2/4/2016 DN History James WSON and Francis RIK were the first to discover the true structure of the DN molecule in 1953 Why would someone want to make a mouse glow? What is DN? Video Double Helix DN History Rosalind Franklin Used X-ray diffraction to study structure of DN Photograph suggested two strands with bases near the center It indicated that DN was a helix. oworker (Maurice Wilkins) showed the photographs to Watson and rick w/o her consent. DN History lfred Hershey and Martha hase 1952 Studied viruses (bacteriophages) Used radioactive markers oncluded genetic material of virus was DN not protein. 1
2/4/2016 DN Structure 8.2 DN Structure DN stands for DEOXYRIBONULEI ID It s a type of nucleic acid What chromosomes (genes) are made of DN consists of two strands that are arranged in a twisted ladder structure called a DOUBLE HELIX DN Structure DN Structure DN is made up of long chains of NULEOIDES Double Helix Structure Each nucleotide consists of a: 1. PHOSPHE ROUP 2. SUR (called deoxyribose in DN) 3. NIROEN BSE Phosphate D Nitrogenous Base he backbone (outer stand) of DN is made up of PHOSPHE and SUR he inner rungs of DN is made up of BSES. Sugar 2
denine ytosine DN Structure here are 4 types of nitrogen bases: hymine uanine Each base will only bond with one other specific base Erwin hargaff: Discovered that the percentages of the nitrogenous bases were similar Rule #1: hargaff s Rules of Base-Pairing he number of is always equal to the number of therefore, bonds with Rule #2: he number of is always equal to the number of therefore, bonds with DN Structure hargaff s Rules of Base-Pairing Example DN is omplementary If a DN molecule contains 20% adenine, how much (%) thymine should it contain? 20% thymine How much (%) cytosine & guanine? omplementary: bases on one strand match up with the bases on the other strand (- and -) Example: Strand 1-30 % cytosine 30 % guanine 3
ry this out.. What sequence of bases would pair with the sequence? DN Replication Example 1.. Original DN: omplementary DN: B. Make identical strands of DN (original) (new) (new) (compl. From 1) DN Structure he backbone is connected by covalent bonds. HYDROEN BONDS between the bases hold the two strands of DN together hydrogen bond ovalent bond 4
DN Function DN Function he primary function of DN is to SORE and RNSMI genetic INFO Protein a ene is read to code for a protein DN is the master copy of an organism s information code. DN contains your genetic information (what you look like). rait proteins function in certain ways to create your traits Eye color gene Dimples gene Hair color gene DN Replication 8.3 Replication is the process in which DN copies itself. Remember: DN replicates once every cell cycle in the (S phase). Proteins (enzymes) carry out the process of replication he original DN strand is used as a template to build 2 identical copies of DN. Watch DN Replication 5
Process of DN Replication 1. Enzymes unzip the double helix. Free-floating nucleotides form hydrogen bonds with the template strand. Process of DN Replication 2. DN polymerase enzymes bond the free-floating nucleotides to the original DN strand. nucleotide new strand nucleotide he DN molecule unzips in both directions. DN polymerase Process of DN Replication 3. wo new molecules of DN are formed, each with one new strand and one old strand. herefore, DN replication is semiconservative. original strand new strand Process of DN Replication Replication is fast and accurate. Occurs at hundreds of origins of replication along a chromosome wo molecules of DN DN polymerase proofreads the new strand and removes any incorrect nucleotides and replaces them with correct ones DN Replication Video 6
Where does DN replication take place? DN Replication nimations In Eukaryotes, DN replicates in the nucleus In Prokaryotes, DN replicates in the cytoplasm Replication lasszone ry this Out! 1. What does "semiconservative replication" mean? 2. What is the goal of DN replication? 3. What is the function of DN polymerase? 4. What feature of replication ensures that DN is copied quickly? 5. How does a cell ensure that no errors are introduced during replication? 7