8 Enzymes

Look at the graph of reaction rate versus substrate concentration for an enzyme. In which region does the reaction rate remain constant? A B C

Refer again to the graph. In which region is the enzyme saturated with substrate? Hints region A region B region C

Consider a situation in which the enzyme is operating at optimum temperature and pH, and has been saturated with substrate. What is your best option for increasing the rate of the reaction? Hints Increase the pH. Increase the temperature. Increase the enzyme concentration. Increase the substrate concentration.

1. A (n)______________ inhibitor has a structure that is so similar to the substrate that it can bond to the enzyme just like the substrate. 2. A (n)______________ inhibitor binds to a site on the enzyme that is not the active site. 3. Usually, a(n) _____________ inhibitor forms a covalent bond with an amino acid side group within the active site, which prevents the substrate from entering the active site or prevents catalytic activity. 4. The competitive inhibitor competes with the substrate for the ______________ on the enzyme. 5. When the noncompetitive inhibitor is bonded to the enzyme, the shape of the ______________ is distorted. 6. Enzyme inhibitors disrupt normal interactions between an enzyme and its ______________.

You have added an irreversible inhibitor to a sample of enzyme and substrate. At this point, the reaction has stopped completely. What can you do to regain the activity of the enzyme? Removing the irreversible inhibitor should get the reaction working again. The enzyme is inactive at this point. New enzyme must be added to regain enzyme activity. Adding more substrate will increase the rate of reaction. Adding more inhibitor should get the reaction up to speed again.

You have an enzymatic reaction proceeding at the optimum pH and optimum temperature. You add a competitive inhibitor to the reaction and notice that the reaction slows down. What can you do to speed the reaction up again? Add more inhibitor to speed up the reaction. Add more substrate; it will outcompete the inhibitor and increase the reaction rate. Increase the temperature. Increase the pH.

Rank these by reaction rate, as measured by the rate of product formation per unit time, from lowest reaction rate to highest reaction rate. To rank items as equivalent, overlap them. Order: -reaction catalyzed by enzyme A -reaction catalyzed by enzyme B -uncatalyzed reaction

1. An enzyme is _____________ when it loses its native conformation and its biological activity. 2. An enzyme is considered a _____________ because it speeds up chemical reactions without being used up. 3. An enzyme is considered _____________ because of its ability to recognize the shape of a particular molecule. 4. A _____________, such as a vitamin, binds to an enzyme and plays a role in catalysis. 5. When properly aligned, the enzyme and substrate form an enzyme-substrate (ES) _____________. 6. A substrate binds to an enzyme at the _____________, where the reaction occurs. 7. In a catalyzed reaction a reactant is often called a _____________.

In general, enzymes are what kinds of molecules? carbohydrates lipids minerals nucleic acids proteins

Enzymes work by _____. reducing EA adding energy to a reaction decreasing the potential energy difference between reactant and product adding a phosphate group to a reactant increasing the potential energy difference between reactant and product

An enzyme _____. is a inorganic catalyst is a source of energy for endergonic reactions increases the EA of a reaction can bind to nearly any molecule is an organic catalyst

What name is given to the reactants in an enzymatically catalyzed reaction? reactors products active sites EA substrate

As a result of its involvement in a reaction, an enzyme _____. is used up loses a phosphate group loses energy permanently alters its shape. is unchanged

Which of the following statements is most likely to be true in the case of the feedback-regulated enzymatic pathway shown? Hints P0 binds E4 and activates it. P2 binds E2 and activates it. P4 binds E1 and deactivates it. P3 binds E2 and activates it P4 binds E3 and deactivates it.

How does an enzyme increase the rate of the chemical reaction it catalyzes? An enzyme reduces the free-energy change (?G) of the reaction it catalyzes. An enzyme's active site binds only the reactants, and not the products of a reaction, pushing the equilibrium for the reaction far to the right. An enzyme reduces the free energy of activation (EA) of the reaction it catalyzes.

Which statement about the binding of enzymes and substrates is correct? Substrate molecules fit into the active site of an enzyme like a key fits into a lock. Substrate molecules bind to the active site of the enzyme only by weak bonds, such as hydrogen bonds or hydrophobic attraction. When substrate molecules bind to the active site of the enzyme, the enzyme undergoes a slight change in shape.

If an enzyme in solution is saturated with substrate, the most effective way to obtain a faster yield of products is to add more of the enzyme. add more substrate. add a noncompetitive inhibitor. add an allosteric inhibitor. heat the solution to 90°C.

Some bacteria are metabolically active in hot springs because high temperatures make catalysis unnecessary. their enzymes have high optimal temperatures. their enzymes are completely insensitive to temperature. they are able to maintain a lower internal temperature. they use molecules other than proteins or RNAs as their main catalysts.