Adenosine Triphosphate

All living organisms need energy for many activities within a cell. This could be protein synthesis or active transport. But this energy needs to be released in manageable quantities rather than large amounts that could possible destroy the cell. To do this, the cell breaks down glucose into manageable intermediates releasing energy at the same time. As a result ATP is formed from the released energy. Also known as Adenosine Triphosphate.

Adenosine Triphosphate is made up of three phosphates to produce a phosphate group, a ribose sugar and an adenine base.

ATP allows the controlled release of energy, which is not possible with glucose. The release of energy from glucose would increase the temperature to a high enough temperature to destroy cells. Therefore intermediates are produced, releasing energy in small steps by phosphorylating ADP. This adds phosphates onto ADP to produce ATP (the addition of phosphates to ADP is referred to phosphorylation). This can be referred to an endergonic reaction as energy is used to produce the ATP molecule. When ATP is broken down by hydrolysis, it is known as an exergonic reaction as it releases its energy stored between the phosphate bonds. Each phosphate bond broken yields approximately 30KJMol^-1 of energy.

There are two types of processes that produce ATP within a cell. These are: + Oxidative Phosphorylation – This occurs on the membranes of the mitochondria under aerobic conditions. + Photophosphorylation – This occurs within plants on the membranes of the chloroplasts during photosynthesis (this is a later topic which I will also be writing about)


ATP is a wonderful molecule in biological systems and has many advantages to that of glucose. + One advantage is that ATP only needs one enzyme to release the energy while glucose requires many. +Secondly, ATP has the ability to release energy in small quantities making energy release more controlled where it is needed, whereas glucose contains large amounts of energy and may not be needed immediately. +Lastly, ATP is a common source of energy for many different chemical reactions increasing the efficiency and control of the cell. It is common to be called the “Universal Energy Currency” due to all living organisms using ATP for energy.

Chemiosmotic Theory

The chemiosmotic theory is a model to show how ATP is synthesised down the electron transport chain with the use of carriers, hydrogen ions and electrons. The theory proposes that the energy required originates from the electrochemical gradient across the mitochondrial membrane.

Within mammals, there is a mechanism within the inner membrane that transports hydrogen ions from the matrix of the mitochondrion to the inter-membrane space of the mitochondrion. Hydrogen ions are pumped by active transport. This process produces an electrochemical gradient of protons within the inner mitochondrial membrane.

The same process also occurs in plants with the exception of chloroplasts rather than that of mitochondria. Protons are built up inside the chloroplast membrane where protons build up outside the membrane of the mitochondrion.


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