Cycle 8: Control of Gene Expression Flashcards
(37 cards)
What is the difference between differential, spatial, and temporal gene expression?
differential gene expression - tissue specific transcription factors for different organisms
temporal gene expression - when are genes expressed (different lifetime, depending on environment)
spatial gene expression - where is the gene being expressed
What are the levels of regulation? Which organisms?
- eukaryotes -
- transcriptional: will transcription occur or not and which genes transcribed
post transcriptional: RNA or premRNA already made, control if translation will occur or not
translational: target 3’ and 5’ UTR determines rate at which proteins are made
- post translational: protein already made, regulate amt of protein
How does the E. coli lac operon work? Structure?
- ex. lactose metabolization gene expression in prokaryote –
structure:
- promotor
- operator
- regulatory gene lac I that codes for Lac repressor protein
- transcription unit of 3 structural genes: lacZ, lacY, & lacA
- termination sequence
- 3’UTR and 5’UTR
- lac repressor binds to operator and stops transcription (no RNA poly)
- when lactose present:
1. lactose coverted to allolactose
2. allolactose bind to repressor causing repressor conformation change to inactive shape
3. RNA poly can transcribe
What is the function of the products of lacZ and lacY gene?
lacZ codes for beta-galactosidase enzyme which metabolizes lactose to galactose and glucose
lacY codes permease transmembrane enzyme which is on the membrane and allows lactose in the cell
What happens when repressor is mutated? lacZ? operator?
repressor - continuous transcript bc RNA poly can bind if inhibition without lactose present or over transcription
lacZ - lactose not broken down
operator - lac repressor unable to bind
How are genes differentially expressed in different cells types (ex. liver vs lens cells)
tissue-specific transcription factors
What is the role of tissue-specific transcription factors in the cell? How do they lead to spatial and temporal gene expression?
tissue-specific transcription factors bind to promoters only when needed
- positive or negative regulators
Where can transcription factors be found?
transcription factors are PROTEINS!
nucleus – when they are transcribed and when functioning to bind to promotor
cytoplasm – when they are translated
across nuclear membrane – when they perform their function in the nucleus
What is the mechanism of pre-mRNA splicing?
- SnRNPs 5’ (donor) and 3’ (acceptor splice sites go together
- 5’ looks for downstream 3’
- constitutive or alternative
What is the 3’ splice site recognition sequence at the intron/exon border?
NCAGG
How does mutations in the 5’ and 3’ splice sties lead to formation of aberrant (deviant) mRNA and proteins?
NCAGG mutated in 3’ :
- 5’ to next 3’ spliced out bc cell thinks the whole thing is an intron
- loss of exonic sequence
5’ splice site mutation:
- original intron is interpreted as exonic sequence
- changed reading frame
- adding intronic sequence
- abnormal when it is not evolutionary predetermined *
What is the splicing mechanism behind the abnormal production of the beta-globin protein in beta-thallasemia?
blood disorder resulting in abnormal hemoglobin (oxygen carrier) made of two B-globin subunits and gamma-globin subunits
- b-globin subunit has mutation that results in it looking like NCAGG (TCAGG) which is 3’ splice site so cell thinks part of intron is exon and in the exon (which was an intron) now has TAG –> UAG –> premature stop codon!
- TAG in intron doesn’t mean anything
- shorter beta globin protein –> less functional heloglobin
** longer mRNA causes shorter protein
How does ApoB100 and ApoB48 form during RNA-editing?
ApoB100 in liver, ApoB48 in small intestine
ApoB1000 - translation <– unedited mRNA –> gets deaminated causing mRNA to have stop codon so ApoB48 is a truncated version
- type of post transcriptional regulation
What is the role of telomerase in telomere length? Why is telomerase activated in cancer cells and why is it present stem cells?
telomerase - enzyme that restores telomeres in some cells (cancer, germ cells, stem cells, early embryogenesis
telomere - repeated sequence at end of chromosome that protects chromosome that decreases in length with each replication
What is the “hayflick limit” and “cell senescence”?
hay flick limit: number of replications that is safe for telomere length
cell senescence: stage where cell will no longer divide but will still function
How do we develop from a one cell zygote?
The zygote is a stem cell that can differentiate into various different types of tissues to produce an entire organism
What are the 3 factors that ensure temporal and spatial regulation?
- every cell contains complete genome established in fertilized egg. DNA of all differentiated cells are “identical”
- only a small percentage of the genome is expressed in each cell, and the transcripts are specific for that cell type
- unused genes in differentiated cells are not destroyed or mutated. they retain the potential for being expressed
What are the 3 factors that ensure temporal and spatial regulation?
- every cell contains complete genome established in fertilized egg. DNA of all differentiated cells are “identical”
- only a small percentage of the genome is expressed in each cell, and the transcripts are specific for that cell type
- unused genes in differentiated cells are not destroyed or mutated. they retain the potential for being expressed (ex. telomerase can be turned on by cancer cells)
What are stem cells? What are its properties?
cells that have the potential to develop into different cell types in the body during embryogenesis and adult life
properties:
- telomerase expressed
- potency
What is potency?
differentiation potential
- potency for different types of stem cells are different –> not all stem cells have the ability to differentiate into any cell type
What are the types of stem cells?
- embryonic stem cells
- somatic (adult) stem cells
- induced pluripotent stem cells (iPS cells)
- umbilical cord stem cells
What are totipotent stem cells?
differential into embryonic and extraembryonic (umbilical cord) cell types creating a complete viable organisms (only zygote)
What are pluripotent stem cells?
descendants of totipotent cells and cal differentiate into nearly all cells of the human body (except extraembryonic) so it can’t make an organism
What are multipoint stem cells?
can differentiate into a number of cells but only those of a closely related family of cells
- ex. bone marrow contains multipotent stem cells that give rise to all cells of the blood, but not other cell types)
