A pharmaceutical researcher is evaluating a nuclear enzyme inhibitor for the treatment of an inherited disorder. During an experiment, he extracts and purifies nuclear enzymes from skin cells of an affected patient. One of these enzymes is found to catalyze the methylation of cytosine residues in DNA using S-adenosyl-methionine (SAM) as the methyl donor. This enzyme most likely plays a crucial role in which of the following genetic processes?

Question

A pharmaceutical researcher is evaluating a nuclear enzyme inhibitor for the treatment of an inherited disorder.  During an experiment, he extracts and purifies nuclear enzymes from skin cells of an affected patient.  One of these enzymes is found to catalyze the methylation of cytosine residues in DNA using S-adenosyl-methionine (SAM) as the methyl donor.  This enzyme most likely plays a crucial role in which of the following genetic processes?

Quizplus · Accepted Answer

DNA methylation refers to the addition of methyl groups to nucleotide residues (often adenine and cytosine) by DNA methyltransferase, an enzyme that uses S-adenosyl-methionine (SAM) as the methyl group donor. DNA methylation is an epigenetic process by which eukaryotic organisms modify gene expression without altering the genetic code. For example, methylation of cytosine-guanine dinucleotide repeats (CpGs) in the promoter region of genes effectively silences transcription of those genes. Fragile X syndrome is an X-linked disorder caused by an increased number of CGG trinucleotide repeats on the fragile X mental retardation 1 (FMR1) gene, leading to hypermethylation of cytosine residues and FMR1 inactivation. Cytosine methylation is also used in genomic imprinting, a phenomenon in which an offspring's genes are expressed in a parent-specific manner. For instance, an allele inherited from the father may be inactivated or "imprinted" by methylation so that only the allele from the mother is expressed. (Choices A and D) Aneuploidy refers to the presence of an abnormal number of chromosomes and is the result of chromosomal nondisjunction during mitosis or meiosis. (Choice B) Epistasis is a phenomenon in which the allele of one gene affects the phenotypic expression of alleles in another gene. (Choice E) Pleiotropy refers to the phenomenon in which a single gene influences multiple phenotypic traits. Educational objective: Genomic imprinting refers to the phenomenon in which an offspring's genes are expressed in a parent-specific manner. Genomic imprinting is caused by DNA methylation, an epigenetic process in which genes can be silenced by attaching methyl groups to cytosine residues in the DNA molecule. __________ References: Mammalian Genomic Imprinting. (http://www.ncbi.nlm.nih.gov/pubmed/21576252)

A Pharmaceutical Researcher Is Evaluating a Nuclear Enzyme Inhibitor for the Treatment