The Cell Theory: A Brief History

Transcription

1 The Cell Theory: A Brief History Robert Hooke (1665) observed compartments in cork, under a microscope, and first named cells (the basic unit of biology) His observations were limited by the low magnification power (30X enlargement) of his microscope Antonie van Leeuwenhoek, a few years later, produced better lenses that magnified up to 300X

2 The cell theory In 1839, Schwann postulated the cell theory 1. All organisms consist of one or more cells 2. The cell is the basic unit of structure for all organisms Later, Virchow (1855) added 3. All cells arise only from preexisting cells

3 The Emergence of Modern Cell Biology Three historical strands weave together into modern cell biology, each with important contributions to understanding cells The cytology strand focuses mainly on cellular structure, and emphasizes optical techniques The biochemistry strand focuses on cellular function The genetics strand focuses on information flow and heredity

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5 The Biochemical Strand Covers the Chemistry of Biological Structure and Function Around the same time cytologists were studying cells microscopically, others began to explore cellular function Much of biochemistry dates from the work of Fredrich Wöhler (1828), who showed that a compound made in a living organism could be synthesized in the lab

6 Developments in early biochemistry Louis Pasteur (1860s) showed that yeasts could ferment sugar into alcohol The Buchners (1897) showed that yeast extracts could do the same Led to the discovery of enzymes, biological catalysts

7 Early discoveries in biochemistry Steps of the pathways of fermentation and others were elucidated in the 1920s and 1930s Gustav Embden and Otto Meyerhof described the steps of glycolysis (the Embden-Meyerhof pathway) in the early 1930s The Krebs cycle was described soon after Both pathways are important in energy metabolism of cells

8 Important advances in biochemistry Radioactive isotopes - to trace the fate of specific atoms and molecules (led to elucidation of the Calvin cycle, 1950s) Subcellular fractionation - such as centrifugation to separate/isolate different structures and macromolecules Ultracentrifuges - capable of very high speeds (over 100,000 revolutions per minute)

9 Important advances in biochemistry (continued): Chromatography - techniques to separate molecules from a solution based on size, charge, or chemical affinity Electrophoresis - uses an electrical field to move proteins, DNA or RNA molecules through a medium based on size/charge Mass spectrometry - to determine the size and composition of individual proteins

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11 The Genetic Strand Focuses on Information Flow The genetic strand has important roots in the nineteenth century Gregor Mendel s experiments with peas (1866) laid the foundation for understanding the passage of hereditary factors from parents to offspring The hereditary factors are now known to be genes

12 Chromosomes and the genetic material Walther Flemming (1880) saw threadlike bodies in the nucleus called chromosomes He called the process of cell division mitosis Wilhelm Roux (1883) and August Weisman (shortly after) suggested that chromosomes carried the genetic material

13 The chromosome theory Three geneticists formulated the chromosome theory of heredity, proposing that Mendel s hereditary factors are located on chromosomes Morgan, Bridges, and Sturtevant (1920s) were able to connect specific traits to specific chromosomes in the model organism, Drosophila melanogaster (the common fruit fly)

14 Progress in understanding DNA Friedrich Miescher (1869) first isolated DNA, which he called nuclein DNA: - known to be a component of chromosomes by known to be composed of only 4 different nucleotides by the 1930s - proteins, composed of 20 different amino acids, thought more likely to be genetic material

15 DNA is the genetic material Experiments with bacteria and viruses in the 1940s began to implicate DNA as the genetic material Beadle and Tatum formulated the one gene-one enzyme concept (each gene is responsible for the production of a single protein) Watson and Crick, with assistance from Rosalind Franklin, proposed the double helix model for DNA structure 1960s - many advances toward understanding DNA replication, RNA production, and the genetic code

16 Important techniques in genetics Ultracentrifugation and electrophoresis, for separating DNA and RNA molecules Nucleic acid hybridization, a variety of techniques that use the ability of nucleic acid bases to bind to each other Recombinant DNA technology, restriction enzymes cut DNA at specific places allowing scientists to create recombinant DNA molecules, with DNA from different sources

17 Important techniques in genetics (continued) DNA sequencing, methods for rapidly determining the base sequences of DNA molecules It is now possible to sequence entire genomes (entire DNA content of a cell) Bioinformatics merges computer science with biology to organize and interpret enormous amounts of sequencing and other data

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23 Prokaryot vs Eukaryot Prokaryot = före kärnan Eukaryot= äkta kärna

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