BIOCHEM LECTURE 2 OF 2 - NOV21

Zoom Recording Update

  • Zoom will no longer be available for recordings in future sessions.

  • Recordings will be posted to Kaltura instead.

  • Students wanting audio only can download from Kaltura.

  • Faculty will continue to record sessions for student access.

Glycolysis Overview

Definition of Glycolysis

  • Glycolysis is the metabolic pathway that breaks down glucose to produce energy.

Pathway Components

  1. Investment Phase

    • Initial energy investment before glucose breakdown begins.

    • Two ATPs are consumed:

      • 1st ATP used by Hexokinase.

      • 2nd ATP used by Phosphofructokinase-1 (PFK-1), a committed step in glycolysis.

  2. Payoff Phase

    • Starts with Glyceraldehyde-3-phosphate (G3P).

    • Converts G3P to 1,3-Bisphosphoglycerate.

    • Produces ATP and NADH:

      • Two ATPs are produced at specific steps in the pathway.

      • For every molecule of glucose:

      • Output includes:

        • 2 NADH produced

        • 4 ATP produced

Inputs and Outputs of Glycolysis

  • Input: 1 glucose (6 carbons) + 2 ATPs = 2 ATPs (investment)

  • Output: 2 pyruvate (3 carbons each) + 2 NADH + 4 ATPs

  • Net Gain: 10 ATPs produced under aerobic conditions - 2 ATPs invested = 8 ATPs net gain.

Aerobic vs. Anaerobic Conditions

Aerobic Conditions

  • Under aerobic conditions (presence of oxygen), NADH contributes to ATP production via the electron transport chain, yielding:

    • 1 NADH = 3 ATPs, total from glycolysis = 10 ATPs.

Anaerobic Conditions

  • Under anaerobic conditions, NADH does not contribute to ATP production, thus yielding 0 ATPs from glycolysis, resulting in:

    • Lactate is produced instead of entering the aerobic pathway.

The Role of Erythrocytes in Energy Production

  • Erythrocytes (red blood cells):

    • Carry oxygen, but lack a nucleus and mitochondria.

    • Lifespan: approximately 90 to 120 days.

    • Energy production occurs through anaerobic glycolysis, producing NADH, but not ATP.

Hemoglobin A1c Testing

  • Frequency: every 90 to 120 days to monitor blood sugar level and its effect on hemoglobin.

  • Measures glycation of hemoglobin due to sugar over time.

NADH in Metabolic Processes

What is NADH?

  • NADH is a key redox cofactor that catalyzes redox reactions in the cell.

  • Functions include:

    • Accepting and donating electrons.

    • Converting NAD+ to NADH during glycolysis via:

    • Enzyme: Glyceraldehyde-3-phosphate dehydrogenase.

Redox Reactions

  • Involves oxidation (loss of electrons) and reduction (gain of electrons).

  • Example:

    • From NAD+ → NADH indicates reduction of NAD+.

  • Redox cofactors facilitate the conversion of substrates to products.

Cori Cycle

Overview

  • The Cori cycle involves the conversion of pyruvate to lactate, then back to pyruvate in the liver.

  • This cycle helps recycle lactate produced in anaerobic glycolysis into glucose (gluconeogenesis).

Conditions of the Cycle

  • Begins with anaerobic glycolysis which produces lactate when there is insufficient oxygen.

  • Lactate diffuses into the bloodstream, reaching the liver where it is converted back to pyruvate.

  • The newly formed pyruvate can be used for:

    • Energy production or gluconeogenesis to replenish glucose levels.

Electron Transport Chain (ETC)

Structure

  • Composed of four complexes (I, II, III, IV) and ATP synthase (Complex V).

  • Electron transport occurs after glycolysis and the Krebs cycle, crucial for aerobic energy production.

Complexes Overview

  1. Complex I (NADH-Q reductase)

    • Accepts electrons from NADH, reducing it to NAD+.

    • Passes electrons to Ubiquinone (Q), converting it to QH2.

  2. Complex II (Succinate-Q reductase)

    • Accepts electrons from FADH2 produced in the Krebs cycle.

    • Passes electrons to Ubiquinone (Q).

  3. Complex III (Q-cytochrome c reductase)

    • Transfers electrons from QH2 to Cytochrome c.

  4. Complex IV (Cytochrome c oxidase)

    • Accepts electrons from cytochrome c and reduces oxygen to water.

Energy Production

  • ATP synthase (Complex V) utilizes the proton gradient created by electron transport to synthesize ATP from ADP and inorganic phosphate.

Overall Summary and Implications

  • Glycolysis, the Cori cycle, and the electron transport chain are interconnected pathways essential for energy production in cells.

  • Understanding the flow of electrons, NADH's role, and the aerobic vs anaerobic pathways is crucial for grasping cellular metabolism and energy dynamics.