DNA

DNA History

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

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

Hershey-Chase video

Structure of DNA• DNA is a long molecule made up of units called

nucleotides. ( double strand)• Each nucleotide is made up of three parts: a 5-

carbon sugar called dioxyribose, a phosphate group, and a nitorgenous base (Nitrogen Containing).

• The backbone of DNA is formed by sugar and phosphate groups of the nucleotide.

• The nitrogenous base stick out from the sides and can be joined together in any order, meaning that any sequence of bases is possible.

Nitrogenous Bases

• There are four nitrogenous bases.• They are divided into two classes: purines and

pyrmidines• Purines – Adenine and Guanine• Pyrmidines – Cytosine and Thymine

Chargaff’s Rules• Chargaff discovered how

the nitrogenous bases bond together.

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

• Weak hydrogen bonds join the nitrogen bases together.

Chargaff video

Prokaryotes & DNA

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

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

Eukaryotes & DNA

• Many eukaryotes have 1000 times as much DNA as prokaryotes.

• DNA is located in the nucleus in the form of chromosomes.

• Chromosomes are DNA wound tightly around proteins called histones.

DNA Replication

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

How It Occurs

• DNA replication is carried out by a series of enzymes.

• The enzymes unzip the DNA molecule creating two strands that serve as templates.

• Complimentary bases are added to the strands, for example a strand of DNA with the bases ATTCGAG would have a complimentary strand of TAAGCTC.

Replication Continued

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

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