DNA: The Road to Understanding

1
DNA The Road to Understanding

• The history behind reaching an understanding and
  some basic structure

2
Science is a process!!!
3
1928 Frederick Griffith

• 2 strains of pneumonia
• Mixing the heat killed virulent with the
  nonvirulent virulent bacteria
• Somehow the heat-killed had passed their disease
  ability to the harmless strain

4
1944 Oswald Avery

• Redid Griffiths experiment to determine which
  molecule was transferred.
• Treated the heat-killed with an enzyme that
  destoys lipids, proteins, carbohydrates, and
  other molecules (including RNA)
• Determined the nucleic acid DNA transmits the
  genetic information

5
1940s Erwin Chargaff

• Chragaffs Rule Percentages of Cytosine (C) and
  Guanine (G) are nearly the same. This applies to
  Adenine (A) and Thymine (T) as well.
• Couldnt explain why though

6
1952 Rosalind Franklin

• Used x-rays to get the first recorded pictures on
  film
• X shaped pattern showed the strands were twisted
  around each other like a spring (helix).
• The angle of the X suggested there are two strands

7
1953 Watson Crick

• Tried to build a 3-D model of DNA
• Then they saw Franklins work . . .
• Within weeks they figured out that it was a
  double helix
• Double Helix Two strands are wound around each
  other

8
DNA is made up of Nucleotides
9
Nucleotide is the monomer of DNA
There are four nitrogenous bases. They
are Guanine, Cytosine, Adenine, Thymine.
In DNA this is Deoxyribose (in RNA it is just
Ribose)
Phosphate. This and the sugar make up the
sugar-phosphate backbone of DNA.
10
Base Pairing

• Certain bases pair up with each other
• One Purine and one Pyrimidine
• Bond together with Hydrogen bonds

11
Lets look at a 3-d model.

• LINK

12
So what is the big deal?

• It is the order of these base pairs that makes up
  you!
• ATAGCTACT
• is different than ATAGCCACT
• It is code that tells exactly who you are!

13
Length of DNA

• E. Coli (prokaryote found in your stomach) has
  4,639,221 base pairs
• About 1.6mm long . . . Which may not seem long
  until you think about the size of a bacterium!
• Have to fold it to one one-thousandth of its
  length

14
What about humans?

• Approximately 3,000,000,000 base pairs
• If the DNA sequence of the human genome were
  compiled in books, the equivalent of 200 volumes
  the size of a Manhattan telephone book
• It would take about 9.5 years to read out loud
  (without stopping) the 3 billion bases in a
  person's genome sequence. This is calculated on a
  reading rate of 10 bases per second, equaling 600
  bases/minute, 36,000 bases/hour, 864,000
  bases/day, 315,360,000 bases/year.

15
How do we store it then?

• 1st Double helix
• 2nd wrapped around Histones (proteins)
• 3rd Wrapped up into Nucleosomes
• 4th Wrapped in coils to make chromatin
• 5th Supercoiled into a chromosome

See Figure 12-10 on Page 297 for better reference
16
The End!
Well . . . sort of . . .
17
Practice time!

• Turn to your partner and introduce yourself
• (Need to be sitting next to them)
• Turn to page 291 in the book
• Get 1 piece of paper, 1 pair of scissors, 1 glue
  (may run out) per pair
• Come up with a key for G, C, T, and A
• Glue down a model beginning with the box shaped
  DNA (You will be
• combining your DNA with your
• partners)