DNA 11292010 What is DNA DNA stands for

DNA! 11/29/2010

What is DNA? • DNA stands for deoxyribonucleic acid. • It holds all of our cell’s information and is located in the nucleus of the cell.

What do we already know about DNA? • It is a macromolecule known as a nucleic acid. • The monomer of a nucleic acid is a nucleotide. • What are three parts of a nucleotide? • 1. Phosphate group • 2. Sugar (deoxyribose) • 3. Nitrogen base

A Nucleotide! Draw and label this!!

Nitrogen bases • The nitrogen base can either be a purine or a pyrimidine. • How many carbon rings does each have?

Nitrogen bases in DNA • DNA has four different nitrogen bases (two purines and two pyrimidines). • The nitrogen bases are: • A is for Adenine • G is for Guanine • C is for Cytosine • T is for Thymine Adenine and Guanine are purines. Cytosine and Thymine are pyrimidines.

Nitrogen bases in DNA

What is DNA’s structure? • Two scientists, Watson and Crick, discovered the structure of DNA and published an article about it in 1953. They didn’t work alone though!

Rosalind Franklin • Rosalind Franklin was a female scientist working with DNA. • She took a x-ray crystallographic of DNA which revealed its structure in 1952. • From her photo, Watson and Crick saw that DNA was a double-helix.

Chargaff • Erwin Chargaff did research on the nitrogen bases of DNA after World War II (when was WWII over? 1945) • He conducted research on many different species and published information on the percentages of each nitrogen base found in DNA. • This helped Watson and Crick determine what bases formed hydrogen bonds with each other.

Rosalind’s x-ray crystallographic

DNA’s Ladder-like Structure • A double-helix has two strands of DNA with bonds in the middle like the rungs of a ladder. • Each nitrogen base bonds with another base to form these rungs. • A bond between two purines would be too wide. • A bond between two pyrimidines would be too narrow. • THUS, Watson and Crick determined that a purine always bonds with a pyrimidine.

What bonds with what? • Using the sizes of each base and Chargaff’s percentages they determined that…. • A bonds with T • G bonds with C

Determining the other strand So, given a sequence of DNA, we could determine what the other strand would be based on what bonds with what. What would the other strand of DNA be given the sequence: AGT GCG TAC CAT CAG AAT TTA GTC TTA AAT TCA CGC ATG

Summary • DNA is a double-stranded helix that stores our hereditary information. • It looks like a twisted ladder. The rungs of the ladder are made by hydrogen bonds between nitrogen bases and the sides of the ladder are formed by the anti -parallel sugar-phosphate backbones. • The ladder is made up by the monomers of DNA, nucleotides.

Circle the nucleotides. • Can you see how the strands are anti-parallel?

DNA Art!