Glycolysis, the Krebs cycle, and oxidative phosphorylation.
Each of these occurs in a specific region of the cell.
1. Glycolysis occurs in the cytosol.
The 6-carbon sugar, glucose (c6H12O6), is broken down into two molecules of a 3-carbon molecule(c3H14O3) called pyruvate . This change is accompanied by a net gain of 2 ATP molecules and 2 NADH molecules.
2. The Krebs cycle takes place in the matrix of the mitochondria.
Pyruvate is transported into the mitochondria and loses carbon dioxide to form acetyl-CoA (Acetyl coenzyme), a 2-carbon molecule. When acetyl-CoA is oxidized to carbon dioxide in the Krebs cycle, chemical energy is released and captured in the form of NADH, FADH2, and ATP.
3. Oxidative phosphorylation via the electon transport chain is carried out on the inner mitochondrial membrane.
The electron transport chain allows the release of the large amount of chemical energy stored in reduced NAD+ (NADH) and reduced FAD (FADH2). The energy released is captured in the form of ATP (3 ATP per NADH and 2 ATP per FADH2).
Note: In the absence of oxygen, respiration consists of two metabolic pathways: glycolysis and fermentation. Both of these occur in the cytosol.
Fermentation complements glycolysis and makes it possible for ATP to be continually produced in the absence of oxygen. By oxidizing the NADH produced in glycolysis, fermentation regenerates NAD+, which can take part in glycolysis once again to produce more ATP.
Each molecule of glucose can generate 36-38 molecules of ATP in aerobic respiration but only 2 ATP molecules in respiration without oxygen (through glycolysis and fermentation).
You have remembered that in cell, Cytosol is the fluid portion of a cell's cytoplasm, which lies outside the organelles and other insoluble components of the cytoplasm
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