Krebs Cycle (Citric Acid Cycle)

The Acetyl form at the end of Link reaction is picked up by the COA (Co enzyme A) present in the matrix to form acetyl COA, then the acetyl combine with Oxaloacetate of 4C acid to form a 6C compound citrate, the COA leaves and it can pick another acetyl to bring into the Krebs Cycle, The citrate undergoes decarboxylation and dehydrogenation to yield carbon dioxide NAD molecule, 5C compounds formed during a series of reaction, An important intermediate Alpha Ketoglutrate is also formed into the Krebs Cycle which is a 5C compound. After this stage the dehydrogenation reaction occur trice resulting in two reduced NAD and 1 reduced FAD. 1 molecule of ATP is also produced during the rearrangement of the substrate.

This ATP formation like that of formed during glycolysis is termed as substrate level Phosphorylation. Decarboxylation results at this state in the complete breakdown of acetyl and the 4C compound Oxaloacetate regenerated to again start a fresh Krebs Cycle.

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Uses of ATP

• In muscles contraction, for example ATP is needed to release the filaments of a sarcomere so it can shorten.
• ATP transports chemical energy within cells for metabolism.
• It is used in cell division.
• ATP is used in synthesis of macromolecules such as DNA, RNA and proteins.
• It is used as an energy source in the process of photosynthesis and cellular respiration.
• Several living beings emit light that is known as bioluminescence and ATP comes into the picture by supplying the requisite energy which is converted into light. Such ability is found in several marine animals, terrestrial animals and some types of bacteria.
• Nerve Impulses and cell signaling is another area in which ATP plays an important role.
• The transportation of ions and molecules across the membranes of the cell requires energy if the transport is from a region of lower concentration to a higher concentration (active transportation). The reverse process though takes place without the use of such energy and is known as diffusion or passive transport.
• Anabolic reactions such as synthesis of fats, polysaccharides etc require energy for their completion.
• The release of the phosphate on ATP making it ADP releases an amount of energy that can do work where ever it is needed. It may help catalyze a reaction, move molecule, or create other molecules.
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