SCIENCE 10 4TH

BIOMOLECULES

Definition of Biomolecules

  • Chemicals or molecules present in living organisms are known as BIOMOLECULES.

  • The total of different types of biomolecules, compounds, and ions present in a cell is called the cellular pool.

  • Biomolecules are compounds primarily composed of carbon, thus the chemistry of living organisms is centered around carbon.

  • Carbon is noted as the most versatile and predominant element of life.

Classification of Biomolecules

Micromolecules

  • Characteristics:

    1. Small sized

    2. Low molecular weight (between 18 and 800 daltons)

    3. Found in the acid soluble pool

  • Examples:

    • Minerals

    • Gases

    • Water

    • Sugars

    • Amino acids

    • Nucleotides

Macromolecules

  • Characteristics:

    1. Large sized

    2. High molecular weight (above 10,000 daltons)

    3. Found in the acid insoluble pool

  • Examples:

    • Carbohydrates

    • Lipids

    • Proteins

    • Nucleic acids

Additional Details on Micromolecules and Macromolecules

  • Micromolecules:

    1. Small in size.

    2. Have low molecular weight.

    3. Have a simple structure.

  • Macromolecules:

    1. Large in size.

    2. Have high molecular weight.

    3. Have complex structure.

    4. Highly soluble in intracellular fluid.

    5. Occur in colloidal states, while some are insoluble in intracellular fluid.

    6. Include only organic polysaccharides.

Major Complex Biomolecules of Cells

  • Overview and Characteristics:

    • Proteins

    • Building block: Amino acid

    • Major functions: Basic structure and function of cell; Protein synthesis.

    • Nucleic Acids:

    • Types: DNA (deoxyribonucleotide) and RNA (ribonucleotide)

    • Function: Hereditary information.

    • Carbohydrates:

    • Building blocks: Monosaccharide

    • Function: Storage form of energy.

    • Lipids:

    • Building blocks: Fatty acids & glycerol

    • Function: Long-term energy storage.

Carbohydrates

Definition

  • Carbohydrates are the most abundant organic molecules in nature.

  • The term carbohydrate comes from the French term hydrate de carbone, referring to organic substances comprising carbon (C), hydrogen (H), and oxygen (O) where H and O are in a 2:1 ratio, similar to water.

Functions of Carbohydrates

  • Major functions include:

    • Most abundant source of energy (providing 4 ext{ cal/g}).

    • Serve as precursors for various organic compounds, including fats and amino acids.

    • Exist as glycoproteins and glycolipids within the cell membrane, facilitating cell growth and fertilization.

    • Act as structural components (e.g., cellulose in plants, exoskeletons of some insects, cell walls of microorganisms).

    • Store energy in the form of glycogen to meet body energy demands.

Classification of Carbohydrates

  • Monosaccharides (one sugar; simple sugars).

    • Examples:

    1. Galactose

    2. Fructose

    3. Ribose

    4. Deoxyribose

    5. Glucose

  • Oligosaccharides (short chains of 2-10 monosaccharides upon hydrolysis).

    • Examples:

    1. Sucrose

    2. Lactose

    3. Maltose

    4. Raffinose

  • Polysaccharides (many monosaccharides; complex and abundant in nature).

    • Examples:

    1. Starch

    2. Glycogen

    3. Cellulose

Derivatives of Monosaccharides

  1. Deoxy Sugars: Created through deoxygenation of ribose to form deoxyribose, a structural component of DNA.

  2. Amino Sugars: Formed when one or more -OH groups of monosaccharides are replaced by an amino group, e.g., Glucosamine, which contributes to the formation of chitin, fungal cellulose, and hyaluronic acid.

  3. Sugar Acids: Generated through oxidation of -CHO or -OH groups (e.g., Ascorbic acid).

  4. Sugar Alcohols: Result from the reduction of aldoses or ketoses (e.g., Glycerol and Mannitol).

Oligosaccharides

  • Formed by the condensation of 2-9 monosaccharides.

    • Types:
      a. Disaccharides (e.g., sucrose, lactose)
      b. Trisaccharides (e.g., raffinose)
      c. Tetrasaccharides (e.g., stachyose)

    • Note: Disaccharides are the smallest and most common oligosaccharides.

Disaccharides

  • Comprise 2 monosaccharide units joined by glycosidic bonds.

  • Characteristics: Crystalline, water-soluble, sweet to taste.

    • Examples:

    • Maltose: Also known as malt sugar; composed of 2 glucose units.

    • Lactose: Known as milk sugar; comprised of glucose and galactose; souring of milk occurs when lactose is converted to lactic acid.

    • Sucrose: Commonly referred to as cane sugar; found in sugar cane and sugar beet; it's the most abundant naturally occurring sugar, made of glucose and fructose.

Polysaccharides

  • Also termed glycans; formed by repeating units of monosaccharides linked by glycosidic bonds.

  • Water is released during their formation, reducing bulk and rendering them almost insoluble to decrease the water potential or osmotic potential of the cell.

  • Unlike sugars, they are not sweet and serve effectively as storage and structural components.

  • Types:

    • Homoglycans: Composed solely of one type of monosaccharide monomers (e.g., starch, glycogen, cellulose).

    • Heteroglycans: Comprised of two or more types of monosaccharides (e.g., hyaluronic acid, agar, chitin, peptidoglycans).

Storage Polysaccharides

  • Starch:

    1. Serves as the carbohydrate reserve in plants and is a vital dietary source for animals.

    2. Found abundantly in cereals, roots, tubers, and vegetables.

    3. It is a homopolymer made up of glucose units (also referred to as glucan).

    4. Composition: Starch = Amylose + Amylopectin.

  • Glycogen:

    1. Acts as the carbohydrate reserve in animals, often called animal starch.

    2. Primarily concentrated in the liver, muscles, and brain.

    3. Also occurs in plants devoid of chlorophyll.

    4. Repeating unit: Glucose.

  • Inulin:

    1. A polymer of fructose, also referred to as fructosan.

    2. Found in Dahlia, bulbs, garlic, onion, etc.

    3. Notably, it is easily soluble in water.

  • Cellulose:

    1. Exclusively found in plants; it is the most abundant organic substance in the plant kingdom.

    2. It constitutes a major component of the plant cell wall.

    3. Completely absent in animals.

  • Chitin:

    1. The second most abundant organic substance.

    2. Complex carbohydrate of the heteropolysaccharide type.

    3. Present in the exoskeletons of some invertebrates, including insects and crustaceans.

    4. Gains hardness upon being impregnated with calcium carbonate.

Proteins

Overview

  • Proteins are the most abundant organic molecules in living systems, constituting about 50% of the dry weight of a cell.

  • Essential for the architecture and functioning of cells.

  • Composed of polymers of amino acids:

    • Complete hydrolysis of proteins yields amino acids.

    • There are 20 standard amino acids that are prevalent in the structure of proteins across animals, plants, and microbes.

    • Collagen is identified as the most abundant animal protein, while Rubisco is recognized as the most abundant plant protein.

    • Protein synthesis is governed by DNA.

Types of Amino Acids

  • Neutral Amino Acids: Possess one amino and one carboxyl group.

  • Acidic Amino Acids: Contain one additional carboxyl group.

  • Basic Amino Acids: Include one extra amino group.

  • S-Containing Amino Acids: Contain sulfur (e.g., Cysteine and Methionine).

  • Alcoholic Amino Acids: Feature -OH groups (e.g., Serine and Threonine).

  • Aromatic Amino Acids: Have cyclic structures (e.g., Phenylalanine and Tryptophan).

  • Heterocyclic Amino Acids: Contains nitrogen in the ring structure (e.g., Histidine and Proline).

Structure of Proteins

  • Primary Structure: Refers to the number and linear sequence of amino acids in the polypeptide chain, including the location of disulphide bridges, and is crucial for the protein's function. The N-terminal amino acid is positioned on the left, while the C-terminal amino acid is on the right.

  • Secondary Structure: Involves the coiling of the linear chain into specific structures, classified into three types:

    1. α-helix

    2. β-pleated sheet

    3. Collagen helix

  • Tertiary Structure: Occurs when a helical polypeptide folds upon itself to form a complex, specific shape—whether spherical, rod-like, or intermediate. These configurations are termed tertiary or third-degree structures.

  • Quaternary Structure: Refers to proteins composed of two or more polypeptide chains. Hemoglobin is a notable example of a protein exhibiting quaternary structure.

Functional Classification of Proteins

  • Structural Proteins: Examples include keratin and collagen.

  • Enzymatic Proteins: Such as pepsin.

  • Transport Proteins: For instance, hemoglobin.

  • Hormonal Proteins: Includes insulin and growth hormone.

  • Contractile Proteins: Such as actin and myosin.

  • Storage Proteins: e.g., ovalbumin.

  • Genetic Proteins: For example, nucleoproteins.

  • Defense Proteins: Such as immunoglobulins.

  • Receptor Proteins: Function in binding hormones and viruses.

Overall Classification Based on Chemical Nature and Solubility

  1. Simple Proteins: Composed solely of amino acid residues.

  2. Conjugated Proteins: Comprised of amino acids along with a non-protein prosthetic group.

  3. Derived Proteins: Represent denatured or degradation products of simple or conjugated proteins.