This document discusses the regulation of genome activity in prokaryotes and eukaryotes. It explains that in prokaryotes like bacteria, gene expression is regulated through operons, which coordinate the expression of genes involved in specific pathways. A key example is the lac operon in E. coli. In eukaryotes, gene expression is more complex and regulated at many stages from chromatin structure to post-translational modification. Epigenetics also plays a role in regulating gene expression and cell differentiation through mechanisms like DNA methylation and histone modification.

1. Regulation of Genome Activity
Dr. Nawfal Hussein
Email: nawfal_hm@yahoo.com
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2. Gene expression
Transcription and translation provide the
mechanisms by which genes are expressed.
However, it is vital that gene expression is
controlled so that the correct gene products
are produced in the cell at the right time.
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3. Regulation of Genome Activity in
prokaryotes
Bacterial cells need to be able to cope with wide
variations in environmental conditions and, thus,
need to keep all their genetic material ‘at the
ready’ in case particular gene products are
needed. By keeping their genomes in this state of
readiness, bacteria conserve energy (by not
making proteins wastefully) and can respond
quickly to any opportune changes in nutrient
availability. This is an example of adaptive
regulation of gene expression
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4.  Operon is a unit of prokaryotic gene expression
which includes (a group of contiguous genes that
are transcribed into a single mRNA molecule) co-
ordinately regulated (structural) genes and
control elements which are recognized by
regulatory gene products, Operon typically
includes:
 The structural genes (any gene other than a
regulator) for enzymes involved in a specific
biosynthetic pathway whose expression is co-
ordinately controlled.
 Control elements such as an operator sequence,
which is a DNA sequence that regulates
transcription of the structural genes.
 Regulator gene(s) whose products recognize the
control elements, for example a repressor which
binds to and regulates an operator sequence 4

5. 5The activation of the lac operon in E. coli.

6. Regulation of Genome Activity in Eukaryotes
 In contrast to bacteria, human cells (usually)
experience a very different set of
environmental conditions. Cells may be highly
specialized and differentiated, and their
external environment is usually stable and
controlled by homeostatic mechanisms to
ensure that no wide fluctuations occur. Thus,
cell specialization brings more complex function
but requires more controlled conditions.
Differentiation is a function of development
and, thus, genes in multicellular eukaryotes are
often developmentally regulated. Gene
regulation during the development and life
cycle of a complex organism is, as you would6

7.  The level of gene expression qualitatively and
quantitatively is highly variable
 Some of genes are induced at certain specific
conditions, by altered environmental factors,
temperature, or certain chemicals or by certain
biological factors such as insect or pathogen
attack. Such factors or chemicals responsible
for the induction or expression of certain genes
or gene groups are known as inducers
 Housekeeping genes: genes are expressed
constitutively at relatively low levels in all cells
of the body system, which express irrespective
of the factors or inducers.
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8.  The different cell types in a multicellular organism differ
dramatically in both structure and function
 A cell can change the expression of its genes in
response to external signals:
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9. Gene expression can be regulated at many steps in
the pathway from DNA to RNA to protein
 Chromatin Structure
 Transcriptional Initiation
 Transcript Processing and Modification
 RNA Transport
 Transcript Stability
 Translational Initiation
 Post-translational Modification
 Protein Transport
 Control of Protein Stability
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10.  Epigenetics the study of mitotically (and in some cases
meiotically) heritable changes of a phenotype, such as the
gene expression of specific cell types that do not result from
changes in the genetic code
Epigenetic regulation mediates the adaption to an environment
ultimately contributing to the phenotype.
These types of changes include methylation patterns, histone
modification patterns, and inactivation of certain genes or
chromosomes by converting the area into heterochromatin.
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12.  In any cell at any given time, some genes
are used to make RNA in very large
quantities while other genes are not
transcribed at all.
 The protein fibroin, for example, is the major
component of silk. In each silk gland cell a
single fibroin gene makes 10 4
copies of
mRNA, each of which directs the synthesis of
10 5
molecules of fibroin - producing a total
of 10 9
molecules of fibroin in just 4 days.
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