Carbohydrates and lipids

Monosaccharides: Simple sugars that serve as the building blocks of carbohydrates. Examples include glucose, fructose and galactose. They have a general formula of (CH2O) n.
Disaccharides: Formed when two monosaccharides are joined by a glycosidic bond via a condensation reaction. Examples include sucrose (glucose+fructose), lactose (glucose+galactose) and maltose (glucose+glucose).
Polysaccharides: Long chains of monosaccharides joined by glycosidic bonds.
- Starch: A storage polysaccharide in plants, consisting of two types of molecules: amylose and amylopectin. It is insoluble in water and doesn’t affect osmosis.
- Glycogen: The energy storage polysaccharide in animals, similar to starch but has more branches.
- Cellulose: A structural polysaccharide that forms the cell wall in plants. It has straight, unbranched chains that run parallel to one another, held together by hydrogen bonds to form strong fibrils.

Lipids are hydrophobic molecules, insoluble in water.
Triglycerides: Made of a glycerol molecule combined with three fatty acids through condensation reactions.
- Saturated fatty acids: If all carbon atoms in a fatty acid chain are connected by single bonds, it is said to be ‘saturated’. Sources include animal fats.
- Unsaturated fatty acids: If there is one or more double bond present in the fatty acid chain, it’s said to be ‘unsaturated’. They come in two forms: mono-unsaturated (one double bond) and poly-unsaturated (more than one double bond). Sources include plant oils.
Phospholipids: Modified triglycerides where one fatty acid is replaced with a phosphate group, making them amphipathic with a hydrophilic head and a hydrophobic tail. They form the basic structure of cell membranes.
Sterols: Four-ring structure lipids. Cholesterol, found in animal cell membranes, helps in maintaining fluidity and is used to synthesise steroid hormones.