Advanced Placement (AP) Biology Practice Exam

What is the process of adding methyl groups to DNA bases called?

1. DNA replication

2. DNA transcription

3. DNA methylation

4. DNA translation

The correct answer is: DNA methylation

The process of adding methyl groups to DNA bases is known as DNA methylation. This biochemical modification can impact gene expression without altering the underlying DNA sequence. Methylation typically occurs at cytosine bases, particularly in regions known as CpG islands, which are often found near gene promoters. When methyl groups are attached to these cytosines, it can inhibit the binding of transcription factors and, thereby, reduce gene expression. DNA methylation plays a crucial role in various biological processes, including development, genomic imprinting, and the maintenance of cellular identity. Additionally, abnormal DNA methylation patterns have been implicated in various diseases, including cancer. In contrast, DNA replication refers to the process of copying the DNA to ensure that each daughter cell receives an identical set of DNA. DNA transcription is the process of copying a specific segment of DNA into RNA, which is then translated into proteins. DNA translation is the process by which the sequence of nucleotides in messenger RNA is converted into a polypeptide chain, ultimately forming proteins. Each of these processes involves different molecular mechanisms and serves distinct roles within the cell, highlighting the uniqueness of DNA methylation in regulating gene expression.