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Chapter 14: Problem 114

The human body is characterized by an extremely complex system of interrelated chemical reactions. A large number of enzymes are necessary for many of these reactions to occur at suitable rates. Enzymes are very selective in the reactions they catalyze, and some are absolutely specific. Use the lock-and- key model to account for the specificity of an enzyme.

Short Answer

Expert verified
The specificity of enzymes arises from the lock-and-key model, where the enzyme's active site has a unique three-dimensional structure that can only accommodate substrates with the correct shape and chemical properties. This unique structure ensures that the enzyme only catalyzes the intended reaction, maintaining the accuracy and selectivity in the numerous chemical reactions within a cell.

Step by step solution

01

Understand the Lock-and-Key Model

The lock-and-key model is a way to explain how enzymes work to catalyze certain reactions. In this model, the enzyme is compared to a lock, and the substrate (the molecule on which the enzyme acts) is compared to a key. Just as a lock can only be opened by the correct key, an enzyme can only act on a specific substrate that has the proper shape and structure that fits into the enzyme's active site (its 'lock').
02

Describe the Active Site of an Enzyme

The active site of an enzyme is the region where the substrate binds and the reaction occurs. It is formed by a specific arrangement of amino acid residues within the enzyme and has a unique three-dimensional shape and structure. This structure is essential for the enzyme's function, as it allows the enzyme to recognize and bind to the specific substrate.
03

Explain the Enzyme-Substrate Interaction

When a substrate with the appropriate shape and structure encounters the active site of the enzyme, it binds to the enzyme, forming an enzyme-substrate complex. This binding is facilitated by the complementarity between the enzyme's active site and the substrate – like a key fitting into a lock. The interactions between the enzyme and substrate can involve hydrogen bonds, hydrophobic interactions, and ionic bonds, which help to stabilize the enzyme-substrate complex and lower the activation energy needed for the reaction to occur.
04

Describe the Specificity of Enzymes

The specificity of an enzyme arises from its unique active site structure, which can only accommodate a particular substrate (or a small group of related substrates) with the correct shape and chemical properties. This ensures that the enzyme only catalyzes the intended reaction and does not interfere with other unrelated chemical processes within the cell. This specificity can be further fine-tuned by the presence of regulatory molecules, such as cofactors or inhibitors, which can modulate an enzyme's activity depending on the cell's needs.
05

Relate the Lock-and-Key Model to Enzyme Specificity

In conclusion, the lock-and-key model accounts for enzyme specificity by illustrating that the enzyme's active site has a unique three-dimensional structure, only allowing substrates with the matching shape and structure to bind and undergo the catalyzed reaction. Since each enzyme has a unique active site, it is highly selective in the reactions it catalyzes, ensuring specificity and accuracy in the myriad of chemical reactions occurring within a cell.

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Most popular questions from this chapter

The reaction $2 \mathrm{NO}(g)+\mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{NO}_{2}(g)\( is second order in \)\mathrm{NO}$ and first order in \(\mathrm{O}_{2} .\) When \([\mathrm{NO}]=0.040 \mathrm{M}\) and \(\left[\mathrm{O}_{2}\right]=0.035 \mathrm{M},\) the observed rate of disappearance of \(\mathrm{NO}\) is $9.3 \times 10^{-5} \mathrm{M} / \mathrm{s} .(\mathbf{a})\( What is the rate of disappearance of \)\mathrm{O}_{2}$ at this moment? (b) What is the value of the rate constant? (c) What are the units of the rate constant? (d) What would happen to the rate if the concentration of NO were increased by a factor of \(1.8 ?\)

(a) What is meant by the term reaction rate? (b) Name three factors that can affect the rate of a chemical reaction. (c) Is the rate of disappearance of reactants always the same as the rate of appearance of products?

Consider the following hypothetical aqueous reaction: $\mathrm{A}(a q) \rightarrow \mathrm{B}(a q)\(. A flask is charged with \)0.065 \mathrm{~mol}$ of \(\mathrm{A}\) in a total volume of \(100.0 \mathrm{~mL}\). The following data are collected: $$ \begin{array}{lccccc} \hline \text { Time (min) } & 0 & 10 & 20 & 30 & 40 \\ \hline \text { Moles of A } & 0.065 & 0.051 & 0.042 & 0.036 & 0.031 \\ \hline \end{array} $$ (a) Calculate the number of moles of \(\mathrm{B}\) at each time in the table, assuming that there are no molecules of \(\mathrm{B}\) at time zero and that A cleanly converts to B with no intermediates. (b) Calculate the average rate of disappearance of A for each 10 -min interval in units of \(M /\) s. (c) Between \(t=0 \mathrm{~min}\) and \(t=30 \mathrm{~min},\) what is the average rate of appearance of \(\mathrm{B}\) in units of \(\mathrm{M} / \mathrm{s}\) ? Assume that the volume of the solution is constant.

Indicate whether each statement is true or false. (a) If you measure the rate constant for a reaction al different temperatures, you can calculate the overall enthalpy change for the reaction. (b) Exothermic reactions are faster than endothermic reactions. (c) If you double the temperature for a reaction, you cut the activation energy in half.

(a) Consider the combustion of ethylene, \(\mathrm{C}_{2} \mathrm{H}_{4}(g)+\) $3 \mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{CO}_{2}(g)+2 \mathrm{H}_{2} \mathrm{O}(g) .\( If the concentration of \)\mathrm{C}_{2} \mathrm{H}_{4}$ is decreasing at the rate of \(0.025 \mathrm{M} / \mathrm{s}\), what are the rates of change in the concentrations of \(\mathrm{CO}_{2}\) and $\mathrm{H}_{2} \mathrm{O}\( ? (b) The rate of decrease in \)\mathrm{N}_{2} \mathrm{H}_{4}$ partial pressure in a closed reaction vessel from the reaction $\mathrm{N}_{2} \mathrm{H}_{4}(g)+\mathrm{H}_{2}(g) \longrightarrow 2 \mathrm{NH}_{3}(g)$ is \(10 \mathrm{kPa}\) per hour. What are the rates of change of \(\mathrm{NH}_{3}\) partial pressure and total pressure in the vessel?
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