ATP is a small molecule that serves as an energy intermediate in human metabolism. Cells extract chemical energy from nutrients like glucose, proteins, and fats and use it to produce ATP through processes like glycolysis, the Krebs cycle, and oxidative phosphorylation in the mitochondria. Mitochondria are the main site of ATP synthesis, producing around 32 molecules of ATP for each glucose molecule oxidized through proton flux in the ATP synthase complex. Muscle cells also store energy in creatine phosphate, which can rapidly phosphorylate ADP to ATP during periods of high energy demand.

1. ENERGETICS

2. • ATP is a relatively small molecule that serves
as an "energy intermediate" in human
metabolism. In essence, cells extract the
chemical energy from various nutrient
molecules like proteins, carbohydrates and
proteins, and use the chemical energy to make
ATP.

3. • The main energy source for cellular
metabolism is glucose, which is catabolized in
the three subsequent processes—glycolysis,
tricarboxylic acid cycle (TCA or Krebs cycle),
and finally oxidative phosphorylation—to
produce ATP.

4. • The majority of ATP synthesis occurs in cellular
respiration within the mitochondrial matrix:
generating approximately thirty-two ATP
molecules per molecule of glucose that is
oxidized.
• Transmembrane proton flux through the
mitochondrial ATPase synthase complex occurs at
an estimated rate of 3 × 1021 protons per second.
This corresponds to ATP reformed at a rate of 9 ×
1020 molecules/sec, or approximately 65 kg ATP
recycled per day in a normal resting adult

5. • Mitochondria are the main site for ATP synthesis
in mammals, although some ATP is also
synthesized in the cytoplasm. Lipids are broken
down into fatty acids, proteins into amino acids,
and carbohydrates into glucose.
• In general, the main energy source for cellular
metabolism is glucose, which is catabolized in the
three subsequent processes—glycolysis,
tricarboxylic acid cycle (TCA or Krebs cycle), and
finally oxidative phosphorylation—to produce
ATP.

6. • Oxidative phosphorylation produces the most
ATP. It is a part of cellular respiration. Here,
energy to drive phosphorylation comes from
oxidation-reduction reactions.

7. • Muscle cells store phosphate in creatine
phosphate, the major phosphate-storing
molecule. Resting muscle is dominated by
creatine phosphate, which is five times as
concentrated as ATP. In times of acute energy
need, creatine kinase phosphorylates ADP to
ATP using creatine phosphate.