Organic Macromolecules

Introduction

Organic macromolecules are large, complex molecules essential for life, including carbohydrates, lipids, proteins, and nucleic acids. These molecules are fundamental to the structure and function of cells and tissues in the human body.

What are Organic Compounds?

Definition and Classification

• Organic Compounds: Molecules that always contain carbon and hydrogen, and often oxygen, nitrogen, sulfur, and phosphorus. They originate in living organisms and are generally complex (e.g., proteins).

• Inorganic Compounds: Molecules that do not contain both carbon and hydrogen. They are usually simple and may come from non-living sources (e.g., water).

Key Point: Organic compounds are distinguished by their carbon-hydrogen backbone and the presence of functional groups.

Monomers and Polymers

Relationship and Examples

• Monomer: A single, small molecular unit (micromolecule) that can join with others to form a polymer.

• Polymer: A large molecule made up of repeating monomer subunits linked together.

• Examples:

  • Monomers: Glucose, amino acids, nucleotides

  • Polymers: Starch, proteins, DNA

Application: The formation and breakdown of polymers are central to metabolism and cellular function.

Dehydration Synthesis and Hydrolysis

Mechanisms of Polymer Formation and Breakdown

• Dehydration Synthesis: An anabolic reaction where monomers are covalently bonded, releasing a water molecule. This process builds polymers.

• Hydrolysis: A catabolic reaction where water is added to break the covalent bonds between monomers, resulting in polymer breakdown.

Examples:

• Dehydration synthesis: Formation of proteins from amino acids, formation of polysaccharides from monosaccharides.

• Hydrolysis: Digestion of starch into glucose, breakdown of proteins into amino acids.

Equation (Dehydration Synthesis):

Equation (Hydrolysis):

Functional Groups in Organic Molecules

Common Functional Groups

• Hydroxyl (-OH): Found in carbohydrates, alcohols

• Carboxyl (-COOH): Found in amino acids, fatty acids

• Methyl (-CH3): Found in lipids, amino acids

• Phosphate (-PO4): Found in nucleic acids, ATP

• Amino (-NH2): Found in amino acids

Application: Functional groups determine the chemical reactivity and properties of organic molecules.

Major Classes of Organic Macromolecules

Carbohydrates

• Elements: Carbon, hydrogen, oxygen

• Monomers: Monosaccharides (e.g., glucose, fructose)

• Polymers: Polysaccharides (e.g., starch, glycogen, cellulose)

• Bond Type: Glycosidic bond

• General Formula:

Example: Glycogen is a storage polymer of glucose in animals.

Lipids

• Elements: Carbon, hydrogen, oxygen (sometimes phosphorus)

• Monomers: Fatty acids and glycerol

• Polymers: Triglycerides, phospholipids, steroids

• Bond Type: Ester bond

• Types:

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

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

  • Phospholipids: Major component of cell membranes

  • Steroids: Four-ring structure (e.g., cholesterol, testosterone)

Example: Phospholipids form the bilayer of cell membranes.

Proteins

• Elements: Carbon, hydrogen, oxygen, nitrogen (sometimes sulfur)

• Monomers: Amino acids (20 types)

• Polymers: Polypeptides, proteins

• Bond Type: Peptide bond

• Structure: Proteins have complex folded structures essential for their function.

Example: Hemoglobin transports oxygen in the blood.

Nucleic Acids

• Elements: Carbon, hydrogen, oxygen, nitrogen, phosphorus

• Monomers: Nucleotides (composed of a sugar, phosphate group, and nitrogenous base)

• Polymers: DNA, RNA

• Bond Type: Phosphodiester bond

Example: DNA stores genetic information; RNA is involved in protein synthesis.

Comparison Table: Organic Macromolecules

Physiological and Structural Roles of Macromolecules

Carbohydrates

• Energy storage: Glycogen in liver and muscle

• Structural: Cellulose in plant cell walls

• Cell recognition: Glycoproteins and glycolipids

Lipids

• Energy storage: Triglycerides

• Structural: Phospholipids in cell membranes

• Hormones: Steroids (e.g., testosterone, estrogen)

Proteins

• Structural: Collagen, keratin

• Transport: Hemoglobin

• Enzymatic: Catalyze biochemical reactions

• Defense: Antibodies

• Movement: Actin, myosin

Nucleic Acids

• Genetic information: DNA stores hereditary material

• Protein synthesis: RNA transcribes and translates genetic code

• Energy transfer: ATP (adenosine triphosphate) is the cell's energy currency

Protein Structure and Function

Levels of Protein Structure

• Primary Structure: Sequence of amino acids in a polypeptide chain

• Secondary Structure: Local folding into alpha-helices and beta-sheets stabilized by hydrogen bonds

• Tertiary Structure: Overall 3D shape of a single polypeptide, stabilized by interactions such as hydrophobic interactions, disulfide bridges, and ionic bonds

• Quaternary Structure: Association of multiple polypeptide chains to form a functional protein

Key Point: Protein shape is critical for function; loss of shape (denaturation) leads to loss of function.

Example: Enzymes require precise 3D structure to bind substrates; hemoglobin's quaternary structure enables oxygen transport.

Denaturation

• Definition: Loss of protein structure due to changes in temperature, pH, or exposure to chemicals

• Effect: Disrupts hydrogen bonding and ionic interactions, resulting in loss of function

Nucleotides and ATP

Structure and Function

• Nucleotide: Composed of a nitrogenous base, a five-carbon sugar (ribose or deoxyribose), and a phosphate group

• ATP (Adenosine Triphosphate): Main energy carrier in cells; consists of adenosine attached to three phosphate groups

• Energy Release: Hydrolysis of ATP to ADP and inorganic phosphate releases energy

Equation (ATP Hydrolysis):

Application: ATP is rapidly consumed and must be continually replenished; its formation requires oxygen.

Summary

• Organic macromolecules are essential for life, providing structure, energy, and information storage.

• Understanding their structure and function is fundamental to anatomy and physiology.