Question

RESPIRATION: What is the purpose of respiration? How does oxic respiration work? What are the inputs, products, and energy required or gained? How does it differ from fermentation?

Answer 1

Respiration is a chemical process where energy is produced by oxidation of glucose and carbon dioxide and water are formed as by-products. Oxygen and carbon dioxide are inhaled in and exhaled out from the lungs by the process of breathing.

Respiration can be summarised in the following equation:

C6H12O6 + 602 +6CO2 + 6H20 + ATP

Oxic respiration involves three steps:

step 1: Glycolysis

In glycolysis, glucose is converted to pyruvate by a series of enzymatic actions in the cytoplasm.

C6H12O6 + 2NAD+ + 4ADP + 4Pi +2ATP→ 2pyruvate + 4ATP + 2NADH + 2H+ + 2 ADP + 2Pi

Total energy produced= 2 ATP

step 2: Citric acid cycle

In citric acid cycle, pyruvate enters mitochondria where it is converted to acetyl Co~A and then this Acetyl Co~A enters citric acid cycle to yield 3 NADH, 1 FADH2  and 1 GTP

2Pyruvate → 2Acetyl Co~A

2Acetyl Co~A + 6NAD+ + 2FAD+ + 2ADP + 2Pi → 6NADH + 2 FADH2 + 2ATP + 4 CO2

Total energy produced = 2ATP

step 3: Oxidative phosphorylation

All the electrons from NADH and FADH2 enter the electron transport chain where they move from to finally reach complex V (known as ATP synthase), In complex V, movement from protons against concentration gradient drives ATP synthesis.

NADH and FADH2 are high energy electron carriers and they transfer electron to electron transport chain for production of energy. These electrons move from different proteins embedded in the inner mitochondrial membrane (complex I, II, III and IV). when an electron passes through these proteins, hydrogen ion is pumped out from the mitochondrial matrix to inner mitochondrial space to make a hydrogen ion gradient.

Hydrogen ion move along the concentration gradient to again enter the mitochondrial matrix via a protein called ATP synthase or complex V. For each ion moved across ATP synthase, 1 ATP is produced.

So, ETC generates 32 ATP

In total oxic respiration generates 36 ATP

Fermentation is a form of anaerobic respiration which occurs in the absence of oxygen.

In the absence of oxygen, glycolysis takes place and 2 ATP and 2 pyruvate are generated.

Then, pyruvate formed in glycolysis forms lactate in the absence of oxygen

2Pyruvate + 2NADH → 2Lactate + 2NAD+

Net energy production in the absence of oxygen is 2 ATP, which is produced by the process of glycolysis.

2NADH produced during glycolysis is utilized by pyruvate in the absence of oxygen to form lactate. Hence, fermentation does not produce ATP.