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Molecular GeneticsGenetics Overview

ProkaryotesNo 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)

Examples of ProkaryotesStaphylococcus Escherichia coli (E. coli) Streptococcus

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

Prokaryote vs. Eukaryote

5Mitosis 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

MeiosisMeiosis is essential for sexual reproductionand therefore occurs in all eukaryotes(including single-celled organisms) thatreproduce sexually.

DNAThe Hereditary Material

Discovery of DNA1869-Friedrich Miescher, Swiss biologistHe 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.

The Location of Hereditary Information1930s- Joachim HammerlingAcetabulariaGreen algaeSingle-celled organism

Acetabularia Experiment

When cap was removed new cap regenerationWhen foot was removed no foot regeneration

Hammerlings experiment strongly suggested that the hereditary material is located in the nucleus

DNA or Protein?Although it was clear that nucleus contains the hereditary information, the exact chemical nature was unknownChromosomes consist of both DNA and proteinsWhich one contains the hereditary information?The Transforming Principle1928-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 DNASp bacterium causing pneumonia, exists in two strains

Griffiths ExperimentThe 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.

Griffiths Experiment

Results of Griffiths Experimentlive R strain was somehow transformed into the S strain Discovery showed that organisms can be genetically re-programmed into a slightly different version of themselvesWhen the S bacteria were killed by heat, many substances were released (mixture contains protein, RNA, DNA, lipids, and carbohydratesWhat is the transforming agent?

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

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

Hershey and Chase