Biochemistry Fundamentals: Organic Compounds, Macromolecules, and Biological Molecules

Organic and Inorganic Compounds

Definitions and Distinctions

Organic and inorganic compounds are two broad categories of chemical substances distinguished by their composition and origin.

• Organic Compounds: Molecules primarily composed of carbon and hydrogen, often containing oxygen, nitrogen, sulfur, and phosphorus. They are typically associated with living organisms.

• Inorganic Compounds: Molecules that do not contain carbon-hydrogen bonds. These include salts, metals, minerals, and water, and are generally not derived from living organisms.

• Example: Glucose (C6H12O6) is an organic compound; sodium chloride (NaCl) is inorganic.

Macromolecules

The Four Major Macromolecules

Macromolecules are large, complex molecules essential for life. The four main types are:

• Carbohydrates

• Proteins

• Lipids

• Nucleic Acids

Monomers and Polymers

Each macromolecule is composed of smaller units (monomers) that join to form larger structures (polymers).

• Carbohydrates: Monomer = monosaccharide (e.g., glucose); Polymer = polysaccharide (e.g., starch, cellulose)

• Proteins: Monomer = amino acid; Polymer = polypeptide/protein

• Lipids: Monomer = fatty acids and glycerol; Polymer = triglycerides, phospholipids (Note: lipids are not true polymers as they are not formed from repeating monomer units)

• Nucleic Acids: Monomer = nucleotide; Polymer = DNA or RNA

Dehydration Synthesis and Hydrolysis

Concepts and Mechanisms

These are two fundamental reactions in biochemistry for building and breaking down macromolecules.

• Dehydration Synthesis: A chemical reaction in which two molecules are joined by removing a water molecule. Used to build polymers from monomers.

• Hydrolysis: A reaction in which a polymer is broken down into monomers by adding a water molecule.

• Example: Formation of a peptide bond between amino acids via dehydration synthesis; breakdown of starch into glucose via hydrolysis.

Lipids

Types and Functions

Lipids are hydrophobic molecules with diverse functions in cells.

• Triglycerides: Energy storage; composed of glycerol and three fatty acids.

• Phospholipids: Structural component of cell membranes; composed of glycerol, two fatty acids, and a phosphate group.

• Steroids: Hormones and signaling molecules; characterized by four fused carbon rings (e.g., cholesterol).

• Waxes: Protective coatings; composed of long-chain fatty acids and alcohols.

Proteins

Structural Levels

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 or beta sheets, stabilized by hydrogen bonds.

• Tertiary Structure: Overall three-dimensional shape of a single polypeptide, determined by interactions among side chains.

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

• Example: Hemoglobin has quaternary structure with four polypeptide subunits.

Classes of Proteins

Proteins are classified based on their shape and function.

• Fibrous Proteins: Structural roles; elongated shape (e.g., collagen, keratin).

• Globular Proteins: Functional roles; compact, spherical shape (e.g., enzymes, antibodies).

• Example: Collagen (fibrous), hemoglobin (globular).

Nucleic Acids: DNA and RNA

Structural Differences

DNA and RNA are nucleic acids with distinct structures and functions.

• DNA: Double-stranded helix; contains deoxyribose sugar; bases are adenine, thymine, cytosine, guanine.

• RNA: Single-stranded; contains ribose sugar; bases are adenine, uracil, cytosine, guanine.

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

Types of RNA and Their Functions

• Messenger RNA (mRNA): Carries genetic information from DNA to ribosomes for protein synthesis.

• Ribosomal RNA (rRNA): Structural and catalytic component of ribosomes.

• Transfer RNA (tRNA): Brings amino acids to ribosomes during translation.

ATP: Adenosine Triphosphate

Function and Role

ATP is the primary energy carrier in cells.

• Function: Stores and transfers energy for cellular processes.

• Structure: Composed of adenine, ribose, and three phosphate groups.

• Example: ATP hydrolysis releases energy for muscle contraction.

Enzymes in ATP Reactions

• Exergonic Reaction: ATP hydrolysis (energy-releasing); catalyzed by ATPase.

• Endergonic Reaction: ATP synthesis (energy-consuming); catalyzed by ATP synthase.

Summary Table: Macromolecules, Monomers, and Functions

Macromolecule	Monomer	Polymer	Main Function
Carbohydrates	Monosaccharide	Polysaccharide	Energy storage, structural support
Proteins	Amino acid	Polypeptide	Enzymes, structure, transport
Lipids	Fatty acids & glycerol	Triglyceride, phospholipid	Energy storage, membranes, signaling
Nucleic Acids	Nucleotide	DNA, RNA	Genetic information, protein synthesis

Key Equations

• Dehydration Synthesis:

• $\text{Monomer}_1 + \text{Monomer}_2 \rightarrow \text{Polymer} + \text{H}_2\text{O}$

• Hydrolysis:

• $\text{Polymer} + \text{H}_2\text{O} \rightarrow \text{Monomer}_1 + \text{Monomer}_2$

• ATP Hydrolysis:

• $\text{ATP} + \text{H}_2\text{O} \rightarrow \text{ADP} + \text{P}_i + \text{Energy}$

Additional info: Lipids are not true polymers, but are grouped with macromolecules due to their biological importance. The summary table provides a concise comparison for exam review.