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43286_Ward's World+MGH Enzyme

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7 Enzyme: Test Your Understanding Teacher's Guide + ward ' s science What distinguishes enzymes from other catalysts? A catalyst is a chemical that increases the rate of a chemical reaction without being changed by that reaction. All enzymes are biomolecules: either proteins or ribonucleic acids. Why are enzymes essential to the survival of all living things? Without enzymes, biochemical reactions would proceed too slowly for cells to survive. Suppose you were given an unlabeled sample of an enzyme. The only thing you have been told about this enzyme is that it catalyzes a reaction in which a phosphate group is attached to a particular carbohydrate. Which class of enzymes would this unknown belong to, and why? The unknown enzyme is probably a transferase, because this class of enzymes catalyzes the transfer of a functional group (such as a phosphate) from one molecule to another. Critical Thinking: All living cells today depend on enzymes for reactions vital to their survival, but the earliest forms of life may not have had the ability to make enzymatic proteins. What other types of molecules might the progenitors of life have used to perform catalytic duties? Ribonucleic acid (RNA) is a likely candidate, because it can act as both information carrier and as catalyst in the synthesis of polynucleotides. A better candidate, though, is what scientists call "RNA-like polymers." Research suggests that the first molecules to possess both catalytic activity and information storage capabilities may have been polymers that resemble RNA but are chemically simpler. 7

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