Discovery of DNA Structure

We began class today by going over some of the conceptions in Meiosis that I saw in the paragraphs you wrote for me yesterday.  The most common mistakes were seen in the events of Prophase I.  I drew pictures and a flow chart on the board which I asked students to copy into their notes.  I also pointed out some other areas of confusion, such as when chromosome duplication happens (it is in the S phase of interphase, just like before mitosis) and how haploid cells relate to gametes (the haploid cells at the end of meiosis will be modified to become functional gametes).

Another great review of the whole process of meiosis can be found here

We then discussed the significance of Griffith's experiments with pneumonia and mice.  The conclusion he was able to draw was that a specific molecule is responsible for genetic traits.  However, his work did not show that this molecule was DNA.  Most scientists still believed that proteins were the more likely candidate.

Your book does not spend much time discussing the significant contributions of Avery, McLeod and MacCarty so I gave each table a worksheet that gave an overview of their experimental design and a picture of the results they received.  Students drew conclusions based on this information and determined that this experiment showed that DNA must be the transforming agent in Griffith's work.

The homework for tonight is to review the structure of DNA. 
Then watch the animation describing DNA structure HERE.
And examine DNA structure at DNA Interactive.  At DNA Interactive examine the module titled "Finding the Structure."  Use the tabs at the top to navigate.  When you look at "pieces of the puzzle" take some time to read about Rosalind Franklin's X-ray and Pauling's triple helix. 

• What two things did Watson and Crick learn from her X-ray?
• Why was Pauling's triple helix impossible?

Try your hand at the "Base Pairing Interactive" under "Putting it Together."  After you have given up take a look at the clues. 

• Click through the Clues and write down the rules of base pairing that are given to you.

Finally, link HERE to read the original publication by Watson and Crick in Nature.  Note that this incredible breakthrough only took up ONE PAGE in the journal!  We will be talking about this in class tomorrow.