Large Biological Molecules

Overview of Biological Macromolecules

Biological macromolecules are essential for life and include carbohydrates, proteins, nucleic acids, and lipids. Three of these classes—carbohydrates, proteins, and nucleic acids—are polymers composed of monomers, while lipids are not true polymers.

• Polymer: A large molecule made by joining many smaller molecules (monomers).

• Monomer: The building block or subunit of a polymer.

• Macromolecule: A very large molecule, often formed by polymerization.

• Dehydration synthesis: A chemical reaction that joins two monomers by removing a water molecule.

• Hydrolysis: A chemical reaction that breaks a polymer into monomers by adding water.

Key Concept: The structure and function of a polymer depend on the type and number of its monomers.

Polymers and Monomers

Formation and Breakdown of Polymers

Polymers are synthesized and degraded by specific chemical reactions:

• Dehydration Reaction: Joins monomers by removing water, forming a covalent bond.

• Hydrolysis: Breaks polymers into monomers by adding water, breaking the covalent bond.

Equation for Dehydration Synthesis:

Equation for Hydrolysis:

Carbohydrates

Structure and Types of Carbohydrates

Carbohydrates are polymers with multiple functions, including energy storage and structural support. They exist in both linear and ring forms.

• Monomer: Monosaccharide (e.g., glucose, fructose)

• Polymer: Polysaccharide (e.g., starch, glycogen, cellulose)

• Functions: Fuel, energy storage, structural support

Examples of Monosaccharides: Glucose, galactose, fructose

Examples of Polysaccharides: Starch (plants), glycogen (animals), cellulose (plants)

Linear and Ring Forms of Sugars

Monosaccharides can exist in linear or ring forms. The ring structure is more common in aqueous solutions.

• Linear form: Open-chain structure

• Ring form: Closed-ring structure formed by reaction between carbonyl and hydroxyl groups

Synthesis of Disaccharides

Disaccharides are formed when two monosaccharides are joined by a dehydration reaction, creating a covalent bond called a glycosidic linkage.

• Example: Sucrose (glucose + fructose)

• Glycosidic linkage: Covalent bond between two monosaccharides

Equation for Disaccharide Formation:

Storage Polysaccharides

Polysaccharides serve as energy storage molecules in plants and animals.

• Starch: Storage polysaccharide in plants, composed of glucose monomers (common form: amylose)

• Glycogen: Storage polysaccharide in animals, stored mainly in liver and muscle cells

Structural Polysaccharides

Some polysaccharides provide structural support.

• Cellulose: Major component of plant cell walls; polymer of glucose with beta glycosidic linkages

• Chitin: Found in the exoskeleton of arthropods and cell walls of fungi

Lipids

Structure and Types of Lipids

Lipids are non-polar biomolecules that are not polymers. They include fats, phospholipids, and steroids.

• Fats: Constructed from glycerol and fatty acids; main function is energy storage

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

• Steroids: Lipids with a characteristic four-ring structure (e.g., cholesterol)

Fat Synthesis: Three fatty acids are joined to glycerol by ester linkages, forming a triacylglycerol (triglyceride).

Equation for Fat Synthesis:

Saturated vs. Unsaturated Fatty Acids

• Saturated fatty acids: No double bonds; solid at room temperature

• Unsaturated fatty acids: One or more double bonds; liquid at room temperature

Phospholipids and Membranes

Phospholipids have hydrophobic tails and hydrophilic heads, forming bilayers in cell membranes.

• Structure: Two fatty acids (hydrophobic) + phosphate group (hydrophilic) + glycerol

• Function: Major component of cell membranes

Proteins

Structure and Functions of Proteins

Proteins are polymers made of amino acid monomers. They perform a wide range of functions in cells.

• Monomer: Amino acid

• Polymer: Polypeptide

• Functions: Enzymatic activity, defense, storage, transport, cellular communication, movement, structural support

Major Protein Functions and Examples

Amino Acids and Peptide Bonds

Amino acids are organic molecules with amino and carboxyl groups. They are linked by peptide bonds to form polypeptides.

• Peptide bond: Covalent bond between amino acids

• Polypeptide: Chain of amino acids

Protein Structure and Denaturation

The function of a protein depends on its three-dimensional structure, which can be affected by environmental conditions. Loss of native structure is called denaturation.

• Primary structure: Sequence of amino acids

• Secondary, tertiary, quaternary structures: Higher levels of folding and organization

• Denaturation: Loss of protein structure due to pH, temperature, or other factors

Nucleic Acids

Structure and Function of Nucleic Acids

Nucleic acids store and transmit hereditary information. There are two types: DNA and RNA.

• Monomer: Nucleotide

• Polymer: Polynucleotide (DNA or RNA)

• Functions: DNA stores genetic information; RNA is involved in gene expression and protein synthesis

Comparison of DNA and RNA

Gene Expression

DNA directs synthesis of messenger RNA (mRNA), which controls protein synthesis in a process called gene expression.

• Transcription: DNA is used to synthesize mRNA

• Translation: mRNA is used to synthesize proteins at ribosomes

Genomics and Proteomics

Significance in Biological Inquiry

Genomics and proteomics are fields that analyze large sets of genes and proteins, respectively, using computational tools. These approaches have transformed biological research and applications.

• Genomics: Study of whole genomes, including sequencing and analysis

• Proteomics: Study of large sets of proteins, including their sequences and functions

• Bioinformatics: Use of computer software and tools to analyze biological data

Example: The Human Genome Project led to rapid development of DNA sequencing technologies and generated vast amounts of genetic data.

Additional info: Some details, such as the specific chemical structures and the process of gene expression, have been expanded for clarity and completeness.