Epigenetics

Question 1

What is Epigenetics?

Answer 1

• DNA modifications that do not change the DNA sequence can affect gene activity
• Chemical compounds that are added to single genes can regulate their activity: these modifications are known as epigenetics changes
• The epigenome comprises all of the chemical compounds that have been added to the entirety of one’s DNA (genome) as a way to regulate the activity (expression) of all the genes within the genome.
• The chemical compounds of the epigenome are not part of the DNA sequence, but are on or attached to DNA (“epi” means above in Greek)
• Epigenetic modifications remain as cells divide and, in some cases, can be inherited through the generations
• Environmental influences, such as a person’s diet and exposure to pollutants, can also impact the epigenome
• Epigenetic changes can help determine whether genes are turned on or off and can influence the production of proteins in certain cells, ensuring that only necessary proteins are produced
• For example, proteins that promote bone growth are not produced in muscle cells
• Because errors in the epigenetic process, such as modifying the wrong gene or failing to add a compound to a gene can lead to abnormal gene activity or inactivity, they can cause genetic disorders
• Conditions including cancers, metabolic disorders, and degenerative disorders have all been found to be related to epigenetic errors

Question 2

Acetylation

Answer 2

• Attaching on acetyl group to the histones to loosen the DNA and promote protein synthesis
• By adding an acetyl group to the tall of a histone it repels the negatively charged DNA, loosening the DNA
• This allows transcription to occur effectively “turning on/up” a gene

Question 3

Methylation

Answer 3

• Adding a methyl group to the DNA at a CpG site inhibits gene expression
• A methyl group is added to the DNA molecule where a cytosine nucleotide is next to a guanine nucleotide: CpG sites.
• This results in the polymerase being unable to bind to the DNA molecule to stops transcription: effectively silencing or “turning off” a gene.

Question 4

Epigenetics

Answer 4

• Methylation increases with time as we become more exposed to varying environmental factors as we age.
• Some of these Methyl group markers/tags, can become IMPRINTED and can then be passed onto offspring.
• Other Epigenetic tags are removed from parents chromosome after fertilisation.

Question 5

Twin Studies

Answer 5

• Identical twins develop from a single zygote, which for some reason divides and becomes 2 individuals.
- These twins are known as MONOZYGOTIC twins.
• For this reason, identical twins have the exact same genetic code, however they often show different phenotypes.
• DIZYGOTIC (or Fraternal) twins are where 2 eggs are fertilised by 2 sperm at the same time and do not have identical genetic code.
• Twins will show slightly different phenotypes because during their lifetime they have been exposed to different environmental conditions that have altered their epigenome, which has caused different genes to be switched on or off.
• These changes increase with age, the older a set of twins get, the more different they become as they spend more time in different environmental conditions.