2.2 Introduction to Enzymatic Reactions

• Enzymes are specialized proteins that catalyze reactions without being changed themselves.
• Enzymes lower the activation energy required for chemical reactions
• Enzymes facilitate the breakdown of substrates or the building of new ones.
• They control metabolic pathways and influence hormone effects.

Lock & Key Model

• Enzyme-substrate interactions ensure that the correct enzyme binds to its specific substrate.
• Matching ensures a particular function is performed
• Only the required substrates fit into a specific enzyme.
• Changes to an enzyme's shape affect its function.

Enzyme Terminology

• Most enzyme names end in "-ase".
• Kinases or phosphorylases catalyze the transfer of a phosphate group.
• Oxidoreductases, such as dehydrogenase or oxidase, catalyze redox reactions by transferring hydrogen atoms.
• Isomerases rearrange molecular structures.
• Synthases synthesize molecules.

Kinase Example

• Hexokinase removes a phosphate group from ATP and adds it to glucose.
• This is the first step of glycolysis and traps glucose in a muscle cell.

Dehydrogenase Example

• Lactate dehydrogenase removes two hydrogens (and electrons) from lactate and adds them to NAD⁺.

Isomerase Example

• Glucose and fructose are isomers, meaning they have the same chemical formula (C₆H₁₂O₆).
• Glucose has a hexagon shape while fructose has a pentagon shape.
• Glucose isomerase changes the shape of glucose without changing the formula.

Synthase Example

• ATP synthase synthesizes ATP by adding a phosphate (PO₃⁻) to ADP.
• This process occurs in the mitochondria during the final step of the electron transport chain (ETC).
• Over 90% of ATP is produced through this reaction.

Coenzymes

• Coenzymes are nonprotein organic substances.
• They facilitate enzyme action by binding a substrate to a specific enzyme, examples include NAD and FAD.
• Coenzymes are often changed by the reaction.

Mass Action Effect

• The mass action effect describes how substrate availability affects metabolic rate.
• The more substrate available, the higher the pathway activity.
• An excess of a given substrate causes cells to rely more on that energy substrate than others.

Rate-Limiting Enzymes

• A rate-limiting enzyme controls the speed of a metabolic process.
• Exercise intensity and speed reflect the body's capacity to transfer chemical energy into mechanical work
• Factors such as temperature, pH, and other chemicals can alter enzyme activity.

Hydrolysis

• Hydrolysis involves splitting chemical bonds through the addition of H⁺ and OH⁻ to reaction byproducts
• Hydrolysis catabolizes macronutrients into simpler forms for easier absorption and assimilation.
• Hydrolysis requires H₂O.
• Examples of hydrolysis enzymes include ATPase, lactase, and sucrase

Condensation

• Condensation involves the binding of structural components.
• Nutrients form more complex molecules and compounds.
• Condensation "releases" H₂O.

Redox Reactions

• Oxidation is a reaction that transfers (loses) electrons or hydrogen atoms.
• Reduction is any process in which atoms in an element gain electrons (or H⁺).
• The lactate dehydrogenase (LDH) reaction in recovery.
• Lactate is oxidized (loses 2 H⁺) to become pyruvate.
• NAD⁺ gains one H (and two electrons) and is reduced to become NADH, while an extra H⁺ is nearby.

Respiratory Chain and Electron Transport

• The vast majority (~90%) of our ATP is produced from redox reactions.
• Electron transport represents the final common pathway in aerobic metabolism.
• For each pair of hydrogen atoms, two electrons flow down the chain and reduce one oxygen atom.
• The process ends when oxygen accepts two hydrogens and forms water.

Explore enzymes as specialized proteins that catalyze reactions by lowering activation energy, and facilitating substrate breakdown or synthesis . Learn about the Lock & Key model and enzyme terminology, with examples like kinases, oxidoreductases, and synthases.