Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
31 Cards in this Set
- Front
- Back
|
If atmospheric nitrogen (N2 or dinitrogen) is so abundant, then why are plants unable to fix N2 direcly? What does fix N2 directly and what is it used for?
|
Because N2 consist of triple bonds, which are extremely difficult to break. Agricultural fertilizer produces fix N2 directly by using high temperatures and pressures to break the bonds. Some Prokaryotes are also able to fix N2 directly but hey require an enviroment lacking oxygen, which means they need a microenviroment.
|
|
|
Where do most plants obtain there nitrogen from?
|
From the soil in the form of nitrate or ammonium.
|
|
|
What type of prokaryotes can be nitrogen fixers?
|
Free-Living and Symbiotic
|
|
|
What is the bext example of symbiosis when speaking of nitrogen fixing and prokaryotes?
|
Rhizobial microsymbionts and leguminous host plants.
|
|
|
The biological fixation of N2 into ammonium requires what and what is it?
|
Dinitrogenase, an enzyme found only in certain prokaryotes.
|
|
|
Symbiotic nitrogen fixing prokaryotes live within specialized organs called what?
|
Nodules
|
|
|
Why do symbioitic nitrogen fixing prokaryotes need to live in nodules?
|
Because they need an oxygen free enviroment because oxgen denatures the the dinitrogenase.
|
|
|
If oxygen denatures dinitrogenase, then how do the bacteria produce ATP, which fixes the N2, withoyt the use of oxygen?
|
They still use oxygen, but they rely on leghemoglobin to transport the oxygen to them without denaturing the dinitrogenease.
|
|
|
What does the connection between the nodule and the vascular system of the root allow?
|
The rhizobia to import photosynthetic carbon and to export fixed nitrogen throughout the host plant.
|
|
|
Explain the rhizobial infection process during nodule formation in detail.
|
Rhizobia are attracted to root hairs by chemical signals released from the host, such as amino acids and flavonoids. Once the Rhizobia have attached they begin to synthesize NOD factors, which are lipochitin oligosaccharides, which then are recognized by the host lectins. The lectins now become activated which aid in the Rhozobia attaching to the cell wall of the root hairs. The root hair begins to grow and curl producing an infection thread which spreads towards the primordorium. The rhizobia then release a mitogenic signal (ethylene or uridine) which stimulates cell division in root cortex and pericycle. These regions ultimately fuse to form the mature nodule.
|
|
|
In a mature nodule, what do the bacteria differentiate into?
|
Specialized nitrogen fixing cells termed bacteroids surrounded by a peribacteroid membrane.
|
|
|
The reaction that symbiotic bacteria carry out to produce ammonia and hydrogen from N2 is catalyzed by what complex?
|
The oxygen sensitive Nitrogenase Complex.
|
|
|
N2 fixation requires how mch ATP
|
16 ATP
|
|
|
The Nitrogenase Complex consist of what?
|
An iron protein and Molybedum Iron protein (Fe
|
|
|
What is the initial and end products of the Nitrogenase Complex
|
Initial: N2 and 8 H+
End: 2 NH3 and H2 |
|
|
What contributes the electrons to break the triple bonds of N2 in the Nitogenase Enzyme Complex?
|
Reduced Ferredoxin, which is supplied by the bacteria and not found in the plant.
|
|
|
Explain the interaction between photosynthesis, respiration, and nitrogen fixation in bacteroids.
|
Photosynthates from the leaf enter the through the bacteroid membrane and enter into glycolysis and the Calvin cycle. The Calvin Cycle reduces NAD+, which is then oxidized by the respiratory chain. This keeps the PMF going. Hyrdrogen is then pumped in across the ATP synthasecreating ATP used to break the triple bond in N2. The reduced ferredoxin used to contribute electrons to the Nitrogenase Enzyme complex is kept reduced by the NAD+ being reduced by the Calvin cycle.
|
|
|
Concerning the fact that nitrogenase enzymes are denatured in oxygen rich enviroments, how do filamentous cyanobacteria fix nitrogen considereing they need oxygen to do it?
|
Thet fix nitrogen in specialized isolated cells called hterocysts that lack photosystem II and Rubisco, but retain Photosystem I and hence can synthesize ATP by cyclic photophosphorylation.
|
|
|
Of the 16 ATP that is supplied to the dinirogenase enzyme, 25-30% of that can be lost in producing H2, a byproduct during N2 fixation. What do some nitrogen fixers have to regain some of that lost energy?
|
An additional enzyme called uptake hydrogenase.
|
|
|
The first stable prodcut of nitrogen fixation is ammonium (at physiological pH's). Ammonium is toxic to both plants and animals why and what does the plant do to protect itself?
|
It is toxic because disipates transmembrane proton gradients. To protect itself, the plant either quickly converts ammonium into an amino acid or it stores excess ammonium in their vacuoles to minimize toxicity.
|
|
|
What are the catalases in the primary pathway of the conversion of ammonium into an amino acid?
|
Glutamine synthetase (GS) and Glutamate synthase (GOGAT)
|
|
|
Two forms of GS exist. Where do they exist and what are there functions?
|
Cytosol - intracellular nitrogen transportin seeds and vascular tissues of roots and shoots
Plastids - in roots, generates amides for local use in shoots, reassimilates photorespiratory NH4 in |
|
|
What are the precursors for other amino acids?
|
Glutamate and Glutamine
|
|
|
How is nitrogen incorporated into amino acids other than glutamate and glutamine?
|
Transamination reactions catalyzed by pyridoxal phosphate requiring aminotransferases. This class of enzyme is found in multiple cellular compartments and plays an important role in mino acid biosynthesis particulary in chlorplasts.
|
|
|
Before amino acids are produced, amonium is converted quickly o other substances in the nodule for transport from root to shoot through the xylem. What are these compounds
|
In temperate region plants, ammonium is converted to amides (ex. asparagine) or in tropical region plants it is converted to ureides. Once converted to this they are transported to the shoot where they are catabolized to ammonium and assimilated.
|
|
|
What is the most abundant form of soil nitrogen taken up by plants?
|
Nitrate
|
|
|
Explain nitrate assimilation.
|
NO3 is converted to NO2 which is then converted to NH4, and then incorporated into glutamine.
|
|
|
Plants can store and assimilate nitrate with no ill effects. So what are the three things done with nitrate taken from the soil?
|
1.) stored in the vacoules
2.) assimilated in the root cells (when nitrate supply in soil is low) 3.) translocated in the xylem to the leaves for assimilation (when nitrate supply in soil is high) |
|
|
To get nitrate to nitrite requires cytosolic reduction catalyzed by what?
|
The Nitrate reductase, a homodimeric enzyme containing several electron transfer cofactors
|
|
|
Once nitrite is produced from nitrate, it is considered highly reactive and potentially toxic, thus it is transported where?
|
Into the plastids
|
|
|
Nitrite in the plastids is reduced to ammonium in a reaction catalyzed by what?
|
Nitite reductase, an enzyme containing several electron transfer cofactors that is represented by Asn and Gln.
|
