Epigenetics
-the heritable change in gene function, without changing the DNA base sequence
-these changes are caused by changes in the environment and can inhibit transcription
epigenome
a single layer of chemical tags on the DNA
-impacts the shape of the DNA-histone complex and whether the DNA is tightly wound so won’t be expressed or unwound so it will be expressed
What happens if DNA is tightly wound?
-transcription factors can’t bind
-the epigenome which is due to changes in environment, can inhibit transcription
what does methylation of dna do?
-increased methylation of DNA inhibits transcription
-this prevents transcriptional factors from binding and attracts proteins that condense the DNA-histone complex. In this way methylation prevents a section of DNA from being transcribed
what does the acetylation of histone proteins do?
-decreased acetylation of associated histone proteins inhibits transcription
-If acetyl groups are removed from the dna then the histones become more positive and are attracted more to the phosphate group on DNA
-this makes the dna and histones more strongly associated and hard for the transcription factors to bind.
heterochromatin
-when dna is tightly coiled and transcription is inhibited which is caused by:
-increased methylation and decreased acetylation
euchromatic
-when transcription will occur and its caused by decreased methylation and increased acetylation
abnormal methylation
links to control of transcription- methylation can cause a gene to turn on or off
hypermethylated
tumour suppressor cells can become hypermethylated- an increased number of methyl groups attached to it- results in the gene being inactivated and becomes turned off
hypomethylated
-may occur in oncogenes
-reducing the number of methyl groups attached- results in the gene being permanently switched on
what factors can add epigenetic tags?
diet, stress and toxins can add epigenetic chemical tags to the DNA and this can control gene expression in eukaryotes
tumour suppressor genes
-these genes produce proteins to slow down cell division and to cause cell death if DNA copying errors are detected
