3.4.9 Regulation of Transcription and Translation Flashcards Preview

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What is epigenetics?

Study of changes to gene expression when there's no change in the gene itself


In eukaryotes, what determines whether a gene is switched on or off? (i.e. whether gene is expressed (transcribed and translated) or not)

Epigenetic Control


How does epigenetic control work?

  • Works through attachment or removal of chemical groups (aka epigenetic marks) to or from DNA or histone proteins
  • Epigenetic marks don't alter base sequence of DNA
  • Alter how easy it is for enzymes and other proteins needed for transcription to interact with and transcribe the DNA


Epigenetic changes can also occur in response to changes in the ________


e.g. pollution and availability of food


Most epigenetic marks on DNA are ______ between generations



Epigenetic changes can be inherited. What is meant by this?

Means expression of some genes in offspring can be affected by environment changes that affected their parents or grandparents

e.g. epigenetic changes in some plants in response to drought have been passed on to later generations


Name 2 methods of epigenetic control

  • Increased methylation of DNA
  • Decreased acetylation of histones


What effect does increased methylation of DNA have on a gene?

Switches a gene off


What effect does decreased acetylation of histones have on a gene?

Switch genes off


What is a promoter?

Sequence of bases before gene where a transcription factor binds


Where does methyl groups (example of epigenetic mark) always attach to?

CpG site


What is a CpG site?

Where cytosine and guanine base are next to each other in DNA


Explain how increased methylation results in a gene not being expressed

  • Increases methylation changes DNA structure so transcriptional machinery (enzymes, proteins etc.) can't interact with gene
  • e.g. If promotor methylated transcription factors (protein) cannot bind and recruit RNA polymerase


What are histones?

Proteins that DNA wraps around to form chromatin which makes up chromosomes


Chromatin can be highly _____ or less _____

Chromatin can be highly condensed or less condensed


What does "how condensed chromatin is" affect?

The accessibility of DNA and whether or not it can transcribed


How can histones be epigenetically modified?

By the addition or removal of acetyl groups (example of epigenetic mark)


Explain how the gene is affected when histones are acetylated

  • When histones are acetylated, chromatin is less condensed
  • Means transcriptional machinery can access DNA = allows genes to be transcribed


Explain how the gene is affected acetyl groups are removed from histones

Chromatin becomes highly condensed and genes in DNA can't be transcribed ∵ transcriptional machinery can't physically access them


What are histone deacetylase (HDAC)?

Enzymes responsible for removing acetyl groups


Give an example of epigenetics that can lead to the development of disease

Abnormal methylation of tumour suppressor gene and oncogenes can cause cancer


 Epigenetic changes are ______


Makes them good targets for new drugs to combat diseases they cause


Epigenetics Treatment

Describe how the drugs work

Drugs designed to counteract epigenetic changes that cause diseases


Epigenetics Treatment

Describe how a drug would counteract increased methylation

Drugs stop DNA methylation = treat diseases

 e.g. drug azacitidine is used in chemotherapy of types of cancer caused by increased methylation of tumour suppressor genes


Epigenetics Treatment

Describe how a drug would counteract decreased acetylation of histones (genes switched off)

  • Drugs (HDAC inhibitor drugs) work by inhibiting activity of histone deacetylase (HDAC) enzymes
  • Results in genes remaining acetylated and proteins they code for being transcribed


State the problem with developing drugs to counteract epigenetic changes

Is that these change take place normally in lot of cells ∴ have to make drugs as specific as possible

e.g. drugs used in cancer therapies can be designed to target dividing cells to avoid damaging normal body cells


What are transcription factors?

Protein molecules that control the transcription of genes


In eukaryotes, transcription factors move from the ______ to the ______

In eukaryotes, transcription factors move from the cytoplasm to the nucleus


What do transcription factors do once they're in the nucleus?

  • They bind to specific DNA sites near start of their target genes (genes they control the expression of)
  • They control expression by controlling the rate of transcription


Give some examples of what transcription factors do

  • Activators: stimulate or increase the rate of transcription
    • e.g. help RNA polymerase bind to start of target gene and activate transcription
  • Repressors: inhibit or decrease rate of transcription
    • e.g. bind to start of target gene, preventing RNA polymerase from binding, stopping transcription

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