Mitochondria and chloroplasts are membrane-bound organelles which are responsible for carrying out vital cellular functions: cellular respiration and photosynthesis. Cellular respiration is conducted within the mitochondrion and photosynthesis is done within the chloroplast. Mitochondria are found in all cell types, whereas chloroplasts are only in plant cells, along with a few other eukaryotes.
Mitochondria are thought to be more ancient than chloroplasts. It is believed that two billion years ago mitochondria formed through endosymbiosis, an event which began with an early anaerobic prokaryotic cell. Conversely, the chloroplast is thought to have evolved one billion years ago, originating from cyanobacteria in one or maybe several engulfing-based events.
In terms of structure, the mitochondrion has multiple compartments. These compartments are an inner membrane, an outer membrane, a matrix and intermembrane space. A cell contains multiple mitochondrion organelles and these organelles are capable of moving around on the cytoskeleton throughout the cell. Mitochondria even have their own DNA, called mtDNA, which is transcribed and translated within the mitochondrion directly.
Chloroplasts represent another dynamic membrane system. Chloroplasts also have their own DNA which is circular and usually around 120 000 – 170 000 bp (base pairs). This DNA is abbreviated as cpDNA or ctDNA.
The main compartments of chloroplasts are named as one group, the chloroplast envelope, which contains the outer membrane, inner membrane and intermembrane, along with the stroma which is the intermembrane space (although this is not part of the chloroplast envelope classification). Other structures within chloroplasts are thylakoids, granum and pigments. Additionally, just like mitochondria, multiple chloroplasts are present within one cell. Overall, these two organelles are both extensive systems which carryout critical roles related to energy conversion in the case of mitochondria and sugar production in the case of chloroplasts.