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Chemistry LibreTexts

Metabolism

(Greek: meltable, change) The biochemical processes by which all living organisms sustain life. Metabolism is the sum of all chemical processes occurring within living cells and organisms. Although most living organisms on earth share common pathways to sustain life they do so with the use of  different sources of energy and carbon.

Introduction

Metabolism consists of two main types of reactions, catabolic and anabolic. Catabolic processes are ones in which biomolecules are being degraded or oxidized. Anabolic processes are ones in which biomolecules are built via biosynthesis and reduction. Below is a diagram of CO2 being reduced completely. Oxidation of methane can be seen by following the process in reverse.   

anabol02.jpg

Catabolism

(Greek ketabole, throwing down) The biochemical processes of metabolism by which molecules are broken down. Often catabolism is an oxidative process in which carbons have hydrogen atoms removed. CO2 is the most oxidized form of carbon. NADH is the primary electron acceptor for catabolic reactions.

catabol01.jpg

Anabolism

(Greek, ana, up, + bolein, to throw)  The biochemical processes of metabolism by which molecules are synthesized or built up. Often anabolism is a reductive process in which carbons have hydrogen atoms added. Fully saturated fatty acids are the most reduced form of carbon. NADPH is the primary electron donator for anabolic reactions.

anabol01.jpg

Organism Classifications

 

Classification

Carbon source

Energy source

Electron donor

Example

Photoautotroph

CO2

Light

H2O, H2S, S, inorganic compounds

Green plants, photosynthetic bacteria

Photoheterotrophs

Organic compounds

Light

Organic compounds

Nonsulfur purple bacteria

Chemoautotrophs

CO2

Redox reactions

Inorganic compounds: H2, H2S, NH4+, Fe2+

Hydrogen, sulfur and iron bacteria

Chemoheterotrophs

Organic compounds

Redox reactions

Organic compounds (e.g. glucose)

All animals, most microorganisms

References

  1. Garrett, H., Reginald and Charles Grisham. Biochemistry. Boston: Twayne Publishers, 2008.
  2. Raven, Peter. Biology. Boston: Twayne Publishers, 2005.

Problems

  1. Photoheterotrophs use this as their primary source of carbon.
  2. Is ATP usually synthesized or degraded during oxidative processes?
  3. True of False Methanol is more reduced than methane.
  4. Name the primary electron acceptor for catabolic reactions.
  5. Is Glycolysis a catabolic or anabolic process?

Contributors

Mike Blaber (Florida State University)

  • Darik Benson (UCD)