Chapter Two pt. 3

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 are 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 do not contain both carbon and hydrogen, are usually simple, and often come from non-living sources (e.g., water).

Key Point: Organic compounds form the basis of biological macromolecules.

Functional Groups in Organic Molecules

Common Functional Groups

• Hydroxyl (-OH): Found in carbohydrates and alcohols.

• Carboxyl (-COOH): Present in amino acids and fatty acids.

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

• Phosphate (-PO4): Found in nucleic acids and phospholipids.

• Amino (-NH2): Present in amino acids.

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

Monomers and Polymers

Relationship and Examples

• Monomers: Small, repeating units (e.g., glucose, amino acids, nucleotides).

• Polymers: Large molecules made by linking monomers (e.g., starch, proteins, DNA).

Dehydration Synthesis: An anabolic reaction where monomers are joined by covalent bonds, releasing water.

Hydrolysis: A catabolic reaction where polymers are broken down into monomers by adding water.

• Example of Dehydration Synthesis: Formation of proteins from amino acids.

• Example of Hydrolysis: Digestion of starch into glucose.

Major Classes of Organic Macromolecules

Carbohydrates

• Elements: Carbon, hydrogen, oxygen (ratio 1:2:1).

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

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

• Bonds: Glycosidic bonds.

Physiological Role: Energy source, energy storage (glycogen), structural support (cellulose).

Lipids

• Elements: Carbon, hydrogen, oxygen (less oxygen than carbohydrates).

• Monomers: Fatty acids and glycerol.

• Polymers: Triglycerides, phospholipids, steroids.

• Bonds: Ester bonds.

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).

Physiological Role: Energy storage, cell membrane structure, hormones.

Proteins

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

• Monomers: Amino acids (20 types).

• Polymers: Polypeptides and proteins.

• Bonds: Peptide bonds.

Physiological Role: Enzymes, structural support, transport, signaling, immune response.

Nucleic Acids

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

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

• Polymers: DNA and RNA.

• Bonds: Phosphodiester bonds.

Physiological Role: Genetic information storage (DNA), protein synthesis (RNA), energy transfer (ATP).

Comparison Table: Macromolecules

Macromolecule	Elements	Monomer	Polymer	Main Function
Carbohydrates	C, H, O	Monosaccharide	Polysaccharide	Energy, structure
Lipids	C, H, O	Fatty acid, glycerol	Triglyceride, phospholipid, steroid	Energy storage, membranes, hormones
Proteins	C, H, O, N, (S)	Amino acid	Polypeptide/protein	Enzymes, structure, transport
Nucleic Acids	C, H, O, N, P	Nucleotide	DNA, RNA	Genetic info, protein synthesis

Levels of Protein Structure

Overview

Proteins have four levels of structure, each contributing to their function:

• 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 formed by interactions among R-groups (hydrophobic interactions, ionic bonds, disulfide bridges, van der Waals forces).

• Quaternary Structure: Association of multiple polypeptide chains into a functional protein (e.g., hemoglobin).

Protein shape is essential for function: Denaturation (loss of shape) disrupts function, often caused by changes in temperature, pH, or chemicals.

Physiological and Structural Roles of Macromolecules

Carbohydrates

• Energy storage: Glycogen in liver and muscle.

• Structural: Cellulose in plant cell walls; glycoproteins and glycolipids in cell membranes.

Lipids

• Energy storage: Triglycerides in adipose tissue.

• Structural: Phospholipids in cell membranes.

• Hormonal: Steroids such as cholesterol, testosterone, and estrogen.

Proteins

• Structural: Collagen in connective tissue, keratin in hair and nails.

• Enzymatic: Catalyze biochemical reactions (e.g., amylase, pepsin).

• Transport: Hemoglobin transports oxygen; membrane proteins transport molecules.

• Defense: Antibodies in immune response.

Nucleic Acids

• Genetic information: DNA stores hereditary material.

• Protein synthesis: RNA transcribes and translates genetic code.

• Energy transfer: ATP is the main energy currency of the cell.

ATP Formation:

• ATP (adenosine triphosphate) is formed from ADP (adenosine diphosphate) and inorganic phosphate ($ADP + P_i \rightarrow ATP$), requiring energy input.

• Hydrolysis of ATP releases energy ($ATP \rightarrow ADP + P_i$).

Summary Table: Nitrogenous Bases in Nucleic Acids

Type	Bases	Structure
Purines	Adenine (A), Guanine (G)	Double-ringed
Pyrimidines	Cytosine (C), Thymine (T), Uracil (U)	Single-ringed

Conclusion

Organic macromolecules are vital for the structure and function of living organisms. Understanding their composition, structure, and roles is essential for studying anatomy and physiology.