Question

how lactase works: enzymes are proteins that act upon substrates. in this case, the enzyme lactase bonds with milk sugar, lactose, which is a disaccharide made of two subunits. this creates an enzyme-substrate complex. the enzyme then breaks the bonds between the two parts of the lactose, glucose and galactose. the lactase enzyme is not used up in the process and can continue to break down other molecules of lactose.

1. use the underlined words in the above paragraph to label the graphic.
2. in the reaction shown above, what substance is the substrate and what is the enzyme?
3. one model of enzymes describes it as a \lock and a key.\ this is because the enzyme and substrate fit together in order to work. if the temperature is too high, an enzyme can become denatured, and it changes shape. how would this affect its activity?
4. how is it that the same enzyme can be used more than once?

Explanation:

• Question 10: The text states "the enzyme lactase bonds with milk sugar, lactose". Enzymes act on substrates. So lactase is the enzyme and lactose is the substrate.
• Question 11: The "lock - and - key" model implies a specific fit. If the enzyme (lock) changes shape (denatures), the substrate (key) won't fit. So it can't catalyze the reaction.
• Question 12: The text says "the lactase enzyme is not used up in the process". Enzymes are catalysts; they speed up reactions but aren't consumed.

Answer:

• Question 10: The substrate is lactose and the enzyme is lactase.
• Question 11: If the enzyme denatures (changes shape), the substrate won't fit into the active site, and the enzyme can't catalyze the reaction (break down lactose).
• Question 12: Enzymes (like lactase) are catalysts. Catalysts are not consumed in the chemical reactions they facilitate. So the same enzyme molecule can bind to multiple substrate (lactose) molecules over time.