Diversity Through Regulation Flashcards
trans-acting regulatory proteins
- regulatory protein acts at a great distance from where it is transcribed (eg. on a different chromosome)
cis-acting regulatory proteins (2)
- regulatory element is on same DNA molecule as gene being regulated
- may be near the gene (eg. promoter sequences) or at some distance (eg. enhancer sequence)
activator proteins (3)
- bind to enhancers, promoting activity of transcription complex
- some are more powerful than others
- some work synergistically
trans-acting repressor proteins
- bind to cis-acting regulatory sequences and block activators to prevent transcription
how can activator proteins work synergistically
- can promote greater levels of transcription in combination than either activator can promote on their own
how can genes expression be regulated in time and space? (3)
- WHERE the gene is expressed
- WHEN is the gene being expressed
- HOW MUCH is this gene expressed/transcript made
WHERE can a gene be expressed (3)
- cell
- tissue
- organ
WHEN can be gene be expressed (2)
- at specific stage or multiple stage in life history
- during development
correlation between mRNA levels to protein levels (2)
- poor correlation
- there are further downstream regulatory levels that can disrupt the correlation
how can upstream regulatory regions be classified (2)
- constitutive
- regulative
constitutive upstream regulatory regions
- this is when a gene is turned on and actively transcribed all the time
regulative upstream regulatory regions
- this is a case where the transcription from a gene is tightly regulated as to where and when it is expressed
transcription factor characteristics (4)
- can act on many genes
- can have dozens of enhancers
- may also have positive feedback loops regulating their own activities
- can be activators or repressors with varying affinities
Pax6 gene (3)
- protein encoded from this gene is a TF that controls expression of genes that are involved in eye development in humans (eyeless for mice)
- gene evolved once and were used as a control gene for eye development in descendant species
- role is conserved across a wide phylogeny
what happens when the Pax6 gene is present in the proper cell
- the eye develops normally
what happens when the Pax6 gene is non-functional or altered
- partial absence of eye
what happens when Pax6 is present in structure other than the eye
- eyes will grow on those structures
regulatory elements in regulatory genes vs structural/housekeeping genes
- regulatory genes (genes for TFs) often have more complex cis-regulatory elements than structure/housekeeping genes
what is an example of how cis-regulatory elements can modulate gene expression
- some genes may only be activated when specific relative concentrations of different TFs lead to activation of the enhancer for the gene
what does a gene regulatory network allow for
- precise control of where and when a gene is expressed, and how much is expressed
how do gene regulatory networks achieve their control (3)
- each regulatory protein can act on many genes
- cis-regulatory regions can be modular, with dozens of enhancers to allow for complex control of gene expression
- regulatory proteins may have feedback loops regulating their own activities
gene evolution (3)
- modes (2)
- result
- evolution of genes
- evolution of regulatory elements
- results in increase in gene function diversity
Sonic Hedgehog (Shh) (2)
- signally molecule that regulated limb development
- critical for development of vital organs
where would you find sequence changes in Shh gene (2)
- in regulatory regions or TF binding site
- would not see changes in protein coding sequences because it is still needed for development of other vital organs
Shh is critical for development of CNN, brain, and other organs, but the ZRS element that regulates its expression is defective in snakes: why do other systems still develop normally?
- there must be other enhancer elements that direct expression of SHH in CNS, brain and other organs
how do combinatorial possibilities of TFs maximize diversity of organisms from a limited number of genes (4)
- more TFs can create more unique combinations of control, allowing for more complex control of gene expression
- expansion of regulatory regions allow for more TF binding sites, and even more combinations
- concentrations and rations of activators and repressors determine whether particular region is activated or repressed
- regulatory regions allow for modular control of gene expression (multiple enhancers, each regulating expression in a different tissue)
