Definitions [13]
Define carbohydrates.
Carbohydrates are optically active polyhydroxy aldehydes or polyhydroxy ketones or compounds that can be hydrolysed to polyhydroxy aldehydes or polyhydroxy ketones.
The sugars that reduce the Tollen's reagent and Fehling's solution are called reducing sugars.
Carbohydrates may be defined as optically active polyhydroxy aldehydes or ketones or compounds which produce such units on hydrolysis, such as cellulose, glycogen, starch, etc.
Carbohydrates that are crystalline solids, sweet in taste and soluble in water are called sugars.
Carbohydrates that are amorphous solids, tasteless and insoluble in water are catled non-sugars.
Define enzymes.
Enzymes are biological catalysts that speed up chemical reactions in living cells without being consumed in the process.
Proteins are complex polyamides formed from amino acids. They are essential for the proper growth and maintenance of the body. They have many peptide (-CO–NH )bonds.
Chemically, proteins are polyamides, which are high molecular weight polymers of the monomer units called \[\alpha\]-amino acids.
Bifunctional organic compounds containing a carboxylic and an amino group either at the same carbon atom or at nearby carbon atoms are called amino acids.
Define α-amino acids.
α-Amino acids are carboxylic acids having an amino (–NH2) group bonded to the α-carbon, that is, the carbon next to the carboxyl (–COOH) group.
Define peptide bond.
The bond that connects α-amino acids to each other is called a peptide bond.
Define the term Protein.
Chemically proteins are polyamides which are high molecular weight polymers of the monomer units, i.e., α-amino acids. OR It can also be defined as proteins are the biopolymers of a large number of α-amino acids and they are naturally occurring polymeric nitrogenous organic compounds containing 16% nitrogen and peptide linkages (-CO-NH-)
A colloidal solution of protein which works as a biological catalyst is known as an enzyme.
Key Points
- Primary Metabolites - Compounds required for basic life processes like photosynthesis, respiration, and protein metabolism. Examples: amino acids, sugars. Found in all animal tissues.
- Secondary Metabolites - Compounds produced mainly by plants, fungi, and microbes with no direct role in growth and development. Examples: alkaloids, rubber, essential oils, antibiotics, pigments, gums, spices.
- Examples by Category - Pigments: Carotenoids, Anthocyanins; Alkaloids: Morphine, Codeine; Terpenoids: Monoterpenes, Diterpenes; Toxins: Abrin, Ricin; Lectins: Concanavalin A; Drugs: Vinblastin, Curcumin; Polymeric substances: Rubber, Gums, Cellulose.
- Importance - Many secondary metabolites are useful to human welfare (e.g., rubber, drugs, spices, pigments), and some have ecological importance.
- Unknown Roles - The role of many secondary metabolites in host organisms is not fully understood.
- Carbohydrates are organic biomolecules made of C, H and O, usually fitting the general formula Cx(H₂O)y and existing as aldoses or ketoses.
- They are classified into monosaccharides, disaccharides and polysaccharides; monosaccharides cannot be hydrolysed further, disaccharides are formed by two monosaccharides via glycosidic bonds, and polysaccharides are long polymers.
- Some sugars like digitoxose (C₆H₁₂O₄) and rhamnose (C₆H₁₂O₅) do not obey the typical Cx(H₂O)y formula.
- All monosaccharides are reducing sugars because they possess a free aldehyde or ketone group.
- Cellulose is a linear polymer of β‑D‑glucose, unlike starch and glycogen, which are polymers of α‑glucose and show branching.
- Biologically, carbohydrates supply energy for metabolism; glucose is the main substrate for ATP synthesis, and lactose provides energy to infants.
- Polysaccharides such as starch and glycogen act as storage products and also contribute to structural components of cell membranes and cell walls.
- Lipids are esters of fatty acids with a hydrogen-to-oxygen ratio greater than 2:1.
- They are classified into simple lipids (fats and waxes), compound lipids (phospholipids, glycolipids, lipoproteins) and sterols (derived lipids).
- Simple lipids are esters of fatty acids with various alcohols, while compound lipids typically contain 1 glycerol, 2 fatty acids and either 1 phosphate group (phospholipid) or 1 simple sugar (glycolipid).
- Glycolipids, also called cerebrosides, are abundant in the myelin sheath of nerve cells.
- In plants, sterols occur as phytosterols; the yam plant (Dioscorea) yields the sterol diosgenin, used to manufacture birth‑control pills.
- Proteins are polymers of amino acids (polypeptides) in which amino acids are linked by peptide bonds.
- There are 20 types of amino acids, so proteins are heteropolymers (not homopolymers).
- Amino acids are of two types: essential (must be obtained from diet) and non-essential (can be synthesised in the body).
- Proteins are high molecular weight biomolecules (polyamides) made of α-amino acids with a general structure R-CH(NH₂)-COOH.
- Proteins perform various functions such as enzymatic activity, transport, hormonal regulation, immunity, and sensory reception.
- Proteins are of two main types: fibrous proteins (insoluble, structural, e.g., keratin) and globular proteins (soluble, functional, e.g., enzymes, insulin).
- Collagen is the most abundant protein in animals, while RuBisCO is the most abundant enzyme in the biosphere.
- Enzymes are biological catalysts, mostly proteins, that increase the rate of biochemical reactions without being consumed.
- Some enzymes are ribozymes, which are RNA molecules that act like enzymes.
- Enzymes have primary, secondary, and tertiary structures, and their 3D structure determines their specificity and function.
- Each enzyme has a specific active site where the substrate binds to form an enzyme–substrate complex.
- Enzymes are highly specific and lower the activation energy of reactions.
- Enzyme activity is affected by temperature and pH; most enzymes are denatured at high temperatures, while thermophilic enzymes remain stable at 80–90°C.
- Examples of enzymes include amylase (starch → glucose), pepsin (proteins → amino acids), lactase (lactose → glucose + galactose), and maltase (maltose → glucose).
Mechanism of Enzyme Action (Lock and Key model):
- Enzyme (E) binds to substrate (S) → ES complex (E + S → ES)
- Product formation: ES → EP
- Product released: EP → E + P (enzyme regenerated)
- Enzymes work best at 298 K to 313 K (25°C to 40°C) — optimum temperature
- Activity decreases with temperature increase or decrease beyond optimum range; stops at ~273 K
