DNA: Deoxyribonucleic acid What is the structure of DNA, and how does it function in genetic inheritance?

Do Now How does your DNA relate to heredity or inheritance?

Thomas Hunt Morgan Researched fruit flies Provided evidence for: –Chromosomal theory of inheritance –Genetic linkage –Crossing over –Non-disjunction

Fredrick Griffith Studied 2 strains of bacteria –Causes pneumonia (S) –Not harmful (R) Goal: Examine how genes work & what they are made of.

Griffith’s Experiment Conclusion: An unknown molecule from the S cells (pneumonia) had transformed the R cells (harmless) into S cells. What was this molecule?

Oswald Avery Took a mixture of molecules from heat killed bacteria Treated this mixture to destroy proteins, lipids, carbohydrates and RNA – one at a time. –Transformation STILL occurred. Treated the mixture to destroy DNA –No transformation occurred. Conclusion: DNA was the transforming molecule that stores and passes genetic information from one generation of bacteria to the next.

Bacterial Viruses – Hershey & Chase Bacteriophage: virus that infects bacteria by injecting its genetic information Hershey and Chase wanted to find out which part of the virus infected the bacteria: –Protein coat or DNA?

Hershey & Chase Experiment Conclusion: DNA is injected into bacterium not protein coat.

The Role of DNA Stores information – main job Copies information Transmits information

Structure of DNA DNA is a nucleic acid made up of nucleotides joined into long strands/chains by covalent bonds. A nucleotide consists of deoxyribose (5-carbon sugar), a phosphate group and a nitrogenous base. Nitrogenous bases are bases that contain nitrogen. There are 4 types of nitrogenous bases in DNA: –Adenine (A), guanine (G) – purines (2 rings) –cytosine (C) and thymine (T) – pyrimidines (1 ring)

Nucleotide Covalent Bond

Chargaff’s Rule – led to base pairing Edwin Chargaff discovered: –% A = % T –% G = % C Called Chargaff’s Rule

Franklin’s X-Rays Rosalind Franklin used X-ray diffraction to get a picture of DNA’s structure. Showed the strands of DNA twisted around each other in a helix. Suggested nitrogenous bases were in the center of the DNA molecule.

James Watson & Francis Crick Studied structure and built models of DNA Credited with discovering the complete structure of DNA. –Franklin’s X-ray diffraction was missing piece.

DO NOW LOOK IN YOUR DNA GUIDED NOTES!! –What are the 3 roles of DNA? –Briefly explain each role.

Double Helix Model Double helix = twisted ladder Anti-parallel strands – two strands run in opposite directions Hydrogen bonding – holds base pairs together Base pairing –A with T (2 H bonds) –C with G (3 H bonds)

DNA Replication The process in which DNA is duplicated or copied Why does DNA need to replicate itself? –Because all cells need a full set of DNA which consists of 46 chromosomes…with one exception which is??? –Sex cells which have 23 chromosomes

The Enzymes of DNA Replication Helicase – unzips or separates strands of DNA DNA polymerase – joins individual nucleotides to produce a new strand of DNA Telomerase - helps replicate DNA at telomeres, ends of the chromosome, and ensures no genes are damaged or lost

DNA Replication – Step 1 2 strands of DNA separate or “unzip” Forms two replication forks DNA replication can happen at multiple points on a strand of DNA

DNA Replication – Step 2 A new, complimentary strand begins to form –What do we mean by complimentary? One nucleotide is added at a time –Nucleotides joined by covalent bonds created by DNA polymerase

DNA Replication – Step 3 Telomerase synthesizes the end of the new DNA strands Results: –Two new DNA molecules are created that are identical to the first. –Semiconservative replication – ½ of the original strand & ½ new strand

Telomeres Repeating sequence of DNA that occurs at the end of the chromosome, difficult to replicate Protects DNA (cap) and signals end of chromosome Problem! –Telomeres shorten w/ each replication –Causes replicative aging –In some cells telomerase = key to making sure telomeres do not deteriorate –Hayflick limit - a limit to how many times they will divide before apoptosis