ATP, ADP, GTP, PEP, NADP, NAD, FAD, Phosphocreatine, Acyl phosphate, Thioesters

1. HIGH ENERGY
COMPOUNDS

2. Introduction
• Most of high energy compounds contain phosphate group hence they are called
high energy phosphates.
• The bonds in the high energy compounds which is energy upon hydrolysis are
called high energy bonds (‘~’).
• The main purpose of this molecule is to transfer either inorganic phosphate
groups (Pi) or hydride ions (H–). The inorganic phosphate groups are used to
make high energy bonds with many of the intermediates of metabolism
• high energy commons have a delta deltaG ^10 of hydrolysis more negative than
– 25 KJ/mol.

3. ATP (Adenosine Triphosphate)
• ATP is comprised of an adenine ring a ribose sugar and three phosphate groups.
• It is used for energy transfer in the cell.
• ATP synthase produces ATP from ADP or AMP+Pi.
Uses:
• it is used as coenzyme in glycolysis
• it is also found in nucleic acid in the process of DNA replication and transcription.
• in a neutral solution ,ATP has negative charged groups that allow it to chelate
metals. Usually Mg2+ stabilizes it

4. • ATP is an unstable molecule which hydrolysis to ADP and inorganic phosphate
when it is in equilibrium with water .
• the high energy of this molecule comes from the two high energy phosphate
bonds. The bonds between phosphate molecules are called phosphateanhydride
bonds .they are energy rich and contain Delta G of -30.5 KJ/mol.

5. HYDROLYSIS OF ATP
• Hydrolysis of ATP is thermodynamically favourable reaction , because of 2 reasons;
i) The substrates have intramolecular repulsion because of multiple negative
charges
ii) the products are resonance stabilized
• ATP powers most of the energy consuming activities of cells, some of which are as
follows:
• Most anabolic reactions including the biosynthesis of proteins, RNA and DNA by
Polymerization reactions from amino acids, ribonucleotides, deoxyribonucleotides
respectively. All these process require energy.
• ATP provides energy for active transport of ions or molecules against their
concentration gradient. Enzymes such as Na+/K+, which transport ions, consume
most of the energy in human brain and kidney.

6. • ATP is needed for bioluminescence in Fireflies ,which convert chemical energy
of ATP into high energy. Light flash is by virtue of luciferin which is activated by
luciferase involving ATP hydrolysis .
• ATP is needed for muscle contraction. Myosin binds tightly to ATP and
hydrolysis it. This drives the cyclic changes in confirmation of myosin . Such
confirmational changes in many such myosin molecules causes sliding of
myosin fibrils along actin filaments henceforth causing muscle fibre contraction .
• conduction of nerve impulses
• phosphorylation of many different proteins which are required under different
physiological conditions including signalling .
• ATP is also responsible for maintaining the pool of NTPs and dNTPs within the
cells by the following reaction

7. ATP+ NDP ⇌ ADP+ NTP
2 ADP ⇌ ATP+ AMP
• beating of cilia and flagella in microorganisms for motility.
• maintenance of cell volume by osmosis.
SYNTHESIS OF ATP
Phosphorylases catalyze synthesis of ATP by phosphorylation of
ADP by the following reaction :
ADP+ Pi ATP+H2O

8. • It requires 7.3 K Cal/ mol energy, and occurs in the cytosol by glycolysis.
Cellular respiration occurring in mitochondria also synthesizes ATP. In plants,
ATP is synthesized by photosynthesis in chloroplasts.
• Cells use ADP as precursor and add a phosphate group to it.
• Mitochondrial electron transport generates a proton gradient across the inner
mitochondrial membrane.
• This is dissipated through the FoF1 ATPase complex, and the energy released is
utilized to phosphorylate ADP to produce ATP.
• The linkage between generation of proton gradient and its dissipation to drive
ATP synthesis is described by chemiosmotic coupling.
• This is why the FoF1 ATPase complex of mitochondria is also known as the
coupling factor.

