1. The Long and Scenic Road to the Double Helix
Modern Biotechnology
The Long and Scenic Road to the Double Helix

2. A. Microscopes Early scientists – relied on naked eye observations.
1590 – Zacharias Janssen – built first compound microscope – 30x mag.
1665 – Robert Hooke – 1st to observe & describe cells (cork)
1676 – Antonie von Leeuwenhoek – 1st to observe living living cells – protozoa, fungi (“animalcules”) - 200x mag.
Early microscopes - poor resolution & magnification, scientists had very little understanding of what they saw.

3. B. Cell Theory
Vitalism – early theory that only a whole, complete organism (not its parts) possessed life.
Microscopic observation of cell division led to revolutionary new theory:
All organisms are composed of 1 or more cells. (Schleiden, 1838 – plants, Schwann, 1839 – animals)
Cells are the basic unit of structure & function of an organism. (Virchow, 1858)
Cells come only from existing cells. (Virchow, 1858)
1880’s - Improved microscopes, stains, tissue preservation techniques revealed more about cell structure & function.

4. C. Discoveries That Enhanced Understanding of Cell Function
1. Biochemistry
biology (living things – organic) and chemistry (non-living things, inorganic) once thought to be entirely separate – no overlap.
1828 – urea (organic molecule) synthesized in lab from inorganic molecules – astounding!! Led to synthesis of other organic compounds.

5. Discoveries That Enhanced Understanding of Cell Function
2. Pasteurization
Louis Pasteur discovered that yeast contamination of wine caused spoilage
Pasteur also discovered that heating contaminated liquids killed microorganisms & preserved food.
Pasteurization still used today (mainly for milk). (161/20)

6. Discoveries That Enhanced Understanding of Cell Function
3. Spontaneous generation disproved (1859).
Pasteur showed life can only come from preexisting life.
Boiled broth in a straight-necked flask got contaminated
Boiled broth in a swan-necked flask (with a liquid trap in part of the neck) did not become contaminated.
Supported the Cell Theory.

7. Discoveries That Enhanced Understanding of Cell Function
4. Discovery of enzymes
1896 – Eduard Buchner fermented sugar using yeast extracts (called “ferments”) rather than intact yeast cells.
Yeast extracts later found to contain enzymes (means “in yeast”), biological catalysts.

8. D. Genetics
1. Inheritance first thought to be carried/transferred to offspring via blood.
This idea challenged & discarded in late 1800’s after microscopic examination of semen showed no blood.

9. Genetics cross-pollinated pea plants, observed inheritance of traits.
2. Gregor Mendel (1857 – botanist, monk)
cross-pollinated pea plants, observed inheritance of traits.
Amassed huge amount of data w/ nearly perfect results
1865 – published findings, proposed Theory of Transmissible Factors (a.k.a. Theory of Inheritance, later known as Mendelian genetics)
Offspring receive 1 unit of heredity from each parent for each trait.
Traits are dominant or recessive.
Scientists of his time paid little attention – they understood little about fertilization & were distracted by Darwin’s “The Origin of Species” (1859).
Genetics

10. Genetics
substance (“Nuclein”) isolated from nucleus of WBC – looking for proteins thought to code for inherited traits.
– equal distribution of threadlike bodies to daughter cells observed during cell division.
Chromosomes (means “colored bodies”, because they stained darkly)
Sister chromatids – pairs of chromosomes, distributed equally to daughter cells.

11. Genetics
– Mendel’s work rediscovered & confirmed by 3 independent European botanists.
– Sutton determined that Mendel’s “Factors” were located on chromosomes.
observed gametes receiving only one chromosome of each type during meiosis (haploid).
Reasoned that heredity units could be distributed in many different combinations during meiosis, depending on how chromosomes lined up before separation.

12. Genetics 7. 1909 - “Factors” named genes by Danish botanist Johannsen.
’s – all cells in an organism were determined to have same amount of DNA
Exception: egg/sperm have half (haploid) but combine to form diploid zygote.
Theories were proposed that genes were involved in heredity and were made of DNA.

13. Genetics
9. Link between DNA and heredity not readily accepted – scientists believed protein to be hereditary material.
protein more complex than DNA (20 amino acids vs. only 4 nucleotide bases – more combinations thought possible.)
proteins can be any length
sequence of AA determined type of protein, so maybe it could determine types of genes, too.

14. 10.
1928 – Griffith discovered that genetic information can be transferred from heat-killed bacteria to live ones -transformation.
Genetics

15. Genetics
11. Experiments with bacterial models in 1944 (Avery) and 1952 (Hershey & Chase) proved that DNA is genetic material.

16. Genetics 11. 1953 – Watson & Crick (James Watson, Francis Crick)
Studied data on X-ray diffraction of DNA (data collected by Rosalind Franklin & Maurice Wilkins).
Also used knowledge of base pairings (A-T, C-G) provided by Chargaff.
Developed the correct structural model (double helix) of DNA
Correctly predicted the replication mechanism for DNA

17. Genetics
12. Watson & Crick’s models were the missing link – discoveries were made rapidly afterwards.
Understanding of gene expression & regulation
enzymes to manipulate DNA in vitro – cut DNA into pieces, rearrange, and rejoin them. This is the basis of genetic engineering.