DNA Replication

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DNA -double helix shape -like a winding staircase
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• Composed of 4 bases
• Guanine (G)
• Cytosine (C)
• Adenine (A)
• Thymine (T)
• Always bond together
• A-T
• C-G
• Each base connected to the _______-_______
  _________
• Nucleotide 1 sugar phosphate base (like
  adenine)

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• DNA is complementary
• The sequence of bases on one strand determines
  the sequence of bases on the other.

What is the complement to this single strand of
DNA?
Watson and Crick 2 scientists that figured out
the double helix shape of DNA. -(although they
actually used the work of other scientists to
figure it out)
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DNA Replication

• When cells ________, DNA makes an exact ________
  of itself.
• DNA serves as a template (the parent).

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Enzymes involved

• Remember enzymes are a type of ________
• that help a reaction occur.
• DNA Helicase
• Enzyme that cuts open double stranded DNA .
• Think scissors!
• Makes a replication fork

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Enzymes II

• Primer (put on by the enzyme primase)
• Short sequence laid down that is starting point
  for DNA Polymerase
• DNA Polymerase
• Enzyme that helps add bases 1 by 1.
• Makes new 2nd strand.
• Can only add bases onto 3 end
• New strand made in 5-3 direction.

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DNA Replication

• 5------------------3
• 3------------------5
• 5 to 3 during DNA replication as well.

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Okazaki Fragments make lagging strand
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Replication Daughter DNA
Creates an exact copy! Each new strand has one of
the original strands in it. Meselson Stahl
experiment proved this.
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Practice question

• What is wrong with the DNA on the left?
• Describe in your own words how the double strand
  of DNA on the left would make a copy of itself.

• AATGGCGAGCT
• TTACCGGTCGT

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• http//www.bioteach.ubc.ca/TeachingResources/Molec
  ularBiology/DNAReplication.swf
• http//highered.mcgraw-hill.com/sites/0072437316/s
  tudent_view0/chapter14/animations.html

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Notice how the only available place for the next
nucleotide to bind is the oxygen off the 3rd
carbon (3 carbon). The 5 carbon (the
phosphate off it) from the nucleotide being
added is connecting to the open 3 end. All
nucleotides are added to the 3 end, thus
Polymerase goes in the 5- 3 direction.
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RNA Structure

• Serves as a messenger between the ______ and the
  ________.
• Carries information in order to make _______ in
  the __________.

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RNA Structure

• A
• G
• C
• U
• _______ replaces _______
• _______ stranded.

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Transcription
Only the leading strand is read!
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Transcription Review Questions

• 1. Describe 3 differences between RNA and DNA.
• 2. Describe the process of transcription in your
  own words.
• 3. What is the purpose of transcription?
• 4.Transcribe the single strand of DNA below.
• ACCGTGTCGAATGC
• 5. How might you compare the process of
  transcription and replication?