5. Regulation of gene expression Flashcards
What is gene expression
is the translation of the genetic information into functional molecular proteins or biologically acctive RNAs
At what points can gene expression be regulated
- transcriptional control
- RNA processing control
- RNA transport and localization control
- translation control
- mRNA degradation control
- protein activity control
When does bacterial gene regulation primarily occur
transcription initiation
How can one specific sigma factor regulate an entire group of genes
when they share the same/similar -10/-35 sequences
How are functionally related bacterial genes often arranged
in operons
Example:
- 5 genes that participate in the synthesis of the amino acid tryptophan are transcribed as a poly cistronic mRNA from a single promoter
- whether initiation occurs is dependent on operator
How does the tryptophan operator work?
- if free tryptophan level are high, tryptophan binds a transcriptional repressor protein
- represses interation with operator and blocks trancriptional initiation
- if low tryptophan level
- represser unable to interact with operator
- genes are transcriped to synthesize more
How are lac and tryptophan operons different
- Lac operon: ligand binds to remove regulatory protein from DNA this switches the gene on
- Tryptophan: ligand binds to allow regularory protein to bind to DNA switches. gene on
What do transcription factors do?
bind to regulatory DNA sequence to activate or repress transcription initiation
- bind to major groove of DNA forming H bonds between amino acid and bases
Only when will a gene be regulated by a particular TF
if the correct DNA sequence is found in its gene control region
What is a helix turn helix DNA binding domain
- red COOH end binds in major groove of DNA by series of hydrogen bonds. Amino acids defines the DNA sequence binding specificity
- the blue acts to stabilise the bound protein DNA complex
What is a Homeodomain
helix turn helix motif and consists of 3 alpha helix bundle with alpha recognition helix binding in the major groove
- exclusively eukaryotic
What are TF genes with homeobox called
hox
What is the zinc finger binding domain
compromises two antiparallel beta strands and one alpha helix forming a ‘finger-like’ projection that binds DNA
- example cysteine and histidine coordinate a zinc ion
how do multiple ZnF motifs within a TFs DNA binding domain help
combination gives extra specificity to which DNA sequence the TF interacts with
What are the principle dimerization domains
- leucine zipper
- helix-loop-helix (HLH)
What does the basic leucine zipper do
conserved hydrophobic leucine residues line one surface of the alpha helical dimerization domain
- exposed hydrophobic leucine patches interacts with like domains on their dimerization partner
- zips the two TFs together in coil
What is the importance of leucine zipper (bZIP)
basic domains are stabley positioned to interact with DNA in the major groove
explain structure of helix loop helix (bHLH) DNA binding domain
compromises two alpha helical regions joined by unstructured polypeptide loop
- one alpha helix contains an exposed surface of hydrophobic amino acids making up the dimerization domain
- second contains basic domain
What do basic helix loop helix DNA binding domain facilitate
unstructured and flexible loop facilitates successful dimerization
What is epigenetics
changes in gene expression that can be retained through cell divisions but are caused by mechanisms other than changes in DNA sequence
What do post-translational histone modifications act as?
signals to regulate chromatin structure and DNA accessibility
What is euchromatin
transcriptionally active
- nucleosomes are further apart or
- has activating histone methylase
what is heterochromatin
transcriptionally repressed
- nucleosomes are more tighly pact hindering accessibility
- repressive histone methylase
What methylates almost all DNA on the cytosines of CpG sequence
DNA methyl transferase
