Chromatin packing in eukaryotic cells Prokaryotic Smaller genomes DNA is in a nucleoid region and is circular. Prokaryotic cells may have a separate circular DNA called a plasmid. Eukaryotic Larger genomes 6 billion base pairs (bp) Genomes are linear More biochemical editing is needed. Remember INTRONS and EXONS

Chromatin packing in Eukaryotic cells Histones- small proteins usually 100 amino acids in length with positive charges that bind to the negatively charged DNA double helix. Nucleosome- is the ENTIRE beadlike unit of DNA packing including histones and DNA.

This model depicts a cross section or end view.

The need to turn transcription on and off. All genes all cells. What are the four basic cell types in eukaryotes?

SUMMARY THUS FAR DNA is coiled around histones. Tightly coiled DNA is inaccessible to gene reading machinery. Methyl groups (-CH 4) molecules bind to the histone tails and block access to genes and inhibit transcription. This may not be bad. Genes need to be turned off. Acetyl (Acetylation) molecules bind to histones and loosen chromatin structure that permits transcription.

IMPLICATIONS Epigenetic inheritance- inheritance of traits not directly involving nucleotide sequences. Say again? Molecular mechanism of heritability may not be limited to DNA sequence differences.

Identical twins in which one acquires a genetic disease and one does not.

Identical twins are derive form an identical zygote that splits at the two cell state. – Monozygotic twins (MZ) identical – Dizygotic twins (DZ) fraternal

Paradigm shift??????????

A change in basic assumptions or paradigms within the ruling theory of science. IT IS A REVOLUTION! ?????

Thomas Kuhn: “The Structure of Scientific Revolution” A scientific revolution occurs, according to Kuhn, when scientists encounter anomalies that cannot be explained by the universally accepted paradigm within which scientific progress has thereto been made. 1962

Barbara McClintock and trasnsposons or transposable genetic elements

Expression of genes can be tied to other factors besides nucleotide sequences. Randy Jirtle Rober Waterland of Duke University

Diets supplemented with methyl donors such as choline, folic acid, and B-12) decreased the incidence of offspring with yellow coat color which results in REDUCING the risk of developing obesity, diabetes and cancer. Jirtle and Waterland, 2003 nature paper