Editing Diatom (section)

===Urea cycle===
A feature of diatoms is the [[urea cycle]], which links them evolutionarily to animals. In 2011, Allen et al. established that diatoms have a functioning urea cycle. This result was significant, since prior to this, the urea cycle was thought to have originated with the [[metazoans]] which appeared several hundreds of millions of years before the diatoms. Their study demonstrated that while diatoms and animals use the urea cycle for different ends, they are seen to be evolutionarily linked in such a way that animals and plants are not.<ref>{{cite journal |doi=10.1038/nature10074 |pmid=21562560 |title=Evolution and metabolic significance of the urea cycle in photosynthetic diatoms |journal=Nature |volume=473 |issue=7346 |pages=203–7 |year=2011 |last1=Allen |first1=Andrew E. |last2=Dupont |first2=Christopher L. |last3=Oborník |first3=Miroslav |last4=Horák |first4=Aleš |last5=Nunes-Nesi |first5=Adriano |last6=McCrow |first6=John P. |last7=Zheng |first7=Hong |last8=Johnson |first8=Daniel A. |last9=Hu |first9=Hanhua |last10=Fernie |first10=Alisdair R. |last11=Bowler |first11=Chris | display-authors = 6 | bibcode=2011Natur.473..203A |s2cid=4350884 |url=http://www.locus.ufv.br/handle/123456789/22722 |access-date=20 May 2021 |archive-date=19 February 2022 |archive-url=https://web.archive.org/web/20220219150348/https://www.locus.ufv.br/handle/123456789/22722 |url-status=live}}
*{{cite press release |date=12 May 2011 |title=Animal-like urea cycle in ocean's tiny diatoms enables marine phytoplankton to use carbon and nitrogen from their environment |website=ScienceDaily |url=https://www.sciencedaily.com/releases/2011/05/110511133553.htm}}</ref>

While often overlooked in photosynthetic organisms, the [[mitochondria]] also play critical roles in energy balance. Two nitrogen-related pathways are relevant and they may also change under [[ammonium]] ({{chem|NH|4|+}}) nutrition compared with [[nitrate]] ({{chem|NO|3|−}}) nutrition. First, in diatoms, and likely some other algae, there is a urea cycle.<ref name=Armbrust2004>{{cite journal | last1=Armbrust | first1=E. Virginia | last2=Berges | first2=John A. | last3=Bowler | first3=Chris | last4=Green | first4=Beverley R. | last5=Martinez | first5=Diego | last6=Putnam | first6=Nicholas H. | last7=Zhou | first7=Shiguo | last8=Allen | first8=Andrew E. | last9=Apt | first9=Kirk E. | last10=Bechner | first10=Michael | last11=Brzezinski | first11=Mark A. | last12=Chaal | first12=Balbir K. | last13=Chiovitti | first13=Anthony | last14=Davis | first14=Aubrey K. | last15=Demarest | first15=Mark S. | last16=Detter | first16=J. Chris | last17=Glavina | first17=Tijana | last18=Goodstein | first18=David | last19=Hadi | first19=Masood Z. | last20=Hellsten | first20=Uffe | last21=Hildebrand | first21=Mark | last22=Jenkins | first22=Bethany D. | last23=Jurka | first23=Jerzy | last24=Kapitonov | first24=Vladimir V. | last25=Kröger | first25=Nils | last26=Lau | first26=Winnie W. Y. | last27=Lane | first27=Todd W. | last28=Larimer | first28=Frank W. | last29=Lippmeier | first29=J. Casey | last30=Lucas | first30=Susan | last31=Medina | first31=Mónica | last32=Montsant | first32=Anton | last33=Obornik | first33=Miroslav | last34=Parker | first34=Micaela Schnitzler | last35=Palenik | first35=Brian | last36=Pazour | first36=Gregory J. | last37=Richardson | first37=Paul M. | last38=Rynearson | first38=Tatiana A. | last39=Saito | first39=Mak A. | last40=Schwartz | first40=David C. | last41=Thamatrakoln | first41=Kimberlee | last42=Valentin | first42=Klaus | last43=Vardi | first43=Assaf | last44=Wilkerson | first44=Frances P. | last45=Rokhsar | first45=Daniel S. | display-authors = 6 | title=The Genome of the Diatom Thalassiosira Pseudonana : Ecology, Evolution, and Metabolism | journal=Science | publisher=American Association for the Advancement of Science (AAAS) | volume=306 | issue=5693 | year=2004 | issn=0036-8075 | doi=10.1126/science.1101156 | pages=79–86| pmid=15459382 | bibcode=2004Sci...306...79A | s2cid=8593895 | url=https://digital.library.unt.edu/ark:/67531/metadc783254/ }}</ref><ref name=Allen2011>{{cite journal | last1=Allen | first1=Andrew E. | last2=Dupont | first2=Christopher L. | last3=Oborník | first3=Miroslav | last4=Horák | first4=Aleš | last5=Nunes-Nesi | first5=Adriano | last6=McCrow | first6=John P. | last7=Zheng | first7=Hong | last8=Johnson | first8=Daniel A. | last9=Hu | first9=Hanhua | last10=Fernie | first10=Alisdair R. | last11=Bowler | first11=Chris | display-authors = 6 | title=Evolution and metabolic significance of the urea cycle in photosynthetic diatoms | journal=Nature | publisher=Springer Science and Business Media LLC | volume=473 | issue=7346 | year=2011 | issn=0028-0836 | doi=10.1038/nature10074 | pages=203–207| pmid=21562560 | bibcode=2011Natur.473..203A | s2cid=4350884 | url=http://repositorio.uptc.edu.co/handle/001/3087 }}</ref><ref>{{cite journal | last1=Weyman | first1=Philip D. | last2=Beeri | first2=Karen | last3=Lefebvre | first3=Stephane C. | last4=Rivera | first4=Josefa | last5=McCarthy | first5=James K. | last6=Heuberger | first6=Adam L. | last7=Peers | first7=Graham | last8=Allen | first8=Andrew E. | last9=Dupont | first9=Christopher L. | display-authors = 6 | title=Inactivation of P haeodactylum tricornutum urease gene using transcription activator-like effector nuclease-based targeted mutagenesis | journal=Plant Biotechnology Journal | publisher=Wiley | volume=13 | issue=4 | date=2014-10-10 | issn=1467-7644 | doi=10.1111/pbi.12254 | pages=460–470| pmid=25302562 | doi-access=free }}</ref> The long-known function of the urea cycle in animals is to excrete excess nitrogen produced by [[Amino acid#Catabolism|amino acid Catabolism]]; like [[photorespiration]], the urea cycle had long been considered a waste pathway. However, in diatoms the urea cycle appears to play a role in exchange of nutrients between the mitochondria and the [[cytoplasm]], and potentially the [[plastid]]{{hsp}}<ref>{{cite journal | last1=Bender | first1=Sara J. | last2=Parker | first2=Micaela S. | last3=Armbrust | first3=E. Virginia | title=Coupled Effects of Light and Nitrogen Source on the Urea Cycle and Nitrogen Metabolism over a Diel Cycle in the Marine Diatom Thalassiosira pseudonana | journal=Protist | publisher=Elsevier BV | volume=163 | issue=2 | year=2012 | issn=1434-4610 | doi=10.1016/j.protis.2011.07.008 | pages=232–251| pmid=21873112 }}</ref> and may help to regulate ammonium metabolism.<ref name=Armbrust2004 /><ref name=Allen2011 /> Because of this cycle, marine diatoms, in contrast to [[chlorophyte]]s, also have acquired a mitochondrial [[urea transporter]] and, in fact, based on [[bioinformatics]], a complete mitochondrial [[Glutamate synthase|GS-GOGAT]] cycle has been hypothesised.<ref name=Allen2011 /><ref name=Glibert2015 />
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