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Biology: Life on Earth

Chapter 9DNA: The Molecule of Heredity

and holds the Genetic Code

Watson & Crick

Wilkins Franklin

Scientists who discovered

structure of DNA 1953

X-ray diffraction

The 4 Nucleotides of DNANitrogen base order is the code for genes Purines Pyrimidines

4Watson-Crick modelof DNA Double Helix

Hydrogen bonds between complementary nitrogen base pairs

Covalent bonds between phosphates & deoxyribose sugars

DNA Replication in Nucleus

Both strands of helix used as template

http://www.youtube.com/watch?v=AGUuX4PGlCc

is Semiconservative

DNA Helicase:DNA Helicase: unwinds unwinds DNA by breaking H DNA by breaking H

bonds between basesbonds between bases

DNA polymerase:DNA polymerase: adds adds loose complementary loose complementary nucleotides to growing nucleotides to growing

strandsstrands

DNA ligase:DNA ligase: connects connects short strands togethershort strands together

Proofreading/Repair Proofreading/Repair enzymes:enzymes: from 1/10,000 from 1/10,000

to 1/billion mistakesto 1/billion mistakes

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Mutation: permanent

change in DNA base sequence

Mutation in gamete is inherited

Werner Syndrome

Mutation in DNA replication enzyme

Causes errors/mutations to accumulate rapidly

Ancient DNA – 100 million year old Biting Midge preserved in amber