1. 2. What does “semi-conservative” mean?
DNA Replication
Critical Questions: 1. Describe the difference between the leading and lagging strands in DNA Replication?
2. What does “semi-conservative” mean?

2. Cells constantly divide to replace old cells
Cell Lifespans:
Small intestine – 2 to 4 days
Stomach – 2 to 9 days
Lung (sacs) – 8 days
Bone cells – 2 weeks
Skin cells – days
Red Blood cells – 4 months
Nerves – never (lifetime)
Female (eggs) – never (lifetime)

3. Purpose of DNA Replication
It is crucial both cells receive the exact amount of DNA when dividing to ensure the cell will function properly
Replication ensures both cells receive the same amount of Chromosomes

4. How does Replication ensure this?
By being semi-conservative
DNA replicates in a semi-conservative 
process, which means
one strand of the parent DNA Molecule is re-used or “conserved” as a template for the new DNA Strand
It’s a helix or B sheet within a single region. Can have both in one protein but a specific region is one or another

5. Steps to DNA Replication
DNA is untwisted in specific places
Helicase unzips the DNA strand at the replication fork
Providing a template for the new DNA strands
Primase primes the DNA strand
DNA Polymerase matches the complimentary bases from 5’ to 3’ direction continuously (leading strand)
Primase primes the 3’ to 5’ strand in small sections of the (lagging strand)
DNA Replication Video

6. DNA Replication Continued
(Continued) DNA Polymerase begins pairing short rows of complimentary bases
These two steps repeat until the lagging strand is finished
Exonuclease removes the primers in the lagging strand and
DNA Polymerase II fills in the gaps left behind
Finally DNA Ligase seals the fragmented pieces

7. Answer your critical questions
1. Describe the difference between the leading and lagging strands in DNA Replication?
2. What does “semi-conservative” mean?

8. Complete the diagram and write a summary/function next to each box
Leading Strand
Lagging Strand
Replication Fork
Ligase
DNA Polymerase
Exonucleus
Helicase
Primase
Primed

9. Exit Ticket What is the purpose of DNA Replication?
How many strands of DNA are in one molecule?
In your own words, summarize the 8 steps in DNA Replication