Chapter 11.4: Transcription Can Be Regulated by Epigenetic Changes to DNA and Histones

Flashcards from Chapter 11.4 of Principles of Life, 3rd Edition.

Epigenetic changes

Reversible changes in DNA that involve varying levels of chromatin packaging, resulting from histone chemical modification or DNA methylation

• Seen through identical twins growing differently as a result of the environment

Nucleosome

A core of eight positively charged histones around which DNA is wound, forming closed chromatin

Acetylation

Performed by histone acetyltransferases, this neutralizes the charges of the amino acid tails on histones and loosens the compact nucleosome for regulatory protein binding

• Can be recruited by transcription factors

• May be reversed by histone deacetylases

Methylation

Performed by DNA methyltransferase, this typically occurs to cytosine bases adjacent to guanines, giving rise to the name CpG sites

• Results in the binding of repressing transcription factors in stable, long-term bonds

• Can be maintained by maintenance methyltransferase or reversed by demethylase for replication needs

CpG islands

Regions of DNA that are rich in CpG sites, typically found in promoters that are not expressed

Euchromatin

DNA that is transcribed into mRNA with lower DNA methylation rates; this stains lightly under a microscope

Heterochromatin

DNA that is more condensed with little transcription and heavy methylation rates; this stains darkly under a microscope

• Seen with female mammals’ X inactivation, resulting in differently expressed traits as one X chromosome is methylated to prevent aneuploidy

Genomic imprinting

The passing down of specific methylated genes from each parent resulting in some transcriptionally active and inactive genes