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DNA Replication

DNA Replication. How Long Does It Take?. Bacteria (E. Coli) has a single chromosome, about 5 million base pairs. It Can replicate in less than an hour! Your cells have 46 chromosomes, about 6 billion base pairs.

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DNA Replication

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  1. DNA Replication

  2. How Long Does It Take? • Bacteria (E. Coli) has a single chromosome, about 5 million base pairs. • It Can replicate in less than an hour! • Your cells have 46 chromosomes, about 6 billion base pairs. • If the code ATCG was typed for the human genome, it would fill about 900 biology text books. • Can replicate in just a few hours!

  3. What is the Purpose? • To make a copy of DNA before mitosis (cell division) for growth and repair.

  4. Basic Steps Parent molecule Two DNA molecules one “old” strand and one “new” strand. both identical to the parent molecule. Two complementary strands serving as templates

  5. A large team of enzymes help out! So How Does it Happen?

  6. Replication bubbles form by enzyme, helicase recognizing specific site to start copying. Helicase breaks the H bonds between the N bases. Eukaryotes form multiple bubbles (100’s to 1000’s) or origins of replication to speed up copying. New strands are elongated at the replication fork in both directions. Step One – Origin of Replication

  7. Another enzyme, DNA Polymerase helps to attach the new nucleotides as they align with their base pair. Q: Where do the new nucleotides come from? A: In surrounding medium from break down of food and other molecules. Step Two – Elongating a New Strand

  8. Leading strand elongates continuously towards the replication fork. Lagging strand (Okazaki fragments) elongate in pieces away from the replication fork Enzyme, DNA ligase attaches the fragments. Elongates in Two Directions

  9. The two strands of the parental molecule separate, and each function as a template for the synthesis of a new complementary strand. Two full molecules are constructed – each having one strand old and one strand new. Semiconservative literally means “part is saved”. Semiconservative Model

  10. Do mistakes Occur? • Replication is very speedy and surprisingly very accurate due to proof reading enzymes. • Errors can occur every 1 in 10,000 base pairs. • After proof reading enzymes, errors are reduced to only 1 in a billion bases. • Q: What does a mistake equate to? • A: Mutation. Small changes can add up over time which is why we study evolution (living things changing over time)

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