Theme 3 module 1 Flashcards
Under favourable conditions and available nutrients…
all cells have the essential machinery that favours cell growth and division
Aerobic environments can be recreated…
Using culture media which is stock filled with nutrients which can include amino acids, vitamins, nucleotides and carbohydrates
Most prokaryotes grow best at certain favourable temperatures…
But environments can undergo variable changes where a prokaryote may need to adapt to what is available
where gene regulation becomes important to help prokaryotes respond to their environments
DNA of the bacterial nucleoid
contains the information required to orchestrate a response to any change in the environment
Housekeeping genes
DNA which contains genes that are required all of the time for normal functioning
constitutively expressed and they are always transcribed and translated
This includes genes important for structural proteins of the cell, RNA
and DNA polymerases and genes that are coding
for ribosomal proteins
constant maintenance of general cellular activities
Regulated genes
genes which can be turned off and on as-needed basis
bacterial cells
respond to changing environments
by altering the expression
pattern of some genes
regulated
bacterial genes can be transcribed and translated
to allow for the production of important enzymes
or proteins that are needed to bring about
changes in growth and division
Regulating the expression of enzymes
it would be very
important to be able to regulate the expression of
enzymes that are important for nutrient
metabolism
we consider that cells must be able to metabolize
macromolecules such as carbohydrates into
usable sources of cellular fuel such as ATP
Altering gene expressing E.Coli bacterial cells
-glucose is carbohydrate that is the preferred energy source of E. Coli
-if we expose a bacterial culture to a limited amount of glucose we find once glucose is used up, bacterial growth is arrested
-E.Coli cells have a unique gene expression mechanism which allows them to be able to switch to a metabolizing an alternate fuel source when the preferred glucose source is depleted
If we grow E. coli cells in an environment which contains both glucose and the disaccharide lactose
bacteria will still metabolize glucose before switching to utilizing lactose as a fuel source
the products of glucose metabolism themselves activate the switch between glucose and lactose use
The significance of this metabolic shift
since bacteria only metabolize lactose when it is available, it would be a waste of resources to synthesize lactose-metabolising enzymes in the absence of lactose
when lactose is an available nutrient source and glucose is not available, bacteria are able to quickly upregulate the
expression of genes that produce lactose-
metabolizing enzymes
As a result
changes in
bacterial growth occur over time when bacteria
are growing in an environment containing both
glucose and lactose
General properties of glucose metabolism at the cellular level
-glucose is a monosaccharide
-the absence of a direct source of glucose, the cell can metabolize the disaccharide, lactose which is
made up of one molecule each of glucose and galactose
B-galactosidase
enzyme that can metabolize lactose to produce glucose and galactose
so, the cell provides itself with
the much needed glucose
How does the cell
accomplish the task of metabolizing lactose?
The cell needs to make the enzyme B-
galactosidase. B-galactosidase is produced by
turning on transcription of the B-galactosidase
gene. The cell will only do this when there is
lactose available and no glucose available.
1960s by Francois Jacob
and Jacques Monod investigated how E. coli are
able to produce the B-galactosidase that is
needed for lactose metabolism
Jacob and
Monod observed that the production of the B-
galactosidase enzyme is dependent upon the
presence of lactose in the environment
grew E. coli in a
lactose-free medium, added lactose to the
medium, and then removed it again. At the same
time, they measured the amount of B-
galactosidase enzyme produced in the cultured
cells. They found that the amount of B-
galactosidase protein produced by the E. coli
cells began to steadily increase in response to
the addition of lactose to the growth media
the production of the B-
galactosidase ceased once the lactose was
removed. Results from their experiment
demonstrated that lactose in the growth medium
induced expression of the B-galactosidase gene
gene expression
the functional product of the gene is made,
modified and activated
for protein coding genes
this means that transcription,
translation, and protein modification must be
completed
Three very distinct levels of
regulation must occur
transcriptional control
to allow for the transcription of DNA to mRNA,
translational control to allow for the translation of
mRNA to proteins, and finally, post-translational
control to allow for modifications and activation of
produced proteins
The regulation of the
expression of an activated protein must take into
consideration how each of these levels of control
are modified
This is true if transcription fails,
if translation fails, or if post-translational
modifications do not occur
Transcriptional regulation controls
the amount of messenger RNA that is produced in the cell. In both prokaryotic and eukaryotic cells, activation of transcription requires that proteins bind to a region near the beginning of the gene, the promoter, and increase the binding of the
enzyme, RNA polymerase
In this way a gene is
transcribed or turned on
By controlling the
binding of proteins to the promoter, the cell can either activate or inhibit transcription. It is this level of regulation that we will focus upon in
module 2 for bacterial cells
Once the messenger RNA is made
the messenger RNA may or may not be immediately translated into a protein
Initiation of translation
in eukaryotes occurs by
the binding of the
ribosome to the 5’ end or 5’CAP of the mRNA
In prokaryotes, the ribosome will bind
to and initiate translation at the specific Shine-Dalgarno sequences
