Lesson 3: Redox Reactions

Key Vocabulary for Redox Reactions

  1. Redox Reaction: A chemical reaction involving the transfer of electrons between two species, consisting of reduction and oxidation processes.

  2. Oxidation: The process of losing electrons, resulting in an increase in oxidation state.

  3. Reduction: The process of gaining electrons, resulting in a decrease in oxidation state.

  4. Oxidizing Agent: A substance that gains electrons and is reduced in a redox reaction; it causes oxidation of another substance.

  5. Reducing Agent: A substance that loses electrons and is oxidized in a redox reaction; it causes reduction of another substance.

  6. Half-Reaction: A representation of either the oxidation or reduction process in a redox reaction, showing the transfer of electrons.

  7. Electrochemical Cell: A device that converts chemical energy into electrical energy through redox reactions.

  8. Standard Electrode Potential (E°): A measure of the tendency of a chemical species to be reduced, measured under standard conditions.

  9. Nernst Equation: An equation that relates the concentration of reactants and products to the cell potential, allowing for calculations under non-standard conditions.

  10. Balancing Redox Reactions: The process of ensuring that the number of atoms and charge are equal on both sides of the reaction, often using the half-reaction method.

  11. Stoichiometry: The calculation of reactants and products in chemical reactions, important for balancing redox reactions.

  12. Electrons (e⁻): Subatomic particles with a negative charge that are transferred during redox reactions.

  13. Oxidation State (Oxidation Number): A number assigned to an element in a compound that reflects its degree of oxidation or reduction.

  14. Corrosion: The gradual destruction of materials (usually metals) due to redox reactions with environmental factors.

  15. Combustion: A type of redox reaction where a substance reacts with oxygen, producing heat and light.

  16. Photosynthesis: A biological redox reaction where carbon dioxide and water are converted into glucose and oxygen using sunlight.

  17. Respiration: A biological redox process where glucose is oxidized to produce energy, carbon dioxide, and water.

  18. Electrolysis: A process that uses electrical energy to drive a non-spont

Lesson 3

Redox reactions


Oxidation Reduction Reaction

  • Oxidation and Reduction have to happen together

  • Oxidation: the gaining of bonds to oxygen

    • Organic fuel substances (wood, coal, etc) can be oxidized. During burning, the carbon in these substances bonds to an oxygen atom, while some of the oxygen used to burn the fuel bonds to the hydrogen atoms from the fuel. 

  • Reduction: the gaining of hydrogen

  • Combustion reactions are good examples of redox reactions where one molecule gains oxygen, and the other gains hydrogen. 

  • Atomic definitions of oxidation and reduction

    • Oxidation = the loss of electrons

    • Reduction = the gain of electrons 

      • These definitions don’t involve oxygen and hydrogen, thus redox reactions can occur in compounds not containing oxygen or hydrogen atoms. 


  • Ae- + B = A + Be- 

           A is oxidized and Be- is reduced

Typically, an oxidized substance has less energy, while a substance that has been reduced has more energy. 


  • When electrons are removed they are sometimes used to produce energy intermediates like NADH, where NAD is reduced, and then cells use that to make ATP, or NADH can donate electrons to other organic molecules and energize them. 

 Anabolic Reactions: biosynthetic reactions because they are necessary to make larger molecules and macromolecules. 


Metabolic pathways are regulated in three general ways

  • Catabolic pathways are regulated so organic molecules are broken down only when no longer needed, or when the cell requires energ

  • During anabolic reactions, regulation ensures cell synthesizes molecules only when needed. 

These regulations occur in three different levels

  • Gene regulation: Genes signal which enzymes to use and when

  • Cellular level: cells use signals and adjust their pathways to adapt to the signals. 

  • Biochemical regulation: “The noncovalent binding of a molecule to an enzyme directly regulates the enzymes function” 

    • Feedback inhibition: the product of a metabolic pathway inhibits and enzyme that acts early in the pathway, which prevents the overaccumulation of the product. This inhibition only occurs when the concentration is high. 

      • The inhibited enzyme has 2 binding sites. One is where the reactants are converted to products, while the other is an allosteric site where a molecule can bind noncovalently and impact the enzyme's function. This binding causes a change in the enzyme to inhibit its function. The allosteric sites are often found in enzymes involved in the early steps of a metabolic pathway, to prevent too much product if it is unnecessary. 

Rate limiting step: the slowest step in the metabolic pathway. Is this step is inhibited or enhanced, the changes will have the greatest influence on the final product of the pathway. So instead of impacting all the enzymes, the cellular/biochemical regulation is often directed at the enzyme at the rate-limiting step. 



6.3

Vocab: metabolic pathway

Catabolic reactions

Anabolic reactions

Energy intermediates

Substrate-level phosphorylation

Chemiosmosis

Oxidation

Reduction

Redox reaction

Nicotinamide adenine dinucleotide (NAD+)

Biosynthetic Reactions

Feedback inhibition

Rate-limiting step


Intro

  • Catabolic reactions result in the breakdown of larger molecules into smaller ones

    • Often exergonic

    • Two uses

      • Recycling of organic building blocks

        • Exa

        • Proteins —--> proteases —----> many individual amino acids

      • Breakdown of organic molecules to obtain energy

        • Energy used to drive endergonic reactions

        • Chemiosmosis: the process for making ATP, where energy stores in an ion electrochemical gradient is used to make ATP from ADP and Pi


  • Anabolic reactions synthesize larger molecules from smaller ones

    • Usually endergonic, in living cells must be couples to an exergonic reactions



Lecture

Bioenergetics: the way that cells make energy


Learning objectives: 

  • Understand why electrons in different shells have different energy potentials

  • Understand the transfer of electrons in redox reactions

  • Understand the role of electron carriers

  • Understand the function and important of ATP in the cell


Energy:

  • Living organisms store and use energy

  • Energy originates from the sun

  • Energy is transformed through a series of redox reactions

  • Energy is the ability to promote change or do work

  • Chemical energy, the energy in molecular bonds, is a form of potential energy


How does breaking down internal energy stores from chemical bonds generate energy? The flow of electrons! Electrons = power


Redox reaction: (look at diagram)


Electron loser:

  • Oxidized

  • Decreased potential energy

  • Becomes electron acceptor

Electron Gainer

  • Reduced

  • Increased potential energy

  • Become electron donor


Atoms, ions and molecules that have a high affinity for electrons “want” electrons) are good oxidizing agents. Oxygen is the ultimate oxidizing agent (wants electrons). Reducing agents give up their electrons. There are a wide variety of reducing agents


ATP

  • Cellular energy

  • ATP is oxidized as it is used

    • Goes from three to two phosphates

  • Look at ATP diagram

  • Stores a lot of electrons

  • Every time there is oxidation, there must be reduction

  • Sometimes intermediate “electron carriers” carry electrons between reactions to other molecules

    • “Taxis”

      • Exa: NADH, NADPH, FADH2

      • Usually electrons have a “friend” welcome with them, usually a proton to balance the charge

      • NAD goes to NADH