Biomolecules are the building blocks of life, forming the basis of cellular structure and function. From carbohydrates and lipids to proteins and nucleic acids, these molecules play crucial roles in energy storage, signaling, and genetic information transfer.

Enzymes catalyze biochemical reactions, while hormones regulate physiological processes. Cellular signaling and structural components rely on biomolecules to coordinate activities and provide support. Understanding these molecules is key to grasping the complexities of life at the molecular level.

Macromolecules

Carbohydrates and Lipids

• Carbohydrates are organic molecules composed of carbon, hydrogen, and oxygen atoms, usually in a 1:2:1 ratio
  • Classified as monosaccharides (glucose, fructose), disaccharides (sucrose, lactose), or polysaccharides (starch, cellulose, glycogen) based on the number of sugar units
  • Serve as primary energy sources for cells and provide structural support in cell walls (plants) and exoskeletons (arthropods)
• Lipids are a diverse group of hydrophobic organic molecules, including fats, oils, waxes, and steroids
  • Triglycerides consist of three fatty acid chains attached to a glycerol backbone and function as energy storage molecules
  • Phospholipids have a hydrophilic head and two hydrophobic tails, forming the basis of cell membranes
  • Steroids (cholesterol) play crucial roles in cell membrane fluidity and serve as precursors for hormone synthesis

Proteins and Nucleic Acids

• Proteins are large, complex molecules made up of amino acid chains folded into specific three-dimensional structures
  • Amino acids are linked by peptide bonds to form polypeptide chains, which fold into secondary structures (alpha helices, beta sheets) and tertiary structures
  • Protein structure determines function, such as enzymes, hormones, antibodies, and structural components (collagen, keratin)
• Nucleic acids, DNA and RNA, store and transmit genetic information
  • DNA (deoxyribonucleic acid) is a double-stranded helix composed of nucleotide monomers with a sugar-phosphate backbone and nitrogenous bases (adenine, thymine, guanine, cytosine)
  • RNA (ribonucleic acid) is single-stranded and contains uracil instead of thymine, serving roles in gene expression (mRNA), protein synthesis (tRNA), and catalysis (ribozymes)

Functional Biomolecules

Enzymes

• Enzymes are specialized proteins that catalyze biochemical reactions by lowering activation energy
  • Substrate specificity is determined by the enzyme's active site, which binds to the substrate via induced fit or lock-and-key mechanisms
  • Cofactors (inorganic ions) and coenzymes (organic molecules) assist in enzyme function
  • Enzyme activity is regulated by factors such as pH, temperature, substrate concentration, and inhibitors (competitive, noncompetitive)

Hormones

• Hormones are signaling molecules secreted by endocrine glands that regulate physiological processes
  • Peptide hormones (insulin) are water-soluble and bind to cell surface receptors, initiating intracellular signaling cascades
  • Steroid hormones (estrogen, testosterone) are lipid-soluble and diffuse through the cell membrane to bind to intracellular receptors, directly influencing gene expression

Cellular Roles

Cellular Signaling and Structural Components

• Cellular signaling involves the transmission of signals between cells to coordinate cellular activities
  • Receptors (G protein-coupled receptors, receptor tyrosine kinases) bind to signaling molecules (hormones, neurotransmitters) and initiate intracellular signaling pathways
  • Second messengers (cyclic AMP, calcium ions) amplify and propagate signals within the cell
• Biomolecules serve as structural components in cells and tissues
  • Cytoskeletal proteins (actin, tubulin) provide shape, support, and movement within cells
  • Extracellular matrix proteins (collagen, elastin) offer structural support and facilitate cell adhesion and communication in tissues

Energy Storage

• Cells store energy in the form of high-energy biomolecules for later use
  • Carbohydrates (glycogen in animals, starch in plants) are readily accessible energy sources
  • Lipids (triglycerides) are energy-dense molecules that provide long-term energy storage
  • ATP (adenosine triphosphate) is the primary energy currency of the cell, storing energy in its high-energy phosphate bonds for immediate use in cellular processes (metabolism, transport, signaling)