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DNA Review. What does DNA store that is important? If a DNA strand read 3’ AGT-CCG-GTA 5’ what would the complementary strand read? What holds the nitrogen bases together? What are the 3 components of a nucleotide?. Genetic information in its sequence of nitrogen bases. 5’ TCA-GGC-CAT 3’. - PowerPoint PPT Presentation
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DNA Review• What does DNA store that is important?
• If a DNA strand read 3’ AGT-CCG-GTA 5’ what would the complementary strand read?
• What holds the nitrogen bases together?
• What are the 3 components of a nucleotide?
Genetic information in its sequence of nitrogen bases
5’ TCA-GGC-CAT 3’
Hydrogen bonds
Sugar, phosphate group, and nitrogen base
DNA Replication• DNA replication- the process of making a copy
of DNA1 DNA molecule 2 identical DNA molecules
• Why is this important?– cells need to copy their DNA before the cells divide in
mitosis (growth, repair, and maintenance)
• Where does DNA replication occur?– in the nucleus (because DNA is found in the
nucleus in eukaryotic cells)
DNA Replication
Summary of what we will learnThere are three steps to DNA replication:
1) helicase unwinds the double helix opens the strand by breaking the hydrogen bonds between the bases
2) DNA polymerases add nucleotides in a 5’ to 3’ direction, moving TOWARD the replication fork
3) DNA polymerases detach once replication is complete and you end with 2 identical molecules of DNA, each made of one old strand and one new strand
DNA ReplicationStep 1:the double helix must unwind before
replication can begin.then the DNA “unzips”
DNA helicase is an enzyme that opens the double helix by breaking the hydrogen bonds that hold the complementary bases together (think of a zipper)
enzymes end in (-ase)
DNA ReplicationStep 1 con’t:once separated,
additional proteins hold the strands apart
the place where the double helix splits is called the replication fork (it’s Y-shaped)
DNA ReplicationStep 2:at the replication fork, enzymes called DNA
polymerases move along each of the DNA strands
DNA polymerases add nucleotides to the 3’ end exposed bases according to the base pairing rules
DNA Replication• The overall direction of adding
nucleotides is toward the replication fork– goes from 5’ to 3’
DNA Replication
Step 3:step 2 continues until all
DNA has been copied and the polymerases detach
produces 2 DNA molecules that are identical to each other
DNA Replication-is semiconservative
- semi – half- conserve – to save
DNA Replication• Semiconservative:– This means that every double stranded molecule
of DNA has one strand that is from the “old” DNA and one strand is “new”
Summary
• DNA unwinds & unzips using helicase• DNA polymerases add nucleotides to the 3’ end
of the strands, moving toward the replication fork (5’ 3’)
• 2 new strands of DNA are made that are identical to the original strands and to each other
• The process is semiconservative
