Coenzymes, Glycolysis

Energy Storage in Living Organisms

  • Recap of previous discussion on ATP synthesis.

  • Energy storage mechanisms are discussed, notably respiration.

  • Mention of terms:

    • "Naturalism" and "Redox" (correction needed).

Reducing Potential

  • Definition of reducing potential:

    • The ability to accept and donate electrons.

    • Key terms:

    • Accepting electron results in reduction, therefore the chemical becomes reduced.

    • The chemical that donates electrons is called the reducing agent.

  • Clarification:

    • Reduced = oxidized agent; oxidized = reducing agent.

Coenzymes

  • Introduction to coenzymes, two key terms associated:

    • Organic and Proteinaceous vs Non-Proteinaceous.

  • Focus on Nicotinamide Adenine Dinucleotide (NAD):

    • NAD+ is the oxidized form, and when reduced, becomes NADH.

    • Function: Acts as an energy intermediate akin to a check that needs to be processed for ATP production in the electron transfer chain.

Structure of NAD

  • The structure of NAD described:

    • Contains a positive charge, with core AMP giving structural stability.

  • Role of nicotinamide monophosphate in electron donation and acceptance is highlighted.

Conversion and Function of NAD

  • Detailed explanation of NAD+ conversion:

    • Balanced equations:

    • NAD+ + 2e- + 1H+ → NADH + H+.

    • Importance of NAD+ as an electron acceptor.

    • NADH as an electron donor.

    • Clarification on the efficiency of NAD+ in biochemical pathways.

Energy Intermediate and Electron Transport

  • In-depth discussion:

    • NAD+ accepts two electrons from the substrate and one proton from cytosol to form NADH which acts as an energy carrier.

    • Emphasizes the process of balancing electron flow in cellular reactions.

Glycolysis Overview

Carbohydrate Catabolic Pathways

  • Four major pathways of carbohydrate catabolism:

    1. Glycolysis

    2. Oxidation

    3. Krebs Cycle (TCA cycle)

    4. Oxidative phosphorylation

  • Explanation of glycolysis:

    • Takes place in the cytosol.

    • Forms two 3-carbon compounds without any loss of carbon.

Phases of Glycolysis

  1. Energy Investment Phase:

    • Detailed steps:

    • Glucose (6-C) → Glucose-6-phosphate (using 1 ATP) via Hexokinase enzyme.

    • Glucose-6-phosphate → Fructose-1,6-bisphosphate (using 1 ATP) via Phosphofructokinase enzyme.

  2. Cleavage Phase:

    • Formation of two isomers:

    • Glyceraldehyde-3-phosphate and Dihydroxyacetone phosphate.

    • Action of Aldolase enzyme for cleavage.

  3. Energy Liberation Phase:

  • Net production of ATP and NADH discussed:

    • Substrate-level phosphorylation occurs, and ATPs produced count is outlined:

    • 4 ATP produced in total, but net gain is 2 ATP after subtracting investment.

    • Also two NADH produced.

Products of Glycolysis

  • Final product yields from glycolysis summarized:

    • 2 Pyruvate, 2 NADH + 2H+, 2 ATP, and 2 H2O.

    • Total net ATP yield from glycolysis is 2 after investment.

Pyruvate Oxidation

  • Transition from glycolysis to mitochondrial activities.

  • Pyruvate oxidation specifically noted cannot yield ATP but can produce NADH in mitochondrial matrix.

  • Mechanisms of pyruvate transport discussed:

    • Passive transport into intermembrane space and secondary active transport (via proton pyruvate pump) into mitochondrial matrix.

Review of Energy Production Mechanisms

  • Importance of NAD and ATP production processes in various metabolic pathways emphasized.

  • Encouragement for practical application and repeated review of material.

  • Reminder for students to ask questions and clarify during sessions.