Metabolism and Energy: ATP and Cellular Processes

Metabolism

• Defined as chemical processes carried out by living organisms
• Divided into two types of reactions: catabolism and anabolism
• Catabolism: complex molecules broken down into smaller molecules + energy
• Anabolism: small molecules + energy used to build complex molecules

ATP (Adenosine Triphosphate)

• Major energy carrier of the cell
• Stores energy in phosphate bonds
• ATP → ADP + Pi + Energy
• Referred to as the “energy currency” for metabolic processes that require energy
• An E. coli cell contains 5 million ATP molecules, but spends 2.5 million ATP molecules per second

Making ATP

• Can be made in several ways (all from ADP and Pi):
  • Substrate level phosphorylation: phosphate added from another organic molecule
  • Oxidative phosphorylation: energy released by electron transport is used
  • Photophosphorylation: light energy is used

ATP and ADP Cycling

• Constant cycling between ATP and ADP + Pi:
  • ADP + Pi + Energy → ATP

Oxidation and Reduction

• Oxidation: removal of electrons (e-) from a molecule (releases energy)
• Reduction: addition of electrons (e-) to a molecule (stores energy)
• Oxidation and reduction reactions are coupled

Enzymes

• Protein catalysts that speed up reactions without being consumed
• React with specific substrates to catalyze biochemical reactions
• Contain an active site for binding specific substrate molecules
• Lower the activation energy required for a reaction to occur
• Can be affected by temperature, pH, enzyme, substrate, and reactant concentrations
• Can be inhibited in several ways, including competitive and non-competitive inhibition

Carbohydrate Metabolism

• Breakdown of carbohydrate molecules to produce energy
• Glucose is the most common carbohydrate source and central player in metabolism
• Two types of carbohydrate metabolism: fermentation and cellular respiration
• Both share a process called glycolysis

Glycolysis

• Breakdown of glucose to pyruvate
• Phosphates are added to glucose from ATP to activate it
• Sugar is split in two
• Reducing power is generated as NAD+ is converted to NADH
• ATP is generated from substrate level phosphorylation
• Summary equation: C6H12O6 + 2 ADP + 2 Pi + 2 NAD+ → 2C3H4O3 + 2 ATP + 2 NADH + 2H+ + 2H2O