Modulating Transcription (Theme 3: Module 1)

Question 1

What is needed for prokaryotic growth?

Answer 1

-favourable temperature

• nutrient-rich environment containing amino acids and carbohydrates

Question 2

DNA of bacterial nucleoid contains:

Answer 2

the info needed to orchestrate a response to any change in the environment

Question 3

House Keeping Genes

Answer 3

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

Question 4

Regulated Genes

Answer 4

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

Question 5

Enzymes are important for:

Answer 5

metabolizing nutrients

Question 6

Why is regulating the expression of enzymes important?

Answer 6

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

Question 7

E-Coli cells unique expression mechanism:

Answer 7

are able to switch to metabolizing on alternate fuel sources when the preferred glucose source is depleted

Question 8

Significance of metabolic switch between glucose and lactose use

Answer 8

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

Question 9

When do changes in bacterial growth occur?

Answer 9

over time when bacteria are growing in an environment containing both glucose and lactose

Question 10

B-galactosidase

Answer 10

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

Question 11

How is B-galactosidase made?

Answer 11

-produced by turning on transcription of the B-galactosidase gene

-only does this when these is no glucose available

Question 12

Francois Jacob & Jacques Monod

Answer 12

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.

Question 13

Transcriptional Regulation

Answer 13

controls the amount of mRNA that is produced in the cell

Question 14

Activation of Transcription (both prokaryotes and eukaryotes) requires:

Answer 14

proteins bind to a region near the beginning of the gene, the promoter, and increase the binding of the enzyme, RNA polymerase

Question 15

By controlling the binding of proteins to the promoter…

Answer 15

the cell can either activate or inhibit transcription

Question 16

Initiation of Translation in eukaryotes vs prokaryotes:

Answer 16

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

Question 17

Rate at which translation occurs effects:

Answer 17

the amount of protein produced (amount depends on the stability of the mRNA)

-if mRNA is quickly degraded, very little protein will be made

Question 18

Post-Translational Control Mechanisms:

Answer 18

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

Question 19

Fastest level of Regulation

Answer 19

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)

Question 20

Slowest but most-efficient Regulation

Answer 20

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)