Unit 2 Practice Questions

Question 1

What is the fundamental difference between an oxygenic and an anoxygenic phototroph?

Answer 1

Oxygenic phototrophs oxidize H2O and produce O2 while anoxygenic phototrophs oxidize H2S and produce S0. Oxygenic phototrophs also have 2 photosystems, while anoxygenic have only 1 photosystem.

Question 2

Why can phototrophic green bacteria grow at light intensities that will not support purple bacteria?

Answer 2

Because only phototrophic green bacteria evolved sensitive structures like chromosomes that can harvest minimal amounts of light.

Question 3

In which phototrophs are carotenoids found?

Answer 3

Oxygenic phototrophs

Question 4

What is reverse electron flow and why is it necessary? Which phototrophs need to use reverse electron flow?

Answer 4

Purple sulfur bacteria use cyclic electron flow to ensure they have enough energy to drive metabolism. Reverse electron flow is noticed in purple sulfur bacteria because they have quinone based photosystem P870, where quinone is not good enough to donate electrons efficiently to NAD+ to make NADH.

Question 5

What evidence is there that anoxygenic and oxygenic photosynthesis are related processes?

Answer 5

The fact that purple sulfur bacteria have quinone based photosystem that resembles PSII (P680) in oxygenic phototrophs and green sulfur bacetria have ferredoxin based photosystem P840 that resembles PSI (P700) in oxygenic phototrophs.

Question 6

What reaction(s) does the enzyme RubisCO carry out?

Answer 6

CO2 fixation and oxygenation.

Question 7

What is a carboxysome and what is its function?

Answer 7

Carboxysome is structural compartment in oxygenic prototrophs that plays the role in CO2 concentration. They are filled with Rubisco that performs CO2 fixation.

Question 8

Contrast autotrophy in the following phototrophs: cyanobacteria; purple and green sulfur bacteria; Chloroflexus.

Answer 8

Autotrophy assumes fixation of CO2 or use of inorganic carbon as the carbon source. In cyanobacteria CO2 fixation is performed via Calvin cycle, as well as in purple sulfur bacteria, in Chloroflexus hydroxypropionate pathway functions to fix CO2, and in green sulfur bacetria is Reverse TCA.

Question 9

For what two purposes are inorganic compounds oxidized by chemolithotrophs?

Answer 9

To obtain energy and electrons for biochemical processes.

Question 10

What enzyme is required for hydrogen bacteria to grow as H2 chemolithotrophs?

Answer 10

Hydrogenase

Question 11

What are the substrates for the enzyme ammonia monooxygenase?

Answer 11

Ammonia and methane

Question 12

Why must anammox reactions be carried out in a special structure within the cell?

Answer 12

Because reaction between NH4+ (ammonium) which is energy (electron) source and nitrite (NO2-) electron acceptor results in toxic intermediate production, and the structure anammoxosome prevent leaking.

Question 13

What is the carbon source for nitrifying and anammox organisms?

Answer 13

For nitrifying AOB and AOA, as well as for NOB, comammox and anammox carbon source is CO2.

Question 14

What is substrate-level phosphorylation?

Answer 14

The set of mini redox reactions that involves presence of enzyme that generate high energy bond (usually kinases or dehydrogenases)

Question 15

How can homo- and heterofermentative metabolism be differentiated in pure cultures of lactic acid bacteria?

Answer 15

Because in Homofermentation we see either ethanol or lactate, and in Heterofermentation we see mixture of lactate, ethanol, CO2, and H2.

Question 16

How does aerobic respiration differ from anaerobic respiration and why does aerobic respiration repress anaerobic respiration?

Answer 16

In aerobic respiration terminal electron acceptor is oxygen and in anaerobic is alterative such as nitrate, nitrite, metals, sulfate, sulfur. Aerobic respiration represses anaerobic because oxygen is the strongest oxidant, the bottom of the tower of power and makes the longest Electron Transport Chain (more energy extracted when respiring oxygen).

Question 17

How do monooxygenases differ in function from dioxygenases?

Answer 17

Monooxygenase incorporates only 1 oxygen atom into the hydrocarbon chain while other reduces to water, while dioxygenase incorporates bot oxygen atoms into the hydrocarbon.

Question 18

What is the final product of catabolism of a hydrocarbon?

Answer 18

Final product can be Fatty Acid (FA) in case of aliphatic hydrocarbon, or catechol, in case of aromatic hydrocarbon.

Question 19

Compare and contrast the utilization of H2S by a purple phototrophic bacterium and by a green sulfur bacterium.

Answer 19

Purple sulfur and green sulfur bacetria both oxidize H2S so elemental sulfur, but purple bacteria store sulfur granules inside, while green sulfur bacteria store them outside of the cell.

Question 20

How does a methanotroph differ from a methanogen?

Answer 20

Methanotrophs consume methane as carbon and energy source, while methanogens produce methane as metabolic byproduct from H2 oxidation and CO2 fixation.

Question 21

Which pathway for C1 assimilation found in methanotrophs is most energetically efficient and why?

Answer 21

Ribuloso Monophosphate is more efficient than serine cycle because of intermediates produced that can be easily assimilated into the central carbon metabolism.