Thermodynamics, Enzymes, and Metabolic Pathways: Key Concepts for Biology

First law of Thermodynamics

Energy cannot be created or destroyed, only transformed or transferred

Second law of Thermodynamics

Every energy transfer increases entropy (disorder) of the universe

Gibbs Free Energy

Energy available to do work in a system 🔼G = 🔼H -T 🔼x S. Free Energy = enthalpy - temp x entropy

Exergonic

Releases energy, 🔼G is less than 0 and is spontaneous

Endergonic

Requires energy input, 🔼G is greater than 0, and is non-spontaneous

Metabolism

The total of all chemical reactions in an organism

Catabolic

Breaking down molecules, releases energy. Ex, Short Jenga, Hydrolysis, exergonic, cell respiration, ⬆️🔼S (entropy), Spontaneous, - 🔼G, Stable

Anabolic

Building molecules → requires energy. Ex. Tall Jenga, Dehydration Synthesis, Endergonic, Photosynthesis, ⬇️🔼S (entropy), non-spontaneous, +🔼G, unstable

Metabolic Pathways

A series of enzyme-catalyzed steps that convert a starting molecule into a product

Catalytic Proteins

Proteins that act as enzymes and speed up reactions

Activation Energy (EA)

The initial energy needed to start a chemical reaction with/without enzyme

Transition State

High-energy, unstable intermediate between reactants and products

Globular Proteins

Compact, spherical proteins (most enzymes are this shape)

Tertiary Structure

The 3D shape of a protein formed by interactions among R-groups (hydrogen bonds, ionic bonds, hydrophobic interactions, disulfide bridges)

Induced-Fit Model

The enzyme slightly changes shape to fit the substrate more tightly when they bind

Enzyme-Substrate Complex

The temporary binding of enzyme + substrate during a reaction

"ase"

Most enzyme names end in "ase". Ex: sucrase, lactase, DNA polymerase

Co-factors

Non-protein helpers needed for enzyme function. Ex: metal ions like Mg2+, Fe2+, Zn2+

Co Enzymes

Organic (carbon-based) cofactors, often derived from vitamins. Ex: NAD+, FAD, CoA, vitamin B6, biotin

Zymogen

Inactive enzyme precursor that must be activated (ex, pepsinogen→ pepsin)

Non-competitive Inhibitors

Bind to an allosteric site (not the active site), change the enzyme's shape, and cannot be overcome by adding more substrate

Competitive Inhibitors

Bind to the active site, compete with substrate, can be overcome by adding more substrate

Allosteric

A site on an enzyme other than the active site where a regulator can bind and change enzyme activity

Allosteric Regulators

Molecules that bind to an allosteric site to activate or inhibit an enzyme. Ex: ATP (inhibitor), ADP (activator), feedback inhibitors

Feedback Inhibition

The end product of a metabolic pathway inhibits an earlier enzyme in the pathway to prevent overproduction

Cooperativity

A form of allosteric regulation where the binding of one substrate makes it easier for more substrates to bind. Ex: Hemoglobin binding to oxygen