1. Carbohydrates
Definition:
Carbohydrates are organic compounds composed of carbon, hydrogen, and oxygen, usually with a hydrogen-to-oxygen ratio of 2:1 (general formula: Cₙ(H₂O)ₙ). They are also known as saccharides or sugars.
Biological Importance:
- Energy Source: Primary source of energy (e.g., glucose).
- Energy Storage: Stored as glycogen in animals and starch in plants.
- Structural Role: Components of cell walls (cellulose in plants) and exoskeletons (chitin in arthropods).
- Cell Communication: Participate in cell recognition and signaling (glycoproteins and glycolipids).
Classification:
- Monosaccharides: Simple sugars with 3-7 carbon atoms (e.g., glucose, fructose, galactose).
- Disaccharides: Formed by the condensation of two monosaccharides (e.g., sucrose = glucose + fructose, lactose = glucose + galactose).
- Oligosaccharides: Contain 3-10 monosaccharide units; often found in glycoproteins and glycolipids.
- Polysaccharides: Long chains of monosaccharides (e.g., starch, glycogen, cellulose).
Chemistry:
- Isomerism: Monosaccharides exhibit structural isomerism (e.g., glucose and fructose have the same molecular formula but different structures).
- Reducing and Non-reducing Sugars: Reducing sugars (e.g., glucose) can donate electrons to other molecules; non-reducing sugars (e.g., sucrose) cannot.
- Glycosidic Bond: A covalent bond formed between carbohydrate molecules during condensation reactions.
2. Lipids
Definition:
Lipids are a diverse group of hydrophobic organic compounds, mainly composed of carbon, hydrogen, and a small amount of oxygen. Unlike carbohydrates, they do not have a fixed hydrogen-to-oxygen ratio.
Biological Importance:
- Energy Storage: Store more energy per gram than carbohydrates (e.g., triglycerides).
- Structural Role: Major components of cell membranes (phospholipids, cholesterol).
- Insulation and Protection: Provide thermal insulation and cushion vital organs.
- Hormones and Signaling: Steroids (e.g., testosterone, estrogen) act as hormones; some lipids serve as signaling molecules (e.g., prostaglandins).
Classification:
- Simple Lipids: Esters of fatty acids with alcohols.
- Fats and Oils: Triglycerides (glycerol + 3 fatty acids).
- Compound Lipids: Contain additional functional groups.
- Phospholipids: Glycerol, 2 fatty acids, and a phosphate group.
- Glycolipids: Lipids with a carbohydrate attached.
- Derived Lipids: Products of hydrolysis of simple and compound lipids.
- Steroids: Cholesterol, bile salts, and steroid hormones.
- Waxes: Esters of long-chain fatty acids and alcohols.
Chemistry:
- Saturated vs. Unsaturated Fatty Acids:
- Saturated: No double bonds (solid at room temperature, e.g., butter).
- Unsaturated: One or more double bonds (liquid at room temperature, e.g., olive oil).
- Hydrogenation: Process of converting unsaturated fats to saturated fats by adding hydrogen.
- Amphipathic Nature: Phospholipids have hydrophilic heads and hydrophobic tails, crucial for forming lipid bilayers in membranes.
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