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The gene will have decreased expression because this chemical
reaction will result in uracil.
| 2. |
(Problem 6) How are patterns of DNA methylation transmitted
across cell division? |
|
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DNA is replicated by conservative replication to ensure that
one copy of the genome retains the DNA methylation pattern and is
passed on to one of the daughter cells. |
|
Special sequence-specific DNA binding proteins methylate the
DNA after it has been replicated so that the methylation pattern is
replicated before cell division. |
|
5-methylcytosine is deaminated to form uracil. The uracil is
then recognized by Uracil-DNA glycosylase, which corrects the base
back to cytosine. |
|
A long noncoding RNA is used as a guide after DNA replication
to target specific sequences for DNA methylation. |
|
DNA methyltransferases recognize hemimethylated DNA and use the
methylated strand as a template to methylate the new DNA
strand.
| 3. |
(Problem 26) Much of DNA methylation in eukaryotes occurs at
CpG dinucleotides, but some individual cytosine nucleotides are
also methylated to form 5-methylcytosine. Considering what you know
about the process by which DNA methylation at CpG dinucleotides is
maintained across cell division, do you think that methylation at
individual C nucleotides would also be maintained by the same
process? |
|
|
Yes. Individual cytosine nucleotides will have a cytosine
nucleotide on the opposite strand that can be methylated following
replication. Therefore, new methyl groups will be added by the
methyltransferases after replication. |
|
No. At CpG dinucleotides, two cytosine nucleotides site
diagonally across from each other on both DNA strands and both are
methylated. The presence of 5-methylcytosine on both strands is
required for maintaining methylation after replication. |
|
No. Methylation of individual cytosine nucleotides is a
consequence of transcriptional activity at that locus. Therefore,
methylation of these nucleotides is not epigenetic marks, and the
organism has no need to maintain them through DNA replication. |
|
Yes. Following replication, one stand of each new DNA molecule
is methylated and one is not. Special methyltransferase enzymes
recognize the methyl group on one strand and methylate the cytosine
on the other strand, perpetuating the methylated state of the DNA,
whether it is CpG or individual C nucleotides.
| 4. |
(Problem 24) Which honeybee in Figure 21.4 (the
worker or the queen) will have more copies of 5-methylcytosine in
their DNA? Explain your answer.
WILDLIFE GmbH/Alamy.
|
|
|
The queen. The bee that develops into the queen is fed royal
jelly, which inhibits the expression of the Dnmt3 gene,
leading to higher DNA methylation. |
|
The worker. The bee that develops into the queen is fed royal
jelly, which promotes the expression of the Dnmt3 gene,
leading to lower DNA methylation. |
|
The worker and the queen have similar copies of
5-methylcytosine in their DNA because queen development depends on
histone acetylation rather than DNA methylation. |
|
The queen. The bee that develops into the queen is fed royal
jelly, which promotes the expression of the Dnmt3 gene,
leading to higher DNA methylation. |
|
The worker. The bee that develops into the queen is fed royal
jelly, which inhibits the expression of the Dnmt3 gene,
leading to lower DNA methylation |
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