Study Notes: The Chemical Building Blocks of Life

Chapter 3 – The Chemical Building Blocks of Life

Macromolecules: Polymers and Monomers

Biological macromolecules are large, complex molecules essential for life. They are typically polymers, made by joining smaller units called monomers through chemical reactions.

• Polymer: A large molecule composed of repeating subunits (monomers) joined by covalent bonds.

• Monomer: A small molecule that can join with other monomers to form a polymer.

• Examples: Proteins (polymers of amino acids), nucleic acids (polymers of nucleotides), polysaccharides (polymers of monosaccharides).

• Polymerization: The process of linking monomers to form polymers, often via dehydration synthesis (removal of water).

• Hydrolysis: The breakdown of polymers into monomers by adding water.

Carbohydrates

Carbohydrates are organic molecules composed of carbon, hydrogen, and oxygen. They serve as energy sources and structural components.

• Monosaccharide: The simplest carbohydrate (e.g., glucose, fructose).

• Disaccharide: Two monosaccharides joined together (e.g., sucrose, lactose, maltose).

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

• Starch: Storage polysaccharide in plants.

• Glycogen: Storage polysaccharide in animals.

• Cellulose: Structural polysaccharide in plant cell walls.

• Functions: Energy storage, structural support.

• Comparison Table:

Type	Monomer	Function
Starch	Glucose	Energy storage in plants
Glycogen	Glucose	Energy storage in animals
Cellulose	Glucose	Structural support in plants

Proteins

Proteins are polymers of amino acids and perform a wide variety of functions in cells.

• Amino Acid: The monomer unit of proteins, containing an amino group, carboxyl group, and a unique side chain (R group).

• Peptide Bond: The covalent bond linking amino acids in a protein.

• Levels of Protein Structure:

  • Primary: Sequence of amino acids.

  • Secondary: Local folding (α-helix, β-sheet).

  • Tertiary: Overall 3D shape of a single polypeptide.

  • Quaternary: Arrangement of multiple polypeptide chains.

• Denaturation: Loss of protein structure due to environmental changes (e.g., heat, pH).

• Functions: Enzymes, structural support, transport, signaling.

• Special Amino Acids: Proline, methionine, cysteine have unique roles in protein structure and function.

Nucleic Acids

Nucleic acids store and transmit genetic information. The two main types are DNA and RNA.

• Nucleotide: The monomer of nucleic acids, composed of a phosphate group, a five-carbon sugar, and a nitrogenous base.

• DNA (Deoxyribonucleic Acid): Stores genetic information; double-stranded helix.

• RNA (Ribonucleic Acid): Involved in protein synthesis; usually single-stranded.

• Differences between DNA and RNA:

  • DNA contains deoxyribose; RNA contains ribose.

  • DNA uses thymine; RNA uses uracil.

  • DNA is double-stranded; RNA is single-stranded.

• ATP (Adenosine Triphosphate): The main energy currency of the cell.

Feature	DNA	RNA
Sugar	Deoxyribose	Ribose
Bases	A, T, C, G	A, U, C, G
Strands	Double	Single

Lipids

Lipids are hydrophobic molecules important for energy storage, membrane structure, and signaling.

• Fatty Acid: Long hydrocarbon chain with a carboxyl group.

• Triglyceride: Composed of three fatty acids linked to glycerol; main form of stored fat.

• Phospholipid: Major component of cell membranes; contains two fatty acids, a phosphate group, and glycerol.

• Saturated vs. Unsaturated Fats:

  • Saturated: No double bonds; solid at room temperature.

  • Unsaturated: One or more double bonds; liquid at room temperature.

• Cholesterol: Steroid molecule important for membrane fluidity and as a precursor for hormones.

• Micelle vs. Lipid Bilayer: Micelles are spherical lipid structures; lipid bilayers form the basis of cell membranes.

Type	Structure	Function
Triglyceride	Glycerol + 3 fatty acids	Energy storage
Phospholipid	Glycerol + 2 fatty acids + phosphate	Membrane structure
Cholesterol	Four fused rings	Membrane fluidity, hormone precursor

Key Equations

• Dehydration Synthesis: Formation of polymers by removing water. $\text{Monomer}_1 + \text{Monomer}_2 \rightarrow \text{Polymer} + H_2O$

• Hydrolysis: Breakdown of polymers by adding water. $\text{Polymer} + H_2O \rightarrow \text{Monomer}_1 + \text{Monomer}_2$

• ATP Hydrolysis: Release of energy from ATP. $\text{ATP} + H_2O \rightarrow \text{ADP} + \text{P}_i + \text{Energy}$

Additional info:

• Protein folding is crucial for function; misfolded proteins can cause diseases.

• Phospholipids form bilayers due to their amphipathic nature (hydrophilic head, hydrophobic tails).

• Enzymes are proteins that catalyze biochemical reactions.