Use the Following Information When Answering the Corresponding Questions)

Multiple Choice

Use the following information when answering the corresponding questions) .
A group of enzymes known as cytosine- specific DNA methylases recognize CpG dinucleotide sequences-that is, a cytosine followed by a guanosine G) in one DNA strand-and add methyl groups to the cytosine. Many proteins bind to methylated CpG, including the methyl- CpG binding protein 2 MeCP2) . MeCP2 binding leads to the formation of a closed state of chromatin, thus silencing gene expression. A recent paper by Chen et al. reported an interesting mechanism of regulating transcription of a gene via MeCP2 W. Chen, Q. Chang, Y. Lin, A. Meissner, A. E. West, E. C. Griffith, R. Jaenish, and M. Greenberg. 2004. Derepression of BDNF transcription involves calcium- dependent phosphorylation of MeCP2, Science 302:885-89) . This gene, called BDNF, encodes brain- derived neurotrophic factor BDNF) -a protein that plays an important role in nerve cell and central nervous system function, including memory and learning. Remarkably, most cases of Rett syndrome, an important cause of mental retardation in females, are due to loss- of- function mutations of MeCP2.
-A scientist has a vial containing DNA and tries to digest it with DNA digesting enzymes. After analyzing it, she finds that no digestion occurred. What would be the most likely reason for this?

A) The DNA was packed into regions called euchromatin.
B) The DNA was embedded in the plasma membrane and was not accessible for the enzyme.
C) The DNA was tightly packed into 30nm chromatin fibres.
D) The DNA was tightly packed into 10nm chromatin fibres.