MadSci Network: Biochemistry
Query:

Re: How does an enzyme break down a substrate to produce a product?

Date: Mon Dec 4 02:23:03 2000
Posted By: Scott Spencer, Staff, DNA Synthesis, Sequencing & Analysis, Applied Biosystems, Foster City, CA
Area of science: Biochemistry
ID: 975301985.Bc
Message:

An enzyme is a strand of protein, formed of individual amino acids, folded [_The Cartoon Guide to Genetics_, Larry Gonick and Mark Wheelis] into a specific shape. It's like a paper wad with a big crevice, and the inside of the crevice is lined with the "functional groups" of the amino acids. Func.groups can attract/repel water (hydro-philic/phobic), form temporary bonds (attraction to nonbonding orbitals or hydrogen bonding) with a substrate, or exclude molecules by size and shape (stearic inhibition). "Texturing" of func.groups within the crevice [_Bio-Organic Chemistry: A Chemical Approach to Enzyme Action_, Hermann Dugas] prevents all but a few types of molecules (substrates) from entering the "active site."

Once inside, the enzyme temporarily "bonds" with the substrate (like a Transitional Form). This process can either change the substrate's func.groups, or break some of them off (and is governed by a combination of Activation Energy, Entropy, and Reaction Kinetics). After the "de- composition," the substrate no longer fits properly in the active site, and is released.

How substrates enter and exit so quickly is still somewhat mysterious. Many enzymes are lodged in cell walls, "channels," or "receptors" (like taste buds), but some just float through the blood or digestive tracts. While most enzymes perform 10-100 substrate conversions per second, some perform more than 10,000/sec.! Many of the details of enzyme action and how Life is created and sustained, are still waiting to be discovered.

American Chemical Society

http://www.iupac.org

Amazon.com (-> science books-> chemistry -> biochemistry)


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