Final answer:
Histone acetylation, performed by histone acetyltransferases, loosens chromatin which allows transcription factors to bind and genes to be expressed. Histone deacetylation, performed by deacetylases, removes acetyl groups which leads to chromatin condensation and decreased gene expression.
Step-by-step explanation:
Gene expression is intricately regulated through various epigenetic mechanisms, including histone acetylation and deacetylation. Histone acetylation is catalyzed by enzymes known as histone acetyltransferases (HAT enzymes). This process involves the addition of acetyl groups to the lysine residues in histones, which results in a loosening of the chromatin structure and promotes access to the DNA for transcription. Transcription factors can now bind to the DNA, allowing for gene expression. Conversely, histone deacetylation, catalyzed by histone deacetylases, removes the acetyl groups, leading to chromatin condensation and a decrease in gene expression.
Histone modifications, including histone methylation and histone phosphorylation, along with acetylation, play a significant role in the regulation of gene expression by altering the chromatin structure. These reversible modifications can either recruit proteins that aid in transcription or block access to transcriptional machinery, thus controlling whether genes are turned on or off. Housekeeping genes, which are essential for basic cellular function, are typically less affected by these mechanisms as their expression is more constant.