Introduction to Biological Macromolecules and Elements of Life

Molecular Shape and Essential Elements

• Molecular shape is intrinsically tied to function; this relationship forms the basis of modern medicine and the study of how compounds interact with biological receptors.
• Morphine and endorphins share similar molecular structures, allowing morphine to bind to brain receptors intended for natural endorphins.
• Approximately $20\%$ to $25\%$ of natural elements are essential to life.
• Four elements make up $96\%$ of living matter: Carbon ($C$), Hydrogen ($H$), Oxygen ($O$), and Nitrogen ($N$).
• Other essential elements include Calcium ($Ca$), Phosphorus ($P$), Potassium ($K$), and Sulfur ($S$).
• Trace elements, including various vitamins and minerals, are required in minute quantities for cellular reactions.

Carbon and Functional Groups

• Carbon serves as the backbone of life, forming the structure of carbohydrates, proteins, fatty acids, and nucleic acids.
• Organic chemistry is specifically the study of compounds containing Carbon ($C$).
• Carbon possesses $4$ valence electrons, enabling it to form four covalent bonds and create complex, diverse molecules such as graphite, diamonds, and buckyballs.
• Functional groups are specific clusters of atoms attached to carbon skeletons that dictate chemical properties. The seven most common are:
  • Hydroxyl
  • Carbonyl
  • Carboxyl
  • Amino
  • Sulfhydryl
  • Phosphate
  • Methyl

Macromolecules and Monomers

• Macromolecules are polymers built from smaller repeating units called monomers.
• Monomers function as individual building blocks, while polymers represent the completed complex structure.
• Three of the four major macromolecules—carbohydrates, proteins, and nucleic acids—are chain-like polymers.

Carbohydrates (Sugars)

• Carbohydrates serve as a primary source of energy in nature.
• The monomers of carbohydrates are monosaccharides (simple sugars), which generally follow the molecular formula ratio of $CH_2O$.
• Glucose ($C_6H_{12}O_6$) is a fundamental monosaccharide.
• Monosaccharides typically feature a carbon chain where most carbons are bonded to a hydroxyl group ($OH$) and one carbon is double-bonded to Oxygen ($C=O$).
• While often drawn as linear skeletons, monosaccharides form ring structures in aqueous solutions.

Proteins and Amino Acids

• Proteins comprise approximately $50\%$ of the dry mass of most cells and perform diverse roles including defense, storage, transport, cellular communication, and structural support.
• Enzymes act as catalysts to accelerate chemical reactions.
• The monomers of proteins are amino acids, of which there are $20$ different types.
• Every amino acid shares a common structure consisting of an alpha ($\alpha$) carbon bonded to an amino group ($NH_2$), a carboxyl group ($COOH$), and a variable side chain known as the R group.
• The R group determines the specific properties of the amino acid, such as whether it is hydrophobic, hydrophilic, acidic, or basic.

Nucleic Acids and Nucleotides

• Nucleic acids store genetic information and are polymers called polynucleotides.
• The monomer is the nucleotide, which consists of three parts: a pentose sugar ($5$-carbon sugar), a nitrogenous base, and at least one phosphate group.
• There are two categories of nitrogenous bases:
  • Pyrimidines (single ring): Cytosine ($C$), Thymine ($T$), and Uracil ($U$).
  • Purines (double ring): Adenine ($A$) and Guanine ($G$).
• Deoxyribose is the sugar found in DNA, while ribose is the sugar in RNA; deoxyribose is identified by the absence of one oxygen atom compared to ribose.