Metabolism and Energy: ATP and Cellular Processes

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12 Questions

What is the primary role of a catalyst in a biochemical reaction?

To lower the activation energy required for a reaction to occur

What is the function of an enzyme's active site?

To bind with a specific substrate molecule

What is the purpose of NAD+ in glycolysis?

To strip electrons from the sugar molecule

What is the end result of the Krebs Cycle?

The complete breakdown of pyruvate to carbon dioxide

What type of inhibition occurs when an inhibitor binds to the active site of an enzyme?

Competitive inhibition

What is the purpose of substrate-level phosphorylation in glycolysis?

To generate ATP from the energy released in glycolysis

What is the primary function of ATP in a cell?

To store energy in the form of phosphate bonds

What is the net result of oxidation and reduction reactions in a cell?

Electrons are removed from one molecule and added to another

What is the purpose of substrate level phosphorylation, oxidative phosphorylation, and photophosphorylation?

To generate ATP from ADP and Pi

What is the significance of the term 'energy currency' in reference to ATP?

It is used for most metabolic processes that require energy

What is the relationship between ATP and ADP + Pi in a cell?

There is a constant cycling between ATP and ADP + Pi

What is the primary function of enzymes in a cell?

To catalyze chemical reactions

Study Notes


  • 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


  • 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


  • 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

Test your understanding of metabolism, ATP, and cellular processes. This quiz covers the definitions and types of metabolism, the role of ATP as an energy carrier, and its functions in the cell.

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