Question 1

Which of the following best describes how chymotrypsin increases the rate of peptide bond hydrolysis compared to uncatalyzed hydrolysis by water?

Accepted Answer

By stabilizing the transition state and using a nucleophilic serine residue to attack the peptide bond

Question 2

Refer to the equation $$	ext{rate} = p \cdot Z \cdot e$$^{-\frac{E_a}$${RT}}. $$What does $$E_a$$ represent in the context of enzyme catalysis?

Accepted Answer

The activation energy required for the reaction to proceed

Question 3

Which amino acid in the chymotrypsin catalytic triad acts as a nucleophile during peptide bond hydrolysis?

Accepted Answer

Serine (Ser 195)

Question 4

What is the role of the oxyanion hole in chymotrypsin catalysis?

Accepted Answer

It stabilizes the negative charge on the transition state intermediate

Question 5

During the catalytic cycle of chymotrypsin, which step involves the formation of the acyl-enzyme intermediate?

Accepted Answer

When the nucleophilic group in the enzyme attacks the peptide C=O, releasing the C-terminal half

Question 6

Which of the following is a correct application of Beer-Lambert Law for measuring enzyme activity?

Accepted Answer

Absorbance $$A = \varepsilon \cdot c \cdot l$$, where $$\varepsilon is $$the extinction coefficient, $$c is $$concentration, and $$l is $$path length

Question 7

If the initial substrate concentration is $$25.0 	imes 10$$^{-4}$$ M and after 10 minutes it is 18.6$$ 	imes $$10^{-4} M in a 2.5 mL $$reaction, what is the rate of reaction in $$	ext{mol} \cdot 	ext{L}^{-1} \cdot 	ext{min}^{-1}$$?

Accepted Answer

$$6.4 	imes 10$$^{-5}$$

Question 8

What does the Michaelis constant ($$K_M) $$indicate about an enzyme?

Accepted Answer

The substrate concentration at which the reaction rate is half of $$V_{max}$$

Question 9

Which equation represents the Michaelis-Menten relationship for enzyme kinetics?

Accepted Answer

$$v_0$$ = \frac{V_{max} [S]}{K_M + [S]}$$

Question 10

In a Lineweaver-Burk plot, what does the y-intercept represent?

Accepted Answer

$$\frac{1}{V_{max}}$$

Question 11

Which type of enzyme inhibition results in an increase in apparent $$K_M$$ but no change in $$V_{max}$$?

Accepted Answer

Competitive inhibition

Question 12

A drug acts as a competitive inhibitor for an enzyme. What effect does increasing substrate concentration have on the enzyme's activity?

Accepted Answer

It restores the enzyme's activity toward normal by outcompeting the inhibitor

Question 13

What is the turnover number (kcat) of an enzyme?

Accepted Answer

The number of substrate molecules converted per molecule of enzyme per second

Question 14

Which of the following statements about non-competitive inhibition is correct?

Accepted Answer

The inhibitor binds to a site other than the substrate binding site and decreases $$V_{max}$$

Question 15

If an enzyme has a $$K_M of$$ $$2.0 	imes 10$$^{-4}$$ M and reacts in the presence of 5.0$$ 	imes $$10^{-4} M $$substrate, what is $$v_0 as a $$fraction of $$V_{max}$$?

Accepted Answer

$$0.71$$

Question 16

What is the effect of replacing His 57 with Lys in the chymotrypsin catalytic triad?

Accepted Answer

The enzyme loses most catalytic activity because Lys is a poor acid

Question 17

Which of the following best describes the function of chromophores in enzyme assays?

Accepted Answer

They absorb visible or UV light, allowing measurement of reaction progress

Question 18

In the context of enzyme purification, what does specific activity measure?

Accepted Answer

The number of enzyme units per milligram of total protein

Question 19

Which of the following is a real-world example of enzyme inhibition used in medicine?

Accepted Answer

Ibuprofen inhibits cyclo-oxygenase enzymes, reducing inflammation

Enzyme Catalysis and Kinetics: Chymotrypsin as a Model

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