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DNA Replication

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DNA Replication How does each cell have the same DNA? How is a prokaryote different than a eukaryote? Chromosome E. coli bacterium Bases on the chromosome Prokaryotic ... – PowerPoint PPT presentation

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Title: DNA Replication


1
DNA Replication
  • How does each cell have the same DNA?
  • How is a prokaryote different than a eukaryote?

2
Prokaryotic Chromosome Structure
Chromosome
E. coli bacterium
Bases on the chromosome
Go to Section
3
Eukaryotic DNA
  • Eukaryotes have 1000 times the amount of DNA as
    prokaryotes, and its more complex
  • DNA is found in the nucleus in chromosomes (the
    number of chromosomes varies widely of different
    species)
  • DNA is very long!... but it is highly folded
    packed tightly to fit into the cell!
  • For example, a human cell contains more than 1
    meter of DNA made of more than 30 million base
    pairs!

4
Eukaryotic Chromosomes
  • Contain DNA and proteins called histones
  • Tightly packed DNA and proteins form chromatin
  • During mitosis, the chromatin condenses to form
    tightly packed chromosomes

5
Figure 12-10 Chromosome Structure of Eukaryotes
Section 12-2
Nucleosome
Chromosome
DNA double helix
Coils
Supercoils
Histones
Go to Section
6
Watson Crick again
  • Earlier Discovered double helix of DNA
  • Then DNA can be copied or replicated, because
    each strand of the DNA double helix has all the
    information needed to reconstruct the other half
    by way of base pairing
  • The strands are complementary!

7
DNA Replication
  • The process of making a copy of the DNA
  • Occurs inside the nucleus of the cell
  • Occurs when the cell is going to divide so each
    resulting cell will have a complete set of DNA
  • During DNA replication, the DNA separates into
    two strands, then produces two new complementary
    strands following the rules of base pairing.
  • Each strand serves as a template, or model, for
    the new strand.
  • Replication occurs in both directions
  • The site where separation occurs is called the
    replication fork

8
DNA Replication
  • The two strands of DNA unwind or unzip breaking
    the hydrogen bonds and separating. Then each
    strand becomes the guide or template for the
    making of a new strand.
  • A protein called an enzyme called DNA polymerase
    breaks the nitrogen base bonds and the two
    strands of DNA separate, polymerizes individual
    nucleotides to produce DNA and proof reads the
    new DNA.
  • The bases on each strand pair up with new bases
    found in the cytoplasm
  • Then the sugar and phosphate groups form the
    sides of each new DNA strand
  • Each new DNA molecule contains an original DNA
    strand and a new DNA strand

9
Figure 1211 DNA Replication
Section 12-2
Original strand
DNA polymerase
New strand
Growth
DNA polymerase
Growth
Replication fork
Replication fork
Nitrogenous bases
New strand
Original strand
Go to Section
10
STEP 1
  • Two original strands of DNA separates by
    unwinding
  • This occurs through the action of an enzyme that
    breaks the hydrogen bonds between the strands
  • The two areas on either end where the DNA
    separates is the REPLICATION FORK

11
STEP 2
  • At the replication fork, DNA polymerase moves
    along the DNA Strands adding nucleotides
  • As DNA polymerase moves along two strands of DNA
    form

12
Step 3
  • DNA Polymerase continues until all the
    nucleotides have been added
  • Two new identical molecules of DNA are formed
  • Another enzyme connects all the pieces of DNA
    together

13
Proofreading
  • At the end of Replication, DNA polymerase goes
    through the DNA to make sure there are no errors
  • This prevents mistakes in the DNA sequences
  • Mutations- Change in the sequence of the DNA

14
Like a Zipper.
15
Figure 1211 DNA Replication
Section 12-2
Original strand
DNA polymerase
New strand
Growth
DNA polymerase
Growth
Replication fork
Replication fork
Nitrogenous bases
New strand
Original strand
Go to Section
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