Molecular Basis of Life - Chemical Kinetics & Enzymes

Flashcards covering chemical kinetics, thermodynamics laws, enzyme catalysis, and the Beer-Lambert Law based on Lecture 9 by Dr David Hill.

Energy

The capacity to do work, classified into kinetic energy (related to motion), gravitational potential energy, and chemical potential energy (stored in molecular bonds).

First Law of Thermodynamics

Also known as the law of conservation of energy; it states that energy ($U$) can neither be created nor destroyed.

Second Law of Thermodynamics

States that spontaneous changes in an isolated system lead to an increase in entropy ($S$); for spontaneous processes, riangle S > 0, and at equilibrium, $riangle S = 0$.

Third Law of Thermodynamics

States that as temperature approaches absolute zero ($0$ Kelvin), the entropy of all perfectly crystalline substances approaches $0$.

Zeroth Law of Thermodynamics

States that if two systems are in thermal equilibrium with a third system, they are also in thermal equilibrium with each other; heat flows from hot objects to colder ones.

Open System

A configuration with no system barrier that may interact with its external environment.

Closed System

A configuration with a system barrier that may not interact with its external environment.

Isolated System

A single closed system that is isolated from all other systems.

Enthalpy ($H$)

The internal energy of a system, defined as the sum of kinetic and potential energies, expressed by the equation $H = E + pV$.

Endothermic reaction

A reaction that absorbs energy from the surroundings where $riangle H$ is positive ($+ve$), causing the system and surroundings to get colder.

Exothermic reaction

A reaction that emits energy to the surroundings where $riangle H$ is negative ($-ve$), causing the system and surroundings to get hotter.

Entropy ($S$)

A measure of the distribution of energy through a system or its surroundings, acting as a measure of energetic disorder and measured in $J K^{-1} mol^{-1}$.

Gibbs Free Energy ($G$)

Describes the energy available to do work within a system, calculated using the equation $riangle G = riangle H - T riangle S$.

Spontaneous reaction

A reaction that proceeds to completion without an input of energy (once started) and is characterized by a negative Gibbs free energy change ($riangle G = -ve$).

Rate of reaction

A measure of how fast a reaction happens, determined by the change in concentration of reactants or products over a fixed time scale.

Rate constant ($k$)

A mathematical constant used in the rate law equation $ext{rate of reaction} = k [A]^x$.

Order of reaction ($x$)

The power to which the concentration of a reactant is raised in the rate law; usually $0$ (zero order), $1$ (first order), or $2$.

Collision theory

The theory stating that two reactants must collide energetically to interact and initiate a reaction.

Activation energy ($E_{a}$)

The minimum energy that reactant molecules must possess for a reaction to proceed through the transition state to form products.

Catalyst

A substance that alters the rate of a chemical reaction by providing an alternative reaction path with a lower activation energy, while remaining chemically unchanged and recoverable.

Enzymes

Biological catalysts, predominantly proteins, that can increase reaction rates by $10^6$ to $10^{17}$ times.

Active site

The specific pocket or cleft within an enzyme where the substrate interacts and the catalytic reaction occurs.

Cofactors

Additional groups associated with an enzyme that are critical to its function, including vitamins (coenzymes like NADH) and minerals (metal ions like $Mg^{2+}$, $Ca^{2+}$, $Zn^{2+}$).

Denaturation

The process where an enzyme loses activity at high temperatures or extreme pH levels because its tertiary structure is disrupted.

Beer-Lambert Law

An equation used in UV-visible spectrophotometry to determine concentration ($c$), defined as A = oldsymbol{ ext{ extepsilon}} c l, where $A$ is absorbance, oldsymbol{ ext{ extepsilon}} is molar absorptivity, and $l$ is path length.

$$ext{ extlambda}_{max}$$

The specific wavelength of light that a molecule absorbs most strongly.

Enzyme unit

The amount of enzyme activity that catalyses the conversion of $1 ext{ extmu mol}$ of substrate into product in $1$ minute under set conditions.