Theme 3 module 1

Question 1

Under favourable conditions and available nutrients…

Answer 1

all cells have the essential machinery that favours cell growth and division

Question 1

Aerobic environments can be recreated…

Answer 1

Using culture media which is stock filled with nutrients which can include amino acids, vitamins, nucleotides and carbohydrates

Question 2

Most prokaryotes grow best at certain favourable temperatures…

Answer 2

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

Question 3

DNA of the bacterial nucleoid

Answer 3

contains the information required to orchestrate a response to any change in the environment

Question 4

Housekeeping genes

Answer 4

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

Question 5

Regulated genes

Answer 5

genes which can be turned off and on as-needed basis

Question 6

bacterial cells

Answer 6

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

Question 7

Regulating the expression of enzymes

Answer 7

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

Question 8

Altering gene expressing E.Coli bacterial cells

Answer 8

-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

Question 9

If we grow E. coli cells in an environment which contains both glucose and the disaccharide lactose

Answer 9

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

Question 10

The significance of this metabolic shift

Answer 10

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

Question 11

As a result

Answer 11

changes in
bacterial growth occur over time when bacteria
are growing in an environment containing both
glucose and lactose

Question 12

General properties of glucose metabolism at the cellular level

Answer 12

-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

Question 13

B-galactosidase

Answer 13

enzyme that can metabolize lactose to produce glucose and galactose
so, the cell provides itself with
the much needed glucose

Question 14

How does the cell
accomplish the task of metabolizing lactose?

Answer 14

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.

Question 15

1960s by Francois Jacob
and Jacques Monod investigated how E. coli are
able to produce the B-galactosidase that is
needed for lactose metabolism

Answer 15

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

Question 16

gene expression

Answer 16

the functional product of the gene is made,
modified and activated

Question 17

for protein coding genes

Answer 17

this means that transcription,
translation, and protein modification must be
completed

Question 18

Three very distinct levels of
regulation must occur

Answer 18

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

Question 19

Transcriptional regulation controls

Answer 19

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

Question 20

In this way a gene is
transcribed or turned on

Answer 20

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

Question 21

Once the messenger RNA is made

Answer 21

the messenger RNA may or may not be immediately translated into a protein

Question 22

Initiation of translation
in eukaryotes occurs by

Answer 22

the binding of the
ribosome to the 5’ end or 5’CAP of the mRNA

Question 23

In prokaryotes, the ribosome will bind

Answer 23

to and initiate translation at the specific Shine-Dalgarno sequences

Question 24

The rate at which translation occurs

Answer 24

will affect the amount of protein that is produced
the amount of protein produced
depends upon the stability of the mRNA. If the
mRNA is quickly degraded, then very little protein
will be made

Question 25

The primary sequence of the polypeptide

Answer 25

is not an active protein
It is post-translational control
mechanisms that allow the polypeptide chain to be folded into a functional three-dimensional structure
this protein must be further
modified to activate it by specific chemical
modifications

Question 26

As
the polypeptide leaves the ribosome

Answer 26

it is seen in
its linear arrangement
More than 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

Question 27

post translational regulation

Answer 27

fastest level. this mechanism allows cell to have a stockpile of protein in the cell that is simply inactive
Once the cell receives an appropriate
signal, this can then lead to a simple modification to turn on all of the inactive proteins
These simple modifications are very fast and can result in quick cellular responses to changes that are
brought about in the environment

Question 28

Transcriptional regulation

Answer 28

slowest
the cell is starting from scratch.
Expression of a functional protein requires that the cell activate transcription, complete translation, and finally modify the protein product
This type of regulation is often prevalent with more drastic environmental changes that a cell
can be exposed to. For example, when glucose is depleted from the environment in which E. coli
cells are growing, we have learned that these bacterial cells are able to transcriptionally regulate and increase the 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

Question 29

Though transcriptional regulation would be the slowest level of regulation

Answer 29

it would also certainly
be the most efficient. The cell does not waste any energy or resources making a mRNA or polypeptide unless it really needs to
this mechanism of regulation
is the slowest, it is the most economical for a cell

Question 30

This efficiency can be observed when

Answer 30

E. coli cells only increase gene expression of the B-galactosidase
gene in the presence of lactose as a nutrient supplement within their local environment