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 are classified into four major groups: carbohydrates, lipids, proteins, and nucleotides.

• Carbohydrates: Serve as energy sources and structural components.

• Lipids: Function in energy storage, membrane structure, and signaling.

• Proteins: Perform a wide range of functions including catalysis, transport, and structural support.

• Nucleotides: Form genetic material and participate in cellular energy transfer.

Chemistry of Lipids

Fatty Acids

Fatty acids are long hydrocarbon chains with a terminal carboxyl group. 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 the combination of glycerol and fatty acids through dehydration synthesis:

• Monoglyceride: Glycerol + 1 fatty acid

• Diglyceride: Glycerol + 2 fatty acids

• Triglyceride: Glycerol + 3 fatty acids (major form of stored energy in animals)

Lipid-Related Molecules

Some molecules are lipid-related but not true lipids:

• Eicosanoids: Derived from 20-carbon fatty acids; function as signaling molecules (e.g., prostaglandins).

• Steroids: Characterized by four linked carbon rings (e.g., cholesterol, cortisol).

• Phospholipids: Composed of two fatty acids, a phosphate group, and glycerol; major components of cell membranes.

Chemistry of Carbohydrates

Monosaccharides

Monosaccharides are simple sugars classified by the number of carbon atoms:

• Pentoses (5-carbon): Ribose, Deoxyribose

• Hexoses (6-carbon): Fructose, Glucose (dextrose), Galactose

Disaccharides

Disaccharides are formed by the combination of two monosaccharides:

• Sucrose: Glucose + Fructose

• Maltose: Glucose + Glucose

• Lactose: Glucose + Galactose

Chemistry of Proteins

Amino Acids

Amino acids are the building blocks of proteins. Each amino acid contains:

• A carboxyl group (-COOH)

• An amino group (-NH2)

• A hydrogen atom

• A variable R group (side chain)

The R group determines the chemical properties and reactivity of each amino acid.

Peptides and Proteins

Proteins are polymers of amino acids linked by peptide bonds. The sequence of amino acids (primary structure) determines the protein's properties and function.

• Oligopeptide: 2-9 amino acids

• Polypeptide: 10-100 amino acids

• Protein: >100 amino acids

Nucleotides and Nucleic Acids

Nucleotide Structure

Nucleotides consist of:

• One or more phosphate groups

• A five-carbon sugar (ribose or deoxyribose)

• A nitrogenous base (purine or pyrimidine)

Purines have a double-ring structure; pyrimidines have a single ring.

Functional Groups in Biomolecules

Common Functional Groups

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

Chemical Bonds in Biomolecules

Types of Chemical Bonds

Chemical bonds are forces that hold atoms together in molecules:

• Covalent bonds: Strong bonds formed by sharing electrons; can be single, double, or triple bonds.

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

• Hydrogen bonds: Weak bonds due to partial charges; important in water and protein structure.

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

Polar vs. Nonpolar Molecules

• Nonpolar molecules: Even distribution of electrons; hydrophobic.

• Polar molecules: Uneven distribution of charge; hydrophilic.

Aqueous Solutions and Solubility

Definitions and Properties

Biological reactions occur in aqueous (water-based) solutions. Key terms:

• Solute: Substance dissolved in a liquid.

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

• Solution: Combination of solutes dissolved in a solvent.

• Solubility: Ease with which a solute dissolves in a solvent.

Concentration Units

Concentration is the amount of solute per unit volume of solution:

• Formula:

Molecular Shape and Function

Protein Structure

Molecular bonds determine the three-dimensional shape of proteins, which is closely related to their function. Proteins exhibit:

• Primary structure: Sequence of amino acids

• Secondary structure: Alpha-helix and beta-pleated sheets

• Tertiary structure: Overall 3D shape, including globular and fibrous forms

• Quaternary structure: Association of multiple polypeptide chains

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 molecular complementarity and affinity.

• Ligand: Molecule that binds to a protein

• Substrate: Ligand acted upon by an enzyme

• Affinity: Strength of binding between protein and ligand

Protein-Binding Reactions and Equilibrium

Protein-ligand binding is reversible and follows the law of mass action:

• Equilibrium constant (Keq): Ratio of bound to unbound molecules at equilibrium

• Formula:

Factors Affecting Protein Binding

Summary Table: Major Biomolecules

Key Equations

• Concentration:

• Equilibrium constant:

Additional info:

• Protein structure and function are central to physiology, as enzymes, transporters, and receptors are all proteins.

• Understanding molecular interactions is essential for grasping cellular processes and physiological regulation.