🌱 Overview
Carbohydrate metabolism refers to the biochemical pathways by which plants synthesize, degrade, and allocate carbohydrates. It includes the primary energy-producing pathways such as photosynthesis, glycolysis, the tricarboxylic acid (TCA) cycle, and the pentose phosphate pathway. These processes are essential for plant growth, development, and response to stress.
📊 Photosynthesis: Carbon Fixation
The Calvin cycle is the biochemical pathway in which atmospheric CO2 is fixed into organic molecules. Primary stages include:
- Carbon fixation — CO2 attaches to ribulose-1,5-bisphosphate (RuBP).
- Reduction — NADPH is used to reduce 3-phosphoglycerate (3-PGA) to G3P.
- Regeneration — RuBP is regenerated to continue the cycle.
This pathway supplies the carbon skeletons for biosynthesis of sugars and other organic compounds.
⚡ Glycolysis: Energy Release
Glycolysis is a cytosolic pathway that breaks glucose into pyruvate, producing ATP and NADH. Key features:
- Occurs in the cytosol.
- Yields 2 ATP per glucose molecule.
- Produces pyruvate for further oxidation in mitochondria.
This pathway links carbon assimilation to energy production.
🔥 TCA Cycle & Energy Metabolism
The TCA cycle (also called the Krebs cycle) takes place in the mitochondria and fully oxidizes acetyl-CoA derived from carbohydrates.
- Generates NADH and FADH2 for oxidative phosphorylation.
- Produces intermediates for amino acid and nucleotide synthesis.
🔁 Pentose Phosphate Pathway (PPP)
The PPP operates parallel to glycolysis and provides:
- Reducing power (NADPH) for biosynthesis.
- Ribose-5-phosphate for nucleotide synthesis.
- Intermediates that reconnect with glycolysis.