Organic Molecules and Macromolecules

Definitions and Key Concepts

Organic molecules are the foundation of biological systems, consisting primarily of carbon atoms bonded with hydrogen, oxygen, nitrogen, and other elements. Macromolecules are large, complex molecules essential for life, including carbohydrates, lipids, proteins, and nucleic acids.

• Organic Molecules: Compounds containing carbon atoms bonded to hydrogen and other elements; examples include glucose and amino acids.

• Macromolecules: Large molecules formed by polymerization of smaller subunits (monomers); examples are proteins and DNA.

• Covalent Bonds: Strong chemical bonds formed by the sharing of electron pairs between atoms.

• Isomers: Molecules with the same molecular formula but different structural arrangements.

• Polymers: Large molecules made by joining many monomers; e.g., starch is a polymer of glucose.

• Carbohydrates: Organic compounds composed of carbon, hydrogen, and oxygen; serve as energy sources and structural materials.

• Lipids: Hydrophobic molecules including fats, oils, and steroids; important for energy storage and membrane structure.

• Fatty Acids: Long hydrocarbon chains with a carboxyl group; building blocks of lipids.

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

Characteristics of Carbon

Carbon is unique in its ability to form four covalent bonds, allowing for diverse molecular structures essential for life.

• Tetravalency: Carbon can form four bonds, enabling complex molecules.

• Versatility: Forms chains, rings, and branched structures.

• Isomerism: Carbon compounds can exist as structural, geometric, or optical isomers.

Isomers

Isomers are molecules with identical molecular formulas but different structures, affecting their chemical properties.

• Structural Isomers: Differ in the connectivity of atoms.

• Geometric Isomers: Differ in spatial arrangement around double bonds.

• Optical Isomers: Mirror images (enantiomers) that cannot be superimposed.

Functional Groups

Functional groups are specific groups of atoms within molecules that confer particular chemical properties.

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

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

• Amino (-NH2): Found in amino acids.

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

• Methyl (-CH3): Found in many organic molecules.

ATP and Its Importance

ATP (adenosine triphosphate) is the primary energy carrier in cells, enabling biological processes.

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

• Function: Provides energy for cellular activities by hydrolyzing to ADP and inorganic phosphate.

Carbohydrates

Types and Functions

Carbohydrates are classified based on the number of sugar units.

• Monosaccharides: Single sugar units (e.g., glucose, fructose).

• Disaccharides: Two monosaccharides joined (e.g., sucrose, lactose).

• Polysaccharides: Long chains of monosaccharides (e.g., starch, glycogen, cellulose).

Dehydration and Hydrolysis Reactions

These reactions are essential for building and breaking down macromolecules.

• Dehydration Reaction: Joins two monomers by removing a water molecule.

• Hydrolysis Reaction: Breaks a polymer into monomers by adding water.

Examples and Functions

• Starch: Energy storage in plants.

• Glycogen: Energy storage in animals.

• Cellulose: Structural component in plant cell walls.

Lipids

Types and Properties

Lipids are hydrophobic molecules with diverse functions.

• Fats (Triglycerides): Composed of glycerol and three fatty acids; used for energy storage.

• Phospholipids: Major component of cell membranes; amphipathic (hydrophilic head, hydrophobic tails).

• Steroids: Four fused rings; includes cholesterol and hormones.

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 Biological Importance

• Amphipathic Nature: Phospholipids have both hydrophilic and hydrophobic regions, crucial for membrane structure.

• Biological Membranes: Phospholipids form bilayers that make up cell membranes.

Proteins

Structure and Function

Proteins are polymers of amino acids, performing a wide range of functions in cells.

• Amino Acids: Building blocks of proteins; 20 different types.

• Peptide Bonds: Covalent bonds joining amino acids.

• Levels of Structure:

  • Primary: Sequence of amino acids.

  • Secondary: Alpha helices and beta sheets formed by hydrogen bonding.

  • Tertiary: 3D folding due to interactions among side chains.

  • Quaternary: Association of multiple polypeptide chains.

Protein Functions

• Enzymes: Catalyze biochemical reactions.

• Structural Proteins: Provide support (e.g., collagen).

• Transport Proteins: Move substances across membranes.

• Signaling Proteins: Hormones and receptors.

Nucleic Acids

DNA and RNA Structure

Nucleic acids store and transmit genetic information. DNA and RNA are polymers of nucleotides.

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

• DNA: Double helix structure; bases are adenine (A), thymine (T), cytosine (C), and guanine (G).

• RNA: Single-stranded; bases are adenine (A), uracil (U), cytosine (C), and guanine (G).

Complementary Base Pairing

• DNA: A pairs with T, C pairs with G.

• RNA: A pairs with U, C pairs with G.

Central Dogma of Molecular Biology

• Replication: DNA makes a copy of itself.

• Transcription: DNA is transcribed into RNA.

• Translation: RNA is translated into protein.

Tables

Comparison of Macromolecules

Types of Fatty Acids

Additional info:

• Questions in the file cover foundational topics in General Biology, including definitions, molecular structure, and biological functions.

• Some questions reference figures (e.g., Fig 5.13); students should consult their textbook for visual aids.