DNA StructureUnit 4 – Part 1

DNA Facts

DNA DeoxyriboNucleic Acid

Basis for all living things Foundation for all diversity & unity on Earth

Every living thing has DNA. That means that you have something in common with a zebra, a tree, a mushroom and a beetle!!!!

DNA is too small to see, but under a microscope it looks like a twisted up ladder!

History of DNA

Frederick Griffith Discovers that a factor in diseased

bacteria can transform harmless bacteria into deadly bacteria (1928)

Rosalind Franklin X-ray photo of DNA. (1952)

Watson and Crick described the DNA molecule from

Franklin’s X-ray.(1953)

Structure of DNA

Nucleotide Small units that

link together to form DNA

Made of 3 parts▪ Phosphate Group▪ 5-C sugar

molecule▪ deoxyribose

▪ Nitrogen Base

Structure of DNA cntd.

Nitrogen (N) base N base makes nucleotides

different 4 bases▪ Adenine (A)▪ Guanine (G)▪ Thymine (T)▪ Cytosine (C)

2 main groups of bases▪ Purines▪ Double ring of C & N atoms▪ Includes adenine and

guanine▪ Pyrimidines▪ Single ring of C & N atoms▪ Includes thymine and

cytosine

Base pairing rules▪ Purines bind to pyrimidines▪ Adenine binds to thymine▪ Guanine binds to cytosine

Structure of DNA cntd.

Double Helix Model created by

James Watson & Francis Crick

Structure of DNA “spiral staircase”

made of 2 strands of nucleotides twisting around a central axis.

Also known as a “twisted ladder”

▪ Sides of ladder are made of alternating sugar and phosphate units held together with a strong covalent bond▪ Rungs are made up of a

purine and a pyrimidine held together by a weak Hydrogen (H) bond.▪ Base pairing results in a

complementary strand (this is how DNA replicates)