Eukaryotic gene expression Flashcards
what is the structure and function of any cell type dependant on
the proteins the cell synthesises
how proteins modify the cell and what do the changes cause
changing cell structure
controlling cell processes
cause the cell to become permanently specialised
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different proteins are made by different cells so give rise to different types of specialised cells
why do genetically identical cells produce different proteins
different cells only express some of their genes
genes expressed are switched on
genes deactivated or repressed are switched off
what causes cell differentiation
switching on and off the transcription of certain genes
what causes cells to be switched on or off
in response to an internal or external stimulus e.g. hormone
chemical gradients
differential gene expression process
all stem cells contain the same genes but not all of them are active
different stimuli (chemical or hormones) switch on different genes
genes activated are transcribed to produce active mRNA
active mRNA is translated from switched on gene and is translated to produce proteins
proteins determine structure and function of cells
permanently modifies cells to become specialised
different genes activated/proteins produced results in different types of specialised cells being produced
process of switching genes on in eukaryotic cells
DNA is uncoiled so the genes can be exposed
RNA polymerase and a regulator protein (transcription factor) binds to promotor region on DNA
gene is switched on (expressed)
transcription of gene occurs which makes active mRNA
active mRNA is then translated to make a protein
process of switching genes off in eukaryotic cells
protein repressor molecule attaches to the DNA at the promotor region
RNA polymerase cannot bind to the operator gene
protein repressor can also attach to the regulator protein (transcription factor)
gene is not switch on so mRNA is not made
no transcription can occur
what makes up the epigenome
chemical markers attached to DNA and histones
what does the epigenome affect
how accessible sections of DNA are
what happens if a section of DNA is not accessible
genes in that section cannot be transcribed so are inactive and not expressed
what are the two ways the epigenome influences the genes transcribed in cells
DNA methylation
histone modification
how does DNA methylation affect how genes are transcribed
addition of methyl to DNA bases prevents transcription by stopping RNA polymerase from binding to the promotor region
stops mRNA being produced
protein synthesis does not occur
gene is inactive
no gene expression
how does histone modification affect how genes are transcribed
addition of methyl groups affects how tightly DNA wraps around the histone
if DNA is wrapped tight then gene is inaccessible
gene cannot be transcribed
mRNA cannot be produced
protein synthesis cannot occur
gene is inactive
no gene expression
