7.2- factors affecting gene expression Flashcards
what does gene expression mean?
-genes can be switched off when they are not needed
-this prevents cellular resources being wasted
-cancer results when genes do not turn off properly
what are transcription factors?
-protein molecules which control transcription of genes, they bind to a specific site called a promoter which are found at the start of a target gene in the DNA in the nucleus and affect transcription of genetic material
what is cell differentiation
-the process by which a cell becomes specialised for a particular function
2 types of transcription factors
- activators- stimulate or increase rate of transcription
2.repressors- inhibit or decrease rate of transcription
how do activators work
-help RNA polymerase bind to the start of the target gene and activate transcriptions
how do repressors work
-inhibit or decrease rate by preventing RNA polymerase from binding to target gene, therefore stopping transcription
type of transcription factor- oestrogen and how it works
-oestrogen is a steroid hormone that can affect transcription by binding to a transcription factor
-the transcription factor is known as an oestrogen receptor
-this then moves to the nucleus where it binds to the promotor region before the target gene
-this then acts as a promotor
what are enhancer sequences?
-specific regions of the DNA to which transcription factors bind and regulate the activity of the DNA by vhanging the structure of the chromatin, making it more or less available to RNA polymerase so either stimulating or preventing transcription of gene
what happens in splicing
-pre mRNA is produced at end or transcription, it contains introns and exons
-introns are removed from mRNA by enzymes which cut them out
-exons are then joined together using spliceosomes to form completed mRNA
-mRNA then leaves nucleus via nuclear pore and enters cytoplasm
3 intracellular systems that can interact to control genes- epigenetics
- DNA methylation
- histone modification
- non coding RNA
what is the concept of epigenetics
-idea that our phenotype can be altered by chemical tags added to the histones and/or DNA which can be changes due to the environment
-these chemical tags can alter gene expression and passed on to next gen
what is DNA methylation?
-adding of methyl groups
-occurs at CG in DNA chain with a phosphate bond between them
-can also modify structure of the histones also having epigenetic effect
-always silences a gene or sequence of genes
-prevents transcription
-demethylation is the opposite and also important
what is histone modification?
-DNA helices wind around histones to form chromatin, the DNA/ protein complex that makes up chromosomes
-chromatin can be condensed or less condensed
-this controls whether or not the DNA can be transcribed
-
what happens in epigenetics?
-determines whether a gene is switched on or off
-done through attachment or removal of chemical groups from DNA or histone proteins (known as epigenetic mark)
-these do not alter the DNA but DO alter how easy it is for enzymes and other proteins needed for transcription to interact and transcription to take place
what is the epigenome of a cell?
-an accumulation of all the signals it has received in a lifetime and so acts like a cellular memory
-this means the environment the foetus develops in has an influence along with external factors during an organisms lifetime
