Basic Chemical Building Blocks & Inorganic Ions

Understanding biological compounds starts with grasping a few key definitions. An atom is the basic unit of a chemical element, whilst an element contains only one type of atom. When atoms join together, they form molecules, and when different elements react, they create compounds.

The distinction between organic and inorganic molecules is crucial for biology. Organic molecules contain carbon and are typically of biological origin, whilst inorganic molecules don't contain carbon and aren't made by living things.

Several inorganic ions play vital roles in your body's metabolism. Magnesium (Mg²⁺) is essential for chlorophyll in photosynthesis, iron (Fe²⁺) forms part of haemoglobin for oxygen transport, phosphate (PO₄³⁻) helps make ATP and nucleotides, and calcium (Ca²⁺) strengthens bones, teeth, and cell walls.

Key Tip: Remember that whilst these ions are inorganic, they're absolutely essential for biological processes - your body can't function without them!

Properties of Water

Water isn't just H₂O - it's a polar molecule with incredible properties that make life possible. The hydrogen end is slightly positive whilst the oxygen end is slightly negative, giving water its unique characteristics.

Cohesion occurs because water molecules stick together through hydrogen bonds, creating a lattice structure. This allows water to be pulled up through plants in continuous columns. Surface tension makes water's surface difficult to break, creating habitats for pond skaters and other organisms.

Water's role as a solvent means it can dissolve charged particles, making it perfect for transporting substances around your body. Its high specific heat prevents rapid temperature changes, keeping cells and aquatic environments stable even when external temperatures fluctuate.

The latent heat of vaporisation requires lots of energy to turn water into vapour, which is why sweating cools you down so effectively. Water's density properties mean ice floats, creating an insulating layer over water bodies in winter.

Remember: Water's transparency allows aquatic plants to photosynthesise underwater - without this, aquatic ecosystems couldn't exist!

Monosaccharides & Disaccharides

Carbohydrates contain carbon, hydrogen, and oxygen, with monosaccharides being the simplest forms. Glucose is the most important monosaccharide, existing as two isomers: α-glucose and β-glucose. The only difference is that the hydroxyl group and hydrogen are swapped on one carbon atom.

Monosaccharides have the general formula (CH₂O)n and include glucose, ribose, and glyceraldehyde. They're brilliant energy sources because breaking their carbon-hydrogen and carbon-carbon bonds releases energy to make ATP. They also serve as building blocks for larger molecules and intermediates in reactions.

Disaccharides form when two monosaccharides join through a condensation reaction, creating a glycosidic bond and eliminating water. Common examples include maltose, sucrose, and lactose. The reverse process, hydrolysis, breaks disaccharides back into monosaccharides by adding water.

Testing for sugars is straightforward: use Benedict's test for reducing sugars $blue to brick-red colour change$ or the non-reducing sugar test involving hydrochloric acid treatment first.

Exam Tip: Always remember that condensation removes water whilst hydrolysis adds water - this concept appears throughout biology!

Polysaccharides

Polysaccharides are massive polymers formed by linking thousands of monosaccharide monomers. The four main types you need to know are starch, glycogen, cellulose, and chitin, each with distinct structures and functions.

Starch comes in two forms: amylose (helical structure with 1,4 glycosidic bonds) and amylopectin (branched with 1,6 glycosidic bonds). Both use α-glucose monomers and serve as energy storage in plant cells like potatoes. Test for starch using iodine solution - it turns blue-black if present.

Glycogen is similar to amylopectin but more highly branched with shorter branches. Found in animal cells (muscles and liver), it's your body's main carbohydrate energy store. Cellulose uses β-glucose monomers in straight, unbranched chains held together by hydrogen bonds, forming microfibrils that strengthen plant cell walls.

Chitin contains β-glucose plus amino acids, creating strong structural material for insect exoskeletons. Like cellulose, it forms straight chains with hydrogen bonding between strands.

Structure-Function Link: Notice how storage molecules (starch, glycogen) are branched for quick access to glucose, whilst structural ones (cellulose, chitin) are straight and strong!

Sugar Functions & Lipids Introduction

Different sugars have specific roles in living organisms. Lactose is the main sugar in milk, fructose dominates in fruits, sucrose transports carbohydrates around plants, and glucose serves as the primary respiratory substrate and energy source for animals.

Lipids contain carbon, hydrogen, and oxygen, but with much less oxygen compared to carbon and hydrogen than carbohydrates. They're non-polar compounds, making them insoluble in water but soluble in organic solvents like alcohol.

Triglycerides form when one glycerol molecule combines with three fatty acid molecules through condensation reactions. This creates three ester bonds and removes three water molecules. Triglycerides are excellent energy storage molecules because they contain more carbon-hydrogen bonds than carbohydrates.

