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MolBio and Genetics I > 5. Regulation of gene expression > Flashcards

5. Regulation of gene expression Flashcards

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1
Q

What is gene expression

A

is the translation of the genetic information into functional molecular proteins or biologically acctive RNAs

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2
Q

At what points can gene expression be regulated

A
  • transcriptional control
  • RNA processing control
  • RNA transport and localization control
  • translation control
  • mRNA degradation control
  • protein activity control
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3
Q

When does bacterial gene regulation primarily occur

A

transcription initiation

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4
Q

How can one specific sigma factor regulate an entire group of genes

A

when they share the same/similar -10/-35 sequences

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5
Q

How are functionally related bacterial genes often arranged

A

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
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6
Q

How does the tryptophan operator work?

A
  • 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
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7
Q

How are lac and tryptophan operons different

A
  • 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
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8
Q

What do transcription factors do?

A

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
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9
Q

Only when will a gene be regulated by a particular TF

A

if the correct DNA sequence is found in its gene control region

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10
Q

What is a helix turn helix DNA binding domain

A
  • 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
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11
Q

What is a Homeodomain

A

helix turn helix motif and consists of 3 alpha helix bundle with alpha recognition helix binding in the major groove

  • exclusively eukaryotic
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12
Q

What are TF genes with homeobox called

A

hox

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13
Q

What is the zinc finger binding domain

A

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
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14
Q

how do multiple ZnF motifs within a TFs DNA binding domain help

A

combination gives extra specificity to which DNA sequence the TF interacts with

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15
Q

What are the principle dimerization domains

A
  1. leucine zipper
  2. helix-loop-helix (HLH)
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16
Q

What does the basic leucine zipper do

A

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
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17
Q

What is the importance of leucine zipper (bZIP)

A

basic domains are stabley positioned to interact with DNA in the major groove

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18
Q

explain structure of helix loop helix (bHLH) DNA binding domain

A

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
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19
Q

What do basic helix loop helix DNA binding domain facilitate

A

unstructured and flexible loop facilitates successful dimerization

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20
Q

What is epigenetics

A

changes in gene expression that can be retained through cell divisions but are caused by mechanisms other than changes in DNA sequence

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21
Q

What do post-translational histone modifications act as?

A

signals to regulate chromatin structure and DNA accessibility

22
Q

What is euchromatin

A

transcriptionally active

  • nucleosomes are further apart or
  • has activating histone methylase
23
Q

what is heterochromatin

A

transcriptionally repressed

  • nucleosomes are more tighly pact hindering accessibility
  • repressive histone methylase
24
Q

What methylates almost all DNA on the cytosines of CpG sequence

A

DNA methyl transferase

25
Q

How does methylation cause transcriptional repression

A
  • 5 methylcytosine binds specialised methyl binding proteins
  • chromatin remodelling enzymes recruited
  • these help form transcriptionally repressed chromatin
  • long term silencing of gene expression
26
Q

What are house keeping genes

A

genes expressed in every cell type

27
Q

What do promoter regions of house keeping genes contain?

A

has CpG islands: region of high densities of CpG motifs that are never methylated

  • can only be silenced using chromatin remodelling
28
Q

What happens to CpG islands associated with promerts of genes that will not be used

A

could be methylated

eg. somatic genes in sperm genes

29
Q

what are tissue specific genes

A

specialized genes that are only expressed in certain cell types

30
Q

How can tissue specific genes become transcriptionally active

A

must have their 5 methyl cytosine marks actively removed

31
Q

What is imprinting

A

describes the phenomen by which certain genes are expressed in a parents of origin specific manner and is controlled by DNA methylation

32
Q

What are Xist

A

non coding RNA that helps to inactivate one or more x chromosomes to form a barr body

33
Q

An example is cell memory is Drosophila Eyeless gene. What does it do and what happens when a group of cells recieve a signal to activate Ey

A
  • encodes a homeodomain TF that activates a cascade of gene expression required for its own continued expression (positive feedback)
  • activation causes expression and division, where they retain memory of this signal
34
Q

What are insulator elements

A

ensure that specific regulatory DNA sequences control gene promoters.(cannot act outside its domain)

They interact by DNA looping

35
Q

What can IBP( insulator binding proteins)/insulator interaction do?

A
  • block inappropriate interaction between a regulator sequence and a gene promoter (i.e. enhancer blocking)
  • provide barrier to the spreading of neighbouring domain of transcriptionally inactive heterochromatin (i.e. barrier function)
36
Q

What do the segments in embryo provide for the structured Drosophila adult?

A

progenitor cells

37
Q

What segmentation genes are needed from the earliest stage of development of drosophilas

A
  • Maternal genes
  • gap genes
  • Pair rule genes
  • segment polarity genes
  • homeotic (Hox) genes
38
Q

What do maternal genes of drosophilas do

A

establish the anterior posterior axis of the body plan

39
Q

Where is the bicoid mRNA localised

A

anterior

40
Q

Where is the nanos mRNA localised

A

posterior

41
Q

What do bicoid and nanons proteins do?

A

they extablish a gradient

  • bicoid protiens bind caudal mRNA and inhibit thier translation leading to addition gradient formation
  • nanons bind to hunch back mRNA (do same)
42
Q

What activates the expression of gap genes and what is the conseqeunce

A

differing threshold concentraions of maternally provided TFs along the A-P axis

  • mutations in gap genes lead to deletion of entire contigous body segments
43
Q

What do mutations in pair rule genes lead to

A

embryos with half as many parasegments

44
Q

What causes the expression of pair rule genes

A

flactuations in the relative concentrations of gap gene proteins along the A-P axis

45
Q

What do pair rule genes do

A

regulate the expression of segment polarity genes that precisly refine the anterior posterior boundaries between the developing body segments

46
Q

What do Segment polarity genes do

A

refine the segmental pattern established by the pair rule genes by defining the A-P segmental boundaries

47
Q

What does the mutation of homeotic genes lead to

A

loss of correct identity in cells of a particular segment and therefore adoption of an incorrect identity

48
Q

How are homeotic genes activated

A

under control of the gap genes and pair rule genes

49
Q

What does the developmental pathway a cell within a particular cell segment takes depend on?

A

complement of homeotic genes expressed within it

  • if homeotic gene is mutated then the functional complement is altered resulting in a different fate/identity
50
Q

permanent record of cell position is established in early embryo genesis and is used much later in development in specify the correct adult structures. How is information retained?

A
  • positive feedback loop by Hox genes self-regulation
  • chromatin remodeling
    • polycomb group (maintains repressed Hox genes
    • trithorax group (maintains transcriptionally active Hox genes)
51
Q

What gives the correct identity to the body segments along the anterior posterior axis during development

A

a transcription factor mediated hierachy of regulated gene expression

MolBio and Genetics I (9 decks)

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