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Is gene expression being switched off or tuned here without a change in DNA sequence?
More, if you want it
Which part of the patient's cells carries the change?Tap a term: its definition, what you can do with it, and how often the exam asks it.
Definition: a methyl tag on cytosine that lowers reading of a gene.
You can: Tell DNA methylation from a mutation by whether the DNA letters change.
Definition: a chemical tag on the proteins that pack DNA.
You can: Tell histone modification from DNA methylation by whether the tag sits on the packing proteins or on cytosine.
Definition: random silencing of one X chromosome in each cell.
You can: Tell Lyonization from adverse Lyonization by whether the silenced X is chosen at random.
Definition: silencing of the X with the normal allele more often than chance.
You can: Tell adverse Lyonization from a full Fragile X change in a male by the presence of a second, normal X.
Definition: sugar added to proteins, with no effect on gene reading.
You can: Tell glycation from histone modification by whether gene reading changes.
Each card is one term. The grey line is what the patient says, which is what the question stem gives.
Summary
DNA methylation is the addition of a methyl group to cytosine, which silences the gene with the sequence unchanged.
DNA methylation is the addition of a methyl group to , which silences the gene with the sequence unchanged. DNA methylation most commonly occurs on cytosine, at the carbon 5 position, forming 5-methylcytosine.
The tag typically sits at CpG sites, where cytosine precedes guanine.
DNA methylation and are the two mechanisms responsible for most epigenetic variation. Textbooks regard DNA methylation as the principal epigenetic mechanism.
The textbook places cytosine methylation in the promoter region of genes. A promoter is the stretch of DNA where reading of a gene starts. A mutation is a genetic change, because it alters the DNA letters. Every DNA letter stays in place when a methyl tag is added. Cytosine is one of the DNA letters.
A silenced gene with an unchanged DNA sequence points to an epigenetic change.
Among psychiatric disorders, DNA methylation is the epigenetic mechanism most strongly associated with schizophrenia. Choose DNA methylation for schizophrenia.
Malnutrition in pregnancy raises schizophrenia risk in the offspring. The proposed cause is altered DNA methylation. Schizophrenia risk genes also converge on histone modification, NMDA receptor signalling and immune function. Candidates sometimes choose histone modification for schizophrenia.
Mnemonic
Methyl caps cytosine, tags wrap histones, sugar just sticks. Cue: without changing the DNA sequence
Methyl caps cytosine means DNA methylation puts a methyl tag on cytosine. Tags wrap histones means histone modification tags the proteins that pack DNA. Sugar just sticks means glycation adds sugar to proteins and leaves gene reading alone, so it is not epigenetic.
5 more sections on Epigenetics: DNA methylation, histone modification, glycation, Lyonization and more
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