DNA Structure and History 2009 by 4SJ1VCK7

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									   DNA STRUCTURE
From “Molecular Biology
 Made Simple and Fun”

 What   does DNA look like?

 Whatare the important parts of
 DNA structure?

 Who determined this structure and
 how did they figure it out?
        Background info . . .
 DNA – Deoxyribonucleic Acid
 Why is DNA important?

Information in DNA determines our traits.
To understand how DNA stores information and
why some DNA leads to genetic disorders,
scientists needed to learn what it looks like.
They had trouble believing that the goop that
you extracted earlier somehow determines your
traits and is inheritable. Although, DNA’s
structure is too small to see with any
microscope, what does DNA look like on a
molecular level?


                 =                  ?
In 1953, James Watson and Francis Crick
discovered the 3-D structure of DNA. What did
people know prior to that and what did Watson and
Crick figure out?
    DNA is made of nucleotides
Nucleotides have 3 parts:
 Sugar

 Phosphate

 Base
                Deoxyribose
A.    Part of DNA
      backbone.
B.    5-sided sugar


     1’ – base
     3’ and 5’– phosphate
     2’ – missing oxygen
     4’ – no connection
                   Phosphate
A.   Gives negative charge
     to DNA
B.   Connects to sugar in
     DNA backbone
C.   Sugar-phosphate
     bonds 
     phosphodiester bonds
D.   Connect to 5’ and 3’
     ends of deoxyribose
           Nitrogenous Base
A.   Four different bases
      1. Adenine

      2. Guanine

      3. Cytosine

      4. Thymine
          Nitrogenous Base
B. Pyrimidines
 - small
- “pyrimidines”? “CUT the Py”
             Nitrogenous Base
C. Purines
- large
          Nitrogenous Base
D. Order of bases “spells out” traits.


A T C G T G T C G A =

 A T C G T T T C G A =


E. Only 1% of human base sequences
    code for anything. The other 99% is
    “junk DNA”
Nucleotide Plus Nucleotide . . .
A.   DNA has 2 strands
B.   A-T pair
     C-G pair

     basepair (bp)

     “Complementary”
Nucleotide Plus Nucleotide . . .
C. Bases are connected using
    hydrogen bonds.

   A – T  2 H bonds

   C – G  3 H bonds
Nucleotide Plus Nucleotide . . .
D. Strands are antiparallel
                Antiparallel
Top-down         L   Phosphate
view of you
                          Sugar
Make a single
strand of               R
DNA
                        Base
 5’                      3’

 3’                      5’

 DNA strands are antiparallel
Nucleotide Plus Nucleotide . . .
E. Clockwise or right-handed
    twist (follow hand UP
    staircase)

F. Twisted so every 10 bp is
    one full turn

G. Humans  3 billion bp; 6 ft
    long in every cell; 1/10th
    width of hair
Nucleotide Plus Nucleotide . . .
H. In order to fit DNA in
    nucleus, DNA is folded
    around proteins called
    histones and arranged in
    packages called
    chromosomes
                    Histones
Who figured this out and how?
   James Watson and Francis Crick
    solved the structure of DNA in 1953.




Did Watson and Crick do
“experiments”?
    What did Watson and Crick know?
   Chargaff’s   Rules




Erwin Chargaff
                                   % A’s = % T’s
                  In all species
                                   % C’s = % G’s
         Who else was in the race?
-Linus Pauling won two
Nobel Prizes (protein
structure; peace)

- Hypothesized that
DNA had 3 strands and
phosphates are on the
inside of triple helix.

- His son Peter shared
his father’s ideas with
Watson and Crick
    What else did Watson and Crick know?

   X-ray
    Crystallography
1. DNA has 2
strands

2. The distance
between
the strands is
constant
    But Watson and Crick didn’t do
      any chemical experiments!
   So whose x-ray data
    is it?

 Rosalind Franklin 
Why did she give her
data to Watson and
Crick?

She didn’t! He did 
                          Maurice Wilkins
“The Secret of Life” - What was learned
     by looking at DNA Structure?

 DNA could be copied: unwind helix
 and follow base pair rules

        of life”: sequence of
 “Script
 nucleotides can store information
 Nobel Prizes . . . or lack thereof
   Watson and Crick awarded
    Nobel Prize in 1962

   No prize for Franklin
Did   Watson and Crick obtain Franklin’s data
“illegally”?
Should Franklin have shared her scientific
knowledge? (Never knew her info had been
“obtained” by Watson and Crick)
Should Franklin receive credit for her
contributions to solving DNA structure?
Did Watson and Crick really do a lot of work?

								
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