Energy Rich Compounds
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
FAQ:
Q1: What are energy-rich compounds? Energy-rich compounds are molecules that store and release energy for various cellular processes. They are characterized by high-energy phosphate bonds that, when broken, release energy for cellular work.
Q2: What is ATP, and why is it considered the primary energy currency of cells? ATP, or Adenosine Triphosphate, is a molecule that carries energy within cells. It is often called the “energy currency” of cells because it provides energy for many cellular functions. ATP’s energy is stored in its phosphate bonds, and when these bonds are broken, energy is released to power cellular processes.
Q3: How is ATP generated in cells? ATP is primarily generated through cellular respiration, which involves the breakdown of glucose and other organic molecules in the presence of oxygen. This process, which occurs in mitochondria, produces ATP as an energy-rich product.
Q4: What are the main biological functions of ATP? ATP is involved in a wide range of biological functions, including muscle contraction, active transport of molecules across cell membranes, enzyme-catalyzed reactions, and synthesis of macromolecules like proteins and nucleic acids.
Q5: What is cAMP, and how does it function in cells? cAMP, or Cyclic Adenosine Monophosphate, is a molecule that acts as a second messenger in cell signaling pathways. It is formed from ATP and is involved in transmitting signals from various extracellular molecules to intracellular targets. cAMP activates specific enzymes and plays a vital role in regulating processes like metabolism, gene expression, and cell communication.
Q6: How is cAMP produced in cells? cAMP is produced by the enzyme adenylate cyclase, which converts ATP into cAMP by removing two phosphate groups from ATP’s structure. This conversion is often triggered by extracellular signaling molecules.
Q7: What is the biological significance of cAMP? cAMP is a critical signaling molecule that mediates the cellular response to various hormones and neurotransmitters. It plays a role in regulating metabolism, gene expression, and other processes that are essential for maintaining cellular homeostasis.
Q8: What are some examples of cAMP’s involvement in cellular processes? cAMP is involved in processes like glycogen breakdown, the activation of protein kinase A (PKA), which affects various metabolic pathways, and the regulation of gene transcription. It also plays a role in mediating the effects of hormones like epinephrine and glucagon.
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