ATP Hydrolysis & Redox

Learning Objectives

• Understand the role of ATP, its function in the cell, and its chemical structure.

• Explain the coupling of exergonic (energy-releasing) and endergonic (energy-requiring) chemical reactions.

• Define oxidation and reduction reactions (redox) and their characteristics.

• Identify which reactants (substances) are oxidized or reduced in a reaction, including the roles of oxidizing and reducing agents.

• Describe the role of electron carrier molecules in cellular processes.

Adenosine Triphosphate (ATP)- Adenosine Triphosphate

• Definition: ATP is the primary energy currency of the cell, vital for energy transfer in metabolic processes. [energy carrier of the cell]

• Functions of ATP

  • provide energy for endergonic reactions and processes

• Chemical Structure:

  • Ribose sugar

  • Adenine base

  • Three phosphate groups (P), connected by high-energy bonds.

ATP Hydrolysis

• Energy Release:

  • ATP releases energy through hydrolysis (exergonic)

  • This reaction is exergonic (releases energy), while synthesizing ATP from ADP is endergonic (requires energy).

    • If roles are reversed it becomes endergonic

Phosphorylation

• Definition: Addition of a phosphate group (Pi) to a molecule, often catalyzed by enzymes.

• Significance in Cell Function:

  • Activates or inactivates proteins/enzymes.

  • Increases the reactivity of substrates.

• ATP is used to phosphorylate molecules

  • Phosphorylate proteins/enzymes → activate or inactivate them

  • Phosphorylate a molecules → molecule becomes more reactive (like a substrate)

Energy Coupling

• Concept:

  • Exergonic and endergonic reactions are coupled; the energy released in exergonic reactions powers endergonic ones.

• Graphs:

  • Exergonic reaction: Energy is released, ext{ΔG} < 0.

  • Endergonic reaction: Energy is absorbed, ext{ΔG} > 0.

  • The overall reaction harnesses free energy to drive necessary cellular processes.

Redox Reactions

• Definitions:

  • Oxidation: Loss of electrons, leading to a decrease in the potential energy of molecules.

    • electrons are lost

    • potential energy decreases

    • molecules may lose protons

  • Reduction: Gain of electrons, leading to an increase in potential energy.

  • Mnemonic: OIL RIG (Oxidation Is Loss; Reduction Is Gain).

    • electrons are gained

    • potential energy increases

    • molecules may gain protons

• Process:

  • Electrons and protons (H+) often move together in redox reactions, simultaneously transferring energy.

Oxidizing Agents vs. Reducing Agents

Oxidizing Agent: a molecule that oxidizes (e- taker = reduced)

Reducing Agent: a molecule that reduces (e- giver+ oxidized)

Electron Carriers (UBER)

• Importance:

  • Electron carriers shuttle electrons around the cell, allowing for energy transfer and biochemical reactions.

• Examples:

  • Nicotinamide adenine dinucleotide (NAD+/NADH): Accepts electrons and carries them within metabolic pathways.

  • Flavin adenine dinucleotide (FAD/FADH2): Similar role in electron transport.

ATP Production

1. Substrate-level phosphorylation:

   • Direct transfer of a phosphate group to ADP from a substrate to form ATP.

   • Typically occurs in glycolysis and the citric acid cycle.

2. Oxidative phosphorylation:

   • Involves the electron transport chain and chemiosmosis to produce ATP.

   • Most ATP is generated this way during cellular respiration.

3. ATP is made by…:

   1. Substrate-level phosphorylation → enzyme transfer phosphate group from substrate to ADP (in active site)

   2. Oxidative Phosphorylation

Key Vocabulary

• Adenosine Triphosphate (ATP): Key energy molecule.

• Adenosine Diphosphate (ADP): Lower energy molecule produced from ATP hydrolysis.

• Energy coupling: Linking exergonic and endergonic processes.

• Phosphorylation: Adding a phosphate group to a compound.

• Redox reactions: Chemical reactions involving electron transfer.

• Oxidation/Reduction: Processes of electron loss/gain.

• NAD+/NADH, FAD/FADH2: Important coenzymes in electron transport.

• Chemiosmosis: The process driving ATP synthesis in mitochondria.

• Proton-motive force: The gradient of protons across a membrane used to generate ATP.