Biology, Eighth Edition (Raven)

Chapter 6: Energy and Metabolism

How Enzymes Work

How are food molecules broken down into simpler molecules by enzymes? A common method for splitting apart complex molecules is hydrolysis. Hydrolysis means to split with water. Enzymes use the chemical properties of water to break chemical bonds and produce smaller molecules. When a molecule is hydrolyzed a chemical bond is broken that divides the molecule into two component molecules. During hydrolysis the water molecule splits into a hydrogen and a hydroxyl (OH). The hydrogen bonds to one of the two component molecules at the point where the bond was broken. The hydroxyl bonds to the other component molecule, also at the point of the broken bond. The opposite process to hydrolysis is dehydration. During dehydration, hydrogens and hydroxyls are removed as individual molecules are attached to one another to form polymers.

View the animation below, then complete the quiz to test your knowledge of the concept.


1.	Enzymes are

		A)	lipids.
		B)	proteins.
		C)	carbohydrates.
		D)	nucleic acids.
		E)	steroids.

2.	Which of the following binds to the active site of an enzyme?

		A)	water
		B)	product
		C)	substrate
		D)	any other enzyme
		E)	none of the above

3.	Which of the following correctly represents the mechanism of enzyme function?

		A)	S + P -> E-P -> E + P
		B)	E + P -> E-P -> E-S -> E + S
		C)	E + P -> E-S -> E-P -> E + P
		D)	E + S -> E-S -> E-P -> E + P
		E)	E + S -> E-P -> E-S -> E + S

4.	An enzyme can only bind one reactant at a time.

		A)	True
		B)	False

5.	An enzyme speeds up a chemical reaction in the cell, but can only be used once.

		A)	True
		B)	False