BCOR 101

Sept 7, 2004

Proof that DNA is the genetic material

•1928 Griffiths discovers “transforming principle”- heat killed strep could occasionally make others virulent.

•1944 Avery digests DNA, RNA, and Protein to show that the transforming factor must be DNA.

•1952 Hershey and Chase label DNA and Protein to show that only DNA label gets into infected cells

Discovery of the Structure of DNA

By the late 1800s people knew nucleic acids contained A,G,C,T, sugar, and phosphate

1944 Chargaff showed constant ratio of bases

1952-3 Franklin’s x-ray photo showed helical structure

1953 Watson and Crick came up with the current model of double helix

Don’t worry about the exact dates, but do understand the sequence events and why those are still considered “classic experiments” in molecular genetics.

Know your structures:

Fig. 2.14 Molecular structure of DNA

Figs. 2.9, 2.10 Structures of deoxyribose and ribose, and of the nitrogenous bases in
DNA and RNA

Fig. 2.11 Chemical structures of DNA and RNA

These figures should become completely familiar to you- practice drawing them!

Fig. 2.15 Structures of the complementary base pairs found in DNA

Understand in particular the different patterns of hydrogen bonding and why that matters.

Test yourself: (we did this in class)

•If a double stranded DNA contains 20% guanine, what are the percentages of all of the other bases?

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RNA has similar structure, except:

•Ribose instead of deoxyribose

•U replaces T

•It is usually single-stranded, therefore many more 3-dimensional shapes are possible

Packaging of DNA into chromosomes

•Supercoiling

•Nucleosomes

–Sets of 8 histones, wrapped with DNA

•Loops

•All serve to make DNA more compact

To do:

•Do the “iActivity” on your disk about analyzing the genome of a rice virus

•Learn the structures of DNA and how it is put together!

•Chapter 2 problems:

–2, 8, 9,10, 12, 14, 16, 22, 25,32