DNA STRUCTURE From

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DNA STRUCTUREFrom Molecular Biology Made
Simple and Fun

• What does DNA look like?
• What are the important parts of DNA structure?
• Who determined this structure and how did they
  figure it out?

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Background info . . .
Deoxyribonucleic Acid

• DNA
• Why is DNA important?

Information in DNA determines our traits.
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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, DNAs structure is
too small to see with any microscope, what does
DNA look like on a molecular level?

?
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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?
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DNA is made of nucleotides

• Nucleotides have 3 parts
• Sugar
• Phosphate
• Base

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Deoxyribose

• Part of DNA backbone.
• 5-sided sugar

1 base 3 and 5 phosphate 2 missing
oxygen 4 no connection
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Phosphate

1. Gives negative charge to DNA
2. Connects to sugar in DNA backbone
3. Sugar-phosphate bonds ? phosphodiester bonds
4. Connect to 5 and 3 ends of deoxyribose

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Nitrogenous Base

• Four different bases
• Adenine
• Guanine
• Cytosine
• Thymine

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Nitrogenous Base
B. Pyrimidines - small - pyrimidines? CUT the
Py
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Nitrogenous Base
C. Purines - large
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Nitrogenous Base
D. Order of bases spells out traits. E.
Only 1 of human base sequences code for
anything. The other 99 is junk DNA
A T C G T G T C G A
A T C G T T T C G A
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Nucleotide Plus Nucleotide . . .

• DNA has 2 strands
• A-T pair
• C-G pair
• basepair (bp)
• Complementary

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Nucleotide Plus Nucleotide . . .
C. Bases are connected using hydrogen bonds. A
T ? 2 H bonds C G ? 3 H bonds
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Nucleotide Plus Nucleotide . . .
?
D. Strands are antiparallel
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Antiparallel
L
Top-down view of you
Phosphate
Sugar
Make a single strand of DNA
R
Base
3
3
5
DNA strands are antiparallel
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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
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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
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Who figured this out and how?

• James Watson and Francis Crick solved the
  structure of DNA in 1953.

Did Watson and Crick do experiments?
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What did Watson and Crick know?

• Chargaffs Rules

Erwin Chargaff
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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 fathers ideas with
  Watson and Crick

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What else did Watson and Crick know?

• X-ray Crystallography

1. DNA has 2 strands 2. The distance between the
strands is constant
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But Watson and Crick didnt do any chemical
experiments!

• So whose x-ray data is it?

Rosalind Franklin ?
Why did she give her data to Watson and Crick?
She didnt! He did ?
Maurice Wilkins
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The Secret of Life - What was learned by
looking at DNA Structure?

• DNA could be copied unwind helix and follow base
  pair rules
• Script of life sequence of nucleotides can
  store information

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Nobel Prizes . . . or lack thereof

• Watson and Crick awarded Nobel Prize in 1962
• No prize for Franklin

• Did Watson and Crick obtain Franklins 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?