Metabolism

Introduction
A summary of metabolism
- The unity of life
- Biological energy exchanges
  - The carrier of chemical energy
  - Catabolism
    - Incomplete oxidation
    - Complete oxidation
  - Anabolism
- Integration of catabolism and anabolism
  - Fine control
  - Coarse control
- The study of metabolic pathways
The fragmentation of complex molecules
- The catabolism of glucose
  - Glycolysis
    - The aldolase reaction
    - The formation of ATP
  - The phosphogluconate pathway
- The catabolism of sugars other than glucose
  - Release of glucose from glycogen
  - Fragmentation of other sugars
- The catabolism of lipids (fats)
  - Fate of glycerol
  - Fate of fatty acids
    - Formation of fatty acyl coenzyme A molecules
    - Fragmentation of fatty acyl coenzyme A molecules
- The catabolism of proteins
  - Removal of nitrogen
  - Disposal of nitrogen
  - Oxidation of the carbon skeleton
The combustion of food materials
- The oxidation of molecular fragments
  - The oxidation of pyruvate
  - The tricarboxylic acid (TCA) cycle
    - Formation of coenzyme A, carbon dioxide, and reducing equivalent
    - Regeneration of oxaloacetate
    - ATP yield of aerobic oxidation
- Biological energy transduction
  - Adenosine triphosphate as the currency of energy exchange
  - Energy conservation
    - Substrate-level phosphorylation
    - Oxidative, or respiratory-chain, phosphorylation
    - The nature of the respiratory chain
    - ATP synthesis in mitochondria
    - ATP formation during photosynthesis
The biosynthesis of cell components
- The nature of biosynthesis
  - The stages of biosynthesis
  - Utilization of ATP
- The supply of biosynthetic precursors
  - Anaplerotic routes
  - Growth of microorganisms on TCA cycle intermediates
- The synthesis of building blocks
  - Gluconeogenesis
    - Formation of PEP from pyruvate
    - Hydrolysis of fructose 1,6-diphosphate and glucose 6-phosphate
  - Lipid components
    - Glycerol
    - Fatty acids
    - Other components
  - Amino acids
  - Mononucleotides
    - Purine ribonucleotides
    - Pyrimidine ribonucleotides
    - Deoxyribonucleotides
- The synthesis of macromolecules
  - Carbohydrates and lipids
    - Formation of storage polysaccharides
    - Formation of lipids
  - Nucleic acids and proteins
    - Synthesis of DNA
    - Synthesis of RNA
    - Synthesis of proteins
Regulation of metabolism
- Fine control
  - End-product inhibition
  - Positive modulation
  - Energy state of the cell
- Coarse control

References & Edit History Quick Facts & Related Topics

Images

Color-enhanced electron micrograph showing yellow mitochondria and blue endoplasmic reticulum within magenta-stained hepatocyte liver cells at high magnification.

Diagram showing the chemical structures of biological energy carriers: ATP, ADP, and AMP at the top, each with labeled phosphate groups, and acetyl coenzyme A at the bottom, highlighting its molecular components.

A metabolic pathway diagram for Escherichia coli showing how various nutrients-including sugars, fats, glycerol, and amino acids-are broken down into intermediates like pyruvate and acetyl-CoA, leading to the production of energy and other metabolites such as lactate, glutamate, and succinate. Arrows indicate the flow of metabolites between compounds, with key nutrient sources and products highlighted in colored boxes.

A biochemical flowchart shows the metabolic pathways for carbohydrate utilization, including glycolysis, the pentose phosphate pathway, and the tricarboxylic acid (TCA) cycle. The diagram traces the conversion of glucose, fructose, and glycerol through various intermediates, leading to energy production, carbon dioxide release, and biosynthesis of amino acids and porphyrins. Key steps and branches are labeled, with colored boxes highlighting biosynthetic outputs.

