Nucleic Acids Overview

Nucleic Acids

• Largest macromolecules
• Composed of nucleotide subunits
• Two main types: DNA and RNA

DNA Structure

• Nucleotides: Phosphate group, pentose sugar, and nitrogenous bases
• Nitrogenous Bases:
  • DNA: Adenine-Thymine (2 hydrogen bonds), Guanine-Cytosine (3 hydrogen bonds)
  • RNA: Adenine-Uracil, Guanine-Cytosine
• Found in nucleus, mitochondria, and chloroplasts
• Double-stranded, helical structure with deoxyribose sugar
• Functions: Stores genetic information, essential for protein coding, cellular functions, and replication

RNA Structure

• Found in nucleus, cytoplasm, and ribosomes
• Single-stranded, with ribose sugar
• Types and functions:
  • Messenger RNA (mRNA): Transmits DNA messages for protein synthesis
  • Ribosomal RNA (rRNA): Major component of ribosomes, aiding mRNA alignment
  • Transfer RNA (tRNA): Transports amino acids for protein synthesis
  • Regulatory RNA: Involves microRNA and siRNA for gene regulation
• Comparison of DNA and RNA:
  • DNA: Double helix, deoxyribose, stays in the nucleus, thymine
  • RNA: Single-stranded, ribose, travels from the nucleus, uracil replaces thymine

Lipids

• Non-polar, hydrophobic hydrocarbons
• Key functions: Long-term energy storage, structural components, insulation, hormone production
• Structure: Composed of glycerol and fatty acids, connected by ester bonds
• Glycerol: Three hydroxyl groups
• Fatty Acids: Aliphatic carboxylic acids, differing by saturation levels
• Types of Fatty Acids:
  • Saturated Fatty Acids: Single bonds, tightly packed, solid at room temperature, often derived from animal sources
  • Unsaturated Fatty Acids: One or more double bonds, liquid form, Cis configuration (hydrogens on the same side) vs. Trans configuration (hydrogens on opposite sides). Mono (one double bond) or polyunsaturated (multiple double bonds)
• Essential Fatty Acids: Omega-3 (Alpha-linolenic acid) and Omega-6 (Linoleic acid) are crucial dietary components
• Lipid Varieties and Functions:
  • Phospholipids: Integral to biological membranes
  • Waxes: Protective coatings on plants and animals
  • Steroids: Fused-ring structure, hydrophobic, includes hormones like cortisol
  • Cholesterol: Precursor for sex hormones and vitamin D synthesis

Cholesterol and Lipoproteins

• High-Density Lipoprotein (HDL): "Good cholesterol," moves cholesterol to the liver
• Low-Density Lipoprotein (LDL): "Bad cholesterol," can lead to plaque buildup in arteries

Carbohydrates

• Commonly referred to as sugars, produced via photosynthesis
• Functions: Energy supply and storage, structural elements in RNA, DNA, and cell communication
• Classification:
  • Monosaccharides (simple sugars): Aldoses (carbonyl group as aldehyde), Ketoses (carbonyl group as ketone)
    • Examples: glucose, fructose, galactose
  • Monosaccharides: Single sugar units
  • Aldoses: Contain aldehyde group
  • Ketoses: Contain a ketone group
  • Structure Conversions: Fischer to Haworth converting open-chain structures into ring forms (pyranose or furanose). Anomeric carbons define alpha and beta anomers based on the position of -OH.
  • Disaccharides: Formed by a dehydration reaction between 2 monosaccharides
    • Examples: Sucrose, lactose, maltose
      • Linked by glycosidic bonds
  • Polysaccharides: Complex carbohydrates made of long chains of monosaccharide units
    • Can be branched or unbranched
    • Examples: Starch, glycogen, cellulose
      • Starch: Main energy storage in plants
      • Glycogen: Main energy storage in animals
      • Cellulose: Structural component of plant cell walls

Proteins

• Macromolecules consisting of long chains of amino acids
• One of the most abundant organic molecules in living systems
• Diverse Functions
• Types of Proteins:
  • Structural (Actin, Keratin, Tubulin, Collagen)
  • Transport (Hemoglobin, Integral Proteins)
  • Defense (Antibodies)
  • Contractile (Actin, Myosin)
  • Storage (Albumin, Legume storage proteins)
• Structure of Proteins
  • Amino Acid: Organic compounds that combine to form proteins, considered the monomers of proteins, linked by peptide bonds
  • Polypeptide: Linear organic polymer consisting of a chain of amino acid residues
  • Types of Amino Acids:
    • Essential Amino Acids: Must be obtained through diet
    • Non-Essential Amino Acids: Can be synthesized by the body
      • Examples: Alanine, Arginine, Asparagine, Aspartic acid, Cysteine, etc.
  • Levels of Protein Organization:
    • Primary Structure: Linear sequence of amino acids
    • Secondary Structure: 3D folding due to interactions
    • Tertiary Structure: 3D folding pattern due to interactions of side chains
    • Quaternary Structure: Structure formed by more than one amino acid chain (globular or fibrous)
• Chitin: Structural polysaccharide in exoskeletons of arthropods and fungal cell walls, similar to cellulose but contains nitrogen.