 Double helix  Nucleotide  Semiconservative replication  DNA polymerase  Chromatin

 Deoxyribonucleic acid (DNA) is a nucleic acid  Composed of two strands of DNA  Shape is a DOUBLE HELIX  Twisted ladder shape formed by two strands of DNA twisted around each other

 DNA made up of subunits called NUCLEOTIDES  Building blocks of nucleic acids  Three parts of every DNA nucleotide a five-sided sugar (deoxyribose) a phosphate group a nitrogen base phosphate group deoxyribose Nitrogen base deoxyribose phosphate group Nitrogen base

 Four nitrogenous bases  Adenine (A)  Thymine (T)  Guanine (G)  Cytosine (C)  Sugar and phosphate group stay the same, nitro base changes  Nitro bases form base pairs  A-T  G-C  Chargaff’s Rule states that the amount of each G=C and A=T

 Sugar and phosphate form “backbone” of DNA and nitro bases form rungs of the ladder  Hydrogen bonds join the bases in the center  Strands run in opposite directions (antiparallel)  One runs 3’- 5’, other 5’- 3’

 SEMICONSERVATIVE REPLICATION: Parental strands of DNA separate, serve as templates, and produce DNA molecules that have one strand of parental DNA and one new strand  DNA unwound and unzipped by enzymes, exposing the genetic code  Forms a replication fork

 DNA POLYMERASE: Enzyme responsible for adding appropriate nucleotides to the growing strands of DNA  Enzyme reads A, places T opposite it  Forms complimentary strands on parent strands Complimentary means opposite

 For eukaryotes, multiple replication sites on DNA  We have multiple strands of DNA that is open-ended, having a definite beginning and end  For prokaryotes, which have a circular chromosome, one replication site

 CHROMATIN: Relaxed form of DNA in the nucleus  DNA is wrapped around a protein at multiple sites  Chromatin condenses to form a chromosome  From unpacked to packed  DNA  Chromatin (DNA + protein)  Chromosome

 Why “move”?  Used for cell growth, replacement, and sexual reproduction  Ensures that all cells receive the exact amount of chromosomes  DNA itself is the “instructions for proteins”

 Rosalind Franklin, 1951  Took an x-ray diffraction photo of DNA molecule to understand it’s structure The Discovery of DNA

 James Watson and Francis Crick, 1953  Published a paper stating that the structure of DNA was a DOUBLE HELIX  Used Rosalind’s image to discover shape  Won Nobel prize

 When do we need new cells? Why would DNA need to be replicated?  What are the three parts of every nucleotide? What makes DNA nucleotides different from each other?  What is the name of the sugar in a DNA nucleotide?  Form a complimentary strand for the following parent strands: 1. ACGTTACCCCCATGGATG 2. CCTGACTTTACTTGGAAC  Why is DNA packed so tightly?

 How is a prokaryotic chromosome different from a eukaryotic chromosome?  In your own words, explain Chargaff’s rule.  Describe the structure of DNA using the appropriate terms.