2.1-ATP-ADP-Cycle

ATP-ADP Cycle

  • ATP (Adenosine Triphosphate)

    • Energy currency used throughout the cell.

    • Provides energy for:

      • Mechanical work

      • Transport substances across the membrane

      • Perform various chemical reactions

  • ADP (Adenosine Diphosphate)

  • Pi (Inorganic Phosphate)

  • ATPase: Enzyme that hydrolyzes ATP to ADP, releasing energy.

  • Process:

    • Energy from food is released in cellular respiration.

    • ATP is regenerated from ADP through phosphorylation by using energy from catabolic reactions.

ATP Synthase

  • Mechanism of ATP synthesis occurs in ATP synthase, a mitochondrial enzyme.

  • Utilizes the proton gradient generated during oxidation to provide energy for ATP synthesis.

Structure of Adenosine Triphosphate (ATP)

  • Composed of:

    • 3 phosphate groups

    • 1 ribose sugar

    • 1 nitrogenous base (adenine)

  • The last two phosphate bonds have especially high energy, making them crucial for cellular work.

  • Hydrolysis (breaking down of bonds) releases energy that can be used for cellular functions.

Function of ATP

  • ATP mediates most energy coupling in cells.

  • Powers cellular work, which can be categorized into three main functions:

    • Chemical Work:

      • Involves synthesis of polymers from monomers (e.g., DNA polymerization).

    • Transport Work:

      • Involves pumping substances across membranes against spontaneous movement (active transport).

    • Mechanical Work:

      • Involves activities such as muscle contraction and movement of cellular components.

Hydrolysis of ATP

  • The process of breaking down ATP into ADP and Pi.

  • Hydrolysis occurs by the addition of water (H2O), which breaks the terminal phosphate bond.

  • This reaction releases a significant amount of energy due to the instability of the triphosphate tail caused by repulsion of negative charges at the phosphate groups.

Regeneration of ATP

  • ATP is renewable and can be regenerated from ADP through phosphorylation.

  • This process couples exergonic (energy-releasing) reactions with endergonic (energy-consuming) reactions in cells.

  • The ATP cycle involves rapid shuttling of inorganic phosphate and energy; approximately 10 million ATP molecules are used and regenerated per second.

  • Without regeneration, humans would require nearly their body weight in ATP daily.

Importance of Chlorophyll and Other Pigments

  • Chromatography:

    • A technique for separating components of mixtures based on their structure/composition.

  • Pigments:

    • Substances that absorb visible light; different pigments absorb different wavelengths.

    • Visible light (380–750nm) is crucial for life; the non-absorbed color is what we see.

  • Plants require multiple pigments to capture a broader spectrum of sunlight for photosynthesis.

Structure and Function of Chlorophyll

  • Found in the thylakoid membrane of plant cells.

  • Types of Chlorophyll:

    • Chlorophyll a (main pigment, directly converts solar energy to chemical energy).

    • Chlorophyll b and carotenoids (accessory pigments, capture additional light energy).

  • Structure includes a hydrophilic porphyrin ring with magnesium and a hydrophobic hydrocarbon tail.

Photoexcitation of Chlorophyll

  • Process:

    • Absorption of photon/light energy elevates an electron into a higher energy state.

    • The excited state is unstable, leading electrons to drop back and release energy.

    • In the thylakoid membrane, chlorophyll forms a photosystem with proteins to minimize energy loss.

Photosystems

  • Light-Harvesting Complex:

    • Aggregate of pigments (chlorophyll a, chlorophyll b, carotenoids) that transfer energy to the reaction center.

  • Reaction-Center Complex:

    • Contains chlorophyll a and a primary electron acceptor, facilitating the transfer of electrons.

  • Types of Photosystem:

    • Photosystem II:

      • Absorbs light at 680nm (P680).

    • Photosystem I:

      • Aborbs light at 700nm (P700).