- Carbohydrates are a major class of organic biomolecules essential for life, serving as a primary source of energy and structural components in living organisms.
- Chemically, they are composed of carbon, hydrogen, and oxygen atoms, typically in the ratio Cₓ(H₂O)ₓ, earning them the name “hydrates of carbon.”
- Carbohydrates are classified into three main groups based on their molecular complexity: monosaccharides (simple sugars like glucose and fructose), oligosaccharides (short chains like sucrose and lactose), and polysaccharides (complex carbohydrates like starch, cellulose, and glycogen).
- Found in foods such as grains, fruits, vegetables, and dairy, carbohydrates are critical to human nutrition, providing energy at approximately 4 kcal per gram, and play diverse roles in biological processes across plants, animals, and microorganisms.
- Monosaccharides, the simplest carbohydrates, are single sugar units with three to seven carbon atoms, such as glucose (C₆H₁₂O₆), a key energy source for cells. These molecules are building blocks for larger carbohydrates, linked through glycosidic bonds to form disaccharides (e.g., sucrose, composed of glucose and fructose) and polysaccharides. Oligosaccharides, containing 2–10 sugar units, serve functions like cell recognition in biological systems, while polysaccharides, with hundreds or thousands of units, provide energy storage (starch in plants, glycogen in animals) or structural support (cellulose in plant cell walls). The structural diversity of carbohydrates, driven by variations in bonding and branching, enables their wide-ranging roles, from fueling cellular respiration to forming the fibrous framework of plants.
- In human nutrition, carbohydrates are a dietary staple, categorized as simple (sugars) or complex (starches and fiber) based on digestion speed. Simple carbohydrates, found in fruits, milk, and refined sugars, are quickly absorbed, providing rapid energy, while complex carbohydrates, like whole grains and legumes, offer sustained energy release and dietary fiber for digestive health. Fiber, such as cellulose, is indigestible by humans but supports gut microbiota and prevents chronic diseases. Carbohydrates are also central to metabolism, with glucose being the preferred fuel for the brain and muscles, regulated by insulin and other hormones. Excessive consumption of refined carbohydrates, however, is linked to health issues like obesity and type 2 diabetes, driving research into balanced dietary guidelines.
- Beyond nutrition, carbohydrates have significant industrial and ecological roles. Starch and cellulose, abundant in plants, are used in food production, textiles, paper, and biofuels, with starch derivatives like corn syrup and cellulose-based bioplastics addressing sustainability needs. In ecosystems, carbohydrates cycle carbon through photosynthesis, where plants convert CO₂ into glucose, and decomposition, where microbes break down polysaccharides. Carbohydrates also contribute to cell signaling and immune responses, as seen in glycoproteins on cell surfaces. Their versatility, renewability, and abundance make carbohydrates a focal point for innovations in biotechnology, such as developing sustainable materials or enhancing crop yields to meet global food demands.
