Enzymes and Nucleic Acids Overview

Overview

This lecture explains the role and structure of enzymes, types of chemical reactions based on energy exchange, how enzymes function and are regulated, and introduces nucleic acids (DNA and RNA), including their structure and differences.

Types of Chemical Reactions (Energy Exchange)

• Chemical reactions are classified as exergonic (energy released) or endergonic (energy absorbed).
• Exergonic reactions have products with less energy than the reactants (e.g., fire, hand warmers).
• Endergonic reactions have products with more energy than reactants (e.g., cold packs).

Activation Energy and Enzyme Basics

• All reactions require an initial energy input called activation energy.
• Catalysts speed up reactions by lowering activation energy.
• Enzymes, mostly globular proteins, act as biological catalysts in living organisms.

How Enzymes Work

• Enzymes increase collision frequency, lower activation energy, and orient reactants.
• Enzymes consist of an apoenzyme (protein part) and a cofactor (inorganic) or coenzyme (organic); together they form a holoenzyme.
• Enzymes are specific, reusable, and catalyze reactions in both directions if possible.

Enzyme Mechanisms and Nomenclature

• The active site is the enzyme’s region where substrate binds.
• Substrate fits the active site via lock-and-key or induced fit models.
• Many enzymes are named by adding "-ase" to the substrate root (e.g., maltase digests maltose, lactase digests lactose).

Factors Affecting Enzyme Activity

• Five main factors: temperature, pH, substrate concentration, inhibitors, and thermodynamics.
• Optimal human enzyme activity is near 37–40°C; above this, enzymes denature.
• Enzymes have optimal pH values; for example, pepsin works at low pH, trypsin near neutral.

Enzyme Regulation and Inhibition

• Competitive inhibitors compete with substrate for the active site.
• Non-competitive inhibitors bind elsewhere (allosteric site), changing enzyme shape.
• Cells use repressors and activators (signal molecules) to inhibit or activate enzymes.
• Feedback inhibition regulates metabolic pathways to prevent excess product.

Thermodynamics and Reaction Direction

• Exergonic reactions release energy (energy is a product); endergonic reactions absorb energy (energy is a reactant).
• Reaction direction can shift based on concentrations of reactants/products and energy changes.

Nucleic Acids: DNA and RNA

• Nucleic acids (DNA and RNA) are vital macromolecules in all living cells.
• DNA stores genetic information in the nucleus; RNA translates genetic code to make proteins.
• Three types of RNA: ribosomal (makes ribosomes), messenger (carries code), and transfer (brings amino acids).

Nucleotide Structure and DNA/RNA Differences

• Nucleotides (building blocks) have a nitrogenous base, a pentose sugar, and a phosphate group.
• DNA bases: adenine (A), guanine (G), cytosine (C), thymine (T); RNA uses uracil (U) instead of T.
• DNA uses deoxyribose sugar; RNA uses ribose.
• Nucleotides join via phosphodiester bonds, forming a sugar-phosphate backbone.
• DNA is double-stranded (double helix, complementary and antiparallel); RNA is single-stranded.

Key Terms & Definitions

• Exergonic Reaction — Reaction that releases energy; products have less energy than reactants.
• Endergonic Reaction — Reaction that absorbs energy; products have more energy than reactants.
• Activation Energy — Minimum energy required to start a reaction.
• Enzyme — Protein that catalyzes (speeds up) chemical reactions in living cells.
• Apoenzyme — Protein portion of an enzyme.
• Cofactor — Inorganic molecule required for enzyme activity.
• Coenzyme — Organic cofactor required for enzyme function.
• Holoenzyme — Complete, functional enzyme (apoenzyme + cofactor/coenzyme).
• Substrate — Molecule upon which an enzyme acts.
• Active Site — Region of enzyme where substrate binds.
• Inhibitor — Molecule that slows or stops enzyme activity (competitive or non-competitive).
• Allosteric Site — Site on enzyme where regulatory molecules bind, affecting function.
• Feedback Inhibition — End product inhibits an early enzyme in a pathway.
• Nucleotide — Building block of nucleic acids; contains base, sugar, and phosphate.
• Phosphodiester Bond — Covalent bond joining nucleotides in nucleic acids.
• Antiparallel — Opposite orientation of DNA strands in the double helix.

Action Items / Next Steps

• Review the differences between exergonic and endergonic reactions.
• Memorize enzyme structure, function, and regulatory mechanisms.
• Learn differences between DNA and RNA structure and function.
• Prepare for upcoming material on the genetic code and protein synthesis.