Biomolecules in Human Physiology

Overview of Biomolecules

Biomolecules are organic compounds essential for life, primarily composed of carbon and hydrogen. They are fundamental to the structure and function of living organisms and include carbohydrates, lipids, proteins, and nucleotides.

• Organic molecules: Contain carbon and hydrogen atoms.

• Biomolecules: Associated with living organisms; include carbohydrates, lipids, proteins, and nucleotides.

• Examples: Glucose (carbohydrate), triglycerides (lipid), hemoglobin (protein), ATP (nucleotide).

Chemistry of Lipids

Fatty Acids

Fatty acids are long hydrocarbon chains with a carboxyl group at one end. They are classified based on the presence and number of double bonds.

• Saturated fatty acids: No double bonds (e.g., palmitic acid).

• Monounsaturated fatty acids: One double bond (e.g., oleic acid).

• Polyunsaturated fatty acids: Two or more double bonds (e.g., linolenic acid).

Formation of Lipids

Lipids are formed by combining glycerol with fatty acids. The number of fatty acids attached to glycerol determines the type of lipid.

Lipid-Related Molecules

Some molecules are related to lipids but have distinct structures and functions.

Chemistry of Carbohydrates

Monosaccharides

Monosaccharides are simple sugars and the building blocks of carbohydrates. They are classified by the number of carbon atoms.

Disaccharides

Disaccharides are formed by joining two monosaccharides via a glycosidic bond.

Chemistry of Proteins

Amino Acids

Amino acids are the monomers of proteins. Each amino acid contains a central carbon atom bonded to a carboxyl group (-COOH), an amino group (-NH2), a hydrogen atom, and a variable R group.

• R group: Determines the chemical properties and reactivity of the amino acid.

• Source of nitrogen: Proteins are a major dietary source of nitrogen.

Structure of Peptides and Proteins

Proteins are polymers of amino acids. Their structure is hierarchical:

• Primary structure: Sequence of amino acids in a peptide chain.

• Oligopeptide: 2-9 amino acids.

• Polypeptide: 10-100 amino acids.

• Protein: More than 100 amino acids.

Chemistry of Nucleotides

Nucleotide Structure

Nucleotides are the building blocks of nucleic acids (DNA and RNA). Each nucleotide consists of:

• One or more phosphate groups

• A five-carbon sugar (ribose or deoxyribose)

• A nitrogenous base (purine or pyrimidine)

Functional Groups in Biomolecules

Common Functional Groups

Functional groups are specific combinations of atoms that confer particular chemical properties to molecules.

Chemical Bonds in Biomolecules

Types of Chemical Bonds

Chemical bonds are forces that hold atoms together in molecules. They are classified by strength and mechanism.

• Covalent bonds: Atoms share electrons; strong bonds requiring significant energy to break.

• Ionic bonds: Atoms gain or lose electrons, resulting in attraction between oppositely charged ions.

• Hydrogen bonds: Weak, partial bonds; important for water surface tension and protein structure.

• Van der Waals forces: Weak, nonspecific interactions between molecules.

Polar vs. Nonpolar Molecules

• Nonpolar molecules: Even distribution of charge; hydrophobic.

• Polar molecules: Uneven charge distribution; hydrophilic.

Aqueous Solutions and Solubility

Definitions and Properties

Biological reactions occur in aqueous (water-based) solutions. The ability of a substance to dissolve in water is called solubility.

• Solute: Substance that dissolves in a liquid.

• Solvent: Liquid in which solutes dissolve (water is universal solvent).

• Solution: Combination of solutes dissolved in a solvent.

• Concentration: Amount of solute per unit volume of solution.

Formula:

Molecular Shape and Function

Protein Structure and Function

Molecular bonds determine the three-dimensional shape of proteins, which is closely related to their function. Proteins can have complex secondary, tertiary, and quaternary structures.

• Secondary structures: Alpha-helix and beta-pleated sheets.

• Fibrous proteins: Long, strand-like; structural roles.

• Globular proteins: Compact, spherical; functional roles.

• Disulfide bonds (S-S): Covalent bonds that stabilize protein structure.

Protein-Ligand Interactions

Binding Specificity and Affinity

Proteins are selective about the molecules they bind, a property known as specificity. Binding occurs at a specific site and is governed by noncovalent interactions.

• Ligand: Molecule that binds to a protein.

• Substrate: Ligand acted upon by an enzyme.

• Affinity: Strength of binding between protein and ligand.

• Induced-fit model: Binding site shape adapts to fit the ligand.

Protein-Binding Reactions and Equilibrium

Protein-ligand binding is reversible and follows the law of mass action. The equilibrium constant () describes the ratio of bound to unbound molecules at equilibrium.

Equilibrium equation:

Factors Affecting Protein Binding and Activity

Modulators and Cofactors

Protein activity can be regulated by various factors, including cofactors, proteolytic activation, and chemical modulators.

Regulation of Protein Amount and Activity

• Up-regulation: Increase in protein amount or activity.

• Down-regulation: Decrease in protein amount or activity.

• Saturation: Maximum reaction rate when all binding sites are occupied.

Reaction rate formula:

Summary Table: Key Biomolecules and Their Functions

Additional info: Some explanations and table entries were expanded for clarity and completeness based on standard academic context.