Life's Molecules: Large Biological Molecules and Water

Life's Molecules: Biological Molecules and Water

Key Concepts

  • Atoms, Bonds, Molecules, Polarity, Solubility

  • Relate electron shells to the molecules formed by:

    • Oxygen (O)

    • Hydrogen (H)

    • Carbon (C)

    • Sodium (Na)

    • Chlorine (Cl)

  • Compare properties of polar and nonpolar bonds

  • Relate hydrogen bond to properties of water as the solvent of life

  • Predict whether a molecule is hydrophilic or hydrophobic based on bonds and electrical charges

  • Recognize four classes of large biological molecules and their building blocks:

    • Proteins (made of amino acids)

    • Carbohydrates (simple sugars/monosaccharides)

    • Lipids (fatty acids and glycerol)

    • Nucleic Acids (DNA and RNA - made from nucleotides)

  • Identify and apply common principles for structure, formation, and breakdown of these four classes of large biological molecules

Water (H2O)

  • Water's unique properties:

    • Conducting Tubes: Water can be pulled from soil to tree tops due to hydrogen bonds allowing water molecules to stick together

Vitamins

  • Water-soluble vitamins can be readily absorbed, while fat-soluble vitamins require fats or oils to be consumed for absorption

  • Deficiencies in vitamins:

    • Rickets: Severe deficiency in Vitamin D leading to bone softening and immune dysfunction

    • Scurvy: Severe deficiency in Vitamin C leading to gum bleeding and a compromised immune system

Elements of Life

  • Elements: Pure substances containing only one type of atom

    • Cannot be broken down by chemical reactions

    • Atoms: Basic units of matter, smallest unit of an element

  • Major Elements: Hydrogen (H), Carbon (C), Nitrogen (N), Oxygen (O)

  • Composition by Weight:

    • Universe:

    • H: 73%

    • He: 25%

    • Bulk Earth:

    • O: 30.1%

    • C: 18.5%

    • Fe: 32.1%

    • Human Body:

    • O: 65%

    • C: 18.5%

    • H: 9.5%

    • N: 3.2%

    • Ca: 1.5%

    • P: 1.0%

    • K: 0.4%

    • Na: 0.2%

    • Cl: 0.2%

    • Mg: 0.1%

    • S: 0.04%

Building and Breaking Large Biological Molecules

  • Large biological molecules are built from smaller monomers and can be classified into four categories:

    • Proteins (made from amino acids)

    • Nucleic Acids (made from nucleotides)

    • Complex Carbohydrates (polysaccharides from monosaccharides)

    • Lipids (mostly fatty acids and glycerol)

  • Dehydration Synthesis:

    • Process of forming larger molecules from smaller ones by removing water (H from one end and OH from another)

    • Example: Polymerization of monomers to create longer chains

  • Hydrolysis:

    • The breakdown of large molecules by adding water

Chemical Bonds

  • Types of Bonds:

    • Covalent Bonds:

    • Formed by sharing electrons between atoms

    • Are strong and require energy to break

    • In biological molecules, they help maintain structure

    • Can be polar or nonpolar based on electronegativity differences

    • Ionic Bonds:

    • Formed by giving or taking electrons

    • Weaker than covalent bonds in water, used for interaction between different molecules

  • Valence Electrons:

    • Electrons in the outer shell participate in bonding

    • Determine the type and number of covalent bonds formed

    • Noble gases have full outer shells, making them inert and less likely to form bonds

  • Electronegativity:

    • Refers to the tendency of an atom to attract electrons towards itself

    • Higher electronegativity means stronger pull on shared electrons

    • Polarity arises when electrons are not shared equally between atoms

Polarity of Water

  • Water Molecule (H2O):

    • Oxygen is electronegative, pulling the electrons closer, leading to a polar molecule

    • The O atom has a partial negative charge, while H atoms have partial positive charges

    • Water's polarity allows it to interact and dissolve other polar molecules and ions

Hydrophilic vs. Hydrophobic

  • Hydrophilic:

    • Water-attracting substances with polar bonds (e.g. O-H, C=O)

    • Include particles with full charges and are water-soluble

  • Hydrophobic:

    • Water-repelling substances with nonpolar bonds (e.g., C-H, C-C)

    • Do not attract water and are water-insoluble

Hydrogen Bonds

  • A hydrogen bond is an electrical attraction between opposite partial charges of molecules (e.g. in water)

  • Hydrogen bonds result from water's polarity and help bind water molecules to one another and to other hydrophilic molecules

Vitamins and Their Properties

  • Vitamin structures can determine their solubility:

    • Water-soluble vitamins must have sufficient polar bonds for solubility

    • Example Structures:

    • Vitamin D2 (C28H44O) - determine hydrophilicity/hydrophobicity by observing functional groups

    • Vitamin B5 (C9H17NO5) - analyze based on its chemical structure and bonding types

  • Relationship to Blood-Brain Barrier:

    • Oil-soluble drugs like Benadryl can pass the barrier, affecting the central nervous system, while water-soluble drugs like Claritin cannot

Carbon's Role in Biological Molecules

  • Carbon can form four covalent bonds, leading to complex structures and facilitating the formation of large biological molecules

  • Its tendency to form bonds allows for a variety of molecular shapes and functions, foundational to life itself.