Lecture Notes: Respiration

Introduction to Respiration

• Definition: Breakdown of carbon-carbon bonds to release energy.
• Involves multiple steps, not a single process.
• Substance undergoing oxidation is called the respiratory substrate.

Respiratory Substrates

• Common substrates in plants:
  • Primarily carbohydrates (e.g., glucose).
  • If carbohydrates are unavailable, plants may utilize:
    • Fats
    • Proteins
    • Other organic acids.

Plant Respiratory Organs

• Do plants have specialized respiratory organs like animals? No.
• Plants utilize stomata and lenticels for gas exchange.

Glycolysis Overview

• Process: One glucose molecule (6 carbons) is broken down into two molecules of pyruvic acid (3 carbons).
• Location: Occurs in the cytoplasm.
• Common in: Both aerobic and anaerobic respiration.

Key Steps of Glycolysis

1. Step 1: Glucose converted to Glucose-6-phosphate (ATP utilized).
2. Step 2: Glucose-6-phosphate to Fructose-6-phosphate (isomerization).
3. Step 3: Fructose-6-phosphate to Fructose-1,6-bisphosphate (ATP utilized).
4. Step 4: Fructose-1,6-bisphosphate splits into PGAL (G3P) and DHAP (3-carbon compounds).
5. Step 5: PGAL is formed from DHAP.
6. Step 6: PGAL converts to 1,3-bisphosphoglycerate (NADH2 released).
7. Step 7: 1,3-bisphosphoglycerate converts to 3-phosphoglycerate (ATP generated).
8. Step 8: 3-phosphoglycerate converts to 2-phosphoglycerate.
9. Step 9: 2-phosphoglycerate converts to phosphoenolpyruvate (PEP).
10. Step 10: PEP converts to pyruvic acid (end product) and ATP generated.

Products of Glycolysis

• End products:
  • 2 molecules of pyruvic acid (3-carbon compound).
  • 2 molecules of NADH2.
  • Net gain of 2 molecules of ATP (4 produced, 2 utilized in steps 1 and 3).

Summary

• Glycolysis: A crucial metabolic pathway for both aerobic and anaerobic respiration, utilizing enzymes and energy carriers.
• Understanding glycolysis is fundamental to grasping cellular respiration processes.