summarize energy production in cells

Energy production in cells

Cells perform numerous functions and all of these require energy. Energy is produced through different ways depending on the type of cell; whether eukaryotic or prokaryotic. Prokaryotic cells produce energy using light through a process known as photosynthesis while eukaryotic cells produce in the form of ATP in the mitochondria through a process known as respiration (Lynch & Marinov, 2017).

The energy production in eukaryotic cells begins in the cytosol whereby complex molecules are metabolized to smaller molecules which are then absorbed in the mitochondria whereby reactions to produce energy take place.  In eukaryotic cells, energy is produced through three steps: glycolysis, citric acid cycle and the electron transport chain. 

Glycolysis is also known as the Embden-Myerhof Pathway and takes place in the cytoplasm and oxygen is not required. Here, ten steps take place whereby 1 molecule of glucose is metabolized 2 pyruvate molecules and 2 molecules of ATP. This process occurs through two stages:

  • Stage 1- Preparatory stage whereby a 6 carbon molecule of glucose is metabolized into 2 3 carbon molecules and 2 ATP molecules are used.
  • Stage 2 – This is the energy conservation stage and occurs when the 2 3 carbon molecules are converted to 2 pyruvic acid molecules in a process involving oxidation. During this stage, 2 NAD+ molecules are reduced to 2 NADH and the oxidation process yields 4 ATP molecules. 

In summary, glycolysis occurs as follows:

1 glucose + 2 NAD + 2P + 2ADP             2 pyruvic acid + 2 NADH + 2 ATP + 2 H

          Before the 2 pyruvic acid molecules are taken to the citric acid cycles, they are broken down to 2 acetyl CoA and 2 carbon dioxide molecules in a process known as decarboxylation and takes place in the mitochondria. Decarboxylation can be summarized as:

2 pyruvic acid + 2 CoA + 2 NAD             2 Acetyl CoA + 2 NADH + 2 CO2

    The citric acid cycle or the Kreb’s cycle and decarboxylation, are both aerobic. This process involves 8 reactions involving enzymes and oxaloacetic acid that is a 4 carbon molecule. The 4 carbon molecule attaches to acetyl CoA to form citric acid, which has 6 carbons and it is the same citric acid molecule that is decarboxylated back to oxaloacetic acid. This process reduces three NAD molecules to three NADH molecules and FAD to FADH2. The process can be summarized as follows:

2 Acetyl CoA + 6 NAD + 2 FAD + 2 ADP + H20 + 2P 2CoA + 6 NADH + 2FADH2 + 2 ATP + 4 CO2 + 4H+

              The electron transport chain also occurs in the mitochondria, in the cristae and ATP is generated from the glucose molecule. The coenzymes generated from glycolysis, decarboxylation and the citric acid cycle are oxidized to form NAD, FAD and ATP.

The energy production process in eukaryotic cells can be summarized as 

C6H12O6 + 6 O2 + 36 ADP + 36 P → 6 CO2+ 6 H2O + 36 ATP

        In prokaryotes, energy production occurs through photosynthesis and the ATP syntheses as well as the electron transport chain are found in the cell membrane. Here, pyruvate is also broken down to carbon dioxide and ATP but prokaryotes heavily rely on glycolysis for the production of energy. The reaction can be summarized as:

1 glucose + 2 NAD + 2P + 2ADP             2 pyruvic acid + 2 NADH + 2 ATP + 2 H

 

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