Introduction to Metabolism

Overview of Metabolism

Metabolism refers to the sum of all chemical reactions that occur within living organisms to maintain life. These reactions are organized into metabolic pathways, which are either catabolic (breaking down molecules) or anabolic (building up molecules). Understanding metabolism is fundamental to biology, as it explains how cells obtain and use energy.

• Catabolic pathways break down complex molecules into simpler ones, releasing energy.

• Anabolic pathways synthesize complex molecules from simpler ones, requiring energy input.

• Energy released or consumed in these reactions is essential for cellular processes.

Catabolic Reactions

Definition and Examples

Catabolic reactions involve the breakdown of larger molecules into smaller units, often releasing energy in the process. These reactions are typically exergonic, meaning they result in a net release of free energy.

• Hydrolysis of polymers into monomers:

  • Polysaccharide → Disaccharide → Monosaccharide

  • Protein → Amino acids

  • Triglyceride → Fatty acids + Glycerol

  • Nucleic acid → Nucleotides

• Exergonic reactions have a negative change in free energy ().

• These reactions are often exothermic, releasing heat to the surroundings.

Example: Cellular respiration is a catabolic process where glucose is broken down to produce ATP.

Anabolic Reactions

Definition and Examples

Anabolic reactions build complex molecules from simpler ones, requiring an input of energy. These reactions are typically endergonic, meaning they absorb free energy from the surroundings.

• Synthesis of polymers from monomers:

  • Monosaccharides → Polysaccharides

  • Amino acids → Proteins

  • Fatty acids + Glycerol → Triglycerides

  • Nucleotides → Nucleic acids

• Endergonic reactions have a positive change in free energy ().

• These reactions are often endothermic, absorbing heat from the surroundings.

Example: Protein synthesis is an anabolic process where amino acids are joined to form proteins.

Organic Compounds in Metabolism

Major Biological Molecules

Cells use four major classes of organic compounds in metabolic processes. Each class has specific monomers and polymers involved in catabolic and anabolic reactions.

Additional info: The table above summarizes the main organic compounds involved in metabolism, their monomers, polymers, and examples.

Energy in Metabolic Reactions

Free Energy and Reaction Spontaneity

The change in free energy () determines whether a reaction is spontaneous or requires energy input.

• Exergonic reactions: , spontaneous, energy released.

• Endergonic reactions: , non-spontaneous, energy absorbed.

Equation:

Where is the Gibbs free energy.

Summary Table: Catabolic vs. Anabolic Pathways

Additional info: Catabolic and anabolic pathways are interconnected; energy released from catabolic reactions often powers anabolic reactions.