3.5 - Control of gene expression Flashcards
what does it mean when a gene is expressed?
turned on, making protein associated to said gene
when do genes expressed and proteins produced vary? (3)
- cell type
- developmental stage
- environmental conditions
housekeeping genes
constitutively (constantly) expressed genes, code for proteins performing basic cell functions
what is the main way or regulating gene expression?
controlling transcription
transcription factors
proteins that bind to DNA, effecting frequency of transcription of specific gene therefore associated protein
how is gene expression in bacteria highly efficient?
genes only expressed when/where they’re required
promoters (2)
- genes have upstream control elements in DNA (promoters)
- in absence of regulation, promoter exhibits basal (base level) level of transcription
repressors
binds to promoter blocking RNA polymerase
activators
stimulate RNA polymerase binding to promoter (bind slightly upstream from promoter)
operons
used in bacterial gene expression, gene cluster and promoter plus additional sequences, function together in regulation
2 eukaryotic transcription factor domains (2)
- DNA-binding domain
- activation domain
DNA-binding domain (2)
- binds to regulatory sequences
- transcription factor proteins structures so they can interact with major groove of DNA helix to affect gene transcription
activation domain
regulates polymerase through binding other proteins
3 main types of eukaryotic transcription factor (3)
- homeodomain DNA-binding unit
- zinc finger domains
- leucine zipper
promoter positive and negative regulatory elements (3)
positive:
1. enhancer
negative:
1. silencers
2. insulators
enhancer elements (promoter regulatory element) location
typically thousands of base pairs away from transcription start site (different thing to promoter). either upstream (5’), downstream (3’) or within an intron of transcribed sequence
silencers and insulators (promoter regulatory elements) role (3)
- distant
- repress transcription
- demarcate (set boundaries) of regulatory unit/prevent the regulatory sequences within affecting adjacent cells
how can enhancer function be assayed
by fusing reporter gene (such as green fluorescent protein) to gene of interest
enhancer (promoter element) role
bind transcription factors and co-activators that help stabilise transcription machinery making it easier for RNA polymerase to initiate transcription.
how does chromatin effect RNA polymerase access to promoters
hinders access to promoters (default repression)
what is required for RNA polymerase to access promoter?
chromatin remodelling
what is required for even base level of gene expression?
positive regulation mechanisms
how is transcription precision maintained in eukaryotes
combinatorial control of many different factors such as enhancers, chromatin remodelling and basal transcription factors
examples of transcription factor activation (2)
- steroid hormone (hydrophobic)
- hormone (hydrophilic)
steroid hormone transcription factor activation (3)
- hydrophobic
- pass through cell membrane and bind to receptor in cytoplasm
- receptors translocate to nucleus, acts as transcription factors to directly regulate gene expression
hormone transcription factor activation (3)
- binds to receptor on cell membrane
- activates protein kinase
- kinase phosphorylates specific inactive transcription factor activating it, triggers activation of particular gene
heterochromatin
dense, inactive regions of chromosome
euchromatin
less dense, active regions of chromosome (allows access to transcriptional machinery)
remodelling complexes
condense/recondense chromatin by sliding nucleosomes in chromosome (allows/prevents access to transcriptional machinery)
what allows the recruitment of enzymes and transcription factors?
reversible covalent modification, mostly at N-terminus domain (amino) - found near exterior of nucleosome
how can histones be modified (3)
- acetylation
- phosphorylation
- methylation (can be heritable - epigenetic)
protein synthesis control points in eukaryotes (7)
- synthesis of primary RNA transcript
- posttranscriptional modifications of mRNA
- degradation of mRNA
- protein synthesis
- posttranslational modification of protein
- targeting and transport of protein
- degradation of protein
role of alternative splicing in perception of different sound frequencies (4)
- sound vibrations activate potassium channels in hair cell membranes
- need 100s of different channel isoforms (different versions) to respond to different frequencies
- alternative exons used at 8 regions encode >500 isoforms of channels
- each responds to different sound frequency
microRNA role
RNAs that regulate eukaryotic gene expression by binding to mRNAs
how to microRNAs regulate gene expression (3)
- binds to mRNA
- larger initial transcript cleaved to yield the mature mRNA, associates with proteins of argonaut family to form complexes
- microRNA component of complex binds to mRNA (base pair formation), mRNA subsequently degraded (by cleaving it or blocking translation)
% human genes regulated by microRNA
60%
proteasome
big complex of enzymes, recycles proteins in eukaryotes
how do proteasomes degrade/recycle proteins? (2)
- proteins targeted for breakdown by labelling with ubiquitin
- resulting amino acids can be re-used in biosynthesis or further broken down to carbon skeletons for other uses
stages of protein life cycle (7)
- transcription initiation
- posttranscriptional processing
- RNA stability
- translational regulation
- protein modification
- protein transport
- protein degradation
what phase of protein do drugs mostly target?
complete proteins eg. receptors and enzymes
when are most genes expressed in life cycle of a differentiated tissue?
early development
how can you induce pluripotent stem cells? (2)
- isolate (eg skin cell - fibroblast) and grow in culture
- introduce genes for a cocktail of transcription factors into the cell
potential applications for induced pluripotent stem cells? (3)
- tissue replacement
- studying diseases
- drug screening
what cells can become any type of cell?
inner mass cells of early embryos