9. ATP PRODUCTION IN CELL
• ATP is produced in cells through a process called cellular respiration , which
occurs in both prokaryotic and eukaryotic cells.
• There are 2 primary pathways for ATP production : aerobic respiration and
anaerobic respiration.
1. AEROBIC RESPIRATION:
• This process takes place in the presence of oxygen and is the most efficient way
to generate ATP.
• It occurs in the mitochondria of eukaryotic cells.
• The main stages of aerobic respiration are glycolysis, the citric acid cycle ( krebs
cycle), and electron transport chain.

10. • During these stages, glucose and other organic molecules are oxidized, and
electrons are transferred through a series of protein complexes, ultimately
generating a proton gradient across the inner mitochondrial membrane.
• The flow of protons back in to the mitochondria through ATP synthase enzyme
complexes drives the synthesis of ATP from ADP and Pi.
2. ANAEROBIC RESPIRATION
• This process occurs in the absence of oxygen and it is less efficient than
aerobic respiration.
• Anaerobic respiration can involve different electron acceptors such as
nitrate, sulfate or fumarate depending on the organism.
• It also includes glycolysis as the initial step but the subsequent reactions
refers from those in aerobic respiration.

11. • In addition to respiration ATP can also be generated through substrate level
phosphorylation processes such as glycolysis and citric acid cycle.
• Photosynthesis in plant cells also plays a significant role in ATP production, as it
converts light energy into chemical energy stored in ATP and other energy rich
molecules.

12. ADP (Adenosine Diphosphate)
• It is a molecule formed in living cells that is involved in transferring and providing
cells with energy.
• It is often converted to ATP used in various biochemical reactions.
• Made up of Adenine( a nucleobase), ribose( sugar), and 2 phosphate molecules
• It is an high energy intermediate.
• It is viewed as an intermediate because it stores less energy within its bonds as
ATP; however, it can be used to produce ATP when needed.
• It plays a significant role in blood clotting(it activates platelet ).

13. • ADP is used in biological functions such as photosynthesis and glycolysis.

14. ATP- ADP Cycle
• The energy stored in ATP is released when a phosphate group is removed from the
molecule
• ATP has three phosphate groups, But the bond holding the 3rd Phosphate groups is
very easily broken.
• When the phosphate is removed, ATP becomes ADP-adenosine diphosphate
• A phosphate is released into the cytoplasm and energy is released.
• ADP is lower energy molecule than ATP, but can be converted to ATP by addition of
a phosphate group.
• ATP ADP+ phosphate + energy available for cell processes.
ATP ADP+ Phosphate + energy
ADP+ phosphate + energy ATP

16. GTP(Guanosine Triphosphate)
• It is a molecule consisting of the nitrogenous base guanine adenine linked to the
sugar ribose and contains three phosphate groups attached to the ribose.
• Like ATP, GTP is an energy rich molecule
• Generally, when such molecules are hydrolyzed, the free energy of hydrolysis is
used to drive reactions that otherwise are energetically unfavorable.
• In case of protein synthesis, GTP facilitates binding of protein factors either to tRNA
or to the ribosome.
• The function of GTP is to induce a conformational change in a macromolecule by
binding to it.

17. • GTP + H2O → GDP + Pi
• GTP hydrolysis is a biologically crucial reaction, involved in regulating almost all
cellular processes. They regulate all stages of cellular function, from signaling
cascades to cell migration, polarity, adhesion, cytoskeletal organization,
proliferation, and apoptosis.1 These transitions can involve fairly significant
conformational changes and are facilitated by interaction with different external
regulatory proteins, the so-called “GTPase activating proteins” (GAPs). These
regulatory proteins also contribute to substantially increasing the rates of GTP
hydrolysis by these enzymes by up to 105-fold
• When GTP is bound, the macromolecule has an active conformation, and when
the GTP is hydrolyzed or removed, the molecule resumes its inactive form.
• GTP Plays a similar role in hormone activation systems.

