DNA

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DNA
DNA Structure and Replication
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Early DNA Discoveries

• DNAs molecular structure is too small to see
  with a microscope, so early discoveries
  depended on chemistry and crude images.
• Chargaff did chemical analysis and found that
• - amount of Adenine amount of Thymine
• - amount of Cytosine amount of
  Guanine
• Rosalind Franklin DNA x-ray photo
  suggested double helix shape
• Watson and Crick Made 3-D model of DNA
• Explained bonds between molecules involved.

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DNADeoxyribose Nucleic Acid

• Found in the nucleus of each cell
• (in the form of chromosomes)
• Genetic blueprint
• Shape a double helix
• (like a twisted ladder)

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A nucleic acid is a chain of NUCLEOTIDES

• Each nucleotide consists of 3 parts
• A Phosphate group
• A Sugar (specifically, deoxyribose)
• A Nitrogen Base (there are 4 possible DNA bases)
• Adenine Thymine
• Guanine Cytosine

BASE
Phosphate
SUGAR
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BASE PAIRING
Adenine always pairs up with Thymine (A-T or
T-A) Guanine always pairs up with Cytosine (G-C
or C-G) These are called COMPLIMENTARY BASE
PAIRS
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BASE PAIRING

• 1) Write the letters for the complimentary
  strand
• 2) Given the following base sequence, write its
  compliment
• C T A A T G T
• __ __ __ __ __ __ __

A
G
T
C
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BASE PAIRING

• 1) Write the letters for the complimentary
  strand
• 2) Given the following base sequence, write its
  compliment
• C T A A T G T
• __ __ __ __ __ __ __

A
G
T
C
T
C
A
G
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BASE PAIRING

• 1) Write the letters for the complimentary
  strand
• 2) Given the following base sequence, write its
  compliment
• C T A A T G T
• G A T T A C A

A
G
T
C
T
C
A
G
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DNA ReplicationMaking copies

• Sometimes, you need more DNA for new cells (every
  cell needs a full set of instructions)
• Must be an EXACT copy, or big (fatal?) problems
  can occur
• Must be done before cell division
• Its time to REPLICATE!
• You can get 2 DNA strands
• each time you copy 1 strand

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REPLICATION 3 easy steps!

• 1) UNZIP STRANDS
• Enzyme (DNA Helicase) breaks the bonds between
  the bases(A,T,C,G)
• Makes a replication fork (looks like a Y )
• 2) ADD COMPLIMENTARY NUCLEOTIDES
• Matchmaker enzymes (DNA Polymerase) move along
  each unzipped strand, matching up bases with
  their compliments (A-T) (C-G)
• 3) PROOFREAD
• Before detaching, Polymerase proofreads to
  minimize errors
• Leaves 2 identical DNA chains, each with 1 new
  strand and 1 old strand

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More replication info

• Your DNA doesnt actually do replication from one
  end straight to the other end.

• An entire human chromosome can be replicated in
  about 8 hours.

Prokaryotes (Bacteria) have circular DNA. They
also have plasmid DNA rings, which are rarely
used by the bacteria are now used in genetic
engineering.
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DNA TERMS TO KNOW SO FAR
Adenine Thymine Guanine Cytosine   Replication Hel
icase Polymerase Mutation

• DNA
• Double helix
• Nucleic Acid
• Nucleotide
• Base Pairs 
• Complimentary