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Molecular Genetics Genetics Overview.

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Presentation on theme: "Molecular Genetics Genetics Overview."— Presentation transcript:

1 Molecular Genetics Genetics Overview

2 Prokaryotes No nuclear membrane (genetic material dispersed throughout cytoplasm) No membrane-bound organelles Simple internal structure Most primitive type of cell (appeared about four billion years ago)

3 Examples of Prokaryotes
Staphylococcus Escherichia coli (E. coli) Streptococcus

4 Eukaryotes Nuclear membrane surrounding genetic material
Numerous membrane-bound organelles Complex internal structure Appeared approximately one billion years ago

5 Prokaryote vs. Eukaryote

6 Mitosis Mitosis is the process in which
a eukaryotic cell separates the chromosomes in its cell nucleus, into two identical sets in two daughter nuclei. Cell division and cytokinesis

7 Meiosis Meiosis is essential for sexual reproduction and therefore occurs in all eukaryotes (including single-celled organisms) that reproduce sexually.

8 The Hereditary Material
DNA The Hereditary Material

9 Discovery of DNA 1869-Friedrich Miescher, Swiss biologist
He isolated various phosphate-rich chemicals from white blood cells, which he called nuclein (now nucleic acids) His discoery paved the way for the identification of DNA as the carrier of inheritance.

10 The Location of Hereditary Information
1930s- Joachim Hammerling Acetabularia Green algae Single-celled organism

11 Acetabularia Experiment
When cap was removed  new cap regeneration When foot was removed  no foot regeneration Hammerling’s experiment strongly suggested that the hereditary material is located in the nucleus

12 DNA or Protein? Although it was clear that nucleus contains the hereditary information, the exact chemical nature was unknown Chromosomes consist of both DNA and proteins Which one contains the hereditary information?

13 The Transforming Principle
1928-Frederick Griffith, English medical officer started experimenting with Streptococcus pneumoniae to develop a vaccine against pneumonia. he discovered what he called a transforming principle, which is today known to be DNA Sp bacterium causing pneumonia, exists in two strains

14 Griffith’s Experiment
The smooth strain (S strain) had a polysaccharide capsule and was virulent when injected, causing pneumonia and killing mice in a day or two. The rough strain (R strain) did not cause pneumonia when injected into mice (it was avirulent), since it lacked a capsule.

15 Griffith’s Experiment

16 Results of Griffith’s Experiment
live R strain was somehow “transformed” into the S strain Discovery showed that organisms can be genetically “re-programmed” into a slightly different version of themselves When the S bacteria were killed by heat, many substances were released (mixture contains protein, RNA, DNA, lipids, and carbohydrates What is the transforming agent?

17 What is the transforming agent?
1944-Further experiments done at The Rockefeller Institute in New York Three scientists: Oswald Avery, Colin MacLeod, and Maclyn McCarty. First, after heat-killing the S strain of bacteria, the mixture was separated into six test tubes Thus, each of the test tubes would contain the unknown “transforming agent” A different enzyme was then added to each tube

18 Illustration of the classic experiment demonstrating that DNA is capable of transforming harmless R strain S. pneumoniae into the pathogenic S strain.

19 Hershey and Chase Despite this very clear result, some scientists remained skeptical and continued to think that proteins were likely the genetic molecule. 1952-two scientists named Alfred Hershey and Martha Chase performed an entirely different type of genetic experiment to determine which molecule, DNA or protein, acted as the genetic material in phages.

20 Hershey and Chase


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