A biochemical diagram illustrating the stepwise fragmentation of acyl coenzyme A with an even number of carbon atoms during metabolism, showing chemical structures, key reactions with FAD, H2O, and NAD+, and the splitting into shorter acyl-CoA and acetyl-CoA molecules.

A stepwise biochemical pathway diagram showing the biosynthesis of purine nucleotides, with labeled molecular structures and arrows indicating the conversion from ribose 5-phosphate through several intermediates to inosine acid, then branching to form adenylate (AMP) and guanylate (GMP); ATP and other cofactors are shown at key steps.

Diagram showing the transfer of phosphate groups in cellular metabolism, with high-energy donors like phosphoenolpyruvate, 1,3-diphosphoglycerate, and phosphocreatine passing phosphate to ADP to form ATP, which then donates phosphate to low-energy acceptors such as glucose and glycerol. Vertical axis represents phosphate-group potential.

Diagram of the electron transport chain in cellular respiration, showing protein complexes in a mitochondrial membrane, the movement of electrons and protons, and the roles of ubiquinone and cytochrome C.

Diagram of the respiratory chain in metabolism, showing the flow of electrons from NADH and FADH2 through complexes and cytochromes, ending with the reduction of oxygen to water. Key molecules, sites, and electron transfers are labeled.

At a Glance

Color-enhanced electron micrograph showing yellow mitochondria and blue endoplasmic reticulum within magenta-stained hepatocyte liver cells at high magnification.

metabolism summary

Metabolism: Media

biology

Images

Color-enhanced electron micrograph showing yellow mitochondria and blue endoplasmic reticulum within magenta-stained hepatocyte liver cells at high magnification.

Mitochondria and cellular respiration

Electron micrograph of hepatocyte cells showing mitochondria (yellow). The primary...

© BISP—Universal Images Group/Getty Images

Diagram showing the chemical structures of biological energy carriers: ATP, ADP, and AMP at the top, each with labeled phosphate groups, and acetyl coenzyme A at the bottom, highlighting its molecular components.

Biological energy carriers

Adenosine triphosphate (ATP) is the major carrier of biologically utilizable energy.

Encyclopædia Britannica, Inc.

A metabolic pathway diagram for Escherichia coli showing how various nutrients-including sugars, fats, glycerol, and amino acids-are broken down into intermediates like pyruvate and acetyl-CoA, leading to the production of energy and other metabolites such as lactate, glutamate, and succinate. Arrows indicate the flow of metabolites between compounds, with key nutrient sources and products highlighted in colored boxes.

Catabolism in E. coli

Pathways for the catabolism of nutrients by Escherichia coli.

Encyclopædia Britannica, Inc.

glucose

glucose

The structure of α-d-glucose.

A biochemical flowchart shows the metabolic pathways for carbohydrate utilization, including glycolysis, the pentose phosphate pathway, and the tricarboxylic acid (TCA) cycle. The diagram traces the conversion of glucose, fructose, and glycerol through various intermediates, leading to energy production, carbon dioxide release, and biosynthesis of amino acids and porphyrins. Key steps and branches are labeled, with colored boxes highlighting biosynthetic outputs.

pathways for the utilization of carbohydrates

Pathways for the utilization of carbohydrates.

Encyclopædia Britannica, Inc.

A biochemical diagram illustrating the stepwise fragmentation of acyl coenzyme A with an even number of carbon atoms during metabolism, showing chemical structures, key reactions with FAD, H2O, and NAD+, and the splitting into shorter acyl-CoA and acetyl-CoA molecules.

fragmentation of acyl coenzyme A

Fragmentation of acyl coenzyme A with an even number of carbon atoms.

Encyclopædia Britannica, Inc.

A stepwise biochemical pathway diagram showing the biosynthesis of purine nucleotides, with labeled molecular structures and arrows indicating the conversion from ribose 5-phosphate through several intermediates to inosine acid, then branching to form adenylate (AMP) and guanylate (GMP); ATP and other cofactors are shown at key steps.

biosynthesis of purine nucleotides

Biosynthesis of purine nucleotides. Not all of the intermediate compounds formed...