19. PEP ( Phosphoenolpyruvate)
• It is considered as a high energy molecule because it has a high energy
phosphate bond (-61.9 kJ/mol).
• It plays a crucial role in glycolysis and glucanogenesis, 2 central metabolic
pathways in cells.
• When the phosphate bond (which is attached to C backbone ) is cleaved, a
significant amount of energy is released.
• This energy is used to drive various biochemical reactions, such as synthesis of
ATP
• The phosphate bond in PEP makes it a key intermediate in these metabolic
pathways, allowing it to transfer and store energy as needed in the cell.

20. • In plants it is also involved in synthesis of a variety of aromatic compounds and
in C fixation
• In bacteria, it is also used ad source of energy for the phosphotransferase
system.
• Hydrolysis of PEP by pyruvate kinase into pyruvate can phosphorylate ADP to
ATP In this manner the energy of PEP now becomes resident on an ATP
molecule.
• This chemistry is favorable since pyruvate is more stable than PEP.
• PEP has only enol form while pyruvate has two tautomeric forms.
• Also, Pi is resonance stabilized.

22. NADP (Nicotinamide Adenine
Dinucleotide Phosphate)
• It is considered as a high energy molecule because it plays a crucial role in energy transfer reaction
within cells.
• It acts as a carrier of high energy electrons and hydrogen ions during various metabolic processes,
particularly in photosynthesis and cellular respiration.
• NADP can exist in two forms: NADP+ (oxidised ) and NADPH (reduced).
• NADPH is high-energy form, as it carries extra electrons and hydrogen ions.
• This molecule is essential for synthesis of fatty acids and nucleotides, and is also involved in the
reduction of compounds like carbondioxide in the process of photosynthesis.
• These high energy electrons and hydrogen ions carried by NADPH are used to drive many cellular
processes, making NADP a vital molecule in the energy metabolism of cells.
• It also functions as a coenzyme..

24. NAD (Nicotinamide Adenine
Dinucleotide)
• It is not typically considered a high energy molecule itself, but it plays a crucial role in
energy metabolism.
• It serves as a coenzyme in various cellular processes, including glycolysis and citric
acid cycle, where it participates in redox reactions that transfer electrons and by
extension, energy.
• NAD can exist in 2 forms: NAD+ (Oxidised) and NADH (reduced)
• NADH is indeed a carrier of high energy electrons and is involved in the transfer of
electrons in the ETC during cellular respiration.
• This transfer of electrons ultimately leads to the synthesis of ATP

25. • Nicotinamide adenine dinucleotide
consists of two nucleosides joined
by pyrophosphate. The nucleosides
each contain a ribose ring, one with
adenine attached to the first carbon
atom (the 1’ position) (adenosine
diphosphate ribose) and the other
with nicotinamide at this position.

26. FAD ( Flavin Adebine Dinucleotide)
• It derived from riboflavin, vitamin B2
• They have function in oxidation and reduction reactions
• FAD is act as coenzyme for various enzymes like a-ketoglutarate dehydrogenase,
succinate dehydrogenase, xanthine dehydrogenase, acyl co dehydrogenase.
• It exist in three different redox states, which are,
1. Quinone (FAD) – fully oxidized form
2. Semiquinone (FADH) –half reduced form
3. Hydroquinone (FADH2) – fully reduced form

27. • Flavin adenine dinucleotide
consists of two main portions:
an adenine nucleotide
(adenosine monophosphate)
a flavin mononucleotide
It is bridged together
through their phosphate groups.
Riboflavin is formed by a carbon-
nitrogen (C-N) bond between a
isoalloxazine and a ribitol.

28. • FAD can be reduced to FADH2 through by the addition of 2 H+ and 2 e-

29. • Catalyze difficult redox reactions such as dehydrogenation of a C-C
bond to an alkene
• FAD has a more positive reduction potential than NAD+ and is a very
strong oxidizing agent.
• FAD plays a major role as an enzyme cofactor
• FAD-dependent proteins function in a large variety of metabolic
pathways,
⚫Electron transport, role in production of ATP
:The reduced coenzyme FADH2 contributes to oxidative
phosphorylation in the mitochondria. FADH2 is reoxidized to FAD, which
makes it possible to produce 1.5 equivalents of ATP.

