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? 2006-2007

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 – 10-30 days Red Blood cells – 4 months Nerves – never (lifetime) Female (eggs) – never (lifetime)

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

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

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) https://www.youtube.com/watch?v=TNKWgcFPHqw DNA Replication Video

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

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

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

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