Gene regulation Flashcards
What does protein production cost
- Large amounts of energy
( transcription; translation; splicing out introns and making other modification to mRNA )
Do all cells have the same genome
Yes, all have same DNA but some are expressed (on ) while others aren’t
Explain cells regulating gene expression
- 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
What processes are involved in gene regulation in eukaryotes
- Transcription factors
- DNA availability
- RNA processing
- mRNA exit from nucleus
- RNA degradation
- Protein synthesis and degradation
What processes are involved in gene regulation in prokaryotes
- Operon model
- helps us understand when we switch on genes under a particular set of conditions
Explain an example of prokaryotes gene regulation
- 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
- In absence of milk these enzymes are not produced – not present\not
How are genes regulated
- Francois Jacob and Jacques Monod (1961) - proposed the operon model to explain gene regulation in prokaryotes following experiments on E.coli
What did Jacob and Monod observe
- 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
What does the operon consist of
- Promoter
- Operator
- Structural genes
- Regulatory proteins
Explain promoters fully
- DNA sequence where RNA polymerase first attaches
- Short segment of DNA
Explain operaters fully
- DNA sequence where active repressor binds
- Short segment of DNA
Explain structural genes fully
- One to several genes coding for enzymes of a metabolic pathway
- Translated simultaneously as a block
- Long segment of DNA
Explain regulatory proteins fully
- 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
Explain negative control
- 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
Explain positive control
- 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 ✓ ✓ ✓
Explain the action CAP
- 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
In conclusion
The circumstances in the cell will determine if transcription can take place, regulatory proteins will start or stop transcription from occurring
Explain what happens is lactose and glucose are present
- 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
Explain what happens is lactose is absent and glucose is present
- 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
Explain what happens is lactose is present and glucose is absent
- 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
Explain what happens when lactose and glucose are absent
- 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
Explain cells stopping gene expression
- Eukaryotic cells use many regulatory mechanisms
- DNA availability
Explain DNA availability
- 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
Explain cell regulate gene expression- eukaryotic organisms used transcription factors
- 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
What are the major signaling molecules involved in the regulation of tooth embryogenesis.
- 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
Explain lactose intolerance in adult phase of humans
- 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.
How else can genes be silenced
- mRNA exit from nucleus
- RNA degradation
- Protein processing and degradation
Explain mRNA exiting from the nucleus
For a protein to be produced, mRNA must leave the nucleus and attach to a ribosome. If mRNA fails to leave, gene is silenced
Explain RNA degradation exiting from the nucleus
Not all RNA molecules are equally stable. Some are rapidly degraded even before they can be translated
Explain protein processing and degradation exiting from the nucleus
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.
Explain epigenetic inheritance
- 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
What epigenetic inheritance
Refers to the study of heritable changes (passing on traits) in gene expression that occur without a change in DNA sequence
Explain X-Chromosome inactivation
- 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)
What distinct mechanisms relate to the initiating and sustaining of
epigenetic modifications
- 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
Explain heterochromatin
- 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
