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Life Sciences 141 > Gene regulation > Flashcards

Gene regulation Flashcards

1
Q

What does protein production cost

A
  • Large amounts of energy

( transcription; translation; splicing out introns and making other modification to mRNA )

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2
Q

Do all cells have the same genome

A

Yes, all have same DNA but some are expressed (on ) while others aren’t

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3
Q

Explain cells regulating gene expression

A
  • Each cell contains the same set of genes, but expresses different subsets of genes pertaining to their function
  • Regulation of gene function also gives cells flexibility to respond to changing conditions
    ( after a large meal to break it down )
  • For growth and development - unique combinations of genes enable cells in different locations of the body to specialize – flowers on a plant
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4
Q

What processes are involved in gene regulation in eukaryotes

A
  • Transcription factors
  • DNA availability
  • RNA processing
  • mRNA exit from nucleus
  • RNA degradation
  • Protein synthesis and degradation
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5
Q

What processes are involved in gene regulation in prokaryotes

A
  • Operon model
    - helps us understand when we switch on genes under a particular set of conditions
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6
Q

Explain an example of prokaryotes gene regulation

A
  • Ecoli
  • Main nutrient source is glucose; lactose and other ingredients
  • If glucose is present, there will not be a need to break down the lactose to glucose
  • When milk is ingested three enzymes are rapidly produced for breakdown
    of lactose ( 3 different genes being switched on and off )
    • In absence of milk these enzymes are not produced – not present\not
      transcribed (negative control)
    • Glucose present, enzymes not needed – not needed not transcribed
    • The lac-operon is responsible for the production of the required enzymes only activated in the absence of glucose, presence of lactose
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7
Q

How are genes regulated

A
  • Francois Jacob and Jacques Monod (1961) - proposed the operon model to explain gene regulation in prokaryotes following experiments on E.coli
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8
Q

What did Jacob and Monod observe

A
  • Related genes that produced the right enzymes for this situation are
    organised as operons
    – A group of genes plus a promoter and an operator that control the transcription of the entire group at once
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9
Q

What does the operon consist of

A
  • Promoter
  • Operator
  • Structural genes
  • Regulatory proteins
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10
Q

Explain promoters fully

A
  • DNA sequence where RNA polymerase first attaches
  • Short segment of DNA
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11
Q

Explain operaters fully

A
  • DNA sequence where active repressor binds
  • Short segment of DNA
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12
Q

Explain structural genes fully

A
  • One to several genes coding for enzymes of a metabolic pathway
  • Translated simultaneously as a block
  • Long segment of DNA
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13
Q

Explain regulatory proteins fully

A
  • Cyclic AMP (cAMP) binds to catabolic activator protein called CAP – activator binding site – facilitates binding of RNA polymerase
  • Repressor proteins – binds to operator stops RNA polymerase
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14
Q

Explain negative control

A
  • Regulation mediated by factors that block or turn off transcription
  • Repressor proteins – binds to operator stops RNA polymerase
  • If lactose is absent and glucose is present XXX
  • When lactose is absent and glucose is absent XXX
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15
Q

Explain positive control

A
  • Regulation mediated by a protein that is required for the activation of a transcription unit.
  • Cyclic AMP (cAMP) binds to catabolic activator protein called CAP – activator binding site – allows binding of RNA polymerase
  • When lactose is present and glucose is
    absent ✓ ✓ ✓
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16
Q

Explain the action CAP

A
  • CONCENTRATION OF cAMP IS CONTROLLED BY THE CONCENTRATION OF GLUCOSE
  • WHEN GLUCOSE IS ABSENT, cAMP IS HIGH AND IT WILL BIND TO CAP – this allows RNA POLYMERASE TO DO ITS WORK AND TRANSCRIPTION CAN TAKE PLACE
  • WHEN GLUCOSE IS PRESENT, cAMP IS LOW IT WILL NOT BIND TO CAP AND RNA POLYMERASE CAN NOT DO ITS WORK – NO TRANSCRIPTION
17
Q

In conclusion

A

The circumstances in the cell will determine if transcription can take place, regulatory proteins will start or stop transcription from occurring

18
Q

Explain what happens is lactose and glucose are present

A
  • Allolactose attaches to the repressor protein changing its shape so that it detaches from the operator but
  • cAMP concentration is low and does not combine with CAP or the binding site – no RNA polymerase
19
Q

Explain what happens is lactose is absent and glucose is present

A
  • A repressor protein binds to the operator preventing the RNA polymerase from transcribing the genes
  • cAMP concentration is low and does not combine with CAP or the binding site – no RNA polymerase
20
Q

