epigenetics

• gene expression is the process of copying information from DNA onto mRNA and then translating the messages into protein
• At any given time, a cell is making mRNA from only a fraction of its genes. for example, insulin production is activated in cells of pancreas but not bone or muscle cells
• genes being used to make mRNA are considered to be switched on, genes that are not are switched off
• Factors determining whether gene is expressed : 

  • Age
  • Time of day
  • Signal from other cells
  • Environment of cells
  • Whether cell is dividing
• epigenetics refers to changes in gene expression that results from mechanisms other than changes in the genes. factors that are epigenetic are factors that make genes more or less likely to be expressed may be inherited 
• What a person does during their lifetime can cause changes that are passed on
• Epigenome is the sum of all factors that determine when, where and which genes are expressed
• Some amino acids in histone protein are changed which causes changes the shape of histone. changes are copied each time new DNA molecule is formed. modified shape ensure stem cell that differentiate do not revert back into a stem cell
• acetylation is the addition of an acetyl group (CH3CO) to histone protein
• acetylation reduces attraction between histone and DNA, relaxing the structure of chromatin. this allows RNA polymerase access, promoting transcription and enhancing gene expression
• Methylation is the addition of a methyl groups (CH3) to histone protein
• methylation usually occurs at sites on DNA where cytosine is adjacent to guanine, also known as CpG sites
• methylation either increase or decrease transcription of genes, depending on where and how many are attached. it usually restricts access to RNA polymerase, inhibiting gene expression 
• Epigenome can change by exposure to certain environmental stimuli like severe stress, nutritional factors and toxins or drugs that enter the cells
• environmental factors do not change DNA but interfere with the transcription and translation process