Biological Molecules: Structure, Function, and Diversity

Biological Molecules: Structure, Function, and Diversity

Overview of Biological Molecules

Biological molecules, also known as biomolecules, are essential components of all living organisms. They play critical roles in structure, function, and regulation of the body's tissues and organs. This section introduces the major classes of biological molecules and explores their diversity and significance.

• Carbon-based molecules form the backbone of most biological molecules due to carbon's ability to form four covalent bonds, allowing for complex and diverse structures.

• Living things are primarily composed of four major classes of large biological molecules: carbohydrates, lipids, proteins, and nucleic acids.

• These molecules are often polymers, constructed from smaller subunits called monomers.

Variation in Carbon-Based Compounds

Carbon's unique bonding properties allow for a wide variety of molecular structures, leading to the diversity of organic compounds found in living organisms.

• Isomers are compounds with the same molecular formula but different structures, resulting in different properties.

• Types of isomers include:

  • Structural isomers: Differ in the covalent arrangement of atoms.

  • Cis-trans isomers: Differ in spatial arrangement around a double bond.

  • Enantiomers: Mirror images of each other, often with different biological activities.

• Form determines function: The structure of a molecule influences its role in biological systems.

Parts of Chemical Reactions

Chemical reactions are processes that make and break chemical bonds, transforming reactants into products. These reactions are fundamental to metabolism and other biological processes.

• Reactants: The starting materials in a chemical reaction.

• Products: The substances formed as a result of the reaction.

• Chemical bonds are broken and formed during reactions, often involving the transfer or sharing of electrons.

• Example equation (water dissociation):

$2H_2O \rightarrow H_3O^+ + OH^-$

• Acids increase the concentration of H+ ions in solution, while bases reduce it.

Properties of Water: Hydrophilic and Hydrophobic Interactions

Water is a vital solvent in biological systems, and its interactions with other molecules are crucial for life.

• Hydrophilic substances are "water-loving" and dissolve easily in water (e.g., salts, sugars).

• Hydrophobic substances are "water-fearing" and do not dissolve in water (e.g., oils, fats).

• These properties influence the structure and function of biological molecules, such as the formation of cell membranes.

The Four Classes of Large Biological Molecules

Living organisms are composed of four main types of large biological molecules, each with distinct structures and functions.

• Carbohydrates – Energy storage and structural support

• Lipids – Long-term energy storage, membrane structure

• Proteins – Catalysis, structure, transport, signaling

• Nucleic acids – Storage and transmission of genetic information

Most living tissues are approximately 70% water by weight, with the remainder consisting largely of these macromolecules.

Macromolecules: Polymers and Monomers

Macromolecules are large molecules formed by the joining of smaller units called monomers. The process of building and breaking down these molecules is essential for life.

• Polymers are long chains of monomers linked by covalent bonds.

• Examples of polymers: starch (carbohydrate), DNA (nucleic acid), proteins (polypeptides).

Building Macromolecules: Dehydration Synthesis

Dehydration synthesis (condensation reaction) is the process by which monomers are joined to form polymers, with the removal of a water molecule.

• Each time a bond forms between two monomers, one molecule of water is released.

$\text{Monomer}_1 + \text{Monomer}_2 \rightarrow \text{Polymer} + H_2O$

Breaking Down Macromolecules: Hydrolysis

Hydrolysis is the process by which polymers are broken down into monomers, with the addition of a water molecule.

• This reaction is essentially the reverse of dehydration synthesis.

$\text{Polymer} + H_2O \rightarrow \text{Monomer}_1 + \text{Monomer}_2$

Carbohydrates: Structure and Function

Carbohydrates are organic molecules composed of carbon, hydrogen, and oxygen, typically with a hydrogen:oxygen atom ratio of 2:1. They serve as energy sources and structural components in cells.

• Monomers: Monosaccharides (simple sugars), such as glucose and fructose.

• Bonds: Monosaccharides are linked by glycosidic linkages (covalent bonds) to form disaccharides and polysaccharides.

• Polysaccharides: Long chains of monosaccharides; examples include starch, glycogen, and cellulose.

Polysaccharide	Function	Source
Starch	Energy storage	Plants
Glycogen	Energy storage	Animals
Cellulose	Structural support	Plant cell walls

• Cellulose is the most abundant organic molecule on Earth and provides structural support in plant cell walls.

Example: Formation of a Carbohydrate Polymer

Three monosaccharide monomers (A, B, and C) can be linked via dehydration synthesis to form a carbohydrate polymer, with glycosidic bonds connecting each monomer.

Additional info: The notes also reference lipids, but detailed content on lipids is not included in the provided slides. For completeness, lipids are another major class of biological molecules, primarily involved in energy storage and membrane structure.