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Cell: Structure and Function - Enzymes (Types, Properties, Enzyme Action)

Grade 11ICSEBiology

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Enzymes are proteinaceous biocatalysts (except ribozymes made of RNARNA) that accelerate the rate of metabolic reactions by lowering the activation energy (EaE_a).

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The 'Lock and Key' hypothesis suggests a rigid active site, while the 'Induced Fit' hypothesis proposes that the enzyme's active site changes shape slightly to fit the substrate (SS).

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Michaelis-Menten Constant (KmK_m): Defined as the substrate concentration at which the reaction velocity is half of its maximum velocity (VmaxV_{max}). It is inversely proportional to the enzyme's affinity for the substrate.

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Factors affecting enzyme activity include temperature, pHpH, and substrate concentration [S][S]. Most enzymes have an optimum temperature (usually 37∘C37^{\circ}C in humans) and pHpH.

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Enzymes are classified into six classes by the IUBMB: 1. Oxidoreductases, 2. Transferases, 3. Hydrolases, 4. Lyases, 5. Isomerases, and 6. Ligases.

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A Holoenzyme is a complete, catalytically active enzyme consisting of a protein part (Apoenzyme) and a non-protein part (Co-factor).

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Competitive Inhibition occurs when an inhibitor molecule closely resembles the substrate and competes for the active site, increasing the KmK_m but leaving VmaxV_{max} unchanged.

📐Formulae

E+S⇌ES→E+PE + S \rightleftharpoons ES \rightarrow E + P

v=Vmax[S]Km+[S]v = \frac{V_{max} [S]}{K_m + [S]}

Holoenzyme=Apoenzyme+Co−factorHoloenzyme = Apoenzyme + Co-factor

Q10=Rate at (t+10)∘CRate at t∘C≈2Q_{10} = \frac{\text{Rate at } (t + 10)^{\circ}C}{\text{Rate at } t^{\circ}C} \approx 2

ΔGcatalyzed‡<ΔGuncatalyzed‡\Delta G^{\ddagger}_{catalyzed} < \Delta G^{\ddagger}_{uncatalyzed}

💡Examples

Problem 1:

If an enzyme-catalyzed reaction reaches its maximum velocity VmaxV_{max} at a substrate concentration of 10 mmol/L10 \text{ mmol/L}, what is the KmK_m if the velocity is 12Vmax\frac{1}{2} V_{max} at 2 mmol/L2 \text{ mmol/L}?

Solution:

The KmK_m is 2 mmol/L2 \text{ mmol/L}.

Explanation:

By definition, the Michaelis-Menten constant (KmK_m) is the substrate concentration [S][S] at which the reaction rate is exactly half of the maximum velocity (V=12VmaxV = \frac{1}{2} V_{max}). Since the velocity is 12Vmax\frac{1}{2} V_{max} when [S]=2 mmol/L[S] = 2 \text{ mmol/L}, then Km=2 mmol/LK_m = 2 \text{ mmol/L}.

Problem 2:

Describe the chemical reaction involving Carbonic Anhydrase in the blood.

Solution:

CO2+H2O→Carbonic AnhydraseH2CO3CO_2 + H_2O \xrightarrow{\text{Carbonic Anhydrase}} H_2CO_3

Explanation:

Carbonic anhydrase is one of the fastest enzymes known, increasing the reaction rate of carbon dioxide (CO2CO_2) and water (H2OH_2O) to form carbonic acid (H2CO3H_2CO_3) by about 10710^7 times compared to the uncatalyzed reaction.

Problem 3:

Identify the components of the enzyme system for Succinate Dehydrogenase and Malonate.

Solution:

Substrate = Succinate; Inhibitor = Malonate.

Explanation:

Malonate acts as a competitive inhibitor for Succinate Dehydrogenase because it structurally resembles the substrate Succinate. This competition for the active site can be overcome by increasing the concentration of Succinate.

Enzymes (Types, Properties, Enzyme Action) Revision - Class 11 Biology ICSE