Biomolecules

Introduction to Biomolecules

Biomolecules are organic molecules that are essential to living organisms. They are classified into four primary classes: carbohydrates, proteins, nucleic acids, and lipids. Each class plays a unique role in the structure and function of cells.

• Carbohydrates: Provide energy and structural support.

• Proteins: Serve as enzymes, structural components, and signaling molecules.

• Nucleic Acids: Store and transmit genetic information.

• Lipids: Store energy, form cell membranes, and act as signaling molecules.

Carbon: The Central Atom in Organic Molecules

Properties of Carbon

Carbon is the most abundant element in living systems (excluding water) and forms the backbone of organic molecules. Its ability to form four covalent bonds makes it an excellent building block for complex molecules.

• Hydrocarbons: Molecules consisting only of carbon and hydrogen.

• Organic molecules: Molecules with covalently bonded carbon atoms, often with hydrogen, oxygen, nitrogen, phosphorus, or sulfur.

Example: Hydrocarbons can be linear or ring-shaped, and can vary in length and branching.

Functional Groups

Definition and Importance

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

• Hydroxyl group ()

• Carbonyl group ()

• Carboxyl group ()

• Amino group ()

• Phosphate group ()

• Sulfhydryl group ()

Example: The presence or absence of functional groups determines the reactivity and properties of biomolecules.

Monomers and Polymers

Building Blocks of Biomolecules

Monomers are small, repeating units that can be linked together to form polymers. The process of forming polymers from monomers is called polymerization.

• Dehydration synthesis: Joins monomers by removing a water molecule.

• Hydrolysis: Breaks polymers into monomers by adding a water molecule.

Example: Formation and breakdown of polysaccharides, proteins, and nucleic acids involve dehydration and hydrolysis reactions.

Carbohydrates

Structure and Classification

Carbohydrates are carbon-based molecules hydrated with many hydroxyl () groups. They are classified by the number of monomer units:

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

• Oligosaccharides: Short chains of monosaccharides.

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

General formula for simple carbohydrates:

Formation and Breakdown of Polysaccharides

• Glycosidic bonds link monosaccharides together.

• Dehydration synthesis forms glycosidic bonds; hydrolysis breaks them.

Example: Formation of maltose from two glucose molecules.

Functions of Carbohydrates

• Structural support: Cellulose in plants, chitin in fungi and arthropods.

• Energy storage: Starch in plants, glycogen in animals.

Proteins

Structure and Function

Proteins are polymers of amino acids linked by peptide bonds. They perform a wide variety of functions, including catalysis (enzymes), structure, transport, and signaling.

• Amino acid structure: Central carbon, amino group (), carboxyl group (), hydrogen atom, and variable R group.

• Peptide bond formation: Dehydration synthesis between amino and carboxyl groups of adjacent amino acids.

Levels of Protein Structure

• Primary structure: Sequence of amino acids.

• Secondary structure: Local folding (alpha helices, beta sheets) stabilized by hydrogen bonds.

• Tertiary structure: Overall 3D shape of a polypeptide.

• Quaternary structure: Association of multiple polypeptide chains.

Denaturation and Chaperones

• Denaturation: Loss of protein structure due to environmental changes.

• Chaperone proteins: Assist in proper folding and refolding of proteins.

Nucleic Acids

Structure and Function

Nucleic acids (DNA and RNA) store and transmit genetic information. They are polymers of nucleotides, each consisting of a phosphate group, a five-carbon sugar (deoxyribose or ribose), and a nitrogenous base.

• Phosphodiester bonds link nucleotides together.

• DNA: Double-stranded, stores genetic information.

• RNA: Single-stranded, involved in protein synthesis and gene regulation.

Nitrogenous Bases

• Pyrimidines: Cytosine, thymine (DNA), uracil (RNA).

• Purines: Adenine, guanine.

• Base pairing: Adenine pairs with thymine (or uracil in RNA), guanine pairs with cytosine.

Lipids

Structure and Types

Lipids are hydrophobic molecules that include fats, oils, phospholipids, steroids, and waxes. They are not true polymers but are grouped based on their hydrophobic properties.

• Fatty acids: Hydrocarbon chains with a carboxyl group.

• Triglycerides: Three fatty acids linked to glycerol.

• Phospholipids: Glycerol, two fatty acids, and a phosphate group; major component of cell membranes.

• Steroids: Four fused carbon rings (e.g., cholesterol).

• Waxes: Long-chain fatty acids esterified to long-chain alcohols.

Saturated vs. Unsaturated Fatty Acids

• Saturated fatty acids: No double bonds, straight chains, solid at room temperature.

• Unsaturated fatty acids: One or more double bonds, kinked chains, liquid at room temperature.

Biological Roles of Lipids

• Energy storage: Triglycerides store energy efficiently.

• Membrane structure: Phospholipids form bilayers in cell membranes.

• Signaling: Steroids act as hormones.

• Protection: Waxes and cholesterol provide structural support and prevent water loss.

Summary Table: Classes of Biomolecules

Additional info: These notes provide foundational knowledge for understanding the structure and function of biomolecules, which is essential for further study in organic chemistry and biochemistry.