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Cytology
pH. Therefore, ATP is best stored as an is synthesised during light dependent
anhydrous salt. It is also considered as phase of photosynthesis. In this case,
the energy currency of the cell and life, when light of appropriate wavelength
because all cells need this energy molecule strikes on the chlorophyll, its electrons
in order to perform their functions in the get excited, as they gain excess energy.
body. In this state, they are boosted to high
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energy levels. As the electrons move
Formation of ATP downhill back to ground state, they
One molecule of ATP contains three lose the gained excess energy, which
phosphate groups, and is produced by a is used to combine with ADP and Pi
wide variety of enzymes, including ATP to form ATP. This process is called
synthase, from adenosine diphosphate photophosphorylation (refer section
(ADP) or adenosine monophosphate 5.2).
(AMP) and various phosphate group (b) Respiratory phosphorylation, which
donors. is the cellular process involving two
stages. The first stage is substrate
level phosphorylation in which ATP
is synthesised in the cytoplasm, by
Adenine glycolytic pathway. The second stage
is oxidative phosphorylation, which
occurs in the electron transport system
Phosphate groups in the inner mitochondrial membranes.
Roles of ATP
Ribose ATP provides energy for the following:
(a) Synthesis of macromolecules, such as
Figure 1.52: The chemical structure of polysaccharides from monosaccharides,
adenosine triphosphate
proteins from amino acids and DNA
replication.
Synthesis of ATP (b) Active transport across the plasma
ATP is synthesised when an inorganic membranes in the cell. For example,
phosphate, Pi, is energetically bonded to sodium-potassium pump.
adenosine diphosphate, ADP. The amount (c) Cellular movements, such as cilia
of energy required in this process is 30.6
kJ. action in trachea and fallopian tubes,
spindle fibers during cell division and
Condensation
30.6 kJ + ADP + Pi ATP + H O muscle contraction.
2
(d) Production of useful secretions by
vesicles.
The process yields ATP, therefore,
involves phosphorylation. There are two (e) Activation of important molecules,
types of phosphorylation: such as glucose, which is activated into
(a) Photosynthetic phosphorylation, ATP glucose-6-phosphate during respiration.
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