Title 3. CELL AND MOLECULAR BIOLOGY.pdf ✅

described, though their function wasn't immediately clear. ▪ Golgi Apparatus (Camillo Golgi, 1898): Identified using a silver staining method. ▪ Chloroplasts, Endoplasmic Reticulum, Lysosomes, Ribosomes, etc.: Identified throughout the late 19th and early 20th centuries. • Chromosomes and Heredity ▪ Walther Flemming (1843–1905): Observed and described the process of mitosis (cell division) in detail, including the behavior of chromosomes. ▪ Theodor Boveri (1862–1915) & Walter Sutton (1877–1916): Independently proposed the Chromosomal Theory of Inheritance (early 1900s), linking Mendel's inherited "factors" to chromosomes within the nucleus. • Electron Microscopy (1930s onwards) ▪ Max Knoll & Ernst Ruska (1931): Developed the first electron microscope. The Molecular Revolution (Mid-20th Century) The focus shifted from cellular structures to the very molecules that govern life. • Oswald Avery, Colin MacLeod, & Maclyn McCarty (1944) ▪ Demonstrated that DNA, not protein, was the "transforming principle" responsible for heredity in bacteria (Avery-MacLeod-McCarty experiment). • Alfred Hershey & Martha Chase (1952) ▪ Confirmed that DNA is the genetic material through their "blender experiment" using bacteriophages (viruses that infect bacteria). • Erwin Chargaff (1905–2002) ▪ Discovered Chargaff's Rules (early 1950s): the amount of adenine (A) equals thymine (T), and guanine (G) equals cytosine (C) in DNA. • Rosalind Franklin (1920–1958) ▪ Her meticulous X-ray diffraction images of DNA, particularly "Photo 51," provided crucial structural information (helical shape, dimensions). • James Watson (1928–Present) & Francis Crick (1916–2004) ▪ In 1953, they proposed the double helix model of DNA structure, incorporating insights from Chargaff's rules and Franklin's X-ray data. Genetic Code & Protein Synthesis (Mid - Late 20th Century) With DNA's structure known, the next challenge was understanding how its information is translated into proteins. • Francis Crick (1958): Proposed the "Central Dogma of Molecular Biology": DNA makes RNA, and RNA makes protein. • Marshall Nirenberg & Heinrich Matthaei (1961) ▪ Cracked the first codon of the genetic code, showing that the RNA sequence UUU codes for the amino acid phenylalanine.