Phospholipids replace one fatty acid with a phosphate group, creating molecules with both hydrophilic $water-loving$ and hydrophobic $water-repelling$ ends. This unique property makes them perfect for forming biological membranes.

Energy Fact: Lipids store more than twice as much energy per gram as carbohydrates - that's why your body uses fat for long-term energy storage!

Phospholipid Structure & Fat Types

The phospholipid structure is crucial for cell membranes. The phosphate head (containing phosphate, glycerol, and choline) is hydrophilic because it has lots of oxygen atoms that interact with water. The fatty acid tails are hydrophobic because they lack oxygen atoms and don't interact with water.

Saturated fats contain only single carbon-carbon bonds, creating straight, regular chains that align easily. This makes them solid at room temperature and they're typically found in animal products. Unfortunately, diets high in saturated fats contribute to coronary heart disease.

Unsaturated fats have double carbon bonds that create kinks in the chain, preventing alignment and keeping them liquid (oils). These are usually plant-based and actually contribute to HDL $high-density lipoprotein$ - the "good cholesterol" that reduces artery deposits.

When fatty deposits form in coronary artery walls, they create atheroma, leading to atherosclerosis (artery narrowing). This process significantly increases heart disease risk, which is why understanding fat types matters for your health.

Health Connection: Your diet's fat composition directly affects your cardiovascular health - choose unsaturated fats when possible!

Lipid Functions & Protein Basics

Phospholipids are essential for biological membranes and provide electrical insulation around nerve cells. Triglycerides serve multiple functions: energy reserves (more efficient than carbohydrates), thermal insulation, protection around delicate organs, and metabolic water production during chemical reactions.

Test for lipids using the emulsion test: mix your sample with ethanol, shake thoroughly, then add water and shake gently. A cloudy white emulsion indicates lipids are present.

Proteins contain carbon, hydrogen, oxygen, and nitrogen. They're polymers made from amino acid monomers, forming chains called polypeptides. Every amino acid has the same basic structure: a central carbon atom bonded to an amino group $-NH₂$, a carboxylic group $-COOH$, a hydrogen atom, and a variable R group.

Amino acids join through condensation reactions, forming peptide bonds between the amino group of one amino acid and the carboxyl group of another. With 20 different amino acids available, the possible protein combinations are virtually endless.

Amazing Fact: Your body contains thousands of different proteins, all made from just 20 amino acids arranged in different sequences!

Protein Structure Levels

Proteins have four levels of increasingly complex structure. Primary structure refers to the specific sequence, type, and number of amino acids linked by peptide bonds. This sequence is determined by DNA and is absolutely crucial - change one amino acid and you can completely alter the protein's function.

Secondary structure forms when the polypeptide chain twists due to hydrogen bonding. The two main shapes are α-helixes (spiral structures) and β-pleated sheets (folded arrangements). These shapes give proteins their initial 3D form.

Tertiary structure occurs when the secondary structure folds and twists further, creating complex, compact 3D shapes. This folding is maintained by hydrogen bonds, ionic bonds, disulphide bonds, and hydrophobic interactions. The tertiary structure determines the protein's specific function.

Quaternary structure involves two or more polypeptide chains combining to form protein complexes. Haemoglobin is a perfect example, consisting of four polypeptide chains working together to transport oxygen.

Structure = Function: Each level of protein structure is essential - damage any level and the protein may stop working entirely!

Fibrous vs Globular Proteins

Fibrous proteins have long, thin molecules arranged in parallel chains or sheets with many cross-linkages forming strong fibres. Their shape makes them insoluble in water, perfect for structural functions. They're incredibly strong and tough, providing support where it's needed most.

Keratin (found in hair and nails) and collagen (providing strength in tendons and skin) are classic examples of fibrous proteins. These proteins literally hold your body together and give it structural integrity.

Globular proteins are compact and folded into spherical shapes, making them soluble in water. This solubility allows them to have diverse functions including enzymes, antibodies, plasma proteins, and hormones. They're the workhorses of your body's biochemical processes.

Haemoglobin exemplifies globular proteins perfectly - its spherical shape allows it to dissolve in blood plasma and transport oxygen efficiently around your body.

Function Follows Form: Fibrous proteins are built for strength and structure, whilst globular proteins are designed for chemical reactions and transport!

Protein Testing

Testing for proteins is straightforward using the biuret test. Simply add biuret solution to your food sample and mix thoroughly. If proteins are present, the solution changes from blue to purple - it's that simple!

This colour change occurs because the biuret reagent reacts specifically with peptide bonds, which are found in all proteins. The intensity of the purple colour can even give you an idea of protein concentration.

Understanding these biological compounds gives you the foundation for advanced biology topics. Whether it's enzyme function, membrane structure, or energy metabolism, these molecules are the building blocks that make life possible.

Exam Success: Master these basic tests and structures now - they're the foundation for understanding more complex biological processes later!