30. ⚫DNA repair
⚫ nucleotide biosynthesis
FAD-dependent enzymes that regulate metabolism are glycerol-3-phosphate
dehydrogenase (triglyceride synthesis) and xanthine oxidase involved in purine nucleotide
catabolism
⚫ beta-oxidation of fatty acids
redox flavoproteins that non-covalently bind to FAD like Acetyl-CoA-
dehydrogenases which are involved in beta-oxidation of fatty acids
⚫ amino acid catabolism
catabolism of amino acids like leucine (isovaleryl-CoA dehydrogenase), isoleucine,
(short/branched-chain acyl-CoA dehydrogenase), valine (isobutyryl-CoA dehydrogenase),
and lysine
⚫ synthesis of other cofactors such as CoA, CoQ and heme groups.

31. PHOSPHOCREATINE
• Phosphocreatine – or creatine phosphate – is the phosphorylated form of creatine.
• Chemical formula C4H10N3O5P
• In this molecule, the P-N bond can be hydrolyzed to generate free creatine and
inorganic phosphate. Forward reaction is favored by the release of Pi and the
resonance stabilization of creatine .The standard free-energy change of
phosphocreatine hydrolysis is -43.0 kJ/mol. Thus it is a high energy compound.

33. • Phosphocreatine is a naturally occuring substance that is found predominantly in
the skeletal muscles of vertebrates.
• Its primary utility within the body is to serve in the maintanence and recycling of
adenosine triphosphate (ATP) for muscular activity like contractions.
• Phosphocreatine is a cardioprotective agent indicated for use in cardiac surgery.
:its use involve conditions caused by energy shortage or by increased
energy requirements – such as in ischemic stroke and other cerebrovascular
diseases. It is administered intravenously for cardiovascular conditions in some
countries.
• Because phosphocreatine is not regulated as a controlled substance it is taken
as a supplement by some professional athletes as a means to perhaps increase
short bursts of muscle strength or energy for professional athletics..

34. ACYL PHOSPHATE
• It is a general term referring to an acyl group with a phosphate attached to the
oxygen.
• An acyl group is a carboxylic acid derivative or it is a carboxylicacid that has the
hydrogen removed from the oxygen and replaced with another group.
• General formula is RCOOPO3
• 2 main types: Acyl monophosphates and acyl adenosine monophosphates.
• It allows uphill reactions to occur.
• Eg: acetyl ACP, 1,3-bisphoshoglycerate
• It is often intermediate in reactions because phosphate can act ad a method to
convert compounds from lower energy state in to higher energy states.

36. THIOESTERS
• Thioesters are the product of esterification
between a carboxylic acid and a thiol. Here
–S replaces the –O in the ester bond.
Thioesters also have high negative
standard free energies of hydrolysis.
Acetyl-coenzyme A (acetyl-CoA) is a well
known thioester. Hydrolysis of this
thioester (acetyl CoA) generates a
carboxylic acid (acetic acid) which can
ionize to carboxylate form (acetate) which
is resonance stabilized. Hydrolysis of
acetyl-CoA has ‘G´O= -31 kJ/mol

37. • Thioesters are involved in the synthesis of all esters, including those found in
complex lipids.
:In the metabolism of lipids (fats and oils), thioesters are the principal form of
activated carboxylate groups. They are employed as acyl carriers, assisting with
the transfer of acyl groups such as fatty acids from one acyl X substrate to another.
The ‘acyl X group’ in a thioester is a thiol. The most important thiol compound used
to make thioesters is called coenzyme A,
• They also participate in the synthesis of a number of other cellular components,
including peptides, fatty acids, sterols, terpenes, porphyrins, and others.

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