Energy Rich Compounds, ATP, cAMP
Energy Rich Compounds
CONTENT
– Energy rich compounds
– ATP
– cAMP and its biological significance
Objective
• At the end of this lecture, student will be able to
– Explain energy rich compounds
– Describe ATP
– Explain cAMP and its biological significance
Energy rich compounds
Certain compounds are encountered in the biological system which, on hydrolysis, yield energy. The term high-energy compounds or energy rich compounds is usually applied to substances which possess sufficient free energy to liberate at least 7 Cal/mol at pH 7.0 Certain other compounds which liberate less than 7.O Cal/mol at pH 7.0 referred to as low energy compounds
Classification of high energy compounds
There are at least 5 groups of high-energy compounds
1. Pyrophosphates e.g. ATP
2. Acyl phosphates e.g.1,3-bisphospho glycerate
3. Enol phosphates e.g. phosphoenol pyruvate
4. Thioesters e.g. acetyl CoA
5. Phosphagens e.g. phosphocreatine
6. Others: cAMP, cGMP
There are at least 5 groups of high-energy compounds
High-energy bonds: The high energy compounds possess acid anhydride bonds, which are formed by the condensation of two acidic groups or related compounds
• These bonds are referred to as high energy bonds, since the free energy is Iiberated, when these bonds are hydrolysed
• Ordinary ester bond of phosphate releases about 3000 calories on hydrolysis & energy rich phosphate bonds release between 7000 to 13000 calories
ATP
• Adenosine triphosphates a unique and the most important high energy molecule in the living cells
• lt consists of adenine, a ribose and triphosphate moiety
• ATP is a high energy compound due to the presence of two phosphoanhydride bonds in the triphosphate unit
• ATP serves as the energy currency of the cell as is evident from the ATP-ADP cycle
• The hydrolysis of ATP is associated with the release of large amount of energy
ATP + H2O → ADP + Pi + -7.3 Cal
• The energy liberated is utilized for various processes like muscle contraction, active transport etc.
• ATP can also act as a donor of high energy phosphate to low energy compounds to make them energy rich
• On the other hand, ADP can accept high energy phosphate from the compounds possessing higher free energy content to form ATP
• ATP serves as an immediately available energy currency of the cell which is constantly being utilized and regenerated
• This is represented by ATP-ADP cycle, the fundamental basis of energy exchange reactions in living system. The turnover of ATP is very high
• ATP acts as an energy link between the catabolism (degradation of molecules) and anabolism( synthesis) in the biological system
Synthesis of ATP
• Synthesized in two ways
1. Oxidative phosphorylation:
• This is the major source of ATP in aerobic organisms, linked with the mitochondrial electron transport chain
2. Substrate level phosphorylation:
• ATP may be directly synthesized during substrate oxidation in the metabolism. The high-energy compounds such as phosphoenolpyruvate and 1,3-bisphosphoglycerate and succinyl CoA can transfer high energy phosphate to ultimately produce ATP
cAMP
• Cyclic adenosine monophosphate (cAMP, cyclic AMP, or 3',5'-cyclic adenosine monophosphate) is a second messenger important in many biological processes
• cAMP is a derivative of adenosine triphosphate (ATP) and used for intracellular signal transduction in many different organisms
Summary
• High-energy compounds usually applied to substances which possess sufficient free energy to liberate at least 7 Cal/mol at pH 7.0
• Low energy compounds Certain liberate less than 7.O Cal/mol at pH 7.0 referred to as low energy compounds
• Adenosine triphosphates a unique and the most important high energy molecule in the living cells
• ATP-ADP cycle, the fundamental basis of energy exchange reactions in living system
• ATP is synthesized by oxidative phosphorylation and substrate level phosphorylation
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