Biological Molecules: Carbohydrates, Lipids, Proteins, and Minerals

Biological Molecules

Carbohydrates

Carbohydrates are essential organic molecules that serve as the primary energy source for living cells. They are found in a variety of foods and exist in several forms, each with distinct biological roles.

• Definition: Carbohydrates are organic compounds composed of carbon, hydrogen, and oxygen, typically with the general formula $C_n(H_2O)_n$.

• Types of Carbohydrates:

  • Monosaccharides: Simple sugars such as glucose (found in fruits and vegetables), fructose (fruit sugar), and lactose (milk sugar).

  • Disaccharides: Composed of two monosaccharide units; for example, sucrose (table sugar).

  • Polysaccharides: Large, complex carbohydrates such as starch (storage carbohydrate in plants), glycogen (storage carbohydrate in animals), and cellulose (structural component in plant cell walls).

• Role in the Body: Carbohydrates are the main 'fuel' for supplying cells with energy, primarily through the oxidation of glucose.

• Digestion and Absorption: Most dietary carbohydrates are obtained from starch, which is broken down into glucose during digestion.

• Cellulose: Although humans cannot digest cellulose due to the absence of specific enzymes, it is important as dietary fiber, aiding in digestive health.

• Example: Starch is abundant in foods like potatoes, rice, wheat, and millet.

Lipids (Fats and Oils)

Lipids are a diverse group of hydrophobic molecules that play critical roles in energy storage, cell structure, and signaling. They are composed of glycerol and fatty acids.

• Definition: Lipids are organic compounds that are insoluble in water but soluble in organic solvents. The most common lipids in the diet are fats and oils.

• Chemical Structure: A typical lipid molecule consists of one glycerol molecule joined to three fatty acid molecules. Equation for triglyceride formation: $\text{Glycerol} + 3\ \text{Fatty Acids} \rightarrow \text{Triglyceride} + 3\ \text{Water}$

• Types of Fatty Acids: The variety of fatty acids leads to different types of lipids.

• Dietary Importance: Lipids are essential for health, but excessive intake, especially of saturated fats and cholesterol, can be harmful.

• Example: Glycerol (also known as glycerine) is used in cosmetics; saturated fats are commonly found in animal products.

Proteins

Proteins are complex polymers made from amino acids. They are vital for growth, repair, and regulation of body processes, but only a moderate amount is needed in the diet.

• Definition: Proteins are large, complex molecules composed of long chains of amino acids.

• Structure: Proteins are polymers of up to 20 different amino acids, each arranged in a specific sequence and folded into a unique shape. Equation for peptide bond formation: $\text{Amino Acid}_1 + \text{Amino Acid}_2 \rightarrow \text{Dipeptide} + \text{Water}$

• Dietary Requirement: Recommended daily intake is about 70g; excess protein is common in developed countries, while deficiency (kwashiorkor) is prevalent in some poorer regions.

• Example: Insulin is a protein hormone composed of a specific sequence of amino acids.

Minerals

Minerals are inorganic nutrients required in small amounts for various physiological functions, including bone formation, nerve function, and oxygen transport.

• Definition: Minerals are chemical elements or ions essential for health, present in foods and the body.

• Role in the Body: Examples include calcium for bones and teeth, iron for oxygen transport, and phosphorus for DNA and ATP.

• Sources: Minerals are found in a wide range of foods, including dairy, meat, vegetables, and grains.

Table: Examples of Essential Minerals

Mineral	Approximate Mass in Body (g)	Location or Role	Examples of Foods
Calcium	1000	Making teeth and bones	Dairy products, green vegetables
Phosphorus	650	Part of many chemicals, e.g. DNA and ATP	Most foods
Chlorine	100	In body fluids, e.g. blood	Common salt, most foods
Iron	4	Part of haemoglobin in red blood cells, helps carry oxygen	Red meat, liver, eggs, spinach

Additional info: The table above is reconstructed from partial data and standard biology knowledge to provide a clear summary of essential minerals and their dietary sources.