DNA: History and Structure

Rosalind Franklin First person to view DNA (using X-Ray) Images showed that DNA is composed of twisted fibers with large groups of molecules spaced at regular intervals.

Watson and Crick Built first 3-D model of DNA (used Franklin’s X-Ray) Identified the shape of DNA as a double helix/spiral. Identified how bases pair.

Nobel Prizes Awarded to Watson, Crick, and Wilkins (Franklin’s assistant). Franklin did not receive the award because she had died.

Nucleotides DNA is made of nucleotides Each nucleotide has three parts. a phosphate group a deoxyribose sugar a nitrogenous base If the DNA in one person was laid in a straight line, it would stretch to the sun and back over 300 times (or around the equator 2.5 million times) phosphate group deoxyribose (sugar) nitrogen base

Structure of DNA Shape is a double helix (twisted ladder) Backbone (sides) are made of alternating deoxyribose (sugar) and phosphate molecules. “rungs” are made of nitrogen bases. Bases attach to deoxyribose.

Nitrogenous Bases Pyrimidines Purines Double ring structure Adenine (A) Guanine (G) Pyrimidines Single ring structure Thymine (T) Cytosine (C)

How Bases Pair A always pairs with T C always pairs with G If the genome was a book, it would be the equivalent of 800 dictionaries. It would take a person typing 60 words per minute, eight hours a day, around 50 years to type this. C G T A