GB1-Chapter 18

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Gene Expression Regulation

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8 Terms

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feedback inhibition

  • regulates the production of enzymes

  • the end product of metabolic pathway shuts down further synthesis of product by inhibiting enzyme activity

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operon

operon is the entire stretch of DNA inclduing operator, promoter, and genes they control

a cluster of functionally related genes that can be coordinately controlled by a single on and off switch called operator that is within the promoter or between promoter and the enzyme coding genes.

<p>operon is the entire stretch of DNA inclduing operator, promoter, and genes they control </p><p>a cluster of functionally related genes that can be coordinately controlled by a single on and off switch called operator that is within the promoter or between promoter and the enzyme coding genes. </p>
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repressible operon

The regulatory gene secretes a repressor that can repress the operon by binding to the operator and preventing RNA polymerase from transcribing.

corepressor- a molecule that works with a repressor to repress the operon

  • negative feedback

  • negative control- operon is switched off by an active form of repressor

  • only active in the presence of tryptophan. Tryptophan (corepressor) binds to the repressor, activating it.

  • usually function in anabolic pathways

<p>The regulatory gene secretes a repressor that can repress the operon by binding to the operator and preventing RNA polymerase from transcribing.</p><p>corepressor- a molecule that works with a repressor to repress the operon</p><ul><li><p>negative feedback</p></li><li><p><mark data-color="green" style="background-color: green; color: inherit">negative control</mark>- operon is switched off by an active form of <mark data-color="yellow" style="background-color: yellow; color: inherit">repressor</mark></p></li><li><p>only active in the presence of <mark data-color="yellow" style="background-color: yellow; color: inherit">tryptophan</mark>. Tryptophan (corepressor) binds to the repressor, activating it.</p></li><li><p>usually function in <mark data-color="yellow" style="background-color: yellow; color: inherit">anabolic</mark> pathways</p></li></ul><p></p>
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inducible operon

usually turned off by a lac repressor, but it can be activated by an inducer, allolactose, that inactivates the repressor by causing it to change shape and allows transcription

Lac operon- contains genes that code for enzymes used in hydrolysis and metabolism of lactose

  • regulatory gene: lacl

  • negative control- active form of repressor

  • usually function in catabolic pathways

<p>usually turned off by a lac repressor, but it can be activated by an inducer, <mark data-color="yellow" style="background-color: yellow; color: inherit">allolactose</mark>, that inactivates the repressor by causing it to change shape and allows transcription</p><p>Lac operon- contains genes that code for enzymes used in <mark data-color="yellow" style="background-color: yellow; color: inherit">hydrolysis</mark> and <mark data-color="yellow" style="background-color: yellow; color: inherit">metabolism</mark> of lactose</p><ul><li><p>regulatory gene: lacl</p></li><li><p>negative control- active form of repressor</p></li><li><p>usually function in catabolic pathways</p></li></ul><p></p>
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positive control

active form of activator

When glucose is scarce, Cyclic AMP receptor protein (CRP) is activated by binding of cyclic AMP (cAMP). Activated CRP attaches to lac operon promoter and increases the affinity of RNA polymerase = speeding up transcription 

When glucose level increase CRP detaches from lac operon and the activator falls off with it. This makes transcription fall back into a normal, low level without the activator. 

<p>active form of activator </p><p>When glucose is scarce, Cyclic AMP receptor protein (CRP) is activated by binding of cyclic AMP (cAMP). Activated CRP attaches to lac operon promoter and increases the affinity of RNA polymerase = speeding up transcription&nbsp;</p><p>When glucose level increase CRP detaches from lac operon and the activator falls off with it. This makes transcription fall back into a normal, low level without the activator.&nbsp;</p><p></p>
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differential gene expression

the expression of different genes by cells with the same genome

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regulation of chromatin structure

heterochromatin- highly packed genes- usually not expressed

euchromatin- loosely packed genes- expressed. Gene transcription is affected by location of nucleosomes along the promoter and where the DNA attaches to chromosome.

histone acetylation- acetyl groups are attached to histone tail’s amino acid and opens up chromatin strcuture- promoting transcriptiton

DNA methylation- addition of methyl groups that reduces transcription- long term inactivation of genes. methylation regulates genomic imprinting determination of maternal of paternal alleles

<p>heterochromatin- highly packed genes- usually not expressed </p><p>euchromatin- loosely packed genes- expressed. Gene transcription is affected by location of nucleosomes along the promoter and where the DNA attaches to chromosome. </p><p>histone acetylation- acetyl groups are attached to histone tail’s amino acid and opens up chromatin strcuture- promoting transcriptiton </p><p>DNA methylation- addition of methyl groups that reduces transcription- long term inactivation of genes. methylation regulates genomic imprinting determination of maternal of paternal alleles </p>
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epigenetics

inheritance of traits transmitted by not directly involving the nucleotide sequence

ex) identical twins- one of them develops genetically based disease, other does not.

  • chromatin modifications may be passed unto offsprings