2. Which organelle is this structure located in? 1. What structure carries genetic information from generation to generation? 2. Which organelle is this structure located in? 3. How long do you think it has taken to discover DNA and its structure? Do you think one person is responsible for the discovery?

DNA is the GENETIC or HEREDITARY material. In other words, DNA is what gets “passed down” to future generations that causes us to have many of the traits we have.

Many important scientists contributed to the discoveries:

Gregor Mendel “Father of Genetics” (1822-1884) Famous experiments with pea plants that explained patterns of inheritance Two “units” of information- one from each parent First scientist to acknowledge material for heredity

Frederick Griffith 1928 Fred was trying to find a vaccine against pneumonia, but instead made a breakthrough in world of heredity. Frederick experimented with pneumonia in mice and found that a hereditary material caused pneumonia.

Determined which molecules in cells caused pneumonia to occur. Oswald Avery, 1944 Determined which molecules in cells caused pneumonia to occur. He separated all organic compounds inside of the cells and found only the DNA caused the disease. *******Conclusion: DNA must be the hereditary material

Alfred Hershey & Martha Chase, 1952 Skeptical of other scientists’ experiments Wanted to be sure DNA was hereditary material

Rosalind Franklin, 1952 Studied structure of many microscopic viruses and cellular structures Researched DNA – used X-RAY Diffraction to show shape of DNA= helical w/ 2 strands. Rosalind’s lab work was stolen

James Watson & Francis Crick, 1953

Watson and Crick’s model of DNA was a DOUBLE HELIX, in which two strands were wound around each other.

The sides of the DNA “ladder” are made of SUGARS and PHOSPHATES. So, DNA is said to have a SUGAR-PHOSPHATE BACKBONE.

The rungs of the DNA “ladder” are made of a sequence of four chemicals called NITROGENOUS BASES.

Erwin Chargaff, in the early 1900s, discovered that certain chemicals in all DNA seemed to be present in almost EQUAL amounts.

ADENINE and THYMINE were always present in equal amounts. GUANINE and CYTOSINE were always present in equal amounts.

Adenine [A] always pairs with Thymine [T] THE BASE PAIRING RULE: Adenine [A] always pairs with Thymine [T] Guanine [G] always pairs with Cytosine [C]

All living things are made of cells... THE BIG PICTURE All living things are made of cells... onion root tip

Each individual cell has a NUCLEUS, or at least a NUCLEAR REGION... THE BIG PICTURE Each individual cell has a NUCLEUS, or at least a NUCLEAR REGION... nucleus

Each cell’s nucleus contains the CHROMATIN... THE BIG PICTURE Each cell’s nucleus contains the CHROMATIN...

The chromatin is composed of deoxyribonucleic acid, or DNA... THE BIG PICTURE The chromatin is composed of deoxyribonucleic acid, or DNA... chromatin DNA

THE BIG PICTURE DNA is composed of a deoxyribose sugars, phosphates, and paired nitrogenous bases... Sugar-phosphate backbone Nitrogenous base pairs

The nitrogenous bases match up according to the BASE PAIRING RULE, THE BIG PICTURE The nitrogenous bases match up according to the BASE PAIRING RULE, A goes with T and C goes with G