Exam 2 - Chapter 6: Enzymes and Metabolism

A set of vocabulary flashcards covering enzyme mechanics, metabolic pathways, and the laws of thermodynamics based on lecture notes.

Reversible reactions

Metabolic reactions that can proceed in either direction; at equilibrium, the forward and reverse rates are equal.

Catabolic pathways

Metabolic pathways that break down large molecules into smaller ones, releasing energy (exergonic).

Anabolic pathways

Metabolic pathways that build larger molecules from smaller ones, requiring energy (endergonic).

First Law of Thermodynamics

The principle stating that energy cannot be created or destroyed, only transferred or transformed.

Second Law of Thermodynamics

The principle stating that every energy transfer increases the entropy (disorder) of the universe, usually by losing usable energy as heat.

Entropy

A measure of disorder or randomness in a system.

Examples of negative entropy

Processes that decrease disorder, such as amino acids becoming proteins, building DNA, cell growth, and tissue formation.

Gibbs Free Energy ($\Delta G$)

A measure used to determine if a reaction is spontaneous; calculated using the formula $\Delta G = \Delta H - T\Delta S$.

Spontaneous reaction

A reaction that releases energy and has a negative Gibbs Free Energy ($\Delta G < 0$).

Nonspontaneous reaction

A reaction that requires energy and has a positive Gibbs Free Energy ($\Delta G > 0$).

Exergonic reaction

A spontaneous reaction that releases energy, such as cellular respiration, where products have less free energy than reactants.

Endergonic reaction

A nonspontaneous reaction that requires energy, such as photosynthesis, where products have more free energy than reactants.

Activation Energy ($E_A$)

The minimum amount of energy required to start a chemical reaction; enzymes work by lowering this value.

ATP (Adenosine Triphosphate)

A molecule composed of adenine, ribose sugar, and three phosphate groups that stores energy for cellular work.

Energy coupling

The cellular process of using an exergonic reaction, such as ATP hydrolysis, to power an endergonic reaction.

Phosphorylation

The transfer of a phosphate group from ATP to another molecule to make that molecule more reactive.

Enzyme

A biological catalyst, usually a protein, that speeds up reactions by lowering activation energy without being consumed.

Active site

The specific region of an enzyme where the substrate binds and the chemical reaction occurs.

Induced Fit

The slight change in the shape of an enzyme's active site to bind a substrate more snugly, rather than a rigid lock-and-key fit.

Optimal temperature for human enzymes

The specific temperature at which human enzymes function most efficiently, which is $37^\circ C$.

Pepsin

An enzyme with an optimal pH of $2$.

Trypsin

An enzyme with an optimal pH of $8$.

Denaturation

The process where an enzyme loses its functional shape and stops working, often due to excessive heat.

Competitive inhibition

A form of enzyme inhibition where an inhibitor resembles the substrate and binds directly to the active site.

Noncompetitive inhibition

A form of enzyme inhibition where an inhibitor binds to a site other than the active site, changing the enzyme's shape so the active site no longer works.

Allosteric site

A regulatory site on an enzyme, distinct from the active site, where activators or inhibitors can bind.

Feedback inhibition

A metabolic control mechanism where the final product of a pathway inhibits an earlier enzyme to prevent wasting resources.

Saturation

The point in a reaction where all enzyme active sites are occupied by substrate, and adding more substrate will not increase the reaction rate.