Comprehensive Notes on Enzymes, Coenzymes, and Biochemical Reactions (copy)

Enzymes and Coenzymes

  • Definition of an Enzyme

    • An enzyme is a biological catalyst that accelerates biochemical reactions.
    • Enzymes consist of long chains of amino acids known as proteins.

  • Coenzymes

    • Definition: Coenzymes are small molecules that assist enzymes in catalyzing reactions.
    • Function: Coenzymes act as enzyme activators that carry electrons to and from the substrate during biochemical reactions.
    • Coenzymes are relatively small compared to enzymes, as enzymes are large protein molecules.

Redox Reactions

  • Redox Reactions

    • Definition: Redox reactions involve the transfer of electrons between two components.
    • Components:
    • Oxidation: Loss of electrons by a molecule.
    • Reduction: Gain of electrons by a molecule.

  • Example of Coenzyme in Redox Reactions

    • Important coenzyme: NAD (Nicotinamide Adenine Dinucleotide)
    • Formation: NAD is synthesized from vitamins in the diet.
    • Supplement: NAD is now available as a supplement (advertised on billboards).

  • NAD Charges

    • NAD exists in two forms, oxidized (NAD⁺) and reduced (NADH + H⁺), depending on its electron carrier status.
    • NAD⁺ oxidizes carbon, oxygen, and bonds and becomes NADH by accepting electrons and a proton.

NAD and Its Role in Oxidation-Reduction

  • Oxidation of Alcohol to Aldehyde

    • Example: Ethanol to acetaldehyde
    • Reaction notation: Ethanol + NAD⁺ ⟶ Acetaldehyde + NADH + H⁺
    • Describes the process of oxidation where ethanol (an alcohol) loses electrons (hydrogens) to form acetaldehyde (an aldehyde).

  • Importance of Coupled Reactions

    • Key concept: Oxidation of ethanol cannot occur without the simultaneous reduction of NAD⁺ to NADH.
    • Note: Oxidation and reduction occur simultaneously in redox reactions.

  • Curved Arrow Notation

    • Visual representation of electron transfer in reactions is done using curved arrows.

  • Reversible Reactions

    • Oxidation and reduction reactions involving NAD are reversible, allowing reactions to proceed in both directions under appropriate conditions.

FAD (Flavin Adenine Dinucleotide)

  • Definition and Function

    • FAD is another important coenzyme similar to NAD.
    • Primarily oxidizes carbon-carbon bonds and carbon-hydrogen bonds in biological systems.

  • Mechanism of FAD Action

    • Example Reaction:
    • Carbon-carbon bond is oxidized, releasing two hydrogens.
    • The reaction converts FAD to FADH₂ by accepting two electrons and two protons.
    • Notation: R-CH₂-CH₃ ⟶ R-CH=CH₂ + FADH₂

Free Radicals

  • Definition

    • A free radical is a molecule that has an odd number of valence electrons.
    • Classification: Free radicals are usually unstable and seek to stabilize by stealing electrons from other molecules.

  • Effects on Biological Tissues

    • Free radicals can cause oxidative damage to tissues, leading to various diseases, including cancer.

  • Formation of Free Radicals

    • Common sources include certain foods and exposure to sunlight, with UV rays acting as catalysts for free radical formation.

  • Antioxidants

    • Antioxidants are substances that can prevent or repair oxidative damage caused by free radicals.
    • Mechanisms of action:
    • Reduce free radicals by donating an electron.
    • Prevent free radical formation.

  • Sources of Antioxidants

    • Foods rich in antioxidants include fruits and vegetables (e.g., vitamins A and E, beta-carotene, anthocyanins).

Chemical Reactions and Mechanisms

  • Definition of a Mechanism

    • A chemical mechanism describes the step-by-step process of how molecules react, involving bond-breaking and bond-forming interactions.

  • Example Reaction

    • Reaction: H₂ + O₂ ⟶ H₂O
    • Mechanism: Bonds in hydrogen and oxygen molecules break before forming water molecules, representing the rearrangement of atoms.

Acyl Groups and Reactions

  • Definition of an Acyl Group

    • An acyl group is derived from a carbonyl group attached to an alkyl group.
    • Difference from carbonyl group: An acyl group includes an "R" group, making it part of larger organic molecules.

  • Condensation Reactions

    • Definition: A condensation reaction combines two molecules while releasing a small molecule (often water).
    • Two subtypes of condensation reactions:
    1. Dehydration Synthesis
      • Type of condensation reaction specifically removing water.
    2. Acyl Transfer Reaction
      • An acyl group is moved from one molecule to another.

Specific Reactions

  • Esterification

    • Reaction is the condensation of a carboxylic acid and an alcohol to form an ester and releases water.
    • Notation:
    • General reaction: Carboxylic acid + Alcohol ⟶ Ester + H₂O
    • Mechanism involves detaching an OH from the acid and an H from the alcohol to form H₂O.

  • Thioesterification

    • Similar to esterification but uses a thiol instead of an alcohol, forming a thioester along with water.

  • Amination

    • Reaction where an amine reacts with a carboxylic acid to form an amide, releasing water.

  • Comparison of Reactions

    • Esterification, thioesterification, and amination are all examples of condensation reactions, specifically dehydration reactions due to water release.

  • Importance in Biology

    • Understanding these reactions is crucial for grasping biochemical pathways, such as protein synthesis and metabolism.