Warm up

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Warm up

• What is DNA?
• Write down one thought.

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The Structure of DNA
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DNA

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

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Why do we study DNA?

• We study DNA for many reasons
• its central importance to all life on Earth,
• medical benefits such as cures for diseases,
• better food crops.

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Chromosomes and DNA

• Our genes are on our chromosomes.
• Chromosomes are made up of DNA.
• DNA is located in the nucleus

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How do we know?

• Rosalind Franklin took diffraction x-ray
  photographs of DNA crystals
• In the 1950s, Watson Crick built the first
  model of DNA using Franklins x-rays

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Rosalind Franklin
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Deoxyribosenucleic Acid

• A DNA nucleotide is made up of three parts
• Sugar
• Phosphate
• Nitrogenous base

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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 Molecule

• The DNA double helix has two strands twisted
  together.

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One Strand of DNA
phosphate

• The backbone of the molecule is alternating sugar
  and phosphate groups
• Covalent bonds between nucleotides
• The teeth are nitrogenous bases.

deoxyribose
bases
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Four nitrogenous bases
DNA has four different bases

• Cytosine C
• Thymine T
• Adenine A
• Guanine G

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Two Kinds of Bases in DNA
N

• Pyrimidines are single ring bases.
• Purines are double ring bases.

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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Double Stranded DNA

• Remember, DNA has two strands that fit together
  something like a zipper.

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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.

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When hydrogen bonds form

• Cytosine always pairs up with guanine
• Adenine always pairs up with thymine

Complimentary base pairs
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Chargaffs Rule

• If A only bonds with T and G only bonds with C
  the ratio of
• A to T
• And
• C to G
• Equals
• 11

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Question

• If there is 30 Adenine, how much Thymine is
  present?
• If the above is true how much Guanine is present
  in the DNA?

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DNA by the Numbers

• Each cell has about 2 m of DNA.
• The average human has 75 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.

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Write out the strand that is complimentary to

• A C G T T C G A G G C T A A C G T

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Answer

• A C G T T C G A G G C T A A C G T

T G C A A G C T C C G A T T G C T
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Review

• What is the function of DNA?
• Where is DNA located?
• What are the three pieces the make up a
  nucleotide?
• What are the four bases?