5.12B: Biosynthesis and Energy

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Biosynthetic processes ensure the production of complex products necessary for cellular and metabolic processes.

Learning Objectives

Discuss the principles of biosynthesis and provide examples

Key Points

Anabolism is the form of metabolism responsible for building large complexes from precursors.
The three categories of carbon fixation pathways are the Calvin cycle, the reverse TCA, and acetyl-CoA pathways.
One example of a biosynthetic process is gluconeogenesis, which is responsible for the production of glucose from noncarbohydrate precursors.

Key Terms

anabolism: Anabolism is the set of metabolic pathways that construct molecules from smaller units.
biosynthesis: Biosynthesis is an enzyme-catalyzed process in cells of living organisms by which substrates are converted to more complex products.
metabolic: Of or pertaining to metabolism; as, metabolic activity; metabolic force.

Biosynthesis and Energy

Biosynthesis in living organisms is a process in which substrates are converted to more complex products. The products which are produced as a result of biosynthesis are necessary for cellular and metabolic processes deemed essential for survival. Biosynthesis is often referred to as the anabolism branch of metabolism that results in complex proteins such as vitamins.

Figure: **Overview of Gluconeogenesis**: A biosynthetic pathway is utilized in microorganisms to produce glucose.

A majority of the organic compounds required by microorganisms are produced via biosynthetic pathways. The components which are utilized by biosynthetic pathways to promote the production of large molecules include chemical energy and catalytic enzymes. Biosynthetic building blocks utilized by organisms include amino acids, purines, pyrimidines, lipids, sugars, and enzyme cofactors. There are numerous mechanisms in place to ensure biosynthetic pathways are properly controlled so a cell will produce a specific amount of a compound. Biosynthetic metabolism (also known as anabolism) involves the synthesis of macromolecules from specific building blocks. A majority of these processes are considered to be multi-step or multi-enzymatic processes.

Carbon Dioxide Fixation

Carbon dioxide fixation is necessary to ensure carbon dioxide can be converted into organic carbon. The major pathways utilized to ensure fixation of carbon dioxide include: the Calvin cycle, the reductive TCA cycle, and the acetyl-CoA pathway. The Calvin cycle involves utilizing carbon dioxide and water to form organic compounds. The reductive TCA cycle, commonly referred to as the reverse Krebs cycle, also produces carbon compounds from carbon dioxide and water. In the acetyl-CoA pathway, carbon dioxide is reduced to carbon monoxide and then acetyl-CoA.

Glucose and Fructose Synthesis

An additional biosynthetic pathway utilized by microorganisms includes the synthesis of sugars and polysaccharides. The ability to synthesize sugars and polysaccharides from noncarbohydrate precursors is key to survival in numerous microorganisms. The process of gluconeogenesis, characterized by the production of glucose or fructose from noncarbohydrate precursors, is an ubiquitous process. This process utilizes precursors such as pyruvate, lactate, or glycerol.