Download Gene Expression (Epigenetics)

Gene Expression
(Epigenetics)
Chapter 19
What you need to know
• The functions of the three parts of an
operon.
• The role of repressor genes in operons.
• The impact of DNA methylation and
histone acetylation on gene expression.
• The role of oncogenes, protooncogenes, and tumor suppressor genes
in cancer.
Bacteria Gene Expression:
Transcription
• Operons are clusters of genes in
bacteria
• They can be turned on and off
Parts:
1. Operator: an on/off switch for all
the genes
2. Promoter: RNA Polymerase
attachment site
3. Genes: DNA for each protein in
Operons: On/Off
• Regulatory genes – make repressor proteins
that bind to operators and blocks RNA
Polymerase (off)
• Repressible operon – usually on (repressor
protein’s off), anabolic, and builds an essential
chemical
– Turned off by a corepressor which activates the
repressor
• Inducible operon – usually off (repressor protein
on) and catabolic
– Turned on by an inducer that deactivates the
repressor
Eukaryotic Gene
Expression : Transcription
• Nucleosomes are DNA tightly
wrapped around histones
• DNA methylation – the addition of
methyl groups to DNA making
genes less accessible
• Histone Acetylation – acetyl groups
are added to histones to loosen
DNA
• http://teach.genetics.utah.edu/conte
nt/epigenetics/
Eukaryotic Gene
Expression : Transcription
• Transcription initiation complexes
also regulate gene expression
• Enhancer region upstream from the
gene is joined to the transcription
initiation complex by activators
(proteins) = start transcription
• http://www.dnai.org/a/index.html
Eukaryotic Gene
Expression : preTranslation
• Tiny single strand RNA molecules
can block mRNA
– micro RNA – miRNA
– small interfering RNA – siRNA
• They will degrade the mRNA or
block its translation
Cell Specialization
• Cell differentiation is the process by
which cells become specialized
– Muscle tissue, neural tissue, etc.
• As the zygote grows and divides
(mitosis) it begins morphogenesis
(organization of cells into tissues)
Morphogenesis
1. Cytoplasmic determinants are maternal
substances in the egg that influence early
development (uneven in early cells)
2. Cell-cell signals are molecules made by
cells (external hormones) that influence
other cells (induction)
– Determination is the series of events that lead
to cell differentiation
• Pattern formation sets up the body plan
(head/tail, left/right, etc.) and is impacted
by both
Cancer
• Proto-oncogenes are healthy genes
that promote cell growth
• Mutation of these genes creates
oncogenes
• Oncogenes are overstimulated
proto-oncogenes that cause cancer
• Tumor-suppressor genes inhibit cell
division (mutations here can also
cause cancer)
Tumor-Suppressor: p53
Three types of suppression:
1. Binds to cyclin-dependent kinases
– halts division until DNA can be
repaired
2. Turns on DNA repairing genes
3. Triggers apoptosis when DNA
damage is too great