Biological Molecules

I. Biological Molecules

Concept 1: Organic Molecules

  • Organic molecules are characterized by carbon skeletons with various chemical groups attached that confer different properties.

A. Important Chemical Groups in Biomolecules

  1. Hydroxyl group (-OH)

    • Can hydrogen bond
    • Polar (water-soluble)
    • Found in alcohols and sugars
    • Example: Ethanol

  2. Carbonyl group (C=O)

    • Polar nature
    • Found in sugars (either ketones or aldehydes)

  3. Carboxyl group (-COOH)

    • Acidic in nature
    • Found in carboxylic acids / organic acids
    • Example: Acetic acid

  4. Amino group (-NH2)

    • Acts as a base
    • Found in amino acids like Glycine

  5. Methyl group (-CH3)

    • Found in methylated compounds

  6. Phosphate group (-PO4)

    • Contributes a negative charge to the molecule
    • Found in organic phosphates

II. Macromolecules: Polymers of Monomers

Concept 2: Major Biological Molecules

  • Three out of the four major types of molecules in biology (excluding lipids) are formed from monomers that share similar compositions and sizes.
A. Polymer Synthesis
  • Occurs via dehydration reactions.
B. Breakdown of Polymers
  • Achieved by hydrolysis reactions.

III. Carbohydrates

A. Function

  • Carbohydrates serve as energy sources and structural components.

B. Monomers

  1. Monosaccharides
    • Basic units of carbohydrates.
    • Examples:
      • Glucose (aldehyde)
      • Fructose (ketone)
      • Ribose (aldehyde)
      • Galactose (aldehyde)
C. Polymers

  1. Disaccharides

    • Formed by two monosaccharides.
    • Examples:
      • Sucrose (glucose + fructose)
      • Maltose (glucose + glucose)
    • Linked by glycosidic bonds formed during dehydration reactions.

  2. Oligosaccharides

    • Composed of 3-9 monosaccharides.
    • Example: Blood group types A, B, and O are determined by oligosaccharides on red blood cells.

  3. Polysaccharides

    • Long chains of monosaccharides, often composed of hundreds to thousands of units.
    • Examples:
      • Starch: Plant polysaccharide formed by α 1-4 glycosidic bonds.
      • Glycogen: Animal polysaccharide (highly branched structure)
      • Cellulose: Plant polysaccharide (β 1-4 glycosidic bonds).
    • Structures involving glucose contribute to the physical properties of these polymers, e.g., cellulose's rigidity.
D. Structures Involving Carbohydrates
  • Linear and ring forms: Many monosaccharides can polymerize and form ring structures.

IV. Proteins

A. Functions of Proteins

  • Enzymatic functions: accelerate chemical reactions.
  • Defensive roles: antibodies.
  • Storage functions: store amino acids.
  • Transport functions: move substances across cell membranes.

B. Monomer

  • Amino acids: Building blocks of proteins.

C. Structure of Amino Acids

  1. Central carbon (C)
  2. Hydrogen (H)
  3. Amino group (NH2)
  4. Carboxyl group (COOH)
  5. Variable group (R group)
D. Classification of Amino Acids
  1. Nonpolar, aliphatic R groups
  2. Polar, uncharged R groups
  3. Positively charged R groups
  4. Negatively charged R groups
  5. Nonpolar, aromatic R groups
E. Peptide Bonds
  • Formed between amino acids by dehydration reactions, linking the amino group of one amino acid to the carboxyl group of another, creating a polypeptide.
F. Levels of Protein Structure
  1. Primary structure: Sequence of amino acids in a polypeptide chain.
  2. Secondary structure: Hydrogen bonding leads to formation of structures such as alpha helices and beta-pleated sheets.
  3. Tertiary structure: Three-dimensional folding due to side chain interactions.
  4. Quaternary structure: Protein consisting of more than one polypeptide chain (e.g., hemoglobin).
G. Importance of Shape
  • The shape of a protein affects its function. Denaturation can disrupt the structure.

V. Lipids

A. Function of Lipids

  • Serve a variety of roles, including energy storage, structural components of cell membranes, and signaling molecules.

B. Major Types of Lipids

  1. Fatty acids
    • Basic building blocks of triglycerides and phospholipids.
  2. Saturated fats: Contain no double bonds between carbon atoms in the fatty acid chains.
  3. Unsaturated fats: Contain one or more double bonds, leading to kinks in the fatty acid chain, affecting their properties.
  4. Trans fats: Formed through chemical hydrogenation, altering the structure of the fatty acids.
  5. Triglycerides (Big Lipid): Comprised of glycerol and three fatty acids connected via ester linkages.
  6. Phospholipids: Formed from glycerol, two fatty acids, and a phosphate group; key components of cell membranes.
  7. Steroids: Lipids characterized by a carbon skeleton consisting of four fused rings.

VI. Nucleic Acids

A. Function

  • Store and transfer genetic information.

B. Monomer

  • Nucleotide: Contains a sugar, a phosphate group, and a nitrogenous base.

C. Structure of Nucleotides

  • Sugar-phosphate backbone linked by phosphodiester bonds.
  • Two main types of nucleic acids: DNA and RNA.
D. Nitrogenous Bases
  • DNA bases: Adenine (A), Guanine (G), Cytosine (C), Thymine (T)
  • RNA bases: Adenine (A), Guanine (G), Cytosine (C), Uracil (U)

E. DNA Structure

  • Double helix structure, with nitrogenous bases pairing via hydrogen bonds between two strands.

F. Importance of Structure

  • The arrangement of bases in nucleic acids is critical for replication and transcription processes.

VII. Summary

  • Recognize and describe key chemical groups (hydroxyl, amino, carboxyl, carbonyl, phosphate, methyl).
  • Distinguish between the four major classes of molecules in biology.
  • Differentiate between mono-, di-, and polysaccharides.
  • Identify the structural differences between saturated and unsaturated fats, including cis and trans configurations.
  • Describe the principles of protein structure across different levels.
  • Compare nucleotides including pyrimidines, purines, ribose & deoxyribose, and the 5’ & 3’ ends.