# Monomers & Polymers - All living organisms share a common biochemical foundation despite the incredible diversity of life - Five essential molecule types enable organisms to build structures and carry out functions: - Carbohydrates - Proteins - Lipids - Nucleic Acids - Water

Monomers are small molecular units that join together to form larger molecules

Polymers are large molecules formed when many monomers bond together in chains through polymerisation

## Building Blocks of Life - Carbon compounds can form individual subunits (monomers) that link together with many repeating units to create large molecules (polymers) - This assembly process is called polymerisation

Macromolecules are extremely large molecules containing 1000+ atoms with high molecular mass

- Polymers can be macromolecules, but not all macromolecules qualify as polymers - For true polymer classification, the subunits must be identical repeating units - Think of it like LEGO: you need the same brick design repeated to build a proper structure, not a random assortment of different pieces ## Covalent Bonding - A covalent bond involves the sharing of two or more electrons between atoms - Electron sharing can occur equally (forming nonpolar covalent bonds) or unequally (forming polar covalent bonds where one atom is more electronegative, shown as $\delta^-$) - Each atom typically forms a specific number of covalent bonds based on available electrons in the outer orbital - Hydrogen = 1 bond - Carbon = 4 bonds - Covalent bonds are highly stable because breaking them requires substantial energy input - Multiple electron pairs can be shared: - Double bonds (e.g. $C=C$ in unsaturated fats) - Triple bonds ### Bond Formation in Biological Molecules - When monomers approach closely enough that outer orbitals overlap, electrons become shared and a covalent bond forms - Adding more monomers initiates polymerisation (and/or macromolecule formation) - Imagine two magnets coming together - when they get close enough, they snap into place; similarly, when atoms get close enough, their electrons "snap" into shared arrangements ## Condensation Reactions

Condensation (dehydration synthesis) occurs when monomers join via covalent bonds to form polymers/macromolecules with water as a byproduct

### The Process - Monomers combine through covalent bonds to create: - Polymers (through polymerisation) - Macromolecules (like lipids) - Water ($H_2O$) is removed during this reaction - Think of wringing out a wet towel - you're removing water as you squeeze the material together ### Written Representation ```text MONOMER + MONOMER + MONOMER → POLYMER + multiple H₂O molecules removed ``` ### What Happens at the Molecular Level - One $H_2O$ molecule is eliminated for each covalent bond formed - The hydrogen atoms and oxygen atoms that would form water are instead removed, allowing the monomers to link directly ## Hydrolysis Reactions

Hydrolysis ('lyse' = break, 'hydro' = water) breaks covalent bonds in polymers by adding water

### The Process - Water is added to break down polymers into monomers - Covalent bonds are split when water molecules are incorporated - This is the reverse of condensation - Like using water to dissolve glue that's holding things together ### Written Representation ```text POLYMER + multiple H₂O molecules → MONOMER + MONOMER + MONOMER ``` ### What Happens at the Molecular Level - Water molecules are inserted back into the structure - This reverses the condensation process - Three water molecules are required to break down a triglyceride into glycerol and three fatty acids ## Covalent Bonds in Organic Molecules | Organic Molecule | Covalent Bond Type | Description | |------------------|-------------------|-------------| | Carbohydrates | Glycosidic | Forms between monosaccharides linking them into disaccharides and polysaccharides | | Proteins | Peptide | Forms between amino acids creating dipeptides and polypeptides | | Lipids | Ester | Forms between glycerol and fatty acids creating triglycerides and phospholipids | | Nucleic Acids | Phosphodiester | Forms between nucleotides creating DNA and RNA polynucleotide chains |

Each bond type is specific to its molecule class, enabling precise formation of biological structures

## Key Biological Molecules and Their Elements ### Carbohydrates - Contain: Carbon (C), Hydrogen (H), Oxygen (O) - $H$ and $O$ atoms present in 2:1 ratio (like water $H_2O$) - General formula: $C_x(H_2O)_y$ (hence the name 'carbo-hydrate') - Three main types: - Monosaccharides (single units) - Disaccharides (two units) - Polysaccharides (many units) #### Functions - **Energy source**: glucose fuels cellular respiration - **Energy storage**: glycogen in animal muscles and liver - **Structural support**: cellulose in plant cell walls ### Lipids - Contain: Carbon (C), Hydrogen (H), Oxygen (O) - Lower proportion of oxygen compared to carbohydrates - Several types: triglycerides (fats and oils), phospholipids, waxes, steroids (e.g. cholesterol) #### Functions - **Energy source**: can be respired (high energy yield) - **Energy storage**: stored as fats in adipose tissue and oil droplets in plants - **Insulation**: thermal insulation (under skin) and electrical insulation (around nerves) - **Membrane component**: essential part of biological membranes ### Proteins - Contain: Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N), sometimes Sulphur (S) #### Functions - **Growth and repair**: required for building and fixing biological materials - **Structural roles**: muscles, collagen (skin), elastin (skin), collagen (bone), keratin (hair) - **Functional roles**: membrane carriers, antibodies, enzymes, hormones ### Nucleic Acids - Contain: Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N) in bases, Phosphorous (P) in phosphate groups #### Functions - **Genetic information**: carrying the genetic code in all living organisms - **Cellular control**: essential for controlling all cellular processes including protein synthesis

Lipids are NOT polymers - fatty acids attach to glycerol, not to each other, so they lack repeating identical subunits

## Summary of Molecular Assembly - Carbon's ability to form four stable covalent bonds makes it the backbone of biological molecules - Carbon atoms can bond with oxygen, nitrogen, and sulphur - Carbon atoms arrange themselves in: - Straight chains - Branched chains - Ring structures - This versatility enables the enormous diversity of biological molecules

When discussing monomers and polymers, always provide specific examples: DNA is a polymer made from nucleotide monomers