Eukaryotic Gene Control
Post on 24-Feb-2016
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Eukaryotic Gene
Control
Gene Organization: •Chromatin:
•Complex of DNA and Proteins
•Structure base on DNA packing
DNA Packing:• Histones: positively charged
amino acids• Five types (H1, H2A, H2B,
H3,H4)• DNA- negatively charged
phosphate groups
DNA Packing: • Nucleosomes: “beads on a string”
• Basic unit• DNA wound around two molecules
composed of histones (H2 – H4)• H1 = histone tail
• 10nm
Higher Level of DNA Packing:
• Coiling of 10nm = 30nm chromatin fiber
• Looped domain = 30nm chromatin fiber attaches to chromosome scaffold = 300nm fiber
• Metaphase chromosome- maximal compaction • 1400 nm
Heterochromatin: •Highly condensed
interphase DNA•Can not be transcribed
Euchromatin: •Less compacted interphase
DNA•Can be transcribed
Differential gene expression on many
levels: • 1. Pre Transcription
• Chromatin
• 2. Transcription
• 2. Post Transcription• RNA processing, transport to cytoplasm,
degradation of mRNA
• 3. Translation
• 4. Post Translation• Cleavage and chemical modification, degradation
of protein
Examples: Pre-transcription
• Histone Acetylation of chromatin:• Histones = group of 5 proteins associated with
the coiling of DNA (positively charged regions)• Histone acetylation: acetyl group (-COCH3
• Attached to positively charged regions• Neutralizes the histones• Causes DNA to become loser• Transcription proteins can access the DNA with
greater ease
• Deacetylation (removing of acetyl groups) creates a tighter, super coiled DNA structure• Difficult for transcription to
proceed
DNA methylation and demethylation:
• Inactive Mammalian X chromosomes (Barr bodies):• Highly methylated (-CH3) bases,
particularly cytosine• Removing of methyl groups can
activate these genes
Gene regulation gone wrong:
• Proto- oncogenes:• Normal cellular genes• Code for proteins that stimulate normal
cell growth and division
• Oncogenes:• Cancer causing genes
How do proto-oncogenes become
oncogenes?• Movement of DNA-
translocation• Amplification:• Point mutations:
Tumor- Suppressor genes
• Genes that inhibit cell division• Mutation of these genes may
stimulate uncontrollable cell growth
Normal Cell Signaling Interference:
• Interference with a cell signal pathway• 1. can stimulate pathways of the cell
cycle to promote uncontrollable cell division
• 2. can inhibit cell cycle pathways that prevent suppression of cell division allowing uncontrolled cell division
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