Modulating Transcription (Theme 3: Module 1) Flashcards
What is needed for prokaryotic growth?
-favourable temperature
- nutrient-rich environment containing amino acids and carbohydrates
DNA of bacterial nucleoid contains:
the info needed to orchestrate a response to any change in the environment
House Keeping Genes
Genes that are required all of the time for normal functions
-constitutively expressed
-always being translated and transcribed
-allow for constant maintenance of general cellular activities
Ex: genes important for structural proteins, DNA, RNA polymerases and genes coding for ribosomal proteins
Regulated Genes
Genes that can be turned on and off as-needed
-when responding to a changing environment, bacterial cells can respond by altering expression pattern
-can be transcribed/translated to allow for the production of important enzymes/proteins that are needed to bring about changed in growth/division (ex: growth hormone)
-expressed only when needed and includes enzymes
Enzymes are important for:
metabolizing nutrients
Why is regulating the expression of enzymes important?
important for nutrient metabolism, especially for cells to be able to metabolize macromolecules, such as carbohydrates, into usable sources of cellular fuel such as ATP
E-Coli cells unique expression mechanism:
are able to switch to metabolizing on alternate fuel sources when the preferred glucose source is depleted
Significance of metabolic switch between glucose and lactose use
when lactose is an available nutrient source in the environment (glucose is not available), bacteria are able to quickly upregulate the expression of genes that produce lactose-metabolizing bacteria
it would be a waste otherwise to synthesize lactose-metabolizing enzymes in the absence of lactose
When do changes in bacterial growth occur?
over time when bacteria are growing in an environment containing both glucose and lactose
B-galactosidase
the enzyme that can metabolize lactase to produce glucose and galactose. this way, the cell provides itself with the much needed glucose
inshort: B-galactosidase metabolizes lactose
How is B-galactosidase made?
-produced by turning on transcription of the B-galactosidase gene
-only does this when these is no glucose available
Francois Jacob & Jacques Monod
investigated how E.Coli are able to produce the B-galactosidase that is needed for lactose metabolism
What they did?
-grew E.Coli in a lactose-free medium, added lactose to the medium, and then removed it again
-measured the amount of B-galactosidase enzyme produced in the cultured cells
Found that:
-the amount of B-galactosidase protein produced by the E.Coli cells began to steadily increase in response to addition of lactose to the growth media.
-The production of B-galactosidase ceased once the lactose was removed
Results: lactose in the growth medium induced expression of the B-galactosidase gene. Led to the explanation of the mechanisms that control B-galactosidase gene expression.
Transcriptional Regulation
controls the amount of mRNA that is produced in the cell
Activation of Transcription (both prokaryotes and eukaryotes) requires:
proteins bind to a region near the beginning of the gene, the promoter, and increase the binding of the enzyme, RNA polymerase
By controlling the binding of proteins to the promoter…
the cell can either activate or inhibit transcription
Initiation of Translation in eukaryotes vs prokaryotes:
Eukaryotes: occurs by binding the ribosome of the 5’ end or 5’ cap of the mRNA
Prokaryotes: the ribosome will bind to and initiate translation at the specific shine-dalgarno sequences
Rate at which translation occurs effects:
the amount of protein produced (amount depends on the stability of the mRNA)
-if mRNA is quickly degraded, very little protein will be made
Post-Translational Control Mechanisms:
allow the polypeptide chain to be folded into a functional 3D structure
-often this protein must be further modified to activate it by specific chemical modifications:
-genes have been transcribed into mRNA
-mRNA is then translated by the ribosomes to produce the liner polypeptide (string of amino acid residues that is exiting each ribosome) as polypeptide leaves ribosome, it is seen in this linear arrangement
-protein folds into a 3D shape. Over a dozen post-translational modifications regulate the ability of the protein to become active or inactive by driving the assembly into complexes, the binding of substrates, or the unmasking of enzymatic domains
Fastest level of Regulation
POST-TRANSLATIONAL
-allows the cell to have a stockpile of protein in the cell that is simply inactive
-once the cell receives an appropriate signal, this can lead to a simple modification to turn on all of the inactive proteins (these modifications are very fast and can result in cellular responses to changes that are brought about in the environment)
Slowest but most-efficient Regulation
TRANSCRIPTIONAL
slowest:
-cell starts from scratch
-expression of a functional protein requires that the cell activate transcription, complete translation, and finally modify the protein product
-often prevalent w/more drastic environmental changes that the cell can be exposed to
-(ex: when glucose is depleted from the environment in which E.Coli cells are growing, these cells are able to transcriptionally regulate and increase levels of B-galactosidase gene transcription to allow for lactose metabolism. Since the bacterial cells must first transcribe , then translate and modify the produced enzyme, this results in the delay of B-galactosidase production in response to the initial exposure of the bacterial cells to lactose)
Most Efficient:
-the cell does not waste any energy or resources making a mRNA or polypeptide unless it really needs to
-(ex: E.Coli cells only increase gene expression of the B-galactosidase gene in the presence of lactose as a nutrient supplement within their local environement. As a result, are able to efficiently metabolize lactose on an as-per-need basis)
