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• Introduction
• Genes
• Gene Regulation
• The Lactose Operon
• The Tryptophan Operon
• Always on-
Also known as ‘House Keeping Gene’.
• Regulate-
a) Normally off-
Also known as ‘Inducible Gene’. Because it
i...
POSITIVE REGULATION
Activator binds to regulatory site to stimulate
transcription; gene off in the absence of
activator.
N...
• An operon is a group of genes that are
transcribed at the same time.
• They usually control an important biochemical
pro...
The lac operon consists of three genes each
involved in processing the sugar lactose
One of them is the gene for the enz...
• E. coli can use either glucose, which is a
monosaccharide, or lactose, which is a
disaccharide
• However, lactose needs ...
• A repressor protein is continuously synthesised. It
sits on a sequence of DNA just in front of the lac
operon, the Opera...
• A small amount of a sugar allolactose is formed within the
bacterial cell. This fits onto the repressor protein at anoth...
• The genes of the trp operon are used to make
the amino acid tryptophan.
• It is turned off when enough tryptophan is in
...
• Operon codes for 5 genes in bacteria.
• Five polypeptides combine to make three
enzymes.
• Each enzyme participates in a...
• Repressor Protein (trpR) binds to operator
when tryptophan is present.
• Prevents RNA polymerase from transcribing
genes...
• Enzymes are required to make tryptophan
• Repressor is NOT bound to operator
• Transcription can proceed
• Tryptophan binds to repressor.
• Repressor can now bind operator to prevent
transcription
Operon is set of gene that are coordinately
controlled by a regulatory protein and
transcribed as a single polycistronic m...
• https://www.google.co.in/search?q=The+lac+operon
+in+e.coli.ppt&client=opera&hs=OtG&biw=1366&bih
=586&source=lnms&tbm=is...
Operon
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Operon

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Intoduction to operon.
gene regulation.
types of operon: Lac andTryp

Published in: Science
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Operon

  1. 1. • Introduction • Genes • Gene Regulation • The Lactose Operon • The Tryptophan Operon
  2. 2. • Always on- Also known as ‘House Keeping Gene’. • Regulate- a) Normally off- Also known as ‘Inducible Gene’. Because it induces or switches on the gene. b) Normally On- Also known as ‘Repressible gene’. Because it represses or switches off the gene.
  3. 3. POSITIVE REGULATION Activator binds to regulatory site to stimulate transcription; gene off in the absence of activator. NEGATIVE REGULATION Repressor binds to regulatory site to stimulate transcription; Gene is off in absence of activator.
  4. 4. • An operon is a group of genes that are transcribed at the same time. • They usually control an important biochemical process. • They are only found in prokaryotes.
  5. 5. The lac operon consists of three genes each involved in processing the sugar lactose One of them is the gene for the enzyme β- galactosidase This enzyme hydrolyses lactose into glucose and galactose.
  6. 6. • E. coli can use either glucose, which is a monosaccharide, or lactose, which is a disaccharide • However, lactose needs to be hydrolysed (digested) first • So the bacterium prefers to use glucose when it can.
  7. 7. • A repressor protein is continuously synthesised. It sits on a sequence of DNA just in front of the lac operon, the Operator site • The repressor protein blocks the Promoter site where the RNA polymerase settles before it starts transcribing Regulator gene lac operonOperator site z y a DNA I O Repressor protein RNA polymeraseBlocke d
  8. 8. • A small amount of a sugar allolactose is formed within the bacterial cell. This fits onto the repressor protein at another active site (allosteric site) • This causes the repressor protein to change its shape (a conformational change). It can no longer sit on the operator site. RNA polymerase can now reach its promoter site Promotor site z y a DNA I O
  9. 9. • The genes of the trp operon are used to make the amino acid tryptophan. • It is turned off when enough tryptophan is in the cell. • Tryptophan is the effector molecule.
  10. 10. • Operon codes for 5 genes in bacteria. • Five polypeptides combine to make three enzymes. • Each enzyme participates in a step to make tryptophan
  11. 11. • Repressor Protein (trpR) binds to operator when tryptophan is present. • Prevents RNA polymerase from transcribing genes when bound to operator. • Transcribed as a different gene from trp operon
  12. 12. • Enzymes are required to make tryptophan • Repressor is NOT bound to operator • Transcription can proceed
  13. 13. • Tryptophan binds to repressor. • Repressor can now bind operator to prevent transcription
  14. 14. Operon is set of gene that are coordinately controlled by a regulatory protein and transcribed as a single polycistronic message. This mechanism allows for synchronization of transcription and translation, a key element in attenuation
  15. 15. • https://www.google.co.in/search?q=The+lac+operon +in+e.coli.ppt&client=opera&hs=OtG&biw=1366&bih =586&source=lnms&tbm=isch&sa=X&ei=OzQ0VJu1N4 2xuATqjIH4BQ&ved=0CAYQ_AUoAQ • https://www.khanacademy.org/science/biology/gene-regulation/gene- regulation-in-bacteria/a/the-trp-operon • https://www.khanacademy.org/science/biology/gene-regulation/gene- regulation-in-bacteria/a/the-lac-operon • http://www.phschool.com/science/biology_place/biocoach/lacoperon/qui z.html

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