Chloroplast and mitochondria were free prokaryotes before their integration, by endosymbiosis, to current eukaryote cells. Inside them contained a single circular chromosome, reduced size, and ribosomes that allow to arrange in sequence proteins to realize their specific functions.

On chloroplast and mitochondria , both primitive prokaryote, is done the same function in opposed directions. So join into chloroplasts CO2 and energy to form carbohydrates and release O2 while in mitochondria carbohydrates and O2 are used to release energy and CO2. We witnessed two mirror functions providing valuable information about the origin of life energy.

Regarding the production and release of energy is known the existence of a protein structure (enzyme) called ribulose-1 ,5-bisphosphate carboxylase-oxygenase, carbon acceptor which acts carboxylase functions (fixing CO2) and oxygenase (oxidizing an organic substrate) from which it derives its name RuBisCO .

FIGURE 1

This protein consists of 16 polypeptides organized into two subunits of different size L and S (Large and Small). The higher catalytic activity and less regulatory functions. We are faced with the basic instrument of external uptake and intracellular release of energy moving life.

If we take a step back and ask ourselves about the origin of RubisCO know that the fraction L is encoded by the rbcL gene and the S fraction by the rbcS gene contained in the Circular chloroplast DNA. The rbcL gene is universal in all plant cells (except in parasitic) contains 1428 base pairs (hydrogen bonds between two bases of each step) and its mutants are unable to produce viable power source. The rbcS gene has itself a very low rate of mutations.

Chloroplasts and mitochondria have a single chromosome formed by circular DNA rolled up on itself in the form of a circle on a single plane or in a covalently closed circle to form a similar twist as Mobius strip.

FIGURE 2

In both cases these structures formed by only a few thousand nucleobases (120-160000 in chloroplasts and 20,000 in mitochondria) if compared to the 3,000 million bases of the genome of modern mammals. For its size and circular structure, or continuous strip, we have a primitive structure of the genetic material encoding the obtaining external power (solar or chemical) and its release inside the cell.

Circular DNA of chloroplasts and mitochondria contain basic genes for producing, chloroplasts, 70S ribosome that serve to produce RuBisCO and thylakoids and, in the mitochondria, for the production of 55S ribosomes in animal and 70S in vegetable.

Besides genetic importance of circular DNA in chloroplasts and mitochondria to be the source of obtaining the vital energy, there is a second aspect that helps to explain the origin of the genetic material of the nucleus of eukaryotic and probably the deployment and DNA replication to reach the nuclei of the most evolved animal cells. It is known that the nucleus of eukaryotic cells containing rbcS and rbcL genes (identical to the chloroplast) and a part of the core, known as nucleolus accumulate ribosomes.

In summary prechloroplasts, first possible prokaryotic by evidence of oxygen production, host a circular primordial structure of DNA that contains immutable genes (rbcL