The Chloroplast Genome Encodes Many Proteins and RNAs

KEY CONCEPT
-Chloroplast genomes vary in size, but are large enough to encode 50 to 100 proteins as well as the rRNAs and tRNAs.
What genes are carried by chloroplasts? Chloroplast DNAs vary in length from about 120 to 217 kb (the largest in geranium). The sequenced chloroplast genomes (more than 200 in total) have 87 to 183 genes. TABLE 1 summarizes the functions encoded by the chloroplast genome in land plants. There is more variation in the chloroplast genomes of algae.
TABLE 1 The chloroplast genome in land plants encodes 4 rRNAs, 30 tRNAs, and about 60 proteins .

The chloroplast genome is generally similar to that of mitochondria, except that there are more genes. The chloroplast genome encodes all the rRNAs and tRNAs needed for protein synthesis in the chloroplast. The ribosome includes two small rRNAs in addition to the major ones. The tRNA set can include all of the necessary genes. The chloroplast genome encodes about 50 proteins, including RNA polymerase and ribosomal proteins. Again, the rule is that organelle genes are transcribed and translated within the organelle. About half of the chloroplast genes encode proteins involved in protein synthesis.
Introns in chloroplasts fall into two general classes. Those in tRNA genes are usually (although not inevitably) located in the anticodon loop, like the introns found in yeast nuclear tRNA genes . Those in protein-coding genes resemble the introns of mitochondrial genes . This places the endosymbiotic event at a time in evolution before the separation of prokaryotes with
uninterrupted genes.
The chloroplast is the site of photosynthesis. Many of its genes encode proteins of photosynthetic complexes located in the thylakoid membranes. The constitution of these complexes shows a different balance from that of mitochondrial complexes. Although some complexes are like mitochondrial complexes in that they have some subunits encoded by the organelle genome and some by the nuclear genome, other chloroplast complexes are encoded entirely by one genome. For example, the gene for the large subunit of ribulose bisphosphate carboxylase (RuBisCO, which catalyzes the carbon fixation reaction of the Calvin cycle), rbcL, is contained in the chloroplast genome; variation in this gene is frequently used as a basis for reconstructing plant phylogenies. However, the gene for the small RuBisCO subunit, rbcS, is usually carried in the nuclear genome. On the other hand, genes for photosystem protein complexes are found on the chloroplast genome, whereas those for the light-harvesting complex (LHC) proteins are nuclear encoded.

اخر الاخبار

اخبار العتبة العباسية المقدسة

العتبة العباسية المقدسة تواصل تنظيم مجالس العزاء الصباحية بذكرى زيارة عاشوراء

مواكب العزاء تستذكر في التاسع من شهر المحرم شهادة عبدالله الرضيع بن الحسين (عليهما السلام)

العتبة العباسية المقدسة تستذكر تضحيات القاسم بن الحسن (عليهما السلام)

شعبة الحرم الشريف تواصل تنفيذ خطتها الخاصة بشهر المحرّم داخل مرقد أبي الفضل العباس (عليه السلام)

المزيد

الآخبار الصحية

لهذا السبب.. إغلاق 25 مركزًا لعلاج الإدمان في مصر ؟

خلافا للاعتقاد الشائع.. علماء يكشفون أسرار بذور البطيخ ؟!

هذا ما يحدث لجسمك عند تناولك الطماطم بانتظام !

تعرف على أطعمة تسرّع "تعافي الجسم" من حروق الشمس

المزيد

الآخبار التكنلوجية

الثلوج تغطي الصحراء الأكثر جفافا في العالم!

بتلسكوب "ألما".. التقاط صورا غير مسبوقة لبدايات الكون !

هل هاتفك مراقب؟.. 5 علامات خطيرة تكشف التجسس عليك

دبي تطلق أول رحلة تجريبية للتاكسي الجوي

المزيد

مواضيع ذات صلة

Other Attenuated Systems: Operons, Bacillus subtilis and HIV

Coupling Translation to Termination

trp Multiple Secondary Structures in trp Leader RNA

Early Explorations of the Hypersynthesis

The Serendipitous Discovery of trp Enzyme Hypersynthesis

Rapid Induction Capabilities of the trp Operon

The Aromatic Amino Acid Synthetic Pathway and its Regulation

How AraC Protein Loops and Unloops

DNA Looping and Repression of araBAD

Binding Sites of the ara Regulatory Proteins

Endoplasmic Reticulum-Associated Degradation and the Unfolded Protein Response

Protein Folding and Modifications in the Endoplasmic Reticulum