of dihydroxyacetone phosphate.

• Both of these molecules are 3-carbon carbohydrates (trioses) and are isomers of each other.

• Dihydroxyacetone phosphate is isomerized to the second molecule of glyceraldehyde-3-phosphate.

• Thus, two molecules of glyceraldehyde-3-phosphate are formed, and here, the preparatory phase of glycolysis ends.

2.) Pay-off phase:

• Both the molecules of glyceraldehyde-3-phosphate are converted to two molecules of 1, 3-biphosphoglycerate by oxidation and phosphorylation.

• Phosphorylation is brought about with the help of inorganic phosphate (Pi) and not ATP.

• Both molecules of 1, 3-biphosphoglycerate are converted into two molecules of pyruvic acid through series of reactions accompanied by the release of energy.

• This released energy is used to produce ATP (4 molecules) by substrate-level phosphorylation.

• 2 ATP/glucose is the net outcome.

• Energy is also converted by the formation of 2-NADH molecules.

B.) Lactic Acid Fermentation (In Muscle):

• In muscles, the NADH+H ion produced during glycolysis is reoxidized to NAD+ by donating one proton and two electrons to pyruvic acid which yields lactic acid. 

 

• In this reaction pyruvate is converted into a 3-carbon molecule called lactic acid.

 

•  No production of carbon dioxide (CO2).

 

• The only benefit is serves is that it allows glycolysis to continue with the small gain of ATP generated. 

 

• Skeletal muscles usually derive their energy by anaerobic respiration. 

 

•  After vigorous exercise lactic acid accumulates, leading to muscle fatigue. 

 

• During rest, however, the lactic acid is reconvereted to pyruvic acid and is channeled back into the aerobic respiration pathway.

C.) Alcoholic Fermentation (In Yeast):

• In yeast, the pyruvate is decarboxylated to acetaldehyde.

 

• The acetaldehyde is then reduced by NADH+H ion to ethanol.

 

• Carbon dioxide (CO2) is also produced in this process.

 

• Accumulation of ethanol by fermentation in a culture of yeast may stop further multiplication and lead to the death of cells.

 

• In the presence of oxygen (O2) however, yeast can respire aerobically.

 

• Examples of food produced are alcoholic drinks, bread, cakes, etc.