Deoxyribonucleic Acid

1
Deoxyribonucleic Acid

• Primarily in nucleus
• Contains the code for making proteins
• Cant get out of the nucleus
• Very large molecule
• Made of nucleotides

2
How does DNA fit into a cell?
3
DNA

• DNA is often called the blueprint of life.
• In simple terms, DNA contains the instructions
  for making proteins within the cell.

4
Griffith's "Transforming Factor" Is the Genetic
Material

• British Biologist Frederick Griffith
• Notices that one strain of bacteria caused a
  fatal form of pneumonia whereas another similar
  strain was harmless

5
Avery Shows DNA Is the Transforming Factor

• Attention focused on two types of chemicals that
  may cause transformation
• Protein and DNA

• Trial 1
• treat Griffith's mixture of heat-treated deadly
  strain and live harmless strain with
  protein-destroying enzymes. The bacterial
  colonies grown from the mixture were still
  transformed.

• Trial 2
• treat the mixture with DNA-destroying enzymes.
  This time the colonies failed to transform. Avery
  concluded that DNA is the genetic material of the
  cell.

6
Virus Experiments Provide More Evidence

• Hershey and Chase Used radioactive isotopes on
  virus components to further confirm that it was
  DNA that transformed cells and contain hereditary
  information

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A nucleic acid strand is a polymer of nucleotides

• Nucleic acids are polymers of monomers called
  nucleotides.
• Each nucleotide consists of 3 parts a nitrogen
  base, a pentose sugar, and a phosphate
  group.

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Nitrogen Bases for DNA

• Adenine
• Thymine
• Guanine
• Cytosine

A pairs with T and G pairs with C
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Two Kinds of Bases in DNA

• Pyrimidines are single ring bases.
• a single six-membered ring.
• 3 different pyrimidines cytosine (C),
  thymine (T), and uracil (U)
• Purines are double ring bases.
• a six-membered ring joined to a five-membered
  ring.
• The two purines are adenine (A) and guanine (G).

N
C
N
C
C
O
C
N
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Thymine and Cytosine are pyrimidines

• Thymine and cytosine each have one ring of carbon
  and nitrogen atoms.

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Adenine and Guanine are purines

• Adenine and guanine each have two rings of carbon
  and nitrogen atoms.

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Nucleotides Connected
4 nucleotides are attached here
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Discoverers of DNA Structure

• James Watson and Francis Crick

• Co-discoverers Rosalind Franklin and M.H.F.
  Wilkins
• Nobel Prize in 1953 (except Franklin, who had
  died)

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• The Watson-Crick Double Helix
• A. Identity of Watson and Crick
• B. Techniques they used to analyze structure of
  DNAx-ray crystallography with aid of Rosalind
  Franklin collaborating with Maurice Wilkins

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The Shape of the Molecule

• DNA is a very long polymer.
• The basic shape is like a twisted ladder or
  zipper.
• This is called a double helix.

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The Double Helix
17

• Two sides of staircase are held together by
  hydrogen bonds between the N- bases (A, C, G, and
  T) like steps of the staircase.
• Each base makes half a stair with the other
  always made up of its complement A T, and G
  C.

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Hydrogen Bonds

• The bases attract each other because of hydrogen
  bonds.
• Hydrogen bonds are weak but there are millions
  and millions of them in a single molecule of
  DNA.
• (The bonds between cytosine and guanine are shown
  here.)

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Hydrogen Bonds, cont.

• When making hydrogen bonds, cytosine always pairs
  up with guanine to make 3 H bonds
• And adenine always pairs up with thymine.
• They have 2 H bonds
• (Adenine and thymine are shown here.)

20
DNA by the numbers

• Each cell has about 2 m of DNA.
• The average human has over a trillion cells.
• The average human has enough DNA to go from the
  earth to the sun more than 400 times.
• DNA has a diameter of only 0.000000002 m.