control of eukaryotic genes :...D

gene expression is altered…

in response to environmental changes, internal and external, most often at the transcription stage

differential gene expression

result of genes being turned on or off in different cells having the same genome

multicellular organisms

serve the needs of the organism, not individual cells

7 points of control

packing/unpacking the DNA, transcription, mRNA processing, mRNA transport, translation, protein processing, protein degradation

DNA packing

DNA coils and folds, wrapped around histone proteins. tightly wrapped means no transcription and genes are turned off

nucleosomes

a section of DNA wrapped around proteins

DNA methylation

the methylation of DNA blocks transcription factors and no transcription will occur, genes are off

histone acetylation

acetylation of histones unwinds DNA, enabling transcription and genes are on

regulatory genes

code for regulatory proteins or RNA

repressors or inducers

interact with regulatory sequences to turn genes off or on, binding to DNA to block or stimulate transcription

genes that are always on

ribosomal DNA

promoter

nearby control sequence on DNA, where RNA polymerase and transcription factors bind

enhancer

distant control sequences on DNA, where activator proteins bind

transcription factors

the number and combination can increase (activator) or decrease (repressor) expression

post-transcriptional control

alternative RNA splicing generates different mRNA molecules

regulation of mRNA degradation

life span of mRNA determines amount of protein synthesis

mRNA degradation

shortening of poly-A tail and removal of 5’ cap, mRNA interference

RNA interference

siRNA (small interfering RNA) are short segments of RNA that bind to mRNA, creating sections of double stranded triggering degradation

control of translation

regulatory proteins attach to 5’ end of mRNA, preventing the attachment of ribosomal subunits and initiator tRNA

protein processing

folding, cleaving, adding sugar groups, targeting for transport

protein degradation

ubiquitin tagging and proteasome degradation

ubiquitin

death tag, marks unwanted proteins which are then broken down in proteasomes