Enzyme Catalysis and Kinetics: Chapter 8

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Questions and Answers

Explain the concept of 'steady-state approximation' in Michaelis-Menten kinetics, and why it is crucial for deriving the Michaelis-Menten equation.

The steady-state approximation assumes that the concentration of the enzyme-substrate complex [ES] remains constant over time during the reaction. This assumption is crucial because it simplifies the rate equations, allowing for the derivation of the Michaelis-Menten equation, which relates reaction velocity to substrate concentration.

How does competitive inhibition affect the apparent $K_m$ and $V_{max}$ of an enzymatic reaction? Explain the mechanism behind these changes.

Competitive inhibition increases the apparent $K_m$ (decreases the enzyme's affinity for the substrate) but does not affect $V_{max}$. A competitive inhibitor binds to the active site, preventing substrate binding. Higher substrate concentrations can outcompete the inhibitor, allowing the reaction to still reach the same $V_{max}$.

Describe the difference between ordered and random sequential bisubstrate reactions in enzyme kinetics. Provide a brief example to illustrate.

In ordered sequential reactions, substrates must bind to the enzyme in a specific order before the reaction can occur. In random sequential reactions, the order of substrate binding is not important. For example, lactate dehydrogenase (LDH) exhibits ordered sequential binding (NAD+ first), while creatine kinase exhibits random sequential binding.

Explain the 'ping-pong' mechanism in enzyme kinetics. What distinguishes it from sequential mechanisms, and give an example of an enzyme that follows this mechanism?

In a ping-pong mechanism, one substrate binds and releases a product before a second substrate binds. This contrasts with sequential mechanisms where both substrates bind before any product is released. An example is chymotrypsin, a protease that uses a ping-pong mechanism involving a covalent intermediate. Signup and view all the answers

How does the catalytic efficiency ($k_{cat}/K_m$) reflect an enzyme's overall ability to catalyze a reaction? What are the theoretical limits on catalytic efficiency, and why do they exist?

Catalytic efficiency ($k_{cat}/K_m$) reflects how effectively an enzyme catalyzes a reaction at low substrate concentrations, considering both the rate of catalysis ($k_{cat}$) and substrate binding affinity ($K_m$). The theoretical limit is the diffusion limit, where the reaction rate is limited by how quickly enzyme and substrate can collide in solution. Signup and view all the answers

Describe how temperature affects the rate of diffusion, and what is the relationship per the Arrhenius equation?

As temperature increases, the rate of diffusion generally increases. The Arrhenius equation, $D = D_0 exp(-E_a/RT)$, describes this relationship, showing that the diffusion coefficient (D) exponentially increases with temperature due to increased kinetic energy overcoming the activation energy ($E_a$). Signup and view all the answers

Explain how the size and shape of a molecule affect its diffusion coefficient. Provide an example of two molecules with different diffusion coefficients based on these factors.

Larger molecules and molecules with irregular shapes generally have smaller diffusion coefficients due to increased frictional resistance. For example, a small, compact molecule like water diffuses faster than a large, complex molecule like a protein. Signup and view all the answers

What is the physical significance of the principal quantum number (n) in the context of atomic structure?

The principal quantum number (n) determines the energy level of an electron and its average distance from the nucleus. Higher values of n correspond to higher energy levels and greater distances from the nucleus. Signup and view all the answers

Explain the concept of blackbody radiation and how it challenged classical physics. What key idea did Planck introduce to resolve this issue?

Blackbody radiation refers to the electromagnetic radiation emitted by an object that absorbs all incident radiation. Classical physics predicted an infinite energy output at high frequencies (the ultraviolet catastrophe), which was incorrect. Planck resolved this by proposing that energy is quantized, meaning it can only be emitted or absorbed in discrete packets (quanta). Signup and view all the answers

Describe the photoelectric effect and explain how it provides evidence for the particle-like nature of light. What is the role of the work function in this phenomenon?

The photoelectric effect is the emission of electrons from a metal surface when light shines on it. The fact that electrons are only ejected above a certain threshold frequency, regardless of intensity, suggests that light consists of particles (photons) with energy proportional to frequency. The work function is the minimum energy required to eject an electron from the metal surface. Signup and view all the answers

What is the de Broglie wavelength, and how does it relate to the momentum of a particle? Explain its significance in understanding the wave-particle duality.

The de Broglie wavelength ($\lambda = h/p$) relates the wavelength of a particle to its momentum ($p$). It demonstrates that all matter exhibits wave-like properties, not just light, thus establishing the principle of wave-particle duality. Signup and view all the answers

Explain the key differences between the Bohr model of the atom and the quantum mechanical model. What limitations of the Bohr model are addressed by the quantum mechanical model?

The Bohr model postulates fixed circular orbits for electrons, while the quantum mechanical model describes electrons in terms of probability distributions (orbitals). The Bohr model fails to explain the spectra of complex atoms and violates the uncertainty principle, limitations addressed by the quantum mechanical model with its wave-like description of electrons. Signup and view all the answers

What is a mathematical operator in quantum mechanics, and how is it used to extract information about a quantum system? Give an example of an operator and what physical property it represents.

In quantum mechanics, a mathematical operator acts on a wavefunction to extract information about a physical property of the system. For example, the momentum operator, $p = -ih(d/dx)$, when applied to a wavefunction, yields the momentum of the particle. Signup and view all the answers

Explain the Heisenberg uncertainty principle. How does it fundamentally limit the precision with which we can know certain pairs of physical properties, such as position and momentum?

The Heisenberg uncertainty principle states that it is impossible to know both the position and momentum of a particle with perfect accuracy simultaneously. Mathematically, $\Delta x \Delta p \geq h/2$. This means the more accurately one property is known, the less accurately the other can be known. Signup and view all the answers

What is the physical interpretation of the wavefunction, $\psi$, in quantum mechanics? How is the probability of finding a particle in a specific region of space related to the wavefunction?

The wavefunction, $\psi$, describes the quantum state of a particle. The square of the wavefunction, $|\psi|^2$, gives the probability density of finding the particle at a particular point in space. The probability of finding the particle in a specific region is the integral of $|\psi|^2$ over that region. Signup and view all the answers

Flashcards

Enzymes

Substances that speed up chemical reactions without being consumed in the process.

Catalytic Efficiency

A measure of how effectively an enzyme converts substrate to product.