DNADeoxyriboNucleic Acid

What can DNA do?

• Carries information from one generation to the next

• Determines the heritable characteristics of organisms

• Genes must be easily copied

DNA Structure

• DNA is a long molecule made up of units called– Nucleotides

• 3 basic components– 5-carbon sugar

(deoxyribose)– Phosphate group– Nitrogenous base

Nitrogenous Bases

• There are four Nitrogenous Bases– Purines: Two rings in

their structures• Adenine• Guanine

– Pyrimidines: One ring in their structure

• Cytosine• Thymine

Have a “Y”

Backbone of DNA

• Twisted Ladder: Double Helix

• Sides: Formed by sugar and phosphate groups of each nucleotide

-Held together by weak hydrogen bonds

• Steps:The nitrogenous bases stick out sideways from the chain

Chargaff’s Rules

• Base pair rules• Adenine always

pairs with Thymine• Cytosine always

pairs with Guanine

Nitrogen Base Pairs…..

• If 28% of the bases of a certain segment of DNA are guanine, then what is the percent of the bases are cytosine?

• If 30% of the bases of a certain segment of DNA are thymine, then what is the percent of the bases are adenine?

Double Helix

• Rosalind Franklin – Used X-ray diffraction to show helical DNA– Had the evidence that the double helix existed

but didn’t put it all together

• Watson and Crick– Tried to put together a model of DNA– Wasn’t until they saw Franklin’s X-rays that

they discovered the double helix pattern

We are all nearly the same?

• ALL organisms have the same DNA structure and nitrogen bases

• Only the amount and sequence of ATGC differentiates the species

• Ex: The person sitting next to you is only .01% different in their DNA