Flashcards in Lecture 17 - Nitrogen Cycling Deck (52)
What is the nitrogen cycle?
the change in the chemical form nitrogen is present
What nitrogen-based compound is a greenhouse gas?
nitrous oxide = can diffuse through membrane
What is the largest reservoir of nitrogen? What percent of nitrogen makes up this reservoir?
atmosphere ; 78%
What reservoir of nitrogen is not actively cycled and why?
atmosphere, most organisms cannot utilize this form of nitrogen (N2)
Where are the actively recycled forms of nitrogen found?
ocean and land
What are the 5 processes of the nitrogen cycle?
nitrogen fixation | ammonium assimilation | nitrification | anammox | denitrification
What is the process of nitrogen fixation?
N2 gas from sky >>> fix into ammonia
What is the form of nitrogen that most/all microbes can use?
Which microbes convert nitrogen gas into ammonia?
nitrogen-fixing microbes (ie: cyanobacteria)
Which type of environment (aerobic or anaerobic) does nitrogen fixation commonly occur in?
What are diazotrophs?
organism capable of fixing nitrogen
Why is the nitrogen-fixing process an energy-intensive reaction?
need 16 ATPs to make 2 ammonia because it is hard to break the triple bonds between N in N2
What is the nitrogen fixation process inhibited by? Why?
high concentrations of ammonia = cells don't want to spend more energy making more ammonia when there is already a lot
What is the enzyme that catalyzes the nitrogen fixation process?
What are characteristics of nitrogenase?
oxygen-sensitive | complex of 2 proteins: dehydrogenase reductase and dinitrogenase
What is dehydrogenase reductase?
an iron-protein = need iron as cofactor
What is dinitrogenase?
shuttling of electrons between the two protein complex
What are the genes called that encode for nitrogenase?
MIF = found on an operon within nitrogen fixers
What occurs when nitrogenase comes into contact with oxygen?
nitrogenase is damaged
What are the 4 strategies that make nitrogen fixers capable of fixing nitrogen when oxygen is toxic to nitrogenase?
heterocyst formation | time and spatial separation | respiration | avoidance
What is the heterocyst formation strategy nitrogen fixers use?
specialized cells with a thicker cell wall where they sequester the nitrogen-fixing components they need such as nitrogenase | not much photosynthesis occurring in these cells | photosynthesis and nitrogen-fixation are separated within bacteria
What is the time-and-spatial separation strategy nitrogen fixers use?
separate by time = doing things at different times ; spatial = separate by area
What is the respiration strategy nitrogen fixers use?
high rates of respiration = chugging oxygen very quickly
What is the avoidance strategy nitrogen fixers use?
such as proteins that bind to oxygen to prevent it from binding to nitrogenase
What are the limits of nitrogen fixation?
needs hella ATP | light and carbon compounds | amount of NH3 | iron and Mo | oxygen
What do the limits of nitrogen fixation depend on?
environment ie: ocean = low iron = low levels of nitrogen fixation
What is ammonia assimilation?
moving NH3 into a form that cells can use such as amino acids
What are the 2 pathways of ammonia assimilation?
Low NH4 = glutamine synthetase (GS) | High NH4 = glutamine dehydrogenase (GDH)
Why is the ammonia assimilation process important for diazotrophs?
to ensure the nascent NH3 doesn't inhibit further N2 fixation = wanna keep N2-fixing going