DNA

A Few Questions What organelle is known at the “control center” of the cell? Nucleus What structures are found in the nucleus? Chromosomes What are located on chromosomes? Genes

A Few More What are chromosomes composed of? DNA How do genes and chromosomes control the activity of a cell? By producing proteins that regulate cellular functions.

DNA Components & Structure Long molecule made of nucleotides Nucleotides: 5-carbon sugar, a phosphate, & nitrogenous base Four kinds of nitrogenous bases

Types of Bases in DNA Two types of bases: pyrimidines and purines. Pyrimidines: Cytosine (C) & Thymine (T) Purines: Adenine (A) & Guanine (G) These bases carry the genetic code.

Base Pairing Chargaff discovered that DNA molecules contain equal numbers of G&C bases and A&T bases. A always pairs with T G always pairs with C

Rosalind Franklin Used X-ray evidence to get information about DNA’s structure. The strands of DNA are twisted around each other, in a helix. The bases are near the center of the molecule.

Franklin

Watson & Crick With the use of Franklin’s work, they developed a structured model. The model was a double helix, in which two strand were wound around each other. The model explained how DNA could carry information, and how it could be copied.

Watson & Crick

Double Helix Looks like a twisted ladder or a spiral stair case. Hydrogen bonds hold the two strand together.