Oxidation and Reduction (Redox Reactions)

• Definition of oxidation:

  • Oxidation is defined as the loss of electrons.

• Role of sodium (Na):

  • Sodium acts as the donor of electrons in reactions.

  • When sodium donates an electron to fluorine, it gets oxidized, resulting in the loss of electrons.

• Reducing agent:

  • The donor of electrons, such as sodium, is known as the reducing agent.

  • Importantly, the reducing agent itself undergoes oxidation.

• Role of chlorine (Cl):

  • Chlorine functions as the electron acceptor in this reaction.

  • As the electron acceptor, chlorine is termed an oxidizing agent.

  • The oxidizing agent is reduced during the reaction.

• Mnemonic for redox reactions:

  • GER: Gain Electrons = Reduction; OIL RIG: Oxidation is Loss, Reduction is Gain.

  • Choose either mnemonic as per preference.

Free Energy

• Definition of free energy (G):

  • Free energy is the amount of energy available to perform work during a reaction, taking into account temperature and pressure.

• Change in free energy (ΔG):

  • This symbol (Δ) denotes changes in free energy.

Exergonic vs Endergonic Reactions

Exergonic Reactions

• Characteristics:

  • Energy is released (the “X” indicates energy going out).

  • Free energy of reactants is higher than that of products.

  • Physically depicted as a downhill reaction.

  • ΔG is less than zero (ΔG < 0).

  • During exergonic reactions, substances are broken down, leading to a release of energy.

Endergonic Reactions

• Characteristics:

  • Energy is required for the reaction (represented as energy flowing in, like an uphill).

  • Free energy of reactants is lower than that of products.

  • Depicted as an uphill reaction.

  • ΔG is greater than zero (ΔG > 0).

ATP Hydrolysis

• Process:

  • ATP (adenosine triphosphate) is hydrolyzed to ADP (adenosine diphosphate) and inorganic phosphate (Pi).

  • The reaction can be represented as:
    ext{ATP} + ext{H}_2 ext{O}
    ightarrow ext{ADP} + ext{Pi}

  • This is a breaking process, which releases energy and has a negative ΔG:

  • ΔG = –7.3 kilocalories or -7,300 calories, used for cellular work.

• Reverse reaction (condensation):

  • Involves building ATP from ADP and Pi, resulting in a positive ΔG of +7.3 kcal.

• Composition of ATP:

  • ATP consists of:

  • Nitrogenous base: Adenine (a purine).

  • Sugar: Ribose (a 5-carbon sugar).

  • Phosphates: Three phosphate groups.

Celluler Energetics and Work

• Types of cellular work powered by ATP:

  • Mechanical work: e.g., muscle contraction, nerve impulse transmission.

  • Active transport: Transportation of molecules against a gradient.

  • Chemical work: Involved in endergonic processes.

Introduction to Enzymes

• Definition of enzymes:

  • Enzymes are biocatalysts that accelerate chemical reactions in biological systems. They are proteins, but not all proteins are enzymes.

• Function of enzymes:

  • Enzymes increase the rate of chemical reactions without altering the amount of final products and can be reused.

Active Sites and Substrate Specificity

• Active sites:

  • The area of the enzyme where substrates bind. Enzymes are highly specific for their substrates.

• Enzyme-substrate complex:

  • Formation of the complex occurs when the substrate binds to the enzyme, leading to product formation after the reaction occurs.

• Example:

  • For sucrose, the enzyme responsible for hydrolysis is called sucrase. Other examples include maltase (for maltose) and lactase (for lactose).

Mechanism of Enzyme Action

• Enzyme action and activation energy:

  • Enzymes lower the activation energy (EA), which is the minimum energy needed for a reaction to proceed.

  • Enzymes exert stress on the substrate bonds, increasing the likelihood of bond breaking or formation.

• Induced fit model:

  • Currently accepted model of enzyme action, where the enzyme undergoes a conformational change to better fit the substrate.

Factors Affecting Enzyme Activity

• Temperature:

  • Enzymes have an optimum temperature range. Higher temperatures can lead to denaturation, losing their functional shape.

• pH:

  • Each enzyme has an optimal pH value; deviations can result in denaturation. For instance, pepsin operates at a pH of 2.5.

• Enzyme concentration:

  • Increasing enzyme concentration generally increases reaction rate up to a point (substrate saturation).

• Substrate concentration:

  • Reaction rates increase with substrate concentration until all available enzymes are occupied. Beyond saturation, no further increase in rate occurs.

Enzyme Inhibition

• Types of inhibitors:

  • Competitive inhibitors: Bind to the active site, competing with the substrate.

  • Noncompetitive inhibitors: Bind to an allosteric site, altering enzyme shape and preventing substrate binding.

• Both types result in decreased enzyme activity, as they prevent the formation of enzyme-substrate complexes.

Summary of Enzyme Function

• Enzymes accelerate reactions by lowering activation energy, facilitating substrate binding, and stressing the substrate to promote reaction. They are necessary for cellular metabolism and efficiency of biochemical processes.