Structure and Functions of Carbohydrates and Proteins

Carbohydrates

Structure of Carbohydrates: Carbohydrates are organic compounds made up of carbon (C), hydrogen (H), and oxygen (O) atoms. They are commonly classified based on their structure into:

• Monosaccharides (Simple Sugars):
  • Examples: Glucose (C6H12O6), Fructose, Galactose
  • These are the simplest form of carbohydrates, consisting of a single sugar unit.
  • They cannot be hydrolyzed into simpler sugars.

• Disaccharides: Examples: Sucrose (glucose + fructose), Lactose (glucose + galactose), Maltose (glucose + glucose) Formed by the condensation of two monosaccharide molecules with the loss of one water molecule.
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• Oligosaccharides: Consist of 3 to 10 monosaccharide units. Examples: Raffinose, Stachyose

• Polysaccharides (Complex Carbohydrates): Composed of more than 10 monosaccharide units. Examples: Starch, Glycogen, Cellulose, Chitin
  • Starch: Storage form of glucose in plants.
  • Glycogen: Storage form of glucose in animals.
  • Cellulose: A major structural component of plant cell walls.

Functions of Carbohydrates:

1. Energy Source: Carbohydrates are the primary source of energy. The breakdown of glucose during cellular respiration releases energy.
2. Energy Storage: Glycogen in animals and starch in plants act as energy reserves. Stored in liver and muscle cells in animals.
3. Structural Function:
   • Cellulose in plants forms the structural component of plant cell walls.
   • Chitin provides structure in the exoskeleton of arthropods.
4. Sparing Protein: Adequate carbohydrate intake prevents the use of proteins for energy, thereby preserving proteins for growth and repair.
5. Regulation of Blood Glucose: Hormones like insulin regulate glucose levels in the blood, ensuring energy supply for bodily functions.
6. Component of Nucleic Acids: Ribose (a pentose sugar) is a key component of RNA, and deoxyribose is a component of DNA.

2. Proteins

Structure of Proteins: Proteins are large, complex molecules made up of amino acids, which are linked by peptide bonds. Proteins have four levels of structure:

1. Primary Structure: The sequence of amino acids in a polypeptide chain, determined by the DNA. Peptide bond: A covalent bond formed between the amino group (-NH2) of one amino acid and the carboxyl group (-COOH) of another.
2. Secondary Structure: Local folding of the polypeptide chain into regular structures such as α-helix or β-pleated sheet, stabilized by hydrogen bonds.
3. Tertiary Structure: The three-dimensional shape of the protein, formed by the folding of the polypeptide chain. Stabilized by interactions such as hydrogen bonds, ionic bonds, disulfide bridges, and hydrophobic interactions.
4. Quaternary Structure: The arrangement of multiple polypeptide chains (subunits) into a functional protein. Example: Hemoglobin (composed of four polypeptide chains).

Functions of Proteins:

1. Enzyme Catalysis: Proteins act as enzymes that speed up chemical reactions in the body. Example: Amylase (breaks down starch), Pepsin (digests proteins).
2. Structural Support: Proteins provide structural support in cells and tissues. Example: Collagen (in connective tissue), Keratin (in hair and skin), Actin and Myosin (in muscles).
3. Transport and Storage: Transport proteins move molecules across cell membranes or within the body. Example: Hemoglobin (carries oxygen), Albumin (transport of fatty acids).
4. Immune Function: Proteins are essential components of the immune system. Example: Antibodies (immune proteins that bind to and neutralize foreign substances).
5. Hormonal Regulation: Many hormones are proteins that help in signaling and regulating bodily functions. Example: Insulin (regulates blood glucose), Growth Hormone (stimulates growth).
6. Movement: Proteins such as actin and myosin are involved in cellular and muscle movements.
7. Buffering: Proteins act as buffers, helping to maintain the pH balance in cells and tissues by accepting or donating protons.
8. Energy Source: In times of prolonged energy shortage, proteins can be broken down into amino acids, which can be used to produce energy.

Comparison of Carbohydrates and Proteins:

Key Points for Competitive Exams

• Carbohydrates are the main source of energy for living organisms, and their storage in the form of starch (plants) and glycogen (animals) is crucial for energy reserves.
• The structure of proteins is hierarchical, with primary, secondary, tertiary, and quaternary structures contributing to the protein’s function.
• Proteins serve a variety of functions including catalysis (enzymes), transport, structure (collagen, keratin), immune defense (antibodies), and hormonal regulation (insulin).
• The biochemical properties of both carbohydrates and proteins are essential in cellular and physiological processes, making them vital for life.