Biology Chapter: Energy and ATP

Energy and ATP

• Life requires energy, and ATP (Adenosine Triphosphate) is the universal biological fuel.
• ATP stores chemical energy in high-energy phosphate bonds.
• ATP consists of an adenosine ring with three phosphate groups.
• The last phosphate group can be cleaved off to release energy, resulting in ADP (Adenosine Diphosphate) and free inorganic phosphate.
• This energy is used for various cellular processes, from muscle contraction to brain activity.
• ATP hydrolysis can be reversed by adding inorganic phosphate to ADP, but this requires energy.
• ATP synthase, a molecular power generator, is responsible for ATP synthesis.

ATP Synthase

• ATP synthase is found in the mitochondria of eukaryotic cells.
• It is responsible for producing most of the ATP in the cell.
• It is composed of two motors: F0 and F1.
• The F0 motor is a proton-powered motor embedded within the mitochondrial membrane.
• Protons flow through a channel in the F0 motor, driven by the proton motive force.
• This rotation is transferred to the F1 motor via a central stalk.

ATP Synthesis

• The F1 motor is responsible for generating ATP by adding a phosphate group to ADP.
• The F1 motor has three catalytic subunits arranged in a ring.
• Each subunit cycles through three distinct states:
  • ADP and phosphate binding.
  • Rearrangement of molecules by a 120-degree rotation of the central stalk.
  • Fusion of ADP and phosphate to form ATP by another 120-degree rotation.
  • Release of ATP and return to the initial state.
• The catalytic subunits remain stationary while the central shaft rotates, facilitated by the peripheral stalk.
• The peripheral stalk, once thought to be rigid, is actually dynamic and adapts for optimal function.

Mitochondrial Structure and Function

• Electron cryotomography reveals that ATP synthase dimerizes within mitochondria.
• Dimerization influences the inner mitochondrial membrane, forming cristae.
• Cristae shape enhances ATP synthesis by concentrating the proton gradient near ATP synthase.