Biological Molecules

Introduction to Organic Molecules

Biological molecules are primarily composed of carbon and are essential for life. Aside from water, most biologically related molecules contain carbon, making them organic molecules. These molecules form the basis of cellular structure and function.

• Organic molecules: Molecules containing carbon.

• Exceptions: Not all carbon-containing molecules are considered organic (e.g., carbon dioxide, carbon monoxide, diamonds).

• Living organisms can create a wide variety of organic molecules due to carbon's versatility.

Carbon atoms are the most versatile building blocks of molecules because:

• Carbon has a valence of 4, allowing it to form up to four covalent bonds.

• Can form single, double, or triple bonds.

• Can bind to 2, 3, or 4 other atoms, enabling complex molecular structures.

Functional Groups

Functional groups are small characteristic groups of atoms that are frequently bonded to the carbon skeleton of organic molecules. They confer specific chemical and physical properties to molecules and are often the sites of chemical reactivity.

• Functional groups are consistent from one organic molecule to another.

• They determine the chemical properties and reactivity of the molecules.

There are seven general functional groups found in organic molecules:

1) Hydroxyl Group (-OH)

• Consists of a hydrogen atom bonded to an oxygen atom, which is bonded to a carbon skeleton.

• Polar group; increases solubility in water.

• Found in alcohols (e.g., ethanol, glycerol).

• Involved in condensation (dehydration) and hydrolysis reactions.

2) Carbonyl Group (-C=O)

• Consists of a carbon atom double bonded to an oxygen atom.

• Polar group; found in two configurations:

  • Terminal (at the end of a carbon skeleton): forms aldehydes (e.g., propanal).

  • Within the carbon skeleton: forms ketones (e.g., acetone).

3) Carboxyl Group (-COOH)

• Carbon atom double bonded to an oxygen atom and single bonded to a hydroxyl group.

• Polar group; acts as an acid (can donate a proton, H+).

• Involved in peptide bonds in proteins.

4) Amino Group (-NH2)

• Consists of two hydrogen atoms bonded to a nitrogen atom, which is bonded to a carbon skeleton.

• Polar group; acts as a base (can accept a proton).

• Found in amino acids (which have both amino and carboxyl groups).

5) Sulfhydryl Group (-SH)

• Consists of a hydrogen atom bonded to a sulfur atom, which is bonded to a carbon skeleton.

• Nonpolar group.

• Critical in stabilizing protein structure (disulfide bridges).

6) Phosphate Group (-PO4)

• Phosphorus atom bonded to four oxygen atoms; one oxygen is attached to the carbon skeleton.

• Polar group; similar to phosphoric acid.

• Acts as an acid (can donate protons).

• Links nucleotides in nucleic acids; important in energy storage and transfer (e.g., ATP).

7) Methyl Group (-CH3)

• Consists of three hydrogen atoms bonded to a carbon atom.

• Nonpolar group; makes molecules more hydrophobic.

• Subtle changes in methyl group position can affect molecular function (e.g., estradiol vs. testosterone).

Synthesizing Organic Molecules: A Modular Approach

Monomers and Polymers

Biological molecules are often assembled from smaller subunits called monomers. When monomers are joined together, they form polymers, which are chains of repeating units. The process of building and breaking down polymers is central to biological function.

• Monomers: Simple molecules that serve as building blocks.

• Polymers: Larger molecules made by joining monomers.

• Polymers are formed or broken apart by adding or removing water.

Dehydration Synthesis and Hydrolysis

• Dehydration synthesis (condensation reaction): Forms a polymer from monomers by removing a water molecule.

  • One monomer loses a hydroxyl group (-OH), the other loses a hydrogen (-H).

  • Results in the formation of a covalent bond.

• Hydrolysis: Breaks the covalent bond between two monomers by adding water.

  • One monomer gains a hydroxyl group (-OH), the other gains a hydrogen (-H).

The Principle Types of Biological Molecules

Four Classes of Macromolecules

There are four major classes of biological macromolecules, each with distinct monomers, polymers, and functions.

Carbohydrates

Carbohydrates are organic molecules made of sugars and their polymers. They serve as fuel and building material for cells.

• Classified by the number of simple sugar units (monosaccharides, disaccharides, polysaccharides).

• Monosaccharides are simple sugars (e.g., glucose).

• Major source of nutrients for cells.

• Can be produced by photosynthetic organisms from CO2, H2O, and light.

General Structure of Carbohydrates

• Each carbon has a hydroxyl group except one, which has a carbonyl group.

• Size of the carbon skeleton varies (commonly 3-7 carbons).

• In aqueous solutions, monosaccharides with 5 or more carbons form ring structures.

Monosaccharides

• Simple sugars with the formula (CH2O)n.

• Glucose (C6H12O6) is the most common monosaccharide.

Disaccharides

Disaccharides are molecules consisting of two monosaccharides joined by a glycosidic linkage, which is a covalent bond formed by dehydration synthesis.

• Glycosidic linkage: Covalent bond between two sugar monomers.

Example: The formation of sucrose from glucose and fructose involves a dehydration synthesis reaction, resulting in the release of a water molecule and the formation of a glycosidic bond.

Additional info: Further details on polysaccharides, lipids, proteins, and nucleic acids would expand on their structure and function, but the provided notes focus primarily on functional groups and carbohydrates.