DNADNA

Lourdes LuengoLourdes Luengo

DNA HistoryDNA History

GriffithGriffith – Experimented on mice and – Experimented on mice and observed some harmless strains of observed some harmless strains of bacteria could change into harmful strains. bacteria could change into harmful strains. He called this transformation. He called this transformation.

AveryAvery – Discovered that DNA is the – Discovered that DNA is the nucleic acid that stores and transmits the nucleic acid that stores and transmits the genetic information from one generation to genetic information from one generation to the next.the next.

GriffithGriffith

More DNA HistoryMore DNA History

Hershey-Chase – Hershey-Chase – Concluded that the Concluded that the genetic material in genetic material in bacteria was DNA not bacteria was DNA not proteinsproteins

Watson & Crick – Watson & Crick – created the double created the double helix model for DNA.helix model for DNA.

Hershey ChaseHershey Chase

Watson & CrickWatson & Crick

Understanding DNAUnderstanding DNA

The Importance of DNAThe Importance of DNA

Structure of DNAStructure of DNA

DNA is a long molecule made up of units called DNA is a long molecule made up of units called nucleotides.nucleotides.Each nucleotide is made up of three parts: a 5-Each nucleotide is made up of three parts: a 5-carbon sugar called dioxyribose, a phosphate carbon sugar called dioxyribose, a phosphate group, and a nitorgenous base (Nitrogen group, and a nitorgenous base (Nitrogen Containing).Containing).The backbone of DNA is formed by sugar and The backbone of DNA is formed by sugar and phosphate groups of the nucleotide.phosphate groups of the nucleotide.The nitrogenous base stick out from the sides The nitrogenous base stick out from the sides and can be joined together in any order, and can be joined together in any order, meaning that any sequence of bases is possible.meaning that any sequence of bases is possible.

DNA SubunitsDNA Subunits

Nitrogenous BasesNitrogenous Bases

There are four kinds of nitrogenous bases.There are four kinds of nitrogenous bases.

They are divided into two classes: purines They are divided into two classes: purines and pyrmidinesand pyrmidines

Purines – Adenine and GuaninePurines – Adenine and Guanine

Pyrmidines – Cytosine and ThyminePyrmidines – Cytosine and Thymine

Chargaff’s RulesChargaff’s Rules

Chargaff discovered Chargaff discovered how the nitrogenous how the nitrogenous bases bond together.bases bond together.

He discovered that He discovered that Adenine Adenine always always bonds with Thymine bonds with Thymine and that Cytosine and that Cytosine alwaysalways bonds with bonds with Guanine.Guanine.

ChargaffChargaff

The Genetic CodeThe Genetic Code

Prokaryotes & DNAProkaryotes & DNA

In prokaryotes, DNA In prokaryotes, DNA molecules are located molecules are located in the cytoplasm of in the cytoplasm of the cell.the cell.

Most prokaryotic DNA Most prokaryotic DNA is a single circular is a single circular molecule that molecule that contains nearly all the contains nearly all the cell’s genetic cell’s genetic information.information.

Eukaryotes & DNAEukaryotes & DNA

Many eukaryotes Many eukaryotes have 1000 times as have 1000 times as much DNA as much DNA as prokaryotes.prokaryotes.DNA is located in the DNA is located in the nucleus in the form of nucleus in the form of chromosomes.chromosomes.Chromosomes are Chromosomes are DNA wound tightly DNA wound tightly around proteins called around proteins called histones.histones.

DNA LengthDNA Length

E. Coli have about 4,639,221 base pairs. E. Coli have about 4,639,221 base pairs. It is about 1.6mm in length. This sounds It is about 1.6mm in length. This sounds small until you realize the bacteria is only small until you realize the bacteria is only 1.61.6µm in diameter.µm in diameter.

Thus DNA must be wrapped tightly to fit Thus DNA must be wrapped tightly to fit into cells. Imagine fitting 900 yards into cells. Imagine fitting 900 yards (300m) of rope into a backpack.(300m) of rope into a backpack.

DNA ReplicationDNA Replication

During DNA replication, the DNA molecule During DNA replication, the DNA molecule separates into two strands, then produces separates into two strands, then produces two new complimentary strands following two new complimentary strands following the rules of base pairing (Chargaff Rules). the rules of base pairing (Chargaff Rules). Each strand of double helix of DNA serves Each strand of double helix of DNA serves as a template, or model, for the new as a template, or model, for the new strand.strand.

How It OccursHow It Occurs

DNA replication is carried out by a series DNA replication is carried out by a series of enzymes.of enzymes.The enzymes unzip the DNA molecule The enzymes unzip the DNA molecule creating two strands that serve as creating two strands that serve as templates.templates.Complimentary bases are added to the Complimentary bases are added to the strands, for example a strand of DNA with strands, for example a strand of DNA with the bases ATTCGAG would have a the bases ATTCGAG would have a complimentary strand of TAAGCTC.complimentary strand of TAAGCTC.

Replication ContinuedReplication Continued

Each new DNA molecule has one new Each new DNA molecule has one new stand and one strand from the original stand and one strand from the original molecule.molecule.

The enzyme DNA polymerase, the The enzyme DNA polymerase, the principal enzyme, “proofreads” the new principal enzyme, “proofreads” the new DNA strands, helping to maximize the DNA strands, helping to maximize the odds that each molecule is a perfect copy odds that each molecule is a perfect copy of the original.of the original.

Replication of DNAReplication of DNA