Energy and Enzymes

Energy and Enzymes

Chapter Overview

• This chapter elaborates on the fundamental concepts of energy, the various types of energy, the laws of thermodynamics that govern energy transformations, enzyme function and the mechanisms through which they catalyze reactions, and the processes involved in metabolism.

I. Energy

• Energy is a crucial concept in both physics and biochemistry defined as:

  • The capacity to do work (Physics)

  • The capacity to cause change (Biochemistry)

A. Types of Energy

1. Potential Energy - This is energy stored in an object due to its position or condition.

   • Examples:

     • Height (e.g., an object elevated against gravity has potential energy due to its position).

     • A compressed spring stores energy that can be released when uncompressed.

     • Chemical energy, which is the energy stored in bonds of chemical compounds (e.g., ATP, glucose).

2. Kinetic Energy - This is the energy of movement or the energy that is actively doing work.

   • Examples:

     • A falling object converts potential energy into kinetic energy.

     • An expanding spring releases kinetic energy when it thrusts forward.

     • Molecular movement, such as protein conformational changes, shifts the dynamics of biochemical reactions.

     • Muscle contraction utilizes ATP consumption to create movement and perform work.

II. Laws of Thermodynamics

A. First Law of Thermodynamics

• Energy is neither created nor destroyed; it is transformed.

  • Example: Food intake involves the conversion of complex organic molecules into usable energy through intricate cellular processes like digestion and metabolism.

B. Second Law of Thermodynamics

• Energy conversions are not 100% efficient. Some energy is transformed into heat and is not usable, which contributes to increased entropy (disorder) in a system.

  • Entropy: The measure of disorder in a system, which tends to increase over time as energy transformations can create less ordered energy states.

C. Free Energy (G)

• Total Energy = Usable Energy + Unusable Energy

• Relation: H = G + TS

  • H = Total Energy

  • G = Free Energy

  • T = Temperature

  • S = Entropy

• Gibbs Free Energy (ΔG):

  • If ΔG < 0: Indicates a reaction that releases free energy (exergonic), such as the breakdown of glucose to release energy for cellular activities.

  • If ΔG > 0: Indicates a reaction that absorbs free energy (endergonic), requiring an input of energy, such as the synthesis of glucose from carbon dioxide and water during photosynthesis.

III. Metabolism

• Metabolism encompasses all the biochemical reactions occurring within a cell or organism, crucial for sustaining life and facilitating growth, reproduction, and maintenance of cellular functions.

A. Types of Metabolic Reactions

1. Anabolic (Synthetic) - These reactions focus on building larger, more complex molecules from simpler precursors, requiring energy input.

   • Example: The synthesis of proteins from amino acids or the formation of glycogen from glucose monomers.

2. Catabolic - These reactions involve the breakdown of complex molecules into simpler ones, releasing energy in the process.

   • Example: The conversion of glucose into pyruvate during glycolysis, which releases ATP.

IV. Enzymes

• Enzymes are specialized proteins that act as catalysts to accelerate biochemical reactions without being consumed in the process.

• Functions:

  • Enzymes lower the activation energy required for reactions, thus increasing the rate at which reactions proceed.

  • Most enzymes have names ending with the suffix -ase (e.g., lactase breaks down lactose, amylase breaks down starch).

A. Components of Enzymatic Reactions

1. Substrates (Reactants) - Molecules that enter the enzymatic reaction and undergo transformation.

2. Enzyme - The biological catalyst that enhances the reaction rate, remaining unchanged after the reaction.

3. Products - The molecules formed as a result of the enzymatic reaction.

4. Co-factors and Co-enzymes - These are additional molecules that assist enzymes in functioning effectively.

   • For example, metal ions such as zinc can serve as cofactors, while vitamins often act as coenzymes.

B. Enzyme Activity

• Enzymes stabilize the transition states of reactions, effectively lowering the activation energy by stabilizing the intermediate forms, which enhances reaction efficiency and specificity.

Sidebar Notes:

• Energy transformations are critically important in biological systems; living organisms must constantly transform energy to survive.

• Enzymes are often highly specific, meaning that a particular enzyme only catalyzes one specific type of reaction.

• Environmental conditions, such as temperature and pH, can significantly affect enzyme activity and stability.

Key Terms

• Energy: The capacity to do work or cause change.

• Potential Energy: Stored energy due to position or condition.

• Kinetic Energy: Energy of movement or work being done.

• Thermodynamics: The study of energy transformations.

• Entropy: A measure of disorder in a system.

• Gibbs Free Energy (ΔG): Indicates the free energy available for work in a system.

• Metabolism: All biochemical reactions within a cell or organism.

• Anabolic Reactions: Building complex molecules from simpler ones.

• Catabolic Reactions: Breaking down complex molecules into simpler ones.

• Enzymes: Biological catalysts that speed up chemical reactions.

• Substrates: Reactants in enzymatic reactions.

• Co-factors: Non-protein molecules that assist enzymes.

• Co-enzymes: Organic molecules that serve as cofactors.