DNA Structure

Today and yesterday were block day classes.  We began the class with Watson and Crick's original publication in Nature from 1953.  You can look at it again here where you will also find links to several other significant papers from that same era.  Notice that an article by Wilkins and one by Franklin also appeared in the same issue!

I asked students to identify, in the brief Watson and Crick article, the significant descriptors of DNA.  We were able to find approximately 15 specific items.  Those were then used to fill in a blank diagram of part of a DNA molecule.  We were able to locate phosphates, sugars and bases, label the carbons of deoxyribose, discuss the difference between deoxyribose and ribose, label the 5' and 3' ends of the molecule, correctly tag cytosine, guanine, adenine and thymine based on their size and # of hydrogen bonds, differentiate between purines and pyrimidines (PuAG2!), learn that the helix shows a full twist every 10 nucleotides and that nucleotides are 0.34 nm apart.  We also added that the two strands of DNA run anti-parallel, that it is double-stranded and the width of the molecule is 2nm. 

Here is a blank DNA diagram so that you can practice
With limited time remaining in class I introduced several upcoming items:
1. We have a test coming up next week.  I am now planning for TUESDAY.  It will cover Ch. 13 (meiosis and sexual reproduction), Ch. 16.1 (DNA structure) and Ch. 16.2 (DNA replication).  You will definitely see a reproduction of the DNA diagram we used today in class on the test.
2.  There is an opportunity for extra credit, which would be due on Monday, 11/29.  This assignment will be described in another blog entry, titled "EXTRA CREDIT DESCRIPTION"
3. I am assigning a project on DNA replication.  I am now planning that it will be due on TUESDAY.  This project will be described in greater detail in another blog entry, titled "DNA REPLICATION MODEL."

Your homework tonight is to skim the section (Ch. 16.2) on DNA replication.  Make a list of the following enzymes and explain what they due during DNA replication (note, if you are in 2nd or 3rd period this same list is on your reading guide and you may just fill it out there)

• helicase
• topoisomerase
• single-strand binding proteins (not really an enzyme, but we will include it anyway)
• DNA polymerase III
• DNA polymerase I
• ligase

In addition, you may want to take a look at one of the following animations of DNA replication.
McGraw Hill - select the first and last animations in the list