Autotrophy and N2 Fixation Flashcards
Are carbon fixation and nitrogen fixation reductive or oxidative processes?
Carbon fixation is a reductive process, while nitrogen fixation is also considered a reductive process.
How is autotrophy defined in this section of the textbook?
Autotrophy is defined as the ability of an organism to produce its own food from inorganic substances.
Virtually all __________________ and ____________________ are autotrophic.
Virtually all plants and some bacteria are autotrophic.
What is the most widespread and important pathway of carbon fixation in the biosphere?
The most widespread and important pathway of carbon fixation in the biosphere is the Calvin cycle, where CO2 is reduced to glucose.
The Calvin cycle is present in what six groups of organisms?
The Calvin cycle is present in plants, algae, cyanobacteria, some proteobacteria, some green sulfur bacteria, and some green non-sulfur bacteria.
What four non-enzymatic molecules are required by the Calvin cycle?
The four non-enzymatic molecules required by the Calvin cycle are ribulose bisphosphate, carbon dioxide, ATP, and NADPH.
What two key enzymes are required by the Calvin cycle?
The two key enzymes required by the Calvin cycle are ribulose bisphosphate carboxylase/oxygenase (RubisCO) and phosphoribulokinase.
What is the “CO2-acceptor molecule” in the Calvin cycle?
The CO2-acceptor molecule in the Calvin cycle is ribulose bisphosphate (RuBP).
How many molecules of (a) ATP, (b) NADPH, and (c) CO2 are required by the Calvin cycle to produce one hexose (6-carbon sugar)?
(a) 18 ATP, (b) 12 NADPH, and (c) 6 CO2 are required to produce one hexose.
What are carboxysomes?
Carboxysomes are microcompartments found in some bacteria that contain enzymes for carbon fixation.
In what two ways do carboxysomes increase the efficiency of RubisCO?
Carboxysomes increase the efficiency of RubisCO by concentrating CO2 and providing an ideal environment for the enzyme.
What carbon fixation pathway is used by green sulfur bacteria, such as Chlorobium?
Green sulfur bacteria, such as Chlorobium, use the reverse citric acid cycle for carbon fixation, which is less efficient than the Calvin cycle.
What is the purpose (function) of the reduced ferredoxin molecules in the reverse citric acid cycle?
The purpose of reduced ferredoxin molecules in the reverse citric acid cycle is to provide electrons for the reduction of carbon compounds.
What carbon fixation pathway is used by filamentous green non-sulfur bacteria, such as Chloroflexus?
Filamentous green non-sulfur bacteria, such as Chloroflexus, use the hydroxypropionate pathway, which is less efficient than the Calvin cycle.
What groups of organisms use the reductive acetyl-coenzyme A pathway to fix carbon?
The reductive acetyl-coenzyme A pathway is used by certain Archaea and bacteria, and it is less efficient than the Calvin cycle.
Nitrogen is required for cells to synthesize what types of molecules?
Nitrogen is required for cells to synthesize amino acids, nucleotides, and other nitrogen-containing compounds.
What are the two most common forms of “fixed” nitrogen available to microbes?
The two most common forms of fixed nitrogen available to microbes are ammonia (NH3) and nitrate (NO3-).
Certain species of Bacteria and Archaea can “fix nitrogen.” What exactly are they doing in this process?
They are converting atmospheric nitrogen gas (N2) into ammonia (NH3) or related compounds.
What advantage do nitrogen-fixing prokaryotes have over non-nitrogen-fixers?
Nitrogen-fixing prokaryotes can utilize atmospheric nitrogen, allowing them to thrive in nitrogen-poor environments.
What is the ecological importance of nitrogen-fixation?
Nitrogen-fixation is ecologically important because it enriches soil nitrogen levels, supporting plant growth and ecosystem productivity.
What enzyme catalyzes nitrogen fixation?
The enzyme that catalyzes nitrogen fixation is nitrogenase, formed by two proteins: dinitrogenase and dinitrogenase reductase.
What cofactor is required for nitrogenase to function?
The cofactor required for nitrogenase to function is molybdenum, which facilitates the reduction of nitrogen.
What effect does oxygen have on nitrogen fixation?
Oxygen inhibits nitrogen fixation because it can inactivate nitrogenase.
In what two ways do nitrogen-fixing obligate aerobes protect nitrogenase from oxygen?
Nitrogen-fixing obligate aerobes protect nitrogenase by using specialized cells or by producing oxygen-scavenging compounds.
