Detailed Synopsis of Cellular Respiration and Photosynthesis

Cellular respiration is the process whereby living cells gain energy through the oxidation of organic substances, which maybe, carbohydrates, proteins or fats. The preferred source of nutrient for most cells in the body is glucose. (Russell, 2004)

The first step in cellular respiration is glycolysis. The end product in this stage of respiration for cells with mitochondria and an adequate supply of oxygen is Pyruvate. This is a series of ten reactions that yields two NADH and two ATP molecules. Oxygen is required here to re-oxidize the NADH formed during the oxidation of glyceraldehyde 3- phosphate. This is called aerobic respiration. Alternatively, in cells with decreased or absent oxygen molecules, glucose is converted to pyruvate, which is reduced to form NADH to form lactate. This is called anaerobic glycolysis since there is no net formation of NADH. Anaerobic respiration occurs in oxygen deprived cells and in red blood cells because they lack mitochondria. (Russell, 2004)

In the next step, pyruvate is converted to acetyl CoA which enters the citric acid cycle. This cycle is regulated through ADP levels. A net of 12 ATPs, 6 NADH and 2 FADH are produced in this cycle. (Russell, 2004)

The electron transport system is the final stage of cellular respiration. This step involves a series of reactions that occur along the mitochondrial cisterns. Electrons are released from NADH and FADH molecules, which produce energy upon release. This energy is used to actively transport hydrogen ions against their concentration gradient into the outer mitochondrial compartment. The hydrogen ions flow back through hydrogen channels in a process through which ATP is synthesized. The remaining ATP molecules are synthesized in this stage, yielding a net production of 38 ATP per glucose molecules. (Russell, 2004)

The overall reaction is represented in the formula:

C6H12O6 + 6O2 -> 6CO2 + 6H2O + ~38 ATP (Russell, 2004)

PHOTOSYNTHESIS:

Green plants and certain other organisms use sunlight to synthesize carbohydrates from carbon dioxide and water releasing oxygen. This process is known as photosynthesis. This process occurs inside organelles called chloroplasts. Inside the chloroplast is a membrane, called the thylakoid membrane. This consists of proteins required to convert light energy into chemical energy. Pigments, such as chlorophyll and beta carotene are organized in clusters in the thylakoid membrane. These pigments absorb light at different intensities and pass it on to a central chlorophyll molecule. This energy is trapped by this molecule in the form of ATP and is used to produce carbohydrate. (Farabee, 2010)