Biological Molecules: Structure, Function, and Classification

Biological Molecules

Introduction to Biological Molecules

Biological molecules are essential for life, forming the structural and functional basis of all organisms. Organic molecules are primarily composed of carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur and phosphorus.

• Organic molecules are carbon-based compounds found in living organisms.

• Carbon's versatility allows it to form stable covalent bonds with many elements, enabling complex molecular structures.

The Importance of Carbon

• Carbon can form four covalent bonds, allowing for a wide diversity of molecules.

• Carbon skeletons can be straight, branched, or ring-shaped, providing structural variety.

• Functional groups attached to carbon skeletons impart specific chemical properties and reactivity.

Monomers, Polymers, and Reactions

Most biological macromolecules are polymers, constructed from repeating monomer units. The formation and breakdown of these polymers involve specific chemical reactions.

• Monomers: Small, repeating units that serve as building blocks.

• Polymers: Large molecules formed by linking monomers together.

• Dehydration synthesis (condensation): Joins monomers by removing water.

• Hydrolysis: Breaks polymers into monomers by adding water.

General Reaction:

• Dehydration: $\text{Monomer}_1 + \text{Monomer}_2 \rightarrow \text{Polymer} + \text{H}_2\text{O}$

• Hydrolysis: $\text{Polymer} + \text{H}_2\text{O} \rightarrow \text{Monomer}_1 + \text{Monomer}_2$

Functional Groups

Functional groups are specific groups of atoms within molecules that confer characteristic chemical properties and reactivity. They are critical in determining the behavior of biological molecules.

Functional Group	Structure	Properties
Hydroxyl	-OH	Polar, forms hydrogen bonds
Carboxyl	-COOH	Acidic, found in amino acids and fatty acids
Amino	-NH2	Basic, found in amino acids
Phosphate	-PO4	Energy transfer, found in nucleotides
Sulfhydryl	-SH	Forms disulfide bonds in proteins
Methyl	-CH3	Nonpolar, affects gene expression

Four Classes of Biological Molecules

Carbohydrates

Carbohydrates are the primary energy source for most organisms and serve structural roles in cells. They are composed of carbon, hydrogen, and oxygen, typically in a 1:2:1 ratio.

• Monosaccharides: Simple sugars, e.g., glucose ($C_6H_{12}O_6$).

• Disaccharides: Formed by joining two monosaccharides through dehydration synthesis. Example: sucrose.

• Polysaccharides: Polymers made of many monosaccharides. Examples: starch (energy storage in plants), glycogen (energy storage in animals), cellulose (structural support in plants).

Proteins

Proteins are polymers of amino acids, joined by peptide bonds. They have diverse functions, including catalysis, transport, structural support, and regulation.

• Amino acids: Building blocks of proteins, each with a central carbon, amino group, carboxyl group, and R group (side chain).

• Peptide bond: Covalent bond that links amino acids.

• Levels of protein structure:

  • Primary: Sequence of amino acids

  • Secondary: Alpha helices and beta sheets formed by hydrogen bonding

  • Tertiary: 3D folding due to interactions among side chains

  • Quaternary: Association of multiple polypeptide chains

General Formula for Amino Acid:

• $\text{Amino Group} - \text{Central Carbon} - \text{Carboxyl Group} - \text{R Group}$

Nucleotides and Nucleic Acids

Nucleic acids store and transmit genetic information. They are polymers of nucleotides, each consisting of a sugar, phosphate group, and nitrogenous base.

• DNA: Deoxyribonucleic acid, stores genetic information.

• RNA: Ribonucleic acid, involved in protein synthesis and gene regulation.

• Nucleotide structure:

  • Pentose sugar (ribose or deoxyribose)

  • Phosphate group

  • Nitrogenous base (Adenine, Thymine, Cytosine, Guanine, Uracil)

Lipids

Lipids are a diverse group of nonpolar molecules, characterized by regions of hydrocarbon chains. They serve as energy storage, insulation, and structural components of cell membranes.

• Triglycerides: Fats, formed by dehydration synthesis of glycerol and three fatty acids.

• Saturated fats: Fatty acids with only single bonds between carbon atoms; solid at room temperature.

• Unsaturated fats: Fatty acids with one or more double bonds; liquid at room temperature.

• Phospholipids: Major component of cell membranes; contain hydrophilic head and hydrophobic tails.

• Steroids: Lipids with four fused rings; include cholesterol and hormones.

Example: Cholesterol is essential for cell membrane structure and hormone synthesis.

Additional info: The notes have been expanded to include definitions, examples, and structural context for each class of biological molecule, as well as a recreated table of functional groups.