Chapter 12- DNA BIG IDEA: What is the structure of DNA, and how does it function in genetic inheritance?

12.1 Identifying the Substance of Genes -Scientists were looking for the molecule that controls heredity. -Frederick Griffith wanted to know how bacteria made people sick. Isolated “R” and “S” bacteria strains S- smooth, disease carrying R- rough, harmless

Griffith cntd’ Performed 4 experiments on mice S strain → Mouse dies R strain → Mouse lives Heat-killed S strain → Mouse lives Mixture of Heat-killed S and R → Mouse dies. Discovered that the bacteria in the last experiment had transformed into the S strain.

Somehow the heat killed S strain passed their disease causing abilities to the live R strain. Griffith concluded that the transforming factor must be a gene

Oswald Avery and a team of scientists repeated Griffith’s experiments To find what molecule caused transformations they treated the mixtures w/ enzymes that killed proteins, lipids, carbohydrates, RNA, and then DNA. -Occured in all except one w/ DNA killed Avery and his team discovered that DNA stores and transmits genetic info. from generation to generation

Hershey-Chase experiment -Wanted to confirm that DNA was the genetic molecule, not protein. Tagged viruses w/ radioactive isotopes to make them glow. -S isotope made just protein coat on viruses glow, P isotope only made DNA glow. Virus w/ DNA tag glowed. Hershey and Chase confirmed that DNA is the genetic material in all living things so if the baceritophage w/ S glow (only proteins have sulfur, DNA does not, then it would tell us that proteins are the genetic molecule. If bacteriophage w/ P glow that means that DNA is the molecule of heredity.

DNA stores, copies, and transmits genetic info. in a cell. Stores info. needed by every living cell Before cell division, genetic info. must be copied After cell division the daughter cell needs a complete copy of genetic info.

12.2 Structure of DNA DNA is a nucleic acid made of nucleotides joined by covalent bonds. Each “Nucleotide”is like ½ the zipper; containing 5-C-sugar, Phosphate group, and nitrogenous base

-This is Chargaff’s Rule Nitrogenous bases: Adenine (A), Thymine (T), Cytosine (C), and Guanine (G) % of A=T, and % of C=G %A+%T+%C+%G= 100% -This is Chargaff’s Rule -look @ pg. 335 draw a picture labeling the nitrogenous bases held together by covalent bonds, sugar/ phosphate backbone

Rosalind Franklin studied the structure of DNA through x ray diffraction. Clues from Franklin’s work enabled Watson and Crick to build a model of DNA

Double-helix explains Chargaff’s rule. DNA strands are “Anti-parallel”, meaning they run opposite directions. They are held together by H bonds.

12.3 DNA Replication Replication is the process by which DNA copies itself before cell division. -Strands separate, and each old strand serves as a template for the new strand to form. produces 2 new strands that are complementary to the original strand by following the rules of base-pairing.

Old strand= ATTCGATGGTA New strand= Old strand= CATGATTACA *Remember base pairs: C-G, A-T

Replication fork is the site where the 2 strands of DNA separate to undergo replication The enzyme DNA polymerase joins the individual nucleotides to produce a new strand of DNA. It also proofreads new strand.

Telomeres are DNA at the tips of chromosomes Telomeres are DNA at the tips of chromosomes. They are difficult to replicate and they prevent genes from being lost or damaged during replication

Comparing replication Prokaryotic 1 starting point proceeds in 2 directions. Eukaryotic Dozens- hundreds of starting points Proceeds in both directions at each point