Encyclopædia Britannica, Inc.

Diagram showing the transfer of phosphate groups in cellular metabolism, with high-energy donors like phosphoenolpyruvate, 1,3-diphosphoglycerate, and phosphocreatine passing phosphate to ADP to form ATP, which then donates phosphate to low-energy acceptors such as glucose and glycerol. Vertical axis represents phosphate-group potential.

ATP and energy exchange

The transfer of phosphate groups from high-energy donors to low-energy acceptors...

Encyclopædia Britannica, Inc.

Diagram of the electron transport chain in cellular respiration, showing protein complexes in a mitochondrial membrane, the movement of electrons and protons, and the roles of ubiquinone and cytochrome C.

Electron transport chain

The series of steps by which electrons flow to oxygen permits a gradual lowering...

Encyclopædia Britannica, Inc./Catherine Bixler

Diagram of the respiratory chain in metabolism, showing the flow of electrons from NADH and FADH2 through complexes and cytochromes, ending with the reduction of oxygen to water. Key molecules, sites, and electron transfers are labeled.

The respiratory chain

Four types of hydrogen or electron carriers are known to participate in the respiratory...

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Diagram illustrating metabolism with two sections: anabolic reaction on the left shows energy used to build larger molecules from smaller ones, while catabolic reaction on the right shows larger molecules breaking down into smaller molecules with energy released.

Metabolism

In anabolic reactions, a cell uses energy to combine small molecules into larger...

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Diagram of the glyoxylate cycle showing the metabolic pathway steps, with arrows indicating the flow between compounds such as acetate, acetyl S-CoA, citrate, isocitrate, glyoxylate, succinate, and malate. CO2 release and biosynthesis branches are highlighted.

Glyoxylate cycle

The glyoxylate cycle, a metabolic pathway found in plants, bacteria, and fungi, allows...

Encyclopædia Britannica, Inc.

A biochemical pathway diagram showing the catabolism and biosynthesis of glucose and glycogen, with glucose breakdown reactions on the left and synthesis reactions on the right, interconnected by labeled arrows and chemical intermediates.

Glucose and glycogen catabolism and biosynthesis

The catabolism and biosynthesis of glucose and glycogen involve multiple chemical...

Encyclopædia Britannica, Inc.

Diagram showing metabolic pathways for amino acid biosynthesis, divided into families: glutamate, aspartate, serine, pyruvate, shikimate, and histidine. Amino acids, underlined to indicate protein components, branch from intermediate compounds, with arrows showing synthesis relationships. Some intermediates and side products are labeled, and related amino acids are grouped by precursor molecules.

family relationships in amino acid biosyntheses

Family relationships in amino acid biosyntheses. Components of proteins are underlined....

Encyclopædia Britannica, Inc.

A metabolic pathway diagram shows the aspartate family in E. coli, with black arrows indicating steps from oxaloacetate to aspartate and onward to lysine, methionine, threonine, and isoleucine. Red X marks and dashed yellow lines highlight enzyme regulation points.

Aspartate amino acids in E. coli

“Fine control” of the enzymes of the aspartate family in E. coli.

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blood alcohol concentration by quantity of alcohol over time

blood alcohol concentration by quantity of alcohol over time

Percent of blood alcohol concentration in an average man at hourly intervals after...

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blood alcohol concentration

blood alcohol concentration

Percent of blood alcohol concentration in an average man at hourly intervals after...

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Line graph showing plasma concentration of a drug over 20 hours after oral administration, with a rapid rise during absorption, a peak, and gradual decline during elimination.

Figure 1: Typical course of changes in the plasma concentration of a drug over time...

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Diagram showing how B-vitamin coenzymes, such as vitamin B6, folic acid, and biotin, assist in metabolic pathways involving carbohydrates, fats, and proteins, highlighting their roles in energy production and the tricarboxylic acid cycle.

B-vitamin coenzymes in metabolism

Functions of B-vitamin coenzymes in metabolism.

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