Epigenetics

a)  Define genome, gene expression, histones and its relation to DNA.                                 (5)

-       A genome is the whole set of genetic instructions within an organism, stored in DNA (or RNA). It contains all the information needed for an organism to develop, function, and reproduce. Gene expression is the process of copying information from DNA on to messenger RNA and then translating the message into a series of amino acids to form a protein. While histones are a specific/special protein around which DNA is coiled to form chromatin.

-       A genome’s relation to DNA, is found in the use of storage, where a genome is stored within DNA. DNA is coiled/wrapped around a group of 8 histones to form a nucleosome. Gene expression is only enabled due to the information provided by DNA to then be translated into a series of amino acids to then form a protein.

b)  A definition and description of epigenetics.                                                                     (4)

-       Factors that make genes more of less likely to be expressed may be inherited, these factors are classified as epigenetics.

-       ‘Epi’ means ‘on top of’, or ‘in addition to’, so epigenetic refers to changes in gene expression that result from mechanisms other than changes in the genes, that is in the DNA or genome.

-       Epigenetics is the study of how cells control gene activity without changing the DNA sequence.

-       An epigenome is the sum of all the factors that determine when, and which genes are ‘switched on’ or expressed. The epigenome helps to control which genes are active in a particular cell and therefore which proteins will be produced.

-       If the epigenome is abnormal, certain cells may be abnormal and disease may result due to the abnormality.

c)   Explain the 2 main epigenetic mechanisms/processes (acetylation and methylation).       (6)

-       A histone modification that may occur is acetylation – the addition of an acetyl group to the histone protein. This reduces the attraction between histones and DNA, relaxing the structure of the chromatin. This promotes transcription by allowing RNA polymerase access. Due to this acetylation can be seen to enhance gene expression.

-       DNA methylation usually occurs at sites on the DNA molecule where a cytosine nucleotide is adjacent toa guanine nucleotide. These are known as CpG sites, cytosine-phosphorus-guanine. Methylation of DNA slows down gene expression by restricting access to RNA polymerase.

-       Histone methylation may either increase or decrease the transcription of genes, depending on where the methyl groups attach and how many become attached. If the methylation causes the chromatin structure to relax, it will increase transcription.

-       Acetylation relaxes the chromatin and increases transcription, whereas methylation tightens the chromatin, which decreases transcription.

d)  Briefly state 2 causes of epigenetic (trans-generational) effects e.g. obesity                      (2)

-       Teo main causes of epigenetic (transgenerational) effects include environmental factors and lifestyle choices. Environmental factors such as diet, exposure to toxins, and social stress can induce changes in the epigenome which is then passed down to future generations. Lifestyle factors such as diet, obesity and physical activity can also change epigenetic patterns and potentially be inherited.

-       Environmental and lifestyle factors are often shown to influence epigenetic mechanisms, such as DNA methylation, histone acetylation and microRNA expression

e)  Describe in detail 2 examples of well researched studies illustrating epigenetic changes

  e.g. twin studies, the effects of famine and the effects of trauma.                                       (8)

- The Dutch famine (1944–1945): Babies who were in the womb during the famine showed different DNA methylation patterns. As adults, they had a higher risk of health problems such as obesity and type 2 diabetes.

-  Trauma in Holocaust survivors and Vietnam veterans with PTSD: These people showed changes in DNA methylation in genes like FKBP5, which is linked to stress response. These changes affected how stress hormones were regulated, and some of these epigenetic marks were seen in their children as well, showing that trauma effects can sometimes be passed to the next generation.