chromatin packing in eukaryotic cells prokaryotic smaller genomes dna is in a nucleoid region and is...
TRANSCRIPT
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