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.

He separated all organic compounds inside of the cells and found only the DNA caused

the disease.

*******Conclusion: DNA must be the hereditary material

Oswald Avery, 1944

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 ofSUGARS 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.

THE BASE PAIRING RULE:Adenine [A] always pairs with

Thymine [T]Guanine [G] always pairs with

Cytosine [C]

THE BIG PICTUREAll living things are made of cells...

onion root tip

THE BIG PICTUREEach individual cell has a

NUCLEUS, or at least a NUCLEAR REGION...

nucleus

THE BIG PICTUREEach cell’s nucleus contains the

CHROMATIN...

THE BIG PICTUREThe chromatin is composed of

deoxyribonucleic acid, or DNA...

chromatinDNA

THE BIG PICTUREDNA is composed of a deoxyribose

sugars, phosphates, and paired nitrogenous bases...

Sugar-phosphate backbone

Nitrogenous base pairs

THE BIG PICTUREThe nitrogenous bases match up according to the BASE PAIRING

RULE,A goes with T and C goes with G