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> > >Unit 4: > > >Post Transcriptional Modifications, Processing of Eukaryotic RNA and
Gene Regulation > > >
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and trp operon > > >
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>The principles of transcriptional regulation involve the control of gene
expression through the binding of regulatory proteins to specific DNA
sequences, the use of regulatory elements, and the involvement of multiple
mechanisms that allow for fine-tuned control of gene expression. >
>One classic example of transcriptional regulation is the lac operon in E.
coli. The lac operon consists of three genes, lacZ, lacY, and lacA, that are
involved in the metabolism of lactose. The expression of these genes is
controlled by a regulatory region that includes a promoter, an operator, and
a regulatory gene called lacI. >
>The regulatory protein, Lac repressor, is encoded by the lacI gene and
binds to the operator sequence of the lac operon, preventing RNA polymerase
from binding to the promoter and initiating transcription. This repressor
protein is active in the absence of lactose. >
>When lactose is present, it is converted into allolactose, which binds to
the Lac repressor protein and causes it to change shape, preventing it from
binding to the operator sequence. This allows RNA polymerase to bind to the
promoter and initiate transcription of the lac operon genes, leading to the
production of enzymes involved in lactose metabolism. >
>This mechanism of transcriptional regulation in the lac operon is an
example of an inducible system where the presence of a specific molecule (in
this case, lactose) triggers the expression of genes involved in its
metabolism. >
>Overall, the lac operon provides an excellent example of the principles of
transcriptional regulation, including the role of regulatory proteins, the
use of regulatory elements, and the involvement of multiple mechanisms in
controlling gene expression. >
>Steps involve in lac operon >
>The lac operon is a well-studied example of transcriptional regulation in
prokaryotes that involves several steps. Here are the steps involved in the
lac operon: >
>Absence of lactose: In the absence of lactose, the Lac repressor protein,
encoded by the regulatory gene lacI, binds to the operator sequence of the
lac operon. This binding prevents RNA polymerase from binding to the
promoter and initiating transcription of the lac operon genes. >
>Presence of lactose: When lactose is present in the environment, it is
transported into the cell and converted into allolactose by the enzyme
beta-galactosidase, which is encoded by the lacZ gene. The allolactose
molecule binds to the Lac repressor protein, causing a conformational
change that prevents it from binding to the operator sequence. >
>Binding of RNA polymerase: With the Lac repressor protein released from
the operator sequence, RNA polymerase can now bind to the promoter
sequence of the lac operon and initiate transcription of the three genes:
lacZ, lacY, and lacA. >
>Transcription and translation: Once transcription has started, RNA
polymerase moves along the DNA strand, synthesizing a complementary RNA
transcript. The mRNA is then translated into proteins by ribosomes. >
>Regulation of gene expression: The expression of the lac operon genes is
tightly regulated by multiple mechanisms, including feedback inhibition,
post-transcriptional regulation, and metabolic control. >
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>Overall, the regulation of the lac operon involves the interplay of several
regulatory proteins, small molecules, and the enzyme RNA polymerase to
control gene expression in response to environmental signals such as the
presence or absence of lactose. >
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operon > >
>The principles of transcriptional regulation involve the control of gene
expression through the binding of regulatory proteins to specific DNA
sequences, the use of regulatory elements, and the involvement of multiple
mechanisms that allow for fine-tuned control of gene expression. Here are
some examples of transcriptional regulation in the lac and trp
operons: >
>The trp operon: In contrast to the lac operon, the trp operon is a
repressible system that is regulated by the presence or absence of
tryptophan. The regulatory protein, Trp repressor, binds to the operator
sequence of the trp operon in the presence of tryptophan, preventing RNA
polymerase from binding to the promoter and initiating transcription. When
tryptophan is absent, the Trp repressor protein cannot bind to the operator
sequence, allowing RNA polymerase to bind to the promoter and initiate
transcription of the trp operon genes. >
>Transcription factors: In eukaryotes, transcriptional regulation is often
mediated by transcription factors, which are regulatory proteins that bind
to specific DNA sequences and either activate or repress gene expression.
For example, the estrogen receptor is a transcription factor that binds to
specific DNA sequences in the promoter region of target genes, leading to
the activation or repression of gene expression. >
>the regulation of gene expression involves multiple mechanisms that allow
for precise control of gene expression in response to environmental signals
or developmental cues. The lac and trp operons are classic examples of
transcriptional regulation in prokaryotes, while transcription factors play
a critical role in regulating gene expression in eukaryotes. >
>Steps involve in trp operon >
>The trp operon is a well-studied example of transcriptional regulation in
prokaryotes. Here are the steps involved in the regulation of the trp
operon: >
>Presence of tryptophan: When tryptophan is present in the environment, it
is transported into the cell and binds to the regulatory protein, Trp
repressor. This causes a conformational change in the Trp repressor that
allows it to bind to the operator sequence of the trp operon. >
>Binding of Trp repressor: The binding of the Trp repressor to the
operator sequence prevents RNA polymerase from binding to the promoter and
initiating transcription of the trp operon genes. >
>Absence of tryptophan: In the absence of tryptophan, the Trp repressor
protein cannot bind to the operator sequence, allowing RNA polymerase to
bind to the promoter and initiate transcription of the trp operon
genes. >
>Transcription and translation: Once transcription has started, RNA
polymerase moves along the DNA strand, synthesizing a complementary RNA
transcript. The mRNA is then translated into proteins by ribosomes. >
>Feedback inhibition: The Trp operon is also regulated by feedback
inhibition. Once the tryptophan concentration in the cell reaches a
certain threshold, excess tryptophan molecules bind to the Trp repressor,
causing it to become active and bind to the operator sequence of the trp
operon. This feedback mechanism helps to prevent the overproduction of
tryptophan. >
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>the regulation of the trp operon involves the binding of the regulatory
protein Trp repressor to the operator sequence of the trp operon in response
to the presence or absence of tryptophan, which controls the expression of
the trp operon genes. The feedback inhibition mechanism helps to maintain
optimal levels of tryptophan in the cell. >