Cellular Respiration and Photosynthesis: Processes and Energy Conversion

Posted on Apr 3, 2025 in Biology

Glycolysis

Catabolic process converting glucose to pyruvate, yielding 2 electrons. The following stages occur:

  1. Phosphorylation of Glucose: Glucose is phosphorylated by hexokinase.
  2. Isomerization: Glucose 6-phosphate is isomerized to fructose 6-phosphate by isomerase.
  3. Phosphorylation of Fructose 6-Phosphate: Fructose 6-phosphate is phosphorylated by phosphofructokinase, requiring ATP to produce fructose 1,6-bisphosphate.
  4. Cleavage of Fructose 1,6-Bisphosphate: Fructose 1,6-bisphosphate is cleaved by aldolase into two triose phosphates: glyceraldehyde 3-phosphate and dihydroxyacetone phosphate.

Respiratory Chain

The respiratory chain involves the following:

  • Energy Release through Electric Potential: Energy is released through changes in electric potential and electronegativity.
  • Energetic Jumps: These energy releases are called energetic jumps.
  • FoF1 ATP Synthase: Particles called FoF1 ATP synthases are located in the membrane.
  • Proton Movement and ATP Synthesis (Oxidative Phosphorylation): Protons move across the membrane due to the energy from electron jumps. This movement drives ATP synthesis by FoF1 ATPases.

Glycolysis Energy Balance

+2 ATP +2 NADH → 6 ATP (2 ATP are lost during transport across the membrane, resulting in a net gain of 4 ATP)

Oxidation of Pyruvate: 2 NADH + 2 Pyruvate → 6 ATP

Krebs Cycle: 2 ATP + 6 NADH (18 ATP) + 2 FADH2 (4 ATP)

Photosynthesis

Anabolic process converting inorganic matter to organic matter using light energy. It occurs in chloroplasts of photosynthetic organisms, releasing oxygen as a byproduct.

Light-Dependent Reactions

Occur in the thylakoid membrane, producing ATP and NADPH. Water photolysis (splitting of water using light energy) provides electrons, releasing O2.

Light-Independent Reactions (Dark Reactions)

Occur in the stroma, using ATP and NADPH to synthesize organic matter from inorganic matter. The Calvin cycle is the central process.

Photosystems and Light Capture

Photosynthetic organisms capture light using chlorophyll within antenna complexes located in the thylakoid membrane. These complexes are grouped into photosystems.

  • Photosystem I (PSI): Maximum light absorption at 700 nm.
  • Photosystem II (PSII): Maximum light absorption at 680 nm.

Chlorophyll molecules in the reaction center absorb light energy and transfer it to the electron transport chain.

Photophosphorylation

PSII → Pheophytin → PQA → PQB → Cytochrome b6f (ATP production) → Plastocyanin → PSI (light input) → A0 → Fq → Fe-Sx → Fe-SA → Fe-SB → Ferredoxin → NADP+