Chapter 16 and 17 Molecular Biology of the Gene new (6 slides per page).pdf

Chapter 16 and 17 Molecular Biology of the Gene new (6 slides per page).pdf

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Chapter 16 and 17- Molecular Biology of the Gene Overview: I. Structure of the Genetic Material II. DNA replication III. The flow of Genetic Information from DNA to RNA to Protein IV. Mutations I. The Structure of the Genetic Material T. H. Morgan’s group showed that genes are located on chromosomes But link between DNA and heredity was not yet made What two classes of large biological molecule are found in chromosomes? Chromosomes are made up of DNA and protein , but which one is the genetic material? OR SCIENTIFIC DISCOVERY: Experiments showed that DNA is the genetic material Until the 1940s, the case for proteins serving as the genetic material was stronger than the case for DNA. Proteins are made from 20 different amino acids. DNA was known to be made from just four kinds of nucleotides. The discovery of the genetic role of DNA was started by Frederick Griffith in 1928 and concluded by Alfred Hershey and Martha Chase in 1952. Griffith discovered that DNA could be passed on from generation to generation in bacteria. Hershey and Chase showed that DNA was the hereditary material that was passed on from bacteriophages (viruses that infect bacteria) to their hosts (bacteria) Experiments with bacteria and bacteriophages Bacterial cell Phage head Tail sheat h Tail fiber DNA More Evidence That DNA Is the Genetic Material It was known that DNA is a polymer of nucleotides, each consisting of a phosphate group, a sugar , and a nitrogenous base 4 types of nitrogenous bases: adenine (T), cytosine (C), thymine (T), and guanine(G) In 1950, Erwin Chargaff found that amount of nitrogenous bases differ between different species Chargaff’s rules Chargaff also noticed curious pattern in the ratios of nucleotides known as Chargaff’s rules Chargaff’s rules state that in any species there is an equal number of Adenine (A) and Thymine (T), and an equal number of Guanine (G) and Cytosine (C) This pattern remained unexplained until the discovery that DNA is a double helix Thymine (T) Cytosine (C) Pyrimidines Purines Adenine (A) Guanine (G) What is the difference between pyrimidines and purines?
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SCIENTIFIC DISCOVERY: DNA is a double- stranded helix In 1952, after the Hershey-Chase experiment demonstrated that the genetic material was most likely DNA, a race was on to describe the structure of DNA and explain how the structure and properties of DNA can account for its role in heredity. Rosalind Franklin and Maurice Wilkins produced a picture of the DNA molecule using a technique called X- ray crystallography Fig. 10.3A (a) Rosalind Franklin (b) Franklin’s X-ray diffraction photograph of DNA Rosalind Franklin and her X-ray diffraction photo of DNA Figure 16.1 1953, Watson and Crick deduced that DNA is a double helix based on X-ray crystallography data from Maurice Wilkins and Rosalind Franklin and Chargaff’s observation that in DNA How was the structure of DNA determined?
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