Biomolecules and Biological Macromolecules

Introduction to Biomolecules

Biomolecules are organic molecules essential for life, including carbohydrates, lipids, proteins, and nucleic acids. Biological macromolecules are large, complex molecules formed by polymerization of smaller subunits.

• Cells: The basic unit of life, composed of various biomolecules.

• Non-covalent interactions: Weak chemical interactions (hydrogen bonds, ionic bonds, van der Waals forces) crucial for biomolecular structure and function.

• Water: The medium of life: Water's polarity and hydrogen bonding make it an ideal solvent for biological reactions.

• Hydrophilic, hydrophobic, and amphipathic: Terms describing molecules' affinity for water; amphipathic molecules have both hydrophilic and hydrophobic regions (e.g., phospholipids).

Acids, Bases, and pH

Fundamentals of Acid-Base Chemistry

Acids donate protons (H+), while bases accept them. The pH scale measures the concentration of hydrogen ions in solution.

• pH: Defined as ; a measure of acidity or alkalinity.

• The Henderson-Hasselbalch equation: Relates pH, pKa, and the ratio of conjugate base to acid:

• Titration curves: Graphs showing pH changes as acid or base is added to a solution; used to determine pKa values.

Amino Acids and Protein Structure

Amino Acids: Building Blocks of Proteins

Amino acids are organic compounds containing amino and carboxyl groups. They polymerize to form proteins.

• Proteins are linear polymers of amino acids: Linked by peptide bonds.

• The peptide bond has partially double bond character: Restricts rotation, contributing to protein structure.

Levels of Protein Structure

• Primary structure: The sequence of amino acids in a polypeptide chain.

• Role of the amino acid sequence in protein structure: Determines higher-order folding and function.

• Architecture: The hierarchy of structural organization: Proteins have primary, secondary, tertiary, and quaternary structures.

Secondary Structure in Proteins

Secondary structure refers to local folding patterns stabilized by hydrogen bonds.

• Secondary valence forces: Non-covalent interactions stabilizing secondary structure.

• Fibrous proteins: Structural proteins with elongated shapes (e.g., collagen, keratin).

• Structure of α- and β-keratins: α-keratin forms coiled coils; β-keratin forms sheets.

• Collagen: Triple-helical structure providing tensile strength to connective tissues.

Tertiary and Quaternary Structure of Proteins

Tertiary structure is the overall 3D shape of a single polypeptide; quaternary structure describes the assembly of multiple polypeptides.

• Chaperones: Proteins that assist in folding other proteins.

• Prions: Misfolded proteins that can induce abnormal folding in others, associated with disease.

Enzyme Kinetics

Basic Aspects of Chemical Kinetics

Enzyme kinetics studies the rates of enzyme-catalyzed reactions and factors affecting them.

• Energy of activation, transition state: The minimum energy required for a reaction; enzymes lower this barrier.

• Action of a catalyst: Catalysts increase reaction rates without being consumed.

• Michaelis-Menten equation: Describes the rate of enzymatic reactions:

• Steady-state: Assumption that the concentration of the enzyme-substrate complex remains constant during the reaction.

• Turnover number: Number of substrate molecules converted per enzyme per unit time.

Enzyme Inhibition

• Enzyme inhibition: Decrease in enzyme activity due to interaction with inhibitors.

• Reversible inhibition: Inhibitor binds non-covalently and can be removed.

• Irreversible inhibition: Inhibitor binds covalently, permanently inactivating the enzyme.

Enzyme Mechanisms

How Enzymes Work

Enzymes accelerate reactions by stabilizing the transition state and lowering activation energy.

• Proximity effect: Enzymes bring substrates close together to facilitate reaction.

• General-base and general-acid catalysis: Enzyme side chains act as acids or bases to transfer protons.

• Nucleophilic and electrophilic catalysis: Enzymes use nucleophilic or electrophilic groups to facilitate bond formation or cleavage.

• Flexibility: Enzyme conformational changes are often essential for catalysis.

• Mechanism of chymotrypsin: A serine protease that uses a catalytic triad for peptide bond hydrolysis.

• Specificity is the result of molecular recognition: Enzymes are highly specific for their substrates due to precise active site architecture.

• Regulation of enzyme activities: Enzyme activity can be modulated by various mechanisms (e.g., allosteric regulation, covalent modification).

• Partial proteolysis: Zymogens: Inactive enzyme precursors activated by proteolytic cleavage.

• Phosphorylation, and phosphorylases: Addition of phosphate groups regulates enzyme activity.

• Adenylylation: Addition of adenylyl groups as a regulatory modification.

• Disulfide reduction: Reduction of disulfide bonds can alter protein structure and function.

• Allosteric effectors (qualitative): Molecules that bind to sites other than the active site to modulate enzyme activity.

Additional info: This study guide is based on a syllabus outline and covers foundational topics in biochemistry, including biomolecules, protein structure, and enzyme mechanisms. For each topic, students should refer to their textbook for detailed mechanisms, structures, and examples.