Organic Molecules and Carbon Chemistry

Elements in Living Systems

Living organisms are primarily composed of a few key elements, often remembered by the acronym CHNOPS: Carbon (C), Hydrogen (H), Nitrogen (N), Oxygen (O), Phosphorus (P), and Sulfur (S). Excluding water, carbon is the most abundant element in biological molecules.

• Organic molecules: Compounds containing covalently linked carbon atoms, often with hydrogen, oxygen, and nitrogen. Examples include carbohydrates, proteins, nucleic acids, and lipids.

• Hydrocarbons: Molecules made only of carbon and hydrogen atoms.

Example: Organic molecules contain carbon and hydrogen; hydrocarbons are a subset containing only these two elements.

Carbon as a Building Block

Carbon's ability to form four covalent bonds makes it a versatile "atomic building block" for a wide variety of molecules. The backbone of organic molecules can vary in:

• Length: Number of carbon atoms in a chain.

• Position of double bonds: Placement of double bonds affects molecule shape and reactivity.

• Branch points: Carbon chains can branch, increasing complexity.

• Ring forms: Carbon atoms can form ring structures, as seen in glucose.

Example: Variations in carbon backbones lead to diverse organic molecules.

Functional Groups in Biology

Definition and Importance

Functional groups are specific groups of atoms within molecules that are responsible for characteristic chemical reactions. They are typically attached to the carbon backbone and are commonly found together in biological molecules.

• Functional groups are reactive and influence the properties and reactivity of organic molecules.

• Common functional groups in biology include hydroxyl, carbonyl, carboxyl, amino, sulfhydryl, phosphate, and methyl groups.

Example: The presence or absence of functional groups determines the molecule's function and interactions.

Biomolecules: Classes and Structure

Major Classes of Biomolecules

Biomolecules are organic molecules essential for life. There are four primary classes:

• Carbohydrates: Energy storage and structural support.

• Proteins: Catalysis, structure, transport, and regulation.

• Nucleic Acids: Information storage and transfer (DNA, RNA).

• Lipids: Energy storage, membrane structure, and signaling.

Example: Each class of biomolecule has unique monomers and polymers.

Monomers and Polymers

Monomers are individual building blocks that can be linked together to form polymers, which are long chains of monomers.

• Carbohydrates: Monomer is monosaccharide.

• Proteins: Monomer is amino acid.

• Nucleic Acids: Monomer is nucleotide.

• Lipids: Do not form true polymers but are assembled from smaller units (e.g., fatty acids, glycerol).

Example: Monomers are joined by covalent bonds to form polymers.

Polymer Formation and Breakdown

Polymers are formed and broken down by specific chemical reactions:

• Dehydration synthesis: Forms covalent bonds between monomers by removing a water molecule.

• Hydrolysis: Breaks covalent bonds by adding a water molecule.

Example:

• Dehydration:

• Hydrolysis:

Carbohydrates

Structure and Classification

Carbohydrates are carbon-based molecules hydrated with many hydroxyl groups (-OH). They are commonly referred to as "sugars." The general formula for simple carbohydrates is:

Carbohydrates are classified by the number of monomer units:

• Monosaccharides: Single sugar units (e.g., glucose).

• Oligosaccharides: Short chains of covalently linked monosaccharides.

• Polysaccharides: Long chains of covalently linked monosaccharides (e.g., starch, glycogen, cellulose).

Formation and Breakdown of Polysaccharides

Polysaccharides are formed by linking monosaccharides via dehydration synthesis, creating glycosidic bonds. Hydrolysis breaks these bonds, releasing monosaccharides.

• Dehydration synthesis:

• Hydrolysis:

Example: Formation of maltose from two glucose molecules.

Functions of Carbohydrates

Carbohydrates serve two main functions:

• Structural support: Building materials for cell walls and exoskeletons (e.g., cellulose in plants, chitin in insects).

• Energy storage: Short-term energy reserves (e.g., starch in plants, glycogen in animals).

Example:

Summary Table: Biomolecule Classes

Practice and Application

• Organic molecules are defined as chemical compounds containing carbon and hydrogen.

• Dehydration reactions create polymers from monomers; hydrolysis reactions break polymers down into monomers.

• Polysaccharides such as cellulose and chitin provide structural support; starch and glycogen are used for energy storage.

Additional info: These notes expand on the provided content with definitions, examples, and tables for clarity and completeness, suitable for General Biology exam preparation.