DNA Structure

What do we know of DNA? 1.Size? 2.Composition- building blocks? 3.Purpose? 4.Structure?

What is DNA? Polymer- nucleic acid Many repeating units. How many do you see? Could it have a similar shape as a tool in your garage?

Structure of DNA Double Helix composed of 2 strands It forms a coil

Building blocks- Monomers 1.Nucleotides- composed of three components: 5-carbon sugar phosphate nitrogen base

DNA Structure The DNA molecule resembles a ladder The sides of the ladder: composed of alternating molecules of phosphate and sugar. Provide support and protection The rungs of the ladder: composed of pairs of nitrogen bases Contain the genetic information.

Two sides to the DNA Molecule The two side are held together between the complimentary nitrogen bases by a weak hydrogen bond. Rungs of the ladder Base pairs

DNA Structure

“Rung” Structure The letters represent 4 different nitrogen bases: Adenine Cytosine Guanine Thymine Is there a base pair pattern?

The Book of Life 1. Where is the information found? 2. What protects the information? 3. How useful would this resource be if the covers were secured to each other with a padlock? 1.Phosphate-sugar backbone- paired 2.Nitrogen bases- information 3.Hydrogen bonds- weak force that holds base pairs together

Chargaff’s Rule Chargaff’s research showed that there was a relationship between the amounts of different base pairs- BUT- he did not recognize the significance of the relationship in terms of DNA Structure!

Classification of Nitrogen bases

Structure Look at the rungs of the ladder: What is holding the base pairs together? Do you notice a pattern in the bonds? What type of bond holds the bases together?

Hydrogen bonds

Structure of DNA Partner work: 1. Draw an DNA molecule with 6 nucleotides: Label the following Phosphate Deoxyribose Hydrogen bond Adenine, guanine, cytosine and thymine

History James Watson & Francis Crick built a model of DNA. -- Cambridge University This was their 2 nd attempt- the 1 st was a complete failure! The beginning of the DNA Revolution!!!

Contributors Physicists at King College. Working on x-ray diffraction image of DNA. Photo 51 “Franklin”

Nobel Prize Awarded in 1962 Franklin did not receive the prize as she had already died from ovarian cancer.

DNA- Self Replication Recognized its ability for self- replication What if you “unzipped” the molecule?

DNA Replication 1.Why would DNA need to replicate? 2.When does DNA replication occur?

DNA Replication

Semi-Conservative Replication Parental strands separate and serve as a template for a new complimentary strand. Product: 2 new DNA molecules composed of: an original side and a new side.

STEP 1- Replication Unwind and Unzip the Hydrogen Bonds Helicase - Unwinds Unzips- breaks the Hydrogen bonds

Synthesis of DNA DNA polymerase adds the appropriate nucleotides to the new DNA strand- Base- pair rules The 2 strands are made in different ways; leading and lagging strands

DNA Synthesis DNA Synthesis- Practice