DNA Replication

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DNA Replication
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• When does DNA replication happen during the cell
  cycle?

• The S phase
• In order to go through cell division we must have
  two copies of DNA
• The process of replication assures that each new
  cell made has a complete set of identical genetic
  information.
• With out replication, our cells would not be able
  to perform their function correctly

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• Are the two strands of DNA considered to be
  complementary to one another?

• YEP! Since A binds with T and C binds with G,
  they are always opposite one another.
• Meaning if one side is ACACACAC then the other
  strand is TGTGTGTG.
• Being complementary to one another allows each
  strand to serve as a TEMPLATE for a new strand!
• This characteristic is important for the process
  of replication.

5
3
5
3
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• What does the 5 and 3 mean on the DNA strands?

• Because DNA strands are complementary (opposite
  one another) we have to be able to determine the
  top from the bottom.
• This is done by marking it as a 5 prime or 3
  prime end.
• This also helps determine the direction of
  replication on the DNA strand
• Replication ALWAYS starts at the 5 prime end

5
3
3
5
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Steps to DNA Replication

• Replication can be studied as 3 steps
• (although all occur simultaneously in the cell)
• Although people may say that DNA copies itself,
  the DNA itself does nothing more than store
  information.
• Enzymes and other proteins do the actual work of
  replication
• Helicase starts the process by unzipping the
  double helix to separate the strands
• DNA polymerase bonds new nucleotides together

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Step 1

• The enzyme Helicase begin to unzip the double
  helix at numerous places along the chromosome
• That is Hydrogen bonds that connect the base
  pairs are broken

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Step 1

• As the strands separate, the bases on each strand
  are exposed for the next step (happening
  simultaneously)
• Unlike unzipping a jacket, replication proceeds
  in two directions at the same time.

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Step 2

• DNA polymerase, another enzyme, creates the
  daughter strands by adding complementary bases to
  the parent strands (which act as a template).

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Step 3

• The two developing DNA strands separate into two
  new, identical daughter strands and DNA
  polymerase proofreads them.
• (Label the parts below on your notes)

Original Strand
New Strand
New Strand
Original Strand
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Replication is fast and accurate.

• DNA replication starts at many points in
  eukaryotic chromosomes.

• DNA polymerases can find and correct errors.

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• In every living thing, DNA replication happens
  over and over again, and it happens remarkably
  fast.
• In humans, about 50 nucleotides are added every
  second to a new strand of DNA
• Your DNA has replicated trillions of times since
  you grew from a single cell.
• http//www.youtube.com/watch?velINXJZr3FE

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Real Picture of DNA replication