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Anabolism

©2000 Timothy Paustian, University of Wisconsin-Madison

Part of existing as a living creature is extract energy from food and we have just finished discussing this process in detail. The overall goal of catabolism is to generate energy (ATP) and reducing power (NADH) that can then be used in part, to grow. Anabolism is the general term for the synthesis of cell structures.

A useful analogy when thinking about anabolism is the tinker toy set you may have played with as a child. (OK, alright, I still play with mine, but I have kids as an excuse.) Cells first must collect the carbon, nitrogen, sulfur, phosphorus, oxygen, hydrogen, potassium, calcium and all the rest of the elements necessary for cell biosynthesis. Then they assemble these tinker toy parts (nutrients) into useful structures. These necessary parts constitute the nutritional requirements of the cell. Elements, usually as part of molecules, must be found in the environment and transported across the membrane. Typically this involves concentrating them against a gradient and that requires energy. Once inside the cell, the elements are assembled into monomers that the cell needs. The diversity of life on Earth uses a surprisingly small number of monomers to form the great variety of cellular structures. These monomers can be classified as amino acids, nucleotides, polysaccharides, fatty acids and vitamins. Monomers are polymerized into macromolecules; proteins, nucleic acids, peptidoglycan and lipids. Finally, macromolecules are aggregated into larger collections that make up important structures in the cell; ribosomes, chromosomes, membranes and cell walls to name a few. While the details of how these reactions take place to make a cell can be very complex, getting your head around the general concepts is much easier.

Figure 1 - An overview of anabolism.

Road map

The rest of this discussion of metabolism is devoted to explaining, in general terms, the biosynthesis of cells from elements to cellular structures.

• Collection of Elements describes the process of finding elements and concentrating then in the cell.

• Synthesis of Monomers details taking the molecules collected from the environment and using them to make the monomers needed by the cell.

• Assembly of Polymers explains how these monomers are linked together to form important polymers in the cell.

• Finally, Assembly of Stuctures describes the concepts that are important in the formation cell structures.

A detailed treatment of anabolism is beyond the scope of this text book. The goal of this section is to present general ideas to help the student get a feel for the issues involved in making a cell and appreciate the beauty and complexity of the process.

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