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