Medical research

Discovery illuminates how cell growth pathway responds to signals

A basic science discovery by researchers at the Johns Hopkins Bloomberg School of Public Health reveals a fundamental way cells interpret signals from their environment and may eventually pave the way for potential new therapies.

Medical research

Viral 'molecular scissor' is next COVID-19 drug target

American and Polish scientists, reporting Oct. 16 in the journal Science Advances, laid out a novel rationale for COVID-19 drug design—blocking a molecular "scissor" that the virus uses for virus production and to disable ...

Medical research

Building bridges: PARP enzymes bring broken DNA together

Scientists at St. Jude Children's Research Hospital have identified the structure of double-strand DNA break repair by PARP enzymes. The findings show that PARP2 can bridge the gap, bringing two broken DNA ends together.

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Enzyme

Enzymes are biomolecules that catalyze (i.e., increase the rates of) chemical reactions. Nearly all known enzymes are proteins. However, certain RNA molecules can be effective biocatalysts too. These RNA molecules have come to be known as ribozymes. In enzymatic reactions, the molecules at the beginning of the process are called substrates, and the enzyme converts them into different molecules, called the products. Almost all processes in a biological cell need enzymes to occur at significant rates. Since enzymes are selective for their substrates and speed up only a few reactions from among many possibilities, the set of enzymes made in a cell determines which metabolic pathways occur in that cell.

Like all catalysts, enzymes work by lowering the activation energy (Ea or ΔG‡) for a reaction, thus dramatically increasing the rate of the reaction. Most enzyme reaction rates are millions of times faster than those of comparable un-catalyzed reactions. As with all catalysts, enzymes are not consumed by the reactions they catalyze, nor do they alter the equilibrium of these reactions. However, enzymes do differ from most other catalysts by being much more specific. Enzymes are known to catalyze about 4,000 biochemical reactions. A few RNA molecules called ribozymes catalyze reactions, with an important example being some parts of the ribosome. Synthetic molecules called artificial enzymes also display enzyme-like catalysis.

Enzyme activity can be affected by other molecules. Inhibitors are molecules that decrease enzyme activity; activators are molecules that increase activity. Many drugs and poisons are enzyme inhibitors. Activity is also affected by temperature, chemical environment (e.g., pH), and the concentration of substrate. Some enzymes are used commercially, for example, in the synthesis of antibiotics. In addition, some household products use enzymes to speed up biochemical reactions (e.g., enzymes in biological washing powders break down protein or fat stains on clothes; enzymes in meat tenderizers break down proteins, making the meat easier to chew).

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