1. DNA Replication

2. Let’s review DNA!

3. Watson & Crick called the structure of DNA a …..
Double Helix

4. DNA is a polymer made up of many monomers called…
Nucleotides

5. Each nucleotide is made up of what three parts?
O -P O O
Deoxyribose C O
Nitrogenous
base
Phosphate C C C

6. Chargraff’s base pair rule states that…
Adenine always pairs with …..
Thymine
Guanine always pairs with …..
Cytosine

7. According to the Base-Pairing Rule, we can determine the complementary strand of DNA.
For example:
A T C C A G T A G G T C

8. You practice base-pairing rule!
Figure out the complementary DNA strand:
A T T C G C A T
T A A G C G T A

9. G G C A A C T T C C G T T G A A One more!
Figure out the complementary DNA strand:
G G C A A C T T
C C G T T G A A

10. Some Facts DNA has to be copied before a cell divides
DNA is copied during the S or synthesis phase of interphase
New cells will need identical DNA strands
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11. Synthesis Phase (S phase)
S phase during interphase of the cell cycle
Mitosis
-prophase
-metaphase
-anaphase
-telophase G1 G2 S
phase
interphase
DNA replication takes
place in the S phase.
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12. Replication: the process of copying DNA to produce new molecules with the same base sequence.

13. Read Handout Read the steps of DNA replication.
Fill in the complementary bases.

14. Replication Step 1: DNA unwinds
The enzyme Helicase “unzips” and separates the 2 strands.
Hydrogen bonds are broken between bases.

15. DNA Replication
The sites where separation and replication occur are called replication forks.
Replication
Fork
Parental DNA Molecule 3’ 5’
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16. An enzyme unwinds the DNA strands.
Talk about the hydrogen bond. 2 strands of nucleotides. 16

17. Replication Step 2: New bases are added
Each strand serves as a template
The enzyme DNA Polymerase adds new nitrogen bases.
DNA Polymerase proofreads it.

18. Antiparallel Strands One strand of DNA goes from 5’ to 3‘
The other strand is opposite in direction going 3’ to 5’
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19. Notice that the 3’ and 5’ refer to a numbering system for the carbon atoms that make up the sugar.
DNA Nucleotide

20. Base Pairing Rule Watson and Crick showed that DNA is a double helix
A (adenine) pairs with T (thymine)
C (cytosine) pairs with G (guanine)

21. Anti-Parallel Strands of DNA
On the left is the DNA double helix. When the helix is unwound, a ladder configuration shows that the uprights are composed of sugar and phosphate molecules and the rungs are complementary bases. Notice that the bases in DNA pair in such a way that the phosphate-sugar groups are oriented in different directions. This means that the strands of DNA end up running antiparallel to one another, with the 3’ end of one strand opposite the 5’ end of the other strand.

22. Direction of Replication
DNA Replication
DNA polymerase can only add nucleotides to the 3’ end of the DNA
This causes the NEW strand to be built in a 5’ to 3’ direction
RNA
Primer
DNA Polymerase
Nucleotide 5’ 3’
Direction of Replication
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24. More enzymes add complimentary bases
Talk about the hydrogen bond. 2 strands of nucleotides. 24

25. DNA Replication Original strand New Strand Nitrogen Bases Growth
During DNA replication, the DNA molecule produces two new complementary strands. Each strand of the double helix of DNA serves as a template for the new strand.
Replication Fork
Replication Fork
DNA Polymerase
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26. End result:
2 new identical DNA molecules

27. DNA replication is “semi-conservative”.

28. Modeling Replication