Biological Macromolecules Overview

Chapter 3 Biological Macromolecules

3.1 Synthesis of Biological Macromolecules

• Introduction:

  • Biological macromolecules are essential for life, composed of smaller organic molecules.

  • Four major classes of biological macromolecules:

  • Carbohydrates

  • Lipids

  • Proteins

  • Nucleic acids

  • Foods such as bread, fruit, and cheese are rich sources of biological macromolecules.

• Importance of Macromolecules:

  • Comprise majority of a cell's dry mass (note that water makes up the majority of its complete mass).

  • Organic compounds, containing carbon, hydrogen, oxygen, nitrogen, and other trace elements.

Dehydration Synthesis

• Definition:- Process where monomers combine to form polymers while releasing water; also known as condensation reaction.

• Mechanism:- Example: Two glucose molecules link to create maltose, releasing water.

  • The hydrogen from one monomer combines with the hydroxyl group of another, releasing a water molecule while sharing electrons to form covalent bonds.

• Polymers Formation: - Repeated monomer combinations result in diverse macromolecules such as starch, glycogen, and cellulose from glucose monomers.

Hydrolysis

• Definition:- Process of breaking down polymers into monomers by inserting a water molecule across the bond.

• Mechanism:- Breaks covalent bonds; one component receives a hydrogen atom (H+), and the other receives a hydroxyl group (OH–) from the split water molecule.

  • Example: Maltose breaking down into glucose monomers through hydrolysis.

• Enzymatic Catalysis:- Catalyzed by specific enzymes (e.g., amylase breaks down carbohydrates, proteases break down proteins, lipases break down lipids).

3.2 Carbohydrates

• Importance of Carbohydrates:

  • A primary energy source and having structural roles in plants, animals, and fungi.

  • Examples of dietary sources: grains, fruits, vegetables.

Molecular Structure

• Stoichiometric Formula: - General formula: (CH2O)n where n = number of carbons.

  • Ratio of carbon to hydrogen to oxygen in carbohydrates is 1:2:1.

Classifications of Carbohydrates

• Three Main Categories:

  1. Monosaccharides:

  • Simple sugars (e.g., glucose, fructose, galactose).

  • Commonly have 3 to 7 carbons. Ends with the suffix -ose. Can be classified as:- Aldoses: sugars with an aldehyde group (R-CHO).

    • Ketoses: sugars with a ketone group (RC(=O)R').

    • Examples: Glucose (C6H12O6), Galactose, Fructose (isomers with different arrangements).

  1. Disaccharides:

  • Formed from two monosaccharides through dehydration synthesis.

  • Types include:- Sucrose: Glucose + Fructose.

    • Lactose: Glucose + Galactose (found in milk).

    • Maltose: Glucose + Glucose.

  • Characterized by glycosidic bonds (either alpha or beta).

  1. Polysaccharides:

  • Long chains of monosaccharides linked by glycosidic bonds. Examples include:- Starch: Storage form in plants, made of amylose (unbranched) and amylopectin (branched).

    • Glycogen: Storage form in animals, similar structure to amylopectin but more branched.

    • Cellulose: Structural component in plant cell walls with β 1-4 linkages.

Functions of Carbohydrates

• In Plants:

  • Energy storage (e.g., starch).

  • Structural function (cellulose in cell walls).

• In Animals:

  • Energy storage (glycogen).

• Other Functions:

  • Regulation of blood sugar levels.

  • Provides dietary fiber, aiding digestion and helping to regulate cholesterol and blood sugar levels.

3.3 Lipids

• Definition of Lipids:

  • A diverse group of hydrophobic compounds, primarily nonpolar and insoluble in water.

Types of Lipids

1. Fats and Oils:

   • Comprised of glycerol and fatty acids.

   • Fatty acids are long hydrocarbon chains with a carboxyl group (COOH). Saturated (single bonds) vs. unsaturated (one or more double bonds).- Examples:

     • Saturated Fats: E.g., stearic acid.

     • Unsaturated Fats: E.g., oleic acid (usually liquid at room temperature).

     • Trans Fats: Created through hydrogenation, linked to cardiovascular diseases.

2. Phospholipids:

   • Comprise the cell membrane; contain two fatty acids and a phosphate group.

   • Amphipathic molecules (hydrophilic head, hydrophobic tails).

3. Steroids:

   • Four linked carbon rings.

   • Examples: Cholesterol, testosterone.

   • Cholesterol: Critical for membrane fluidity and precursor to steroid hormones and bile salts.

Functions of Lipids

• Energy storage (long-term), insulation, and forming cellular membranes.

3.4 Proteins

• Definition of Proteins:

  • Macromolecules composed of one or more polypeptide chains of amino acids.

Types of Proteins and Their Functions:

• Enzymes:

  • Catalysts for biochemical reactions.

  • Examples: Amylase – breaks down starch.

• Structural Proteins:

  • Provide support and shape (e.g., collagen).

• Transport Proteins:

  • Carry substances (e.g., hemoglobin).

• Hormones:

  • Chemical messengers (e.g., insulin).

Amino Acids:

• Basic building blocks of proteins, 20 common types.- Structure includes:

  • Central carbon, amino group (NH2), carboxyl group (COOH), hydrogen, and R group.

  • Peptide bond formation connects amino acids during protein synthesis (primary structure).

Protein Structure Levels:

1. Primary Structure: Linear sequence of amino acids.

2. Secondary Structure: Local folding into helices or pleated sheets due to hydrogen bonding.

3. Tertiary Structure: Overall 3D shape formed by interactions among R groups.

4. Quaternary Structure: Complex of multiple polypeptide chains (e.g., hemoglobin).

Denaturation of Proteins

• Change of protein structure due to environmental factors (temperature, pH).

• Loss of function may occur. Example: Denaturation of albumin in an egg when cooked.

3.5 Nucleic Acids

Types of Nucleic Acids:

• DNA (Deoxyribonucleic Acid):

  • Genetic material with a double-helix structure.

  • Composed of nucleotides with deoxyribose sugar, nitrogenous bases (A, T, G, C).

• RNA (Ribonucleic Acid):

  • Involved in protein synthesis, usually single-stranded with ribose and nitrogenous bases (A, U, G, C).

Nucleotide Structure:

• Each nucleotide comprises:- Pentose sugar (ribose or deoxyribose), phosphate group, nitrogenous base.

• Formation of nucleic acid chains linked by phosphodiester bonds.

Function of Nucleic Acids:

• DNA: Stores genetic information and directs cellular functions.

• RNA: Involves in translating that information into proteins (mRNA, tRNA, rRNA).

Key Terms

• Dehydration Synthesis: Reaction forming bonds while releasing water.

• Hydrolysis: Breaks bonds using water.

• Glycosidic Bond: Link between monosaccharides in carbohydrates.

• Triglyceride: Fat composed of glycerol and three fatty acids.

• Peptide Bond: Link between amino acids in proteins.

• Phosphodiester Linkage: Bond in nucleic acids between sugars and phosphate groups.

• Primary, Secondary, Tertiary Structure: Levels of protein organization.

• DNA: Genetic material with a double-helix structure.

• RNA: Involved in protein synthesis, typically single-stranded.