Epigenetics Flashcards
What does the structure and function of a cell depend on
The proteins that it synthesises
How do cells become specialised
Signals in environ cause some genes are switched on and produce active mRNA that is translated into proteins within the cell
What is the epigenome
All of chemical markers attached to the surface of histone proteins and the DNA wrapped around them
What does the attachment of a methyl group(CH3) to DNA of a gene do
Attachment of a methyl group prevents the transcription to mRNA by stopping the RNA polymerase enzyme and transcription factors from binding as condenses the chromatin making it wrap more tightly around histone (heterochromatin)
How can histones be modified and effect this has
Can be modified by addition of acetyl groups to histone tails which affects how tightly the DNA is wrapped around the histones, when wound tightly the genes are inactive as inaccessible so cannot be transcribed to mRNA and make proteins. When acetyl group added wrapped more loosely
What happens to epigenetic markers during DNA replication
The epigenetic markers are copied with the DNA so that when eg a pancreas cell divides it forms another pancreas cell and the correct set of genes remain active
Study into the lac operon model in prokaryotes
-studied bacteria that only produce enzyme beta-galactosidase when disaccharide lactose present in surrounding medium to make glucose and galactose monosaccharides
-when lactose not present in environment a lactose represor molecule binds to DNA which prevents transcription of beta-galactosidase gene
What happens in bacteria if lactose present
Lactose binds to represor which is prevented from binding to the DNA and the beta-galactosidase gene is expressed and the mRNA coding for it is transcribed and translation produces the beta-galactosidase
What is a promoter region
Site for RNA polymerase attachment adjacent to the gene to be transcribed
Which genes can be expressed in eukaryotes
Genes in uncoiled, accessible regions of DNA can be transcribed into mRNA
How does transcription start
-RNA polymerase binds to the section of DNA adjacent to the gene to be transcribed(promoter region)
-attachment of a regulator protein also usually required to start transcription
Two ways transcription of a gene can be prevented
-protein represor molecule attaching to the DNA of promoter region to block attachment site
-protein represor molecules can attach to regulator protein themselves to prevent them from attaching
What are transcription factors
Proteins that bind to DNA, affecting the rate of transcription eg activators amd repressors
What are activators
Increase the rate of transcription by helping RNA polymerase bind to DNA
What are operons
Clusters of structural genes all transcribed together that code for useful proteins eg enzymes
What are Repressors
Decrease the rate of transcription by preventing RNA polymerase from binding to DNA
What is gene expression
Refers to how often or when proteins are created from the instructions within your genes
Where do methyl groups attach on DNA sequence
CpG sites, bind to cytosine base found next to guanine base in DNA sequence
What is demethylation
The removal of methyl groups meaning chromatin more loosely packed and gene exposed so accessible for transcription
What is heterochromatin
Tightly packed chromatin,DNA wrapped around histone not accessible to RNA polymerase and transcription factors so transcription cannot occur and gene not expressed
What is euchromatin
Loosely packed chromatin, DNA exposed and accessible for RNA polymerase and transcription factors to bind to and gene activated and transcribed
What causes chemicals to be added to DNA/histones
Caused by environmental factors eg diet/smoking/activity level
What happens if gene not activated
The protein it codes for is not produced as mRNA cannot be made
Name of enzyme that adds methyl group to CpG site
DNA methyltransferase
