Key Concepts from Cellular Respiration and Mitochondrial Function

Pyruvate and Mitochondrial Entry

  • Pyruvate Transport: Pyruvate enters the mitochondria through specific transport proteins. It crosses the outer membrane via porins and the inner membrane via specific transporters (e.g., pyruvate dehydrogenase complex).

GLUT4 Transporter

  • GLUT4: A glucose transporter that translocates to the cell membrane when needed; it helps glucose enter cells, especially muscle and fat cells.

    • Fructose also enters through different transporters and needs conversion into glucose.

Glycolysis

  • First Process of Glucose Breakdown: Glycolysis occurs in the cytoplasm and converts glucose (a 6-carbon sugar) into two molecules of pyruvate (3-carbon).

    • Requirements:

    • 2 ATP (used to activate glucose)

    • 2 NAD+ (electron carriers)

    • Output:

    • 4 ATP produced (net gain of 2 ATP after the initial investment)

    • 2 NADPH produced

    • Glycolysis is anaerobic (does not require oxygen).

Role of ATP and NAD+

  • ATP: Provides the energy necessary for enzyme functions in glycolysis.

  • NAD+: Functions as an electron carrier, transporting electrons generated during glucose breakdown.

Location and Function of Mitochondria

  • Structure:

    • Made of a double membrane (outer and inner phospholipid bilayers).

    • Contains mitochondrial matrix.

    • Has its own DNA, inherited maternally.

  • Functions:

    • Oxygen enters mitochondria to aid in ATP production through electron transport.

Krebs Cycle (Citric Acid Cycle)

  • Process Outline: Acetyl CoA (from pyruvate) enters the Krebs cycle, which occurs in the mitochondrial matrix.

    • One acetyl group combines with oxaloacetate, yielding citric acid (6 carbons).

    • The cycle processes carbon atoms, eventually releasing CO2 and transferring electrons to NAD+ and FAD.

  • Outputs:

    • 2 CO2 per cycle.

    • 3 NADH and 1 FADH2 per acetyl CoA.

    • 1 ATP (or GTP) produced.

Electron Transport Chain

  • Function:

    • NADH and FADH2 donate electrons to the chain.

    • Electrons are eventually transferred to oxygen to form water.

    • The energy released from electron transfer is used to pump protons into the intermembrane space, creating a proton gradient that drives ATP synthesis.

Summary of ATP Yield

  • Total ATP Calculation:

    • From Glycolysis: 2 ATP + 2 NADH (6 ATP equivalent) = 8 ATP

    • From Krebs Cycle (Input from 2 Pyruvate):

    • 2 ATP (or GTP)

    • 6 NADH (18 ATP equivalent)

    • 2 FADH2 (4 ATP equivalent)

    • Summing yields:

    • 2 (Glycolysis) + 2 (Krebs) + 18 (NADH from Krebs) + 4 (FADH2) = Total 36 ATP

  • Variability: Yields may vary slightly between 36 to 38 ATP due to cellular mechanisms and transport efficiencies.