Energy, Transport and Scavenging in Bacteria

Question 1

What is the cap site for the lac operon?

Answer 1

cAMP/CRP complex binds to a specific sequence in the lac control region called the “CAP” site. The CAP site is just upstream from the RNA polymerase binding site.

Question 2

What does CAP do in the lac operon?

Answer 2

The CAP binding site is a positive regulatory site that is bound by catabolite activator protein (CAP). When CAP is bound to this site, it promotes transcription by helping RNA polymerase bind to the promoter.

Question 3

What are the two binding sites of the promoter?

Answer 3

The promoter of the lac operon has two binding sites. One site is the location where RNA polymerase binds. The second location is the binding site for a complex between the catabolite activator protein (CAP) and cyclic AMP (cAMP)

Question 4

Where is the cap site found?

Answer 4

Promoter of the lac operon

Question 5

What kind of relationship does the concentration of glucose have with cyclic AMP?

Answer 5

Inverse, no glucose there will be high levels of cAMP

Question 6

What is cyclic AMP?

Answer 6

cAMP is a “hunger signal” made by E. coli when glucose levels are low. cAMP binds to CAP, changing its shape and making it able to bind DNA and promote transcription.

Question 7

What is the purpose of cyclic AMP?

Answer 7

CAP isn’t always active (able to bind DNA). Instead, it’s regulated by a small molecule called cyclic AMP (cAMP).

Question 8

What is a CAP and give an example of one

Answer 8

CAP is a catabolite repressor activator protein example -

CRP in bacteria

Question 9

What is the effect of the cAMP-CAP complex binding to the CAP site in the promoter region?

Answer 9

It acts as an inducer and triggers the binding of RNA Polymerase and helps transcription process

Question 10

How does the lac repressor sense lactose indirectly

Answer 10

Through its isomer allolactose - an inducer of the lac operon

Question 11

How do catabolite activator proteins work?

Answer 11

act as a glucose sensor - activates transcription of the operon, but only when glucose levels are low.

Question 12

How do catabolite activator proteins sense the glucose molecule?

Answer 12

CAP senses glucose indirectly, through the “hunger signal” molecule cAMP.

Question 13

Two protein regulators turn the operon “on” and “off” in response to lactose and glucose levels, what are they?

Answer 13

the lac repressor and catabolite activator protein (CAP).

Question 14

How do the two protein regulators of the lactose operon act as regulators?

Answer 14

Lac repressor - lactose sensor. It normally blocks transcription of the operon, but stops acting as a repressor when lactose is present. The lac repressor senses lactose indirectly, through its isomer allolactose.
CAP - glucose sensor. It activates transcription of the operon, but only when glucose levels are low. CAP senses glucose indirectly, through the “hunger signal” molecule cAMP

Question 15

What is a lac operon?

Answer 15

Group of genes with a single promoter (transcribed as a single mRNA). The genes in the operon encode proteins that allow the bacteria to use lactose as an energy source.

Question 16

How can bacteria such as e.coli use lactose?

Answer 16

To use lactose, the bacteria must express the lac operon genes, which encode key enzymes for lactose uptake and metabolism. To be as efficient as possible, E. coli should express the lac operon only when two conditions are met:

• Lactose is available, and
• Glucose is not available

Question 17

What are the genes found in the lac operon and what are their functions?

Answer 17

• lacZ gene encodes an enzyme called β-galactosidase, which is responsible for splitting lactose (a disaccharide) into readily usable glucose and galactose (monosaccharides).
• lacY gene encodes a membrane protein called lactose permease, which is a transmembrane “pump” that allows the cell to import lactose.
• lacA gene encodes an enzyme known as a transacetylase that attaches a particular chemical group to target molecules. It’s not clear if this enzyme actually plays any role in lactose breakdown.

Question 18

What does the lac Z gene encode for?

Answer 18

enzyme called β-galactosidase

Question 19

What does the lac Y gene encode for?

Answer 19

membrane protein called lactose permease

Question 20

What does the lac A gene encode for?

Answer 20

enzyme known as a transacetylase

Question 21

What is negative regulation?

Answer 21

The binding of a specific protein (repressor) inhibits transcription from occurring

Question 22

What is positive regulation?

Answer 22

permit RNA polymerase binding to the promoter region, thus allowing transcription to occur.

Question 23

What is the promoter?

Answer 23

binding site for RNA polymerase, the enzyme that performs transcription.

Question 24

What is the operator?

Answer 24

operator is a negative regulatory site bound by the lac repressor protein. The operator overlaps with the promoter, and when the lac repressor is bound, RNA polymerase cannot bind to the promoter and start transcription.

Question 25

Where does the lac repressor come from?

Answer 25

gene that encodes the lac repressor is named lacI, and is under control of its own promoter. The lacI gene happens to be found near the lac operon, but it is not a part of the operon and is expressed separately. lacI is continually transcribed, so its protein product – the lac repressor – is always present.

Question 26

What is the lac repressor?

Answer 26

lac repressor is a protein that represses (inhibits) transcription of the lac operon. It does this by binding to the operator, which partially overlaps with the promoter. When bound, the lac repressor gets in RNA polymerase’s way and keeps it from transcribing the operon.

Question 27

Is lac I part of the operon?

Answer 27

No - LacI is always transcribed.

Question 28

How does allolactose inactivate the repressor?

Answer 28

Allolactose binds to an allosteric site on the repressor protein causing a conformational change. As a result of this change, the repressor can no longer bind to the operator region and falls off. RNA polymerase can then bind to the promoter and transcribe the lac genes.

Question 29

What is adenylyl cyclase

Answer 29

Adenylyl cyclase produces a molecule called cAMP

Question 30

When is adenylyl cylcase activated?

Answer 30

When glucose is absent an enzyme called adenylyl cyclase is active.

Question 31

What is the function of ATP synthase (F1F0-ATPase)?

Answer 31

catalyses the synthesis of ATP during oxphos. enzyme is reversible and is able to use ATP to drive a
proton gradient for transport purposes

Question 32

Where is the F1F0-ATPase found?

Answer 32

Inner mitochondrial membrane, inner membrane of bacteria, thylakoid membrane of chloroplasts

Question 33

What is F1F0-ATPase consist of?

Answer 33

• a water-soluble F1
  sector - three α subunits, three β subunits and one
  copy of each of the γ, δ and ε subunits
• membrane embedded Fo sector consisting of one a, two b and 12 c
  subunits

Question 34

Where is the proton channel formed in the F1F0-ATPase?

Answer 34

a and c subunits in F0 sector

Question 35

Has it been demonstrated that ATPase can be an effective target for drugs?

Answer 35

it has been demonstrated that bacterial ATP synthase can be an effective target for antibacterial treatment. It is the target of a novel class of compounds that are bactericidal for actively replicating and dormant mycobacteria (5, 6) and that show promising effects against multidrug-resistant tuberculosis in phase II clinical trials

Question 36

How does the ATPase in bacteria produce energy?

Answer 36

• Protons from periplasm enter cell through F0 rotary motor and cause rotation by changing local charge.
• Rotary motion is converted to chemical energy when ATP synthesised from ADP and Pi by the F1 complex in cytoplasm.

Question 37

Where is the F1 complex found in ATPase?

Answer 37

Cytoplasm

Question 38

Where is the F0 complex found in ATPase?

Answer 38

Embedded in membrane

Question 39

What is used to power flagella in bacteria?

Answer 39

Proton-powered motors are also used by bacteria to run their flagella-based
motility systems