Overview
The lecture explains how life is made from non-living elements through the formation of biomolecules, describing their types, structures, and biological roles.
Origin of Life and Chemical Elements
- The Earth began as a hot mass of gases that cooled to form compounds and molecules essential for life.
- Elemental analysis shows both Earth's crust and living cells contain elements like hydrogen, carbon, oxygen, nitrogen, and sulfur.
- Differences in life arise from the compounds (biomolecules) formed by these elements, not the elements themselves.
Types of Biomolecules
- Biomolecules are organic molecules found only in living cells and are mainly carbohydrates, lipids, proteins, and nucleic acids.
- Carbohydrates, lipids, and proteins all contain carbon, hydrogen, and oxygen, often with other elements.
Carbohydrates
- Carbohydrates serve as primary energy sources, found in foods like bread, rice, and potatoes.
- Simplest forms are glucose, galactose, and fructose, used by cells to produce ATP (energy).
- Excess glucose is stored as glycogen in animals and starch in plants; cellulose in plants provides structural support.
- Carbohydrates are formed by dehydration (removal of water) and broken down by hydrolysis (addition of water).
- Lactose is a carbohydrate in milk, made of glucose and galactose.
Lipids
- Lipids (fats and oils) provide long-term energy storage and insulation.
- Made of glycerol and three fatty acid chains (triglycerides).
- Saturated fats (all single bonds) are solid at room temperature; unsaturated fats (double bonds) are liquid.
- Lipids are hydrophobic ("water-fearing") and form important cell structures.
- Phospholipids, with hydrophilic phosphate heads and hydrophobic tails, create the cell membrane's bilayer.
Proteins
- Proteins are made of amino acids (20 types), which are absorbed from food.
- Each amino acid has a central carbon, hydrogen, amino group, carboxyl group, and a variable R group.
- Amino acids join by peptide bonds (via dehydration) to form polypeptides.
- Protein structure: primary (chain), secondary (helices/sheets), tertiary (functional protein), quaternary (multiple polypeptide chains, e.g., hemoglobin).
Nucleic Acids
- Nucleic acids (DNA and RNA) direct cellular activities and heredity.
- Built from nucleotides: phosphate group, pentose sugar, and nitrogenous base.
- DNA bases: adenine, guanine, cytosine, thymine; RNA uses uracil instead of thymine.
- Nucleotides link by covalent bonds (sugar-phosphate backbone) and, in DNA, hydrogen bonds between bases stabilize the structure.
Key Terms & Definitions
- Biomolecule — a molecule produced by living organisms, including carbohydrates, lipids, proteins, and nucleic acids.
- Dehydration — chemical reaction where water is removed to join two molecules.
- Hydrolysis — chemical reaction adding water to break a bond.
- Polysaccharide — long chain of carbohydrate molecules.
- Triglyceride — lipid made of glycerol and three fatty acids.
- Phospholipid — lipid with a phosphate group, forms cell membranes.
- Amino Acid — building block of proteins.
- Peptide Bond — covalent bond linking amino acids.
- Nucleotide — monomer of nucleic acids, consisting of phosphate, sugar, and base.
Action Items / Next Steps
- Review diagrams of biomolecule structures (carbohydrates, lipids, proteins, nucleic acids).
- Study the differences between DNA and RNA bases.
- Read further articles or watch follow-up videos for deeper understanding.