August 11, 2015 Bell Work: Objective: The student will be able to… What are the four nitrogen bases found in DNA? Objective: The student will be able to… Build a model of DNA using puzzle pieces and class notes. Describe DNA replication by taking notes and using a model.

Today in History 2000 Pat Buchanan won the Reform Party presidential nomination. 2006 The Transportation Security Administration banned all liquids, gels and aerosols from passenger cabins on airliners one day after a thwarted terrorist attack.

DNA Model Build a model and answer the questions on the worksheet.

DNA Replication

DNA Replication The process of making a copy of DNA is called DNA replication Occurs during the S phase of the cell cycle

DNA Replication Step 1 The double helix unwinds using DNA helicases DNA helicases break the hydrogen bonds that link the complimentary nitrogen bases between the two strands. Once separated additional proteins attach and keep the strands apart (preventing them from assuming their double-helical shape)

DNA Replication Step 1 Step 2 Replication forks: the area where the double helix separates Step 2 Enzymes known as DNA polymerases move along each of the DNA strands Add nucleotides to the exposed nitrogen bases forming two new strands of DNA

DNA Replication Step 3 End product The process continues until all of the DNA has been copied and the polymerases are signaled to detach End product Two identical DNA molecules each composed of one new and one original strand

Checking for Errors Errors do occur during DNA replication DNA polymerases have a “proofreading” role This means that DNA polymerases can back track if they have mismatched nucleotides Reduces errors to about 1 per billion nucleotides

Rate of Replication DNA Replication does not begin on one end and end at the other Prokaryotes: two replication forks start at the same point and move away from each other until they have completely replicated the circular strand of DNA.

Rate of Replication In eukaryotic cells each chromosome is composed of a single long strand of DNA. There are multiple replication forks on each strand Each chromosomes is replicated in approximately 100 sections that are 100,000 sections long.

DNA Worksheet

Crash Course Biology

Ticket Out Explain why DNA replication is semi- conservative.