ATP

• If ΔG (Gibbs free energy) is close to zero (∆G ≈ 0), the system is at equilibrium, and the reaction is reversible.
• If ΔG is positive (∆G > 0), the reaction is endergonic, indicating that it requires an input of energy to proceed. These reactions are typically non-spontaneous.
• If ΔG is negative (∆G < 0), the reaction is exergonic, meaning it releases energy. Such reactions are often spontaneous.
• ΔG=ΔH −TΔS

  • ΔH is the change in enthalpy (heat energy),
  • ΔS is the change in entropy (disorder),
  • T is the absolute temperature in Kelvin.
• a favorable reaction has a negative ∆G, indicating that it releases energy.
• An unfavorable reaction has a positive ∆G, meaning it requires an input of energy to proceed
• The hydrolysis of ATP to adenosine diphosphate (ADP) and inorganic phosphate (Pi) is an exergonic reaction (∆G < 0), meaning it releases energy.
• Cells often couple an unfavorable reaction (with a positive ∆G) to the hydrolysis of ATP (with a negative ∆G) in order to make the overall process thermodynamically favorable.
• ATP structure:

  A) Adenine

  B) Ribose

  C) 3 phosphate groups

  
• • α-Phosphate: The phosphate closest to the ribose sugar.
  • β-Phosphate: The middle phosphate.
  • γ-Phosphate: The furthest phosphate.
• ATP is energy rich because of the two phosphoanhydride bonds.
• The "high phosphoryl potential" of ATP refers to its ability to transfer a phosphate group (phosphoryl group) to another molecule during a chemical reaction.
• Phosphoryl potential refers to the potential energy stored in the high-energy phosphate bonds of ATP.
• The high phosphoryl potential of ATP is primarily associated with the high-energy bond between the β and γ phosphates. This bond is a phosphoanhydride bond.
• Kinases add a phosphate.e.g. Diacylglycerol kinase.
• Phosphatases remove a phosphate.
• Glycolysis is the initial stage of cellular respiration that takes place in the cytoplasm. It involves the breakdown of one molecule of glucose (a six-carbon sugar) into two molecules of pyruvate (a three-carbon compound). Glycolysis produces a net gain of 2 ATP molecules per glucose molecule through substrate-level phosphorylation. It generates NADH, which carries high-energy electrons to the next stage.
• Pyruvate Decarboxylation (Transition Reaction):

  • Location: Mitochondrial matrix (in eukaryotes)
  • Overview: Each pyruvate produced in glycolysis enters the mitochondria, where it undergoes decarboxylation (loss of a carbon atom) to form acetyl-CoA, which is a two-carbon compound.
  • ATP Production: This step does not directly produce ATP, but it prepares the acetyl group for entry into the next stage.
• Citric Acid Cycle (Krebs Cycle):

  • Location: Mitochondrial matrix (in eukaryotes)
  • Overview: The acetyl-CoA produced in the transition reaction enters the citric acid cycle, a series of enzyme-catalyzed reactions that further break down the carbon atoms, releasing carbon dioxide and generating high-energy carrier molecules (NADH and FADH2).
  • ATP Production: Through substrate-level phosphorylation, the citric acid cycle generates 2 ATP. However, the primary purpose is to produce high-energy carriers (NADH and FADH2) for the next stage.
• The high-energy carriers (NADH and FADH2) produced in glycolysis and the citric acid cycle donate their electrons to the electron transport chain.
• The electron transport chain consists of a series of protein complexes embedded in the inner mitochondrial membrane.
• As electrons move through the electron transport chain, energy is used to pump protons across the inner mitochondrial membrane, creating a proton gradient.
• The flow of protons back into the mitochondrial matrix through ATP synthase drives the synthesis of ATP from ADP and inorganic phosphate, a process called oxidative phosphorylation.
• Molecular oxygen (O2) is the final electron acceptor, and water is produced as a byproduct.