Cellular Metabolism and Energy Production

Posted on Mar 23, 2025 in Biology

Cellular Metabolism: Key Concepts and Processes

Anabolism

Anabolism refers to the set of chemical reactions occurring in the cell that aims at synthesizing complex molecules from simpler ones, requiring energy input. (Synthesis of complex products with energy expenditure).

Metabolism

Metabolism is the comprehensive set of chemical reactions that occur within a cell.

Glycolysis

Glycolysis is a series of typically catabolic reactions.

Chemosynthetic Bacteria

Chemosynthetic bacteria are autotrophs, meaning they obtain energy and materials from inorganic substances.

Catabolism

Catabolism is the breakdown of complex molecules into simpler ones to generate energy.

Cellular Respiration

If glucose (C6H12O6) in the cells reacts with O2, it transforms into CO2 and H2O, and energy is produced. This is a catabolic process.

ATP

ATP (Adenosine Triphosphate) is a coenzyme that acts as an energy carrier.

ATP differs from ADP (Adenosine Diphosphate) in that ADP has one less phosphate group.

ATP is used in living organisms to provide energy for endergonic (energy-requiring) reactions.

FAD

FAD (Flavin Adenine Dinucleotide) is a coenzyme involved in electron transport.

Autotrophic Organisms

Autotrophic organisms obtain energy from light and inorganic substances.

Photosynthesis

Objective of Photosynthesis

The objective of photosynthesis is to manufacture organic compounds from inorganic compounds.

Location of Photosynthesis

The dark phase of photosynthesis occurs in the green parts of the plant.

Photosynthesis: Both the light phase (where ATP and NADPH + H+ are obtained) and the dark phase occur during the day in the chloroplasts of the plant.

Electron Source in Photosynthesis

The electrons that serve to reduce NADP+ in the light phase of photosynthesis come from water. Oxygen is released from water.

Cyclic vs. Acyclic Photophosphorylation

In cyclic photophosphorylation, only ATP is obtained. In acyclic photophosphorylation, both NADPH and ATP are produced.

Miscellaneous Points on Photosynthesis

  • The electrons in acyclic photophosphorylation are initially excited in the chlorophyll of photosystem II.
  • The electrons produced by the water will eventually be found in glucose.
  • Electron transport in the light phase of photosynthesis generates a proton gradient inside the thylakoid, which is used to synthesize ATP.
  • Most plants obtain nitrogen from nitrates and other inorganic nitrogen compounds in the soil.

Cellular Respiration

Objective of Cellular Respiration

The goal of cellular respiration is to obtain the energy contained in organic substances. The equation is: C6H12O6 + 6O2 —-> 6CO2 + 6H2O. This process occurs in both animals and plants, partly in the hyaloplasm and partly in the mitochondria.

Energy Source for Animals

Animals obtain energy from organic materials and are heterotrophic.

Stages of Glucose Catabolism

Of the various stages of glucose catabolism, the Krebs cycle and the respiratory chain occur in the mitochondria. Glycolysis, however, does not occur in the mitochondria.

End Product of Glycolysis

The end product of glycolysis is pyruvic acid.

Glycolysis Details

  • O2 is not necessary.
  • It allows cells to obtain energy anaerobically.
  • It is performed in the hyaloplasm of eukaryotic cells.
  • Very little energy is obtained in the form of ATP (2 ATP molecules).
  • Electrons in glycolysis, which reduce NAD+, originate from the carbon atoms of glucose.

Complete Degradation of Glucose

The complete degradation of glucose produces CO2. If the cell has oxygen, the CO2 is harvested in the Krebs cycle.

Respiratory Chain

  • Most of the energy contained in glucose is obtained in the respiratory chain.
  • The energy obtained in the respiratory chain is stored in ATP.
  • In the respiratory chain, electrons are transported from NADH or FADH2 to oxygen.

Total ATP Production

Cellular respiration yields a total of 36 ATP molecules per glucose molecule.

Fermentation

Purpose of Fermentation

The purpose of fermentation is to regenerate NAD+.

ATP Yield in Fermentation

Fermentations yield only 2 ATP molecules per glucose molecule.

Lactic vs. Alcoholic Fermentation

The difference between lactic acid fermentation and alcoholic fermentation is that alcoholic fermentation produces CO2, while lactic acid fermentation does not.

Examples of Fermentation

  • Alcoholic fermentation occurs during bread making.
  • Lactic acid is produced in muscles when there is insufficient oxygen.