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The Production and Functions of ATP

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The Production and Functions of ATP The basic process in which ATP is used involves an organic molecule being phosphorylated by ATP, which produces an organic molecule with a phosphate group, and reduces ATP to ADP. This phosphorylated molecule becomes more reactive, thus lowering the activation energy needed for reactions, mainly used when enzymes are involved. This overview should demonstrate the importance of ATP- it allows living systems to convert stored chemical energy to kinetic or heat energy quite efficiently, resulting in the ability for homeostasis and skeletal movement among other things. There are two methods of ATP production, in plants it is a product of both respiration and the light dependent stage of photosynthesis whereas in animals it is a result of respiration. Adenosine triphosphate itself needs energy to be created. It constantly goes through the cycle of donating a phosphate group and being reduced to Adenosine diphosphate, and then being phosphorylated back to ATP. The energy for the formation of ATP in animals is derived from respiration in which theoretically thirty eight ATP molecules can be restored when the chemical bonds in a single mole of glucose are broken. Aerobic respiration commences with the process of glycolysis (literally: sugar splitting). This process takes place in the cytosol in the cytoplasm of the cell whereas the remaining processes occur in the mitochondrial matrices. Two ATP molecules each donate a phosphate group to a glucose molecule which lowers the activation energy for its break down into two pyruvate molecules. ...read more.


At the end of this process the electron is accepted by oxygen which combines with hydrogen atoms to form water. Overall, the reaction is: C6H12O6 + 6O2 --> 6CO2 + 6H2O This reaction occurs in both plants and animals. However, light independent reaction is another source of ATP production exclusive to photosynthetic organisms. It occurs in the thylakoid part of the chloroplast. This houses chlorophyll and it is here that the light dependant reaction takes place. The commencing process is called the photolysis of water. It is the complete breakdown of water using energy from sunlight: H2O --> 1/2O2 + 2H* + 2e� The two electrons gain a lot of energy from the sunlight and are transported to electron carriers. Here, ATP can be produced in much the same way as it is produced in the electron transport chain. A series of oxidation and reduction reactions derive energy and this energy is used to chemically bond inorganic phosphate groups with ADP molecules. At the end of the process the electron can be used to reduce NADP. This molecule is very similar to NAD used in respiration. The only exception is that NADP has a phosphate group (nicotinamide adenine dinucleotide phosphate). The reaction is: NADP* + 2e� + 2H* --> NADPH (reduced NADP) + H* This whole process uses a single molecule of water and produces two ATP molecules and one NADPH molecule. Oxygen is given off as a waste product. This completes the process of non-cyclic photophosphorylation and the NADPH and ATP go on to be used in the light independent stage of photosynthesis. ...read more.


This is important in order to maintain the correct diffusion gradients. Another use for ATP is in muscle contraction. Because mitochondria provide the site for aerobic respiration and ATP production, there are substantial numbers of them in muscle tissue. A single muscle fibre is constructed by rows of sarcomeres. These comprise of a band of myosin with bands of actin on either side. When muscle contraction occurs, the actin bands move in towards the centre of the myosin bands, thus making the 'H-band' smaller. With the majority of skeletal muscles, there is always a second antagonistic muscle. This counteracts its opposite muscle to return the limb to the original position. On each myosin molecule there is a head containing ADP and an inorganic phosphate group. This head can attach to an actin group, and upon bonding the tertiary structure of the myosin head changes, causing the rest of the myosin to move along to accommodate the change in structure. The reaction between the actin and myosin now causes the head to release the ADP and Pi which is taken up by a mitochondrion. In the processes outlined above, this is converted to ATP via respiration, and ATP is released back into the muscle tissue. This ATP is needed by the actin-myosin bridge to be released. ATP diffuses into the myosin head, and the donation of a phosphate group to the bond lowers the activation energy, allowing the head to be released. It resumes its original tertiary structure and is available to bridge with another myosin further down the fibre. This process occurs over and over again, making the overall contraction a ratchet motion. Gib Hemani ...read more.

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