biomolecules

Living Systems and Biochemistry

A living system grows, sustains, and reproduces itself, astonishingly composed of non-living atoms and molecules. The branch of science that explores the chemical processes within living systems is known as biochemistry. Living organisms are constituted of various complex biomolecules such as carbohydrates, proteins, nucleic acids, and lipids. Proteins and carbohydrates are essential nutrients in our diets, while simple molecules such as vitamins and mineral salts significantly contribute to the functions of organisms. The objectives of studying these biomolecules include:

  • Explaining the characteristics of biomolecules like carbohydrates, proteins, and nucleic acids;

  • Classifying these biomolecules based on their structures;

  • Outlining the differences between DNA and RNA;

  • Describing the roles of biomolecules in biological systems.

Carbohydrates

Carbohydrates, primarily produced by plants, form a large group of naturally occurring organic compounds. Examples include cane sugar, glucose, and starch, with a general formula of Cx(H2O)y, derived from the term 'hydrates of carbon.' For instance, glucose is represented by the formula C6H12O6, fitting into this classification. However, not all compounds fitting this general formula qualify as carbohydrates. For example, acetic acid (CH3COOH) matches the formula but is not classified as a carbohydrate.

Carbohydrates can be chemically defined as optically active polyhydroxy aldehydes or ketones or compounds producing such units upon hydrolysis. Sweet-tasting carbohydrates are referred to as sugars. Common sugars include sucrose and lactose (milk sugar).

Classification of Carbohydrates

Carbohydrates are classified based on their hydrolysis behavior into:

  • Monosaccharides – Cannot be hydrolyzed further. Examples: glucose, fructose, ribose.

  • Oligosaccharides – Yield 2-10 monosaccharides upon hydrolysis, including disaccharides like sucrose and maltose.

  • Polysaccharides – Yield large numbers of monosaccharides on hydrolysis, examples include starch and cellulose.

Reducing and Non-Reducing Sugars

Carbohydrates are further divided into reducing and non-reducing sugars based on their ability to reduce Fehling's solution or Tollens' reagent. All monosaccharides are classified as reducing sugars, while sucrose is an example of a non-reducing sugar.

Structure and Preparation of Glucose

Glucose, an aldohexose and a fundamental carbohydrate, can be prepared from sucrose by acid hydrolysis or from starch via boiling with dilute H2SO4 under pressure. Its molecular structure includes a straight chain with a carbonyl group that confirms its classification as an aldohexose. Notably, glucose exhibits both an open-chain form and cyclic structures known as pyranose (the six-membered ring) and furanose (the five-membered ring) forms.

Proteins

Proteins are the most abundant biomolecules in living systems, with primary dietary sources including milk, cheese, fish, and legumes. They are crucial for the structure and function of all living cells. Proteins are polymers made up of amino acids, characterized by the presence of amino (NH2) and carboxyl (COOH) functional groups. Amino acids can be classified as essential (obtained from the diet) or non-essential (synthesized by the body).

Classification of Amino Acids

Amino acids are classified by the relative number of amino and carboxyl groups, affecting their acidity or basicity. Key amino acids include glycine, alanine, and phenylalanine.

Proteins form through peptide bonds, connecting amino acids to form dipeptides, tripeptides, and larger polypeptides. The structure is categorized into four levels:

  • Primary Structure – Sequence of amino acids.

  • Secondary Structure – Structures like a-helix and b-pleated sheets formed via hydrogen bonding.

  • Tertiary Structure – Overall 3D folding due to various interactions among R groups.

  • Quaternary Structure – Arrangement of multiple polypeptide chains.

Enzymes

Enzymes function as biocatalysts in biochemical reactions, significantly increasing reaction rates. Most enzymes are globular proteins, specific to their substrates. Their action can reduce activation energy, facilitating biological processes.

Vitamins

Vitamins are essential compounds required in small amounts for maintaining health. They are classified into fat-soluble (A, D, E, K) and water-soluble (B-complex and C) vitamins. Each vitamin is crucial, with deficiencies leading to specific diseases.

Nucleic Acids

Nucleic acids, comprising DNA and RNA, are key to heredity and protein synthesis. DNA is characterized as a double-stranded molecule, while RNA is single-stranded and includes three types: mRNA, rRNA, and tRNA. Nucleic acids consist of nucleotides, each formed from a sugar, a phosphate group, and a nitrogenous base. Understanding their structure is vital to comprehending genetic information transmission and gene expression.

Conclusion

The integration of carbohydrates, proteins, enzymes, vitamins, and nucleic acids illustrates the complex biochemical interactions that sustain life. Each biomolecule plays a unique role in maintaining and regulating biological functions.