Explain what happens is lactose is present and glucose is absent

A
  • Allolactose attaches to the repressor protein changing its shape so that it detaches from the operator
  • Cyclic AMP (cAMP) binds to catabolic activator protein and attaches to the activator binding site
  • RNA polymerase binds efficiently to the promotor
  • Transcription takes place
21
Q

Explain what happens when lactose and glucose are absent

A
  • A repressor protein binds to the operator
  • Cyclic AMP (cAMP) binds to catabolic activator protein and attaches to the activator binding site
  • RNA polymerase binds efficiently to the promotor but is blocked by repressor
22
Q

Explain cells stopping gene expression

A
  • Eukaryotic cells use many regulatory mechanisms
  • DNA availability
23
Q

Explain DNA availability

A
  • Chromosomes must be unwound for genes to be expressed. In addition a cell can ‘tag’ unneeded DNA with methyl groups (-CH3).
  • Proteins inside cells bind to tagged DNA, preventing gene expression and signalling cell to fold that section of DNA more tightly.
  • Transcription factors and RNA polymerase cannot access highly compacted
    DNA, so these modifications turn off the genes
  • DNA is unavailable
24
Q

Explain cell regulate gene expression- eukaryotic organisms used transcription factors

A
  • In eukaryotic cells groups of proteins called transcription factors bind to DNA at specific sequences that regulate transcription
  • RNA polymerase cannot bind to a promoter or initiate transcription of a gene if transcription factors are not present
    – TF respond to external stimuli that signal a gene to turn on
  • A transcription factor may bind to a gene’s promoter or to an enhancer, a regulatory DNA sequence that lies outside the promoter
25
Q

What are the major signaling molecules involved in the regulation of tooth embryogenesis.

A
  • The BMP (bone morphogenetic protein),
  • FGF (fibroblast growth factor), TGFb (transforming growth factor b),
  • EGF (epidermal growth factor),
  • SHH (sonic hedgehog), and the
  • WNT (wingless) families
26
Q

Explain lactose intolerance in adult phase of humans

A
  • Most infants produce lactase, the enzyme that digests the lactose in milk
    If babies are lactose intolerance then a mutation of the LCT
    gene has occurred.
  • Some adults may be lactose intolerant because the lactase-encoding gene is turned off after infancy.
    Modification of the gene has not occurred.
  • Other adults may continue to digest milk due to modification of an enhancer that allows transcription of the lactase gene throughout life.
27
Q

How else can genes be silenced

A
  • mRNA exit from nucleus
  • RNA degradation
  • Protein processing and degradation
28
Q

Explain mRNA exiting from the nucleus

A

For a protein to be produced, mRNA must leave the nucleus and attach to a ribosome. If mRNA fails to leave, gene is silenced

29
Q

Explain RNA degradation exiting from the nucleus

A

Not all RNA molecules are equally stable. Some are rapidly degraded even before they can be translated

30
Q

Explain protein processing and degradation exiting from the nucleus

A

Some proteins must be altered before they become functional. If not they cannot function. Some proteins are degraded shortly after they form, while others persist longer.

31
Q

Explain epigenetic inheritance

A
  • Changes to the genome without changes to the nucleotide sequences
  • Leads to changes in gene expression and therefore traits
  • Across cell generations
  • Across organism generations
32
Q

What epigenetic inheritance

A

Refers to the study of heritable changes (passing on traits) in gene expression that occur without a change in DNA sequence

33
Q

Explain X-Chromosome inactivation

A
  • In the mammalian female, one of the X-chromosomes (either one) in each cell become inactivated through the methylation of cytosine on the DNA sequences which makes transcription impossible
  • Unlike the gene-poor Y chromosome, the X chromosome contains over 1,000 genes that are essential for proper development and cell viability.
  • However, females carry two copies of the X chromosome, resulting in a potentially toxic double dose of X-linked genes
  • Either X-chromosome can be inactivated, this is a completely random process
  • This specific chromosome becomes condensed and is visible as a dark spot, called the Barr body, against the nuclear membrane during the interphase phase
  • The same chromosome then becomes inactivated in all the cells that are descendants of the particular cell (mitosis)
34
Q

What distinct mechanisms relate to the initiating and sustaining of
epigenetic modifications

A
  • DNA methylation and
  • Histone modification
  • This results in changes in the offspring that cannot be linked directly to the genetic make-up of the parents
35
Q

Explain heterochromatin

A
  • In electron micrographs we observe darker-stained regions of the chromatin, called the heterochromatin, where the chromatin is highly condensed, and the lighter less condensed region called the euchromatin
  • In euchromatin the histone molecules have so-called tails (strings of amino
    acids) which have acetyl groups (-COCH3) attached
    Transcribed
  • Heterochromatin methyl groups (-CH3) are attached
    Not transcribed

Life Sciences 141 (22 decks)

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