Basic Chemistry of Biomolecules

Basic Chemistry of Biomolecules

• Biomolecules are numerous substances produced by cells and living organisms.
• They have diverse sizes and structures, serving various functions.
• Small biomolecules include sugars, fatty acids, amino acids, and nucleotides.
• Major types of biomolecules (macromolecules) are carbohydrates, lipids, nucleic acids, proteins, vitamins, hormones, and enzymes.

Carbohydrates

• Carbohydrates are naturally occurring compounds, or derivatives, with the general chemical formula Cn(H₂O)n.
• They are composed of carbon (C), hydrogen (H), and oxygen (O).
• Carbohydrates are the most widespread organic substances.
• Chemically, they are polyhydroxy aldehydes or ketones, their simple derivatives, or their polymers.
• Also defined as optically active polyhydroxy aldehydes or ketones, or compounds producing such units upon hydrolysis.
• Common sources are potatoes, maize, milk, popcorn, and bread.
• Classified by chemical structure or digestibility.
• Divided into monosaccharides, disaccharides, oligosaccharides, and polysaccharides.
• Monosaccharides have the formula C₆H₁₂O₆.
• Disaccharides are two simple sugars.
• Oligosaccharides have 3-6 monosaccharide units.
• Polysaccharides have more than 6 monosaccharide units.

Classification Based on Functional Groups

• Classified as aldoses (aldehyde group) or ketoses (ketone group).
• Classified based on the number of carbon atoms: trioses (3C), tetroses (4C), pentoses (5C), hexoses (6C), and heptoses (7C).
• Examples of hexoses include glucose, fructose, and galactose.
• Examples of pentoses include ribose.

Monosaccharides

• These cannot be hydrolyzed further.
• Glucose is also known as aldohexose and dextrose.

Reducing Sugars

• These have a free aldehyde or ketone functional group.
• Examples include D-glucose, D-mannose, and D-fructose.

Disaccharides

• Composed of two sugar units joined by O-glycosidic bonds.
• Sucrose (table sugar) is composed of glucose and fructose.
• Other examples include lactose and maltose.

Polysaccharides

• Consist of three or more monosaccharide units.
• Examples include cellulose, starch, and glycogen.
• Glycogen is an energy storage form in animals.
• Starch is an energy storage form in plants.

Types of Polysaccharides

• Homopolysaccharides: consist of a single type of sugar unit. Examples include chitin and cellulose
• Heteropolysaccharides: consist of two or more different types of sugar units. Examples include heparin (anticoagulant), hyaluronic acid (shock absorber), and peptidoglycans/mureins (in bacterial cell walls).

Chemical Reactions of Carbohydrates

• Alkylation: reacting with alkylating agents (diazomethane, alkyl iodides, benzyl halides) to form ethers.
• Acylation: reacting with acylating substances (acid halides, anhydrides) to form esters.
• Reduction: reducing the C=O group to an alcohol using sodium borohydride.
• Oxidation: oxidizing the C=O group to form carboxylic acids, creating reducing sugars.
• Hydrolysis: breaking the glycosidic bond to produce a and ẞ isomers.

Primary, Secondary, and Tertiary Alcohols

Glycoside Formation

• Formed when the anomier hydroxyl group undergoes condensation with another carbohydrate molecule and removes a water molecule.

Optical Activity of Carbohydrates

• Ability to rotate polarized light.
• Carbohydrates are usually optically active due to chiral carbon atoms.
• Molecules rotating light to the right are dextrorotatory (+).
• Molecules rotating light to the left are levorotatory (-).

Biological and Pharmaceutical Importance of Carbohydrates

• Instant energy source (4 calories/gram).
• Maintaining normal blood glucose levels is crucial.
• Deficiency of carbs = hypoglycemia.
• Excessive intake = diabetes.
• Used in various food preparations (syrups, tablets).
• Used as diluents and binders in manufactured tablets.
• Used as laxatives (e.g., mucilage, lactulose).