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Explain the Role of Enzymes in Chemical Reactions & Metabolic Pathways

by
author image Matthew Fox, MD
Dr. Matthew Fox graduated from the University of California with a Bachelor of Arts in molecular, cell and developmental biology and received a M.D. from the University of Virginia. He is a pathologist and has experience in internal medicine and cancer research.
Explain the Role of Enzymes in Chemical Reactions & Metabolic Pathways
Lens of a microscope Photo Credit Stockbyte/Stockbyte/Getty Images

Enzymes are a common and integral part of all body systems. They are coded for and constructed by cells, with each cell making different enzymes specific to the cell's function, as well as enzymes common to all or most cells. Enzymes help chemical reactions progress in the body; a series of chemical reactions is called a biochemical pathway.

Enzyme Synthesis

Enzymes are a special type of protein. Proteins are composed of amino acids. The DNA in a cell's nucleus contains a sequence of chemicals, called bases, which correspond to the letters A, T, C and G. A long sequence of bases codes for a protein. This sequence is called a gene. Every three bases is called a codon; it codes for an amino acid. For example, the code AGA codes for the amino acid arginine; if this were followed by GTT, valine would be the next amino acid in the protein. Each active gene in DNA is essentially copied into a similar chemical called RNA, which is taken out of the nucleus of the cell. Then the RNA is used to assemble the proteins on structures called ribosomes.

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Enzyme Structure

The amino acids are chained together one by one. As they come together, the amino acids begin to fold into more complex structures. A very long sequence of amino acids will ultimately form a three-dimensional machine we call an enzyme. The enzymes have areas of magnetic and electrical charge and have moving parts like a machine.

Chemical Reactions and Enzyme Function

Chemicals bind to an enzyme in a manner analogous to a lock and key. For example, a chemical with three sides like a triangle may have a positive side and two negative sides. An enzyme that binds that chemical will have a negative side and two positive sides to magnetically bind the chemical. This area of chemical binding is called the active site. Once bound, the enzyme can change shape to change the chemical. It can break a bond between atoms in the molecule, or form new bonds, or join two chemicals together. These chemical reactions can happen normally without enzymes, but may occur very slowly. Enzymes speed up chemical reactions and direct chemicals through a sequence of changes.

Enzyme Pathways

Many enzyme pathways exist in the body, and many of these have yet to be discovered and fully elucidated. The process described above, with the reading of DNA, construction of RNA from its bases and synthesis of proteins such as enzymes from the RNA involves a series of chemical reactions. These reactions are sped up, or catalyzed, by enzymes. As another example, the carbohydrates in food undergo a sequence of chemical reactions to ultimately make fuel for the cell; these chemical reactions occur through numerous enzymes. Enzymes can break down fat, or build up fat, or synthesize hormones such as testosterone; all of these processes involve chemical reactions.

Enzyme Regulation

Enzymes also have binding sites separate from their main binding site, called allosteric sites, that can bind to other chemicals to speed up or slow down the rate at which they work. In addition, other chemicals can bind to the active site and inhibit it by competing for the site. Many drugs work in this manner. NSAIDs such as ibuprofen bind to the enzyme COX and inhibit it from making chemicals of inflammation.

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References

  • "Lehninger Principles of Biochemistry"; David L. Nelson and Michael M. Cox; 4th Ed., 2004
  • “Molecular Biology of the Cell”; Bruce Alberts et al.; 4th Ed., 2002
  • “Basic and Clinical Pharmacology”; Bertram Katzung, Susan Masters, and Anthony Trevor; 11th Ed., 2009
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