Metabolism: Energy and Structural Balance

Metabolism: Energy and Structural Balance

Metabolism is the sum of all chemical reactions that occur within a living organism, sustaining life and performing biological functions. The two main processes in metabolism are catabolism and anabolism, working together to maintain energy and structural balance in the body.

Catabolism: The breakdown of complex nutrient molecules (carbohydrates, lipids, proteins) into simpler molecules, releasing energy.

• Catabolic reactions are typically exothermic, providing energy for the body:

• About 40% of the energy is converted into ATP – the “energy currency” of the cell.

• The remaining 60% is released as heat.

• Most catabolic reactions are oxidation processes, using NADH and NADPH as intermediates.

• The energy required for biosynthesis is always greater than the energy obtained from catabolizing that substance.

Anabolism: The process of synthesizing complex biological molecules from simpler precursors, requiring energy.

• Anabolism requires a supply of chemical energy, often obtained from catabolic processes.

• Anabolism and catabolism are not mutually exclusive but operate in parallel, creating energy and structural balance in the body.

The catabolism of different substances all converge on common products: carbon dioxide (CO2), water (H2O), and ammonia (NH3).

Catabolism is divided into three main stages:

1. Stage 1: Breakdown of nutrient macromolecules into their corresponding building blocks:

• Proteins are broken down into 20 constituent amino acids.

• Polysaccharides are broken down into glucose.

• Lipids are broken down into glycerol and fatty acids.

2. Stage 2: The products of stage 1 undergo further degradation:

• Amino acids undergo deamination, forming ?-keto acid carbon skeletons.

• Glucose and glycerol form pyruvate.

• Fatty acids are cleaved into 2-carbon units as acetyl-CoA.

• Pyruvate also forms acetyl-CoA.

3. Stage 3: The acetyl group in acetyl-CoA is oxidized in the citric acid cycle, followed by oxidative phosphorylation, producing final products of CO2, H2O.

Anabolic pathways:

• Anabolic pathways only start from a few simple precursors:

• ?-keto acid carbon skeletons form amino acids.

• Pyruvate is converted into hexose for polysaccharide synthesis.

Amphibolism:

• Some metabolic reactions can serve both anabolic and catabolic purposes.

Differences between anabolic and catabolic pathways:

• Corresponding anabolic and catabolic pathways of a substance may share some intermediate products but differ in their specific enzymes and metabolites.

• For example, glycolysis (catabolism of glucose to pyruvate) uses 10 enzymes, while gluconeogenesis (synthesis of glucose from pyruvate) uses 7 enzymes from glycolysis plus 4 specific enzymes.

Forms of metabolic pathways:

• Linear pathway: The metabolic flow moves in a straight line.

• Cyclic pathway: The metabolic flow moves in a closed loop.

• Spiral pathway: The metabolic flow moves in a spiral, continuously repeating and expanding.

Methods for studying intermediary metabolism:

• Levels:

• Determining the sequence of reactions and energy of conversion.

• Studying the mechanism of conversion from one substance to another.

• Studying the mechanism of regulating metabolic flow through that pathway.

• Techniques:

• Using whole organisms (fungi, animals).

• Using techniques for studying metabolism on whole organs, thin tissue sections, cell cultures, and isolated organelles.

• Current research directions:

• Studying genes and proteins.

• Labeling metabolites using techniques like chemical labeling, isotopic labeling, and nuclear magnetic resonance.

• Disrupting the system to study the characteristics of intermediates and enzymes involved in the metabolic pathway.

• Systems biology uses techniques to analyze simultaneously the number of gene transcripts, proteins, and metabolites, combined with new computational and mathematical tools, to better understand metabolism.

In conclusion: Metabolism is a complex and essential process that sustains life in the body. Understanding metabolism helps us better understand the body’s mechanisms of action and develop effective treatment methods for metabolic diseases.