1. Chapter 12-2 DNA Replication and Chromosomes

2. I. Prokaryote DNA Replication
Lack nuclei
B. Single circular strand of DNA in cytoplasm of cell. Called a nucleoid or plasmid.
C. DNA strand stretched out is approx 1.6mm in length.
D. Replication begins at single point and goes in TWO directions until entire plasmid is replicated.
Plasmid

3. II. Eukaryote DNA Replication
A. DNA contained in nucleus of every cell.
B. More over 1 meter (6 feet) of DNA in every human cell nucleus!
C. Begins at 100’s of points and goes in TWO directions until chromosome is replicated.

4. When does a cell copy DNA?
When in the life of a cell does DNA have to be copied?
cell reproduction
mitosis
gamete production
meiosis
when cells divide, they must duplicate DNA exactly for the new “daughter” cells
Why is this a good system?

5. But how is DNA copied? Replication of DNA
base pairing suggests that it will allow each side to serve as a template for a new strand

6. Models of DNA Replication
Can you design a nifty experiment to verify?
Models of DNA Replication
Alternative models
become experimental predictions
conservative
semiconservative
dispersive P 1 2

7. Five Steps of DNA Replication

8. Step 1:UNCOILS
Ladder unwinds a.
Replication Bubbles

9. a. Starts at each end of the bubble.
Step 2: (UNZIPS)
a. Starts at each end of the bubble.
b. the point where separation and replication begin is called a replication fork.
c. The enzyme Helicase breaks the Hydrogen bonds between the base pairs inside the replication bubbles.
d. DNA helicase: unwinds the strands
Replication forks
Replication bubble

10. Replication forks
In eukaryotes, the linear DNA has many replication forks
Remember: There are multiple replication bubbles along the DNA molecule

12. a. DNA polymerase Builds the new Strand toward the Replication fork.
Step 3: Nucleotides matching the bases exposed by the unwinding base pair with their match. DNA polymerase can direct base pairing and begin to build a new complementary strand according to the parent strand(template) a a.
DNA polymerase
Builds the new
Strand toward the
Replication fork. a

13. a.

14. They continue to grow until they join together
c. They continue to grow until they join together.
They continue to grow until they join together

15. phosphates does the new nucleotide have?
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C. How many
phosphates does the new
nucleotide have?
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16. d. Energy is released
When this bond is
broken.
Step 4: REZIP
This energy is used by to Ligase to seal the pieces together. Ligase
Re-establish the
Hydrogen bonds between the Nitrogen bases

17. They continue to grow until the join.
d. Now there are two molecules of DNA.
e. Each made of two strands composed of:
-one Original (parent) strand and
-one New (daughter) strand.
They continue to grow together and live happily.
They continue to grow until the join.

18. f. This is called semi-conservative replication

19. Step 5: (RECOIL) Now the 2 strands can wind back up.

20. a. Now the cell is ready for mitosis (cell division.)

21. b.

22. III. Chromosome/DNA Composition
A. Chromatin –a thread-like mass made of DNA and protein.
B. How is DNA able to fit into a cell?
DNA wraps around histones (round proteins)
Histones cluster to form bead-like structures called nucleosomes.
Nucleosomes wind DNA strand into compact structure.
2 chromatids (a single copy of DNA) make up a chromosome (contains 2 copies of DNA)
2 chromatids make up a chromosome
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Chromatin
Histones clustered into
Nucleosome core
DNA winds around nucleosome hi
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