Editing Chloroplast (section)

==== Chloroplast ribosomes ====

{{plain image with caption|File:Chloroplast and bacterial ribosome comparison.png|'''Chloroplast ribosomes''' Comparison of a chloroplast ribosome (green) and a bacterial ribosome (yellow). Important features common to both ribosomes and chloroplast-unique features are labeled.|300px|right|bottom|triangle|#7ccc1b}}
Chloroplasts have their own ribosomes, which they use to synthesize a small fraction of their proteins. Chloroplast ribosomes are about two-thirds the size of [[Eukaryotic Ribosome (80S)|cytoplasmic ribosomes]] (around 17 [[Nanometre|nm]] vs 25 [[Nanometre|nm]]).<ref name="Burgess-1989a" /> They take [[mRNAs]] transcribed from the [[chloroplast DNA]] and [[translation (biology)|translate]] them into protein. While similar to [[bacterial ribosomes]],<ref name="Campbell-2009c" /> chloroplast translation is more complex than in bacteria, so chloroplast ribosomes include some chloroplast-unique features.<ref name="Manuell-2007">{{cite journal | vauthors=Manuell AL, Quispe J, Mayfield SP | title=Structure of the chloroplast ribosome: novel domains for translation regulation | journal=PLOS Biology | volume=5 | issue=8 | pages=e209 | date=August 2007 | pmid=17683199 | pmc=1939882 | doi=10.1371/journal.pbio.0050209 | doi-access=free }}</ref><ref name="Bieri-2017">{{cite journal |last1=Bieri |first1=P |last2=Leibundgut |first2=M |last3=Saurer |first3=M |last4=Boehringer |first4=D |last5=Ban |first5=N |title=The complete structure of the chloroplast 70S ribosome in complex with translation factor pY. |journal=The EMBO Journal |date=15 February 2017 |volume=36 |issue=4 |pages=475–486 |doi=10.15252/embj.201695959 |pmid=28007896 |pmc=5694952}}</ref>

Small subunit [[ribosomal RNA]]s in several [[Chlorophyta]] and [[euglenid]] chloroplasts lack motifs for [[Shine-Dalgarno sequence]] recognition,<ref name="Lim-2014">{{cite journal | vauthors=Lim K, Kobayashi I, Nakai K | title=Alterations in rRNA-mRNA interaction during plastid evolution | journal=Molecular Biology and Evolution | volume=31 | issue=7 | pages=1728–40 | date=July 2014 | pmid=24710516 | doi=10.1093/molbev/msu120 | doi-access=free }}</ref> which is considered essential for [[Translation (biology)|translation]] initiation in most chloroplasts and [[prokaryote]]s.<ref>{{cite journal | vauthors=Hirose T, Sugiura M | s2cid=10774032 | title=Functional Shine-Dalgarno-like sequences for translational initiation of chloroplast mRNAs | journal=Plant & Cell Physiology | volume=45 | issue=1 | pages=114–7 | date=January 2004 | pmid=14749493 | doi=10.1093/pcp/pch002 | doi-access=free }}</ref><ref>{{cite journal | vauthors=Ma J, Campbell A, Karlin S | title=Correlations between Shine-Dalgarno sequences and gene features such as predicted expression levels and operon structures | journal=Journal of Bacteriology | volume=184 | issue=20 | pages=5733–45 | date=October 2002 | pmid=12270832 | pmc=139613 | doi=10.1128/JB.184.20.5733-5745.2002 }}</ref> Such loss is also rarely observed in other [[plastid]]s and prokaryotes.<ref name="Lim-2014"/><ref>{{cite journal | vauthors=Lim K, Furuta Y, Kobayashi I | title=Large variations in bacterial ribosomal RNA genes | journal=Molecular Biology and Evolution | volume=29 | issue=10 | pages=2937–48 | date=October 2012 | pmid=22446745 | pmc=3457768 | doi=10.1093/molbev/mss101 }}</ref> An additional 4.5S rRNA with homology to the 3' tail of 23S is found in "higher" plants.<ref name="Bieri-2017"/>