January 6, 2017 Objective: To be able to explain and model how DNA replicates To describe how the structure of DNA relates to how it replicates Journal: Draw a nucleotide and label it’s three parts.
DNA Replication
Replication Process by which DNA makes an exact copy of itself Results in 2 identical DNA molecules
Discussion Question Turn to someone next to you and come up with an answer to the following question. Why would an organism want two identical molecules of DNA?
Why replication?? Copies the genetic code Allow new cells to have exactly the same genetic info as old cells This is how traits are passed on Can be used to make new cells
Sites of Replication Specific nucleotide sequences called origins of replication are required to be present for DNA replication to begin There can be many origins of replication along same DNA strand Speeds up the process
How does replication work? Step 1:An enzyme called DNA helicase unwinds the DNA by breaking the hydrogen bonds between the nitrogen bases Forms a replication fork
How Replication Works Step 2: Single Stranded Binding Proteins keep the DNA strands apart
How Replication Works Step 3: An enzyme called DNA polymerase then matches up complementary DNA nucleotides with the nucleotides on the old DNA strand continuously in a 5’ to 3’ direction. This is called the leading strand
How Replication Works Step 4: The other DNA strand, the lagging strand, still has nucleotides added to it by DNA polymerase, but they have to add in short strands called Okazaki fragments since the lagging strand goes in the 3’ to 5’ direction
How Replication Works Step 5: DNA ligase connects the Okazaki fragments together
How Replication Works Step 6: DNA polymerase then bonds the sugar and the phosphate from each nucleotide together forming a complete strand of DNA
How Replication Works Results: Each new DNA strand contains ½ of the original strand and ½ new nucleotides This is known as semiconservative because each strand has half the old strand.
Crash Course Video https://www.youtube.com/watch?v=8kK2zwjRV0M