1. Chapter 9.3
Grade 10 Biology
Spring 2011
The Replication of DNA

2. Bell Ringer
DNA is considered to be a relatively stable molecule. What gives DNA this stability, even though the hydrogen bonds between the nitrogen bases are easily broken?

3. Bell Ringer: Answer
The bonds connecting the deoxyribose sugar and phosphate groups, which form the backbone of DNA, are covalently bonded. Covalent bonds are strong and keep strands of nucleotides intact.

4. Activity Divide into groups
Each group will outline one of the three steps of DNA replication
Include:
Description of step
Key terms
Diagram that is labeled

5. Objectives Summarize the process of DNA replication
Describe how errors are corrected during DNA replication
Compare the number of replication forks in prokaryotic and eukaryotic DNA

6. Roles of Enzymes in DNA Replication
Complementary relationship between sequences of nucleotides
Predicted complementary relationship used as basis to make exact copies of DNA
One DNA strand serves as a template (pattern) on which the other strand is built

7. Roles of Enzymes in DNA Replication
DNA replication: the process of making a copy of DNA
Replication occurs during S phase of the cell cycle, before a cell divides
Fig. 9 page 198

8. Roles of Enzymes in DNA Replication
Step #1 in DNA Replication:
Double helix unwinds
Unwinds with help of enzyme DNA helicase
DNA helicase: opens the double helix by breaking the hydrogen bond that link the complementary nitrogen bases between the two strands

9. Roles of Enzymes in DNA Replication

10. Roles of Enzymes in DNA Replication
Step #1 in DNA Replication:
Once strands are separated, proteins attach to each strand to hold them apart
Replication Fork: areas where double helix separates
Y shape

11. Roles of Enzymes in DNA Replication
Step #2 in DNA Replication:
At the replication fork, DNA polymerase enzymes move along each of the DNA strands
DNA polymerase: adds nucleotides to the exposed nitrogen bases
Follows base-pairing rules
Two new double helixes are being formed

12. Roles of Enzymes in DNA Replication
Step #3 in DNA Replication:
All DNA is copied
Polymerase is signaled to detach
Produces 2 DNA molecules
Each DNA molecule is composed of a new and an original strand of DNA
Nucleotide sequence is identical in both strands and identical to original DNA molecule

13. Checking for Errors Wrong nucleotides can be added when copying DNA
DNA polymerase: has proofreading ability
Adds nucleotides to growing strand only if the previous nucleotide is correctly paired to its complementary base
If paired wrong, DNA polymerase can backtrack and fix it

14. DNA Polymerase Proofreading

15. The Rate of Replication
Prokaryotes:
Circular DNA molecule
Usually has 2 replication forks that begin at single point
Replication forks move away from each other until they meet

16. The Rate of Replication
Eukaryotes:
Chromosomes contain a single, long strand of DNA
Each human chromosome is replicated in about 100 sections that are 100,000 nucleotides long
Each section has its own starting point
Multiple replication
forks
Speeds up
replication
(about 8 hours in humans)

17. Review Watch this video for a quick review of DNA replication!