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Molecular Basis of Biological Processes
Molecular Basis of Biological Processes
Biomacromolecules
Biological processes in all living organisms are based on large, complex molecules. These molecules are called biomacromolecules because of their large size and crucial role in the cell. Without them, life as we know it would not be possible.
The main classes of biomacromolecules are:
- Carbohydrates (Polysaccharides)
- Carbohydrates are organic compounds made of carbon, hydrogen, and oxygen.
- Their simplest form is sugar, but in living systems they often occur as polysaccharides, long chains of sugar units.
- They are the main source of energy for the cell and also serve as structural materials (e.g., cellulose in plants).
- Lipids
- Lipids include fats, oils, and waxes.
- They are built mostly from carbon and hydrogen atoms, making them insoluble in water.
- Their main functions are:
- Long-term energy storage
- Building cell membranes (phospholipids)
- Acting as signaling molecules (steroids, hormones)
- Nucleic Acids
- Nucleic acids (DNA and RNA) are the molecules that store and transfer genetic information.
- DNA (deoxyribonucleic acid) carries the instructions for building proteins and controls hereditary traits.
- RNA (ribonucleic acid) helps translate these instructions into functional proteins.
- They are made of repeating units called nucleotides.
- Proteins
- Proteins are perhaps the most diverse biomolecules in living organisms.
- They are built from chains of amino acids.
- Functions of proteins:
- Act as enzymes (biological catalysts) that speed up chemical reactions.
- Provide structural support (collagen, keratin).
- Enable transport (hemoglobin).
- Act in defense (antibodies).
- Regulate processes as hormones.
Carbohydrates (Polysaccharides)
Carbohydrates are one of the most important biomacromolecules in living organisms. They provide energy, serve as structural materials, and can act as recognition signals on the surfaces of cells.
By chemical composition, carbohydrates contain carbon (C), hydrogen (H), and oxygen (O), usually in the ratio of C : H : O = 1 : 2 : 1. This ratio explains the name “carbo-hydrates.”
Classification of Carbohydrates
- Monosaccharides (simple sugars)
The smallest units, such as glucose, fructose, galactose.
They are easily soluble in water and serve as quick energy sources.
Glucose is often called the “fuel of life” because it is the primary energy source for cells.
beta-d-glucose
beta-d-fructose
beta-d-galactose
2. Disaccharides
Formed when two monosaccharides bond together.
Examples:
Sucrose (glucose + fructose) → common table sugar
Lactose (glucose + galactose) → sugar in milk
Maltose (glucose + glucose)
3. Polysaccharides (complex carbohydrates)
Long chains of many monosaccharide units.
Functions:
Energy storage
Starch (plants)
Glycogen (animals, stored in liver and muscles)
Structural support
Cellulose (plant cell walls, gives rigidity)
Chitin (exoskeleton of insects, shells of crustaceans)
Importance of Carbohydrates
Provide fast energy (glucose in respiration).
Store reserve energy (starch, glycogen).
Build biological structures (cellulose, chitin).
Participate in cell communication and recognition (glycoproteins, glycolipids on membranes).
Lipids
Lipids are a diverse group of biomacromolecules that share one important feature: they are insoluble in water but soluble in nonpolar solvents. This property comes from their hydrocarbon chains or rings, which make them hydrophobic.
Although they differ in structure, lipids have crucial biological functions: long-term energy storage, building cell membranes, and signaling.
Main Types of Lipids
Fats and Oils (Triglycerides)
Composed of glycerol + 3 fatty acids.
Store large amounts of energy (more than carbohydrates).
Fats → usually solid at room temperature (contain saturated fatty acids).
Oils → usually liquid at room temperature (contain unsaturated fatty acids).
Phospholipids
Similar to triglycerides, but one fatty acid is replaced by a phosphate group.
Amphipathic molecules:
Hydrophilic head (phosphate)
Hydrophobic tails (fatty acids)
They spontaneously arrange into a bilayer, forming the basic structure of cell membranes.
Steroids
Lipids with a structure based on four fused carbon rings.
Examples: cholesterol, sex hormones (estrogen, testosterone), cortisol.
Function as signaling molecules and help regulate physiological processes.
Waxes
Long-chain fatty acids bonded to long-chain alcohols.
Provide protection:
In plants (cuticle on leaves).
In animals (protective coating in earwax, feathers, fur).
Importance of Lipids
Energy storage → twice as much energy as carbohydrates.
Cell structure → phospholipids build membranes.
Hormones → steroids regulate growth, metabolism, and reproduction.
Protection → waxes and fats protect against water loss and mechanical damage.