What type of methylation occurs throughout the life of a cell?

Maintenance methylation is the process that occurs throughout the life of a cell, ensuring that DNA methylation patterns are preserved during DNA replication. After DNA is replicated, maintenance methylation adds methyl groups to the cytosines in the newly synthesized strand, mirroring the methylation pattern present on the template strand. This mechanism is crucial for maintaining genomic stability and regulating gene expression over time, allowing for the inheritance of epigenetic marks from one generation of cells to the next.

In contrast, de novo methylation refers to the establishment of new methylation patterns, typically occurring during development or when environmental factors stimulate epigenetic changes. Active methylation and passive methylation are not standard terms widely used in the context of maintaining DNA methylation through replication processes and may refer to more transient or specific conditions of methylation, rather than the consistent, ongoing process involved in maintaining established patterns.