생명과학>>The structure of DNA

The structure of DNA

                                                                 update 2015-9-09

Today, I learned Biology again. My dad showed me some great new videos about Biology today in youtube, since I have almost finished most stuff on KA.
The lecture was about the structure of DNA, my personal favorite.
The lesson showed me some great new stuff and cut of some worries that were on my mind. I will tell you some stuff as well.
Francis Crick and James Watson - The famous duo who first made the model of a double helix DNA, the first inspiration was by a chemist named Rosalind Franklin. She discovered how the DNA sort of looked like when testing a strand of DNA with X - Ray crystallography, it looked like an X shape with an ellipse black background.
These are the Data - Proofs that Crick and Watson used for their famous double - helix model :

#1 - By looking at the X shape of the DNA Molecule, we could highly assume that it is a double helix - like so : XXXXXXX (Look at the pattern, do you see the double helix when you flip it in 90 degrees?)

#2 - When Crick examined the DNA with X - Ray crystallography, he discovered that when you flip it to 180 degrees, a frequent pattern was discovered.
This generally proves that the DNA strands - They are non - parallel to each other.
Example :
----> ->> <----
----> ->> <----

----> ->> <----
<---- ->> ---->

The second one describes a pattern to you, doesn't it?

#3 - There is something called "Chargaff's law" (or the least I think it is, maybe it's rule.....  which says: The % of Adenine is equal to the % of Thymine, and the % of Cytosine is equal to the % of Guanine.

#4 - That time, there was a 'Fight' over the four arrangements - the new one was the Keto and Amino arrangements and the "betting" original ones were the Enol and Amide arrangements.
(To be honest, I really didn't diddle with those arrangements a lot, sorry about that.)
As a result, the new arrangements has won the game. Which gave the Crick and Watson duo a better 'chance' to prove that the DNA was shaped like a double helix.

Those are the Proofs of how the famous double helix DNA molecule model was formed!
Now, for my critical part - You do remember that I said "The lesson showed me some great new stuff and cut of some worries that were on my mind!" right?
Well, I'll tell you those "Stuff" that disabled my mind frequently. And I also hope you won't be in the same situation I had.
The problem's name is called " 5` to 3` errors " and the answer was pretty easy then I thought. here it is:

Error 1 - We all know when DNA is replicating, the 5` end and 3` end pairs splits from each other, then the RNA primase starts the leading strand and the lagging strand and then DNA polymerase and then ligase... you know the rest, don't ya?
Well, the thing is, I didn't know how could you prove that why did the 5` matched with the 3` and why is there no such thing as 3` or 1` or maybe 2` ends.
Because my intuition of replication of DNA's exampling DNA model was quite "Horrible - graphic"ed, I had to ask a lot of question that times and then.
Proof: Look back at Data proof number 2, you can know that the backbone(Sugar and Phosphate) is Non - Parallel to each other.
That proves that the starting and ending strand is gonna be different!

Error 2 - Look at the picture with the sky - blue backbones and the Nitrogenous pairs, do you see it? I do.
Well, if you look at the "Backbones" that I just said, the place that holds the base pairs A, T, C, G. that place is the 1` place. Now all you have to do is count clockwise! then you can see the pattern!
Note: The 5` end is a bit below where the big yellow P is placing.

There you go! That's all of the stuff I learned today, and I will come back with some more "Refreshing" news! :
By Jane Kim  <<해인이가>>