Structure of DNA

The discovery of DNA : The discovery of DNA DNA- The genetic material of living organisms

James Watson (L) and Francis Crick (R), and the model they built of the structure of DNA : James Watson (L) and Francis Crick (R), and the model they built of the structure of DNA X-ray diffraction photograph of the DNA double helix

The structure of DNA and RNA : The structure of DNA and RNA Genetic material of living organisms is either DNA or RNA. DNA – Deoxyribonucleic acid RNA – Ribonucleic acid

DNA and RNA are polynucleotides : DNA and RNA are polynucleotides Both DNA and RNA are polynucleotides. They are made up of smaller molecules called nucleotides. DNA is made of two polynucleotide strands: RNA is made of a single polynucleotide strand: Nucleotide Nucleotide Nucleotide Nucleotide Nucleotide Nucleotide Nucleotide Nucleotide Nucleotide Nucleotide Nucleotide Nucleotide Nucleotide Nucleotide Nucleotide Nucleotide

DNA Structure : DNA Structure A gene is a section of DNA that codes for a protein. Each unique gene has a unique sequence of bases. This unique sequence of bases will code for the production of a unique protein. It is these proteins and combination of proteins that give us a unique phenotype.

Slide 6 : Hidden within every cell of this bird are the genes that direct the growth of feathers, that command the release of energy to fuel flight , that tell it when to migrate and how to build a nest and where to build.

Slide 7 : The twisting two sided shape of a double helix is familiar to any one who has climbed a spiral staircase or ridden a modern roller coaster

Nucleotides : Nucleotides The phosphate and sugar form the backbone of the DNA molecule, whereas the bases form the “rungs”. There are four types of nitrogenous bases.

Slide 9 : Because of this complementary base pairing, the order of the bases in one strand determines the order of the bases in the other strand. DNA Structure

Nitrogenous bases – Two types : Nitrogenous bases – Two types Pyramidines Thymine - T Cytosine - C Uracil - U Purines Adenine - A Guanine - G

The Rule: : The Rule: Adenine always base pairs with Thymine (or Uracil if RNA) Cytosine always base pairs with Guanine. This is beacuse there is exactly enough room for one purine and one pyramide base between the two polynucleotide strands of DNA.

Complementary base pairing : Complementary base pairing Purines Pyramidines Adenine Thymine Adenine Uracil Guanine Cytosine

Adenine : Adenine

Guanine : Guanine

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Base pairing : Base pairing The Nitrogenous Bases pair up with other bases. For example the bases of one strand of DNA base pair with the bases on the opposite strand of the DNA.

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Structure of a nucleotide : Structure of a nucleotide A Nitogenous base In DNA the four bases are: Thymine Adenine Cytosine Guanine In RNA the four bases are: Uracil Adenine Cytosine Guanine

Nature of the Genetic Material : Nature of the Genetic Material Property 1 - it must contain, in a stable form, information encoding the organism’s structure, function, development and reproduction Property 2 - it must replicate accurately so progeny cells have the same genetic makeup Property 3 - it must be capable of some variation (mutation) to permit evolution

Replication of DNA and Chromosomes : Replication of DNA and Chromosomes Speed of DNA replication: 3,000 nucleotides/min in human 30,000 nucleotides/min in E.coli Accuracy of DNA replication: Very precise (1 error/1,000,000,000 nt)

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