Biological Molecules: Carbohydrates

Introduction to Biological Molecules

• Biological molecules are the fundamental components of all living organisms.
• These molecules are primarily composed of carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur (CHONPS).
• Four major classes of biological molecules are carbohydrates, lipids, proteins, and nucleic acids.
• These molecules participate in diverse cellular processes such as energy storage, catalysis, and information transfer.

Carbohydrates

• Carbohydrates are composed of carbon, hydrogen, and oxygen, typically in a 1:2:1 ratio (CH₂O)n.
• They serve as primary energy sources and structural components.
• Simple sugars (monosaccharides) are the simplest form; examples include glucose, fructose, and galactose.
• Disaccharides are formed by the linkage of two monosaccharides; sucrose, lactose, and maltose are common examples.
• Polysaccharides are complex carbohydrates made of many monosaccharides; starch, glycogen, and cellulose are examples.
• Starch and glycogen are energy storage polysaccharides in plants and animals, respectively.
• Cellulose is a structural polysaccharide found in plant cell walls.

Lipids

• Lipids are a diverse group of hydrophobic molecules.
• They are primarily composed of carbon and hydrogen.
• Lipids serve as important energy storage molecules, structural components of cell membranes, and signaling molecules.
• Triglycerides are a major type of lipid, consisting of glycerol and three fatty acids.
• Fatty acids can be saturated (containing only single bonds) or unsaturated (containing one or more double bonds). Unsaturated fats are often liquid at room temperature (oils). Saturated fats are solid at room temperature (e.g., butter).
• Phospholipids form the bilayer structure of cell membranes, with hydrophilic heads and hydrophobic tails.
• Steroids are a type of lipid, with a four-ring structure; cholesterol is a crucial steroid in animal cells.

Proteins

• Proteins are polymers of amino acids.
• They have diverse functions in living organisms, including catalysis, transport, structural support, and defense.
• Twenty different amino acids link together via peptide bonds to form polypeptide chains.
• The sequence of amino acids determines the protein's unique shape and function.
• Protein structure is crucial for function. Four levels of protein structure exist:
  • Primary structure: the linear sequence of amino acids.
  • Secondary structure: local folding patterns (alpha-helices and beta-sheets).
  • Tertiary structure: the overall three-dimensional shape of the polypeptide chain.
  • Quaternary structure: the arrangement of multiple polypeptide chains in a protein complex.
• Proteins can be denatured by changes in temperature or pH, losing their three-dimensional structure and function.

Nucleic Acids

• Nucleic acids are polymers of nucleotides.
• They store and transmit genetic information.
• Two major types of nucleic acids are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).
• DNA carries the hereditary information, forming a double helix with two strands.
• RNA plays various roles in protein synthesis, including messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA).
• Nucleotides are composed of a sugar (deoxyribose in DNA, ribose in RNA), a phosphate group, and a nitrogenous base (adenine, guanine, cytosine, thymine in DNA; adenine, guanine, cytosine, uracil in RNA).
• DNA uses complementary base pairing (A with T, and G with C).
• RNA also uses complementary base pairing (A with U, and G with C).

Other Important Concepts

• The chemical reactions that occur in a biological system are called metabolism.
• Anabolic pathways build complex molecules from simple molecules, requiring energy.
• Catabolic pathways break down complex molecules into simpler ones, releasing energy.

Explore the structure and function of biological molecules with a focus on carbohydrates. Learn about monosaccharides, disaccharides, and polysaccharides and their roles in energy storage and structure. Understand the diverse functions of these key organic compounds in living organisms.