Bioenergetics: Respiration

Bioenergetics: Understanding Respiration

Respiration refers to a series of chemical reactions that occur in living cells, resulting in the breakdown of nutrient molecules and the production of energy.

Aerobic respiration involves the breakdown of glucose in the presence of oxygen to produce carbon dioxide, water, and a large amount of energy. This energy is stored in a molecule called adenosine triphosphate (ATP).
The equation for aerobic respiration is: glucose + oxygen -> carbon dioxide + water + energy.
Aerobic respiration occurs in four steps: glycolysis, link reaction, Krebs cycle, and oxidative phosphorylation.
Glycolysis is the first stage of aerobic respiration, occurring in the cell cytoplasm. In this process, glucose is split into two molecules of pyruvate, releasing two molecules of ATP.
The link reaction occurs in the mitochondria where each pyruvate is decarboxylated to produce acetyl coenzyme A, carbon dioxide, and one molecule of NADH.
The Krebs cycle is another step in the mitochondria where acetyl CoA is combined with a four-carbon molecule to go through a series of reactions, producing ATP, NADH, FADH2 and carbon dioxide.
Lastly, oxidative phosphorylation involves the transfer of electrons through a series of proteins in the inner mitochondrial membrane, known as electron transport chain, resulting in the formation of a large amount of ATP.

Anaerobic Respiration

Anaerobic respiration takes place when there is insufficient oxygen for aerobic respiration, such as during high-intensity exercise.
Glucose is metabolised to lactic acid, which causes muscle fatigue.
The equation for anaerobic respiration is: glucose -> lactic acid + energy.
Anaerobic respiration produces significantly less ATP compared to aerobic respiration.

Alcoholic Fermentation

Some organisms, like yeast, can carry out alcoholic fermentation, a type of anaerobic respiration.
In this process, glucose is converted to ethanol, carbon dioxide, and a tiny amount of energy.
The equation for alcoholic fermentation is: glucose -> ethanol + carbon dioxide + energy.

Practical Applications of Respiration

Both types of respiration – aerobically and anaerobically – have importance in everyday life. For instance, the yeast used in bread-making causes the dough to rise due to the CO2 produced during the process of respiration.
In the body, respiration (especially aerobic respiration) is vital for providing energy for an array of functions like muscle contraction, maintaining body temperature and various other physiological processes.