Chromosomal DNA located in the nucleus codes of about 40000 genes but it is not the only DNA in cells. Chloroplasts have their own DNA that codes for about 100 genes and mitochondria have DNA as well. DNA strands in these two organelles is single strand, unlike the two-stranded DNA in the plant nucleus. This feature, as well as the double-layered membrane of these two organelles, have contributed to the concept that they originated early in the evolutionary change to advanced forms of life. Chloroplasts are believed to happen 3-400 million years ago when a cyanobacterium (a blue green algae) became engulfed in a non-green single celled organism. The chloroplast self-duplicates in plant today, dividing much like bacteria. Its DNA gets translated into RNA, that moves to ribosomes within the chloroplast for production of the proteins needed as enzymes to convert light into chemical energy. Despite producing some of its own proteins, about 90% of the proteins in chloroplasts come from the cells’s nuclear DNA.
Mitochondria, the organelles that convert sugars into the chemical energy of ATP, also have single stranded DNA, double-layered outer membrane and divide like bacteria. Thus, the theory that they originated as bacterial. Like chloroplasts, they are also dependent upon the host cell’s DNA for part of their existence. Just as with chloroplasts, mitochondria have a symbiotic relationship with the host cells.
While the whole corn plant gets our attention, the real work is happening in its smallest components.
About Corn Journal
The purpose of this blog is to share perspectives of the biology of corn, its seed and diseases in a mix of technical and not so technical terms with all who are interested in this major crop. With more technical references to any of the topics easily available on the web with a search of key words, the blog will rarely cite references but will attempt to be accurate. Comments are welcome but will be screened before publishing. Comments and questions directed to the author by emails are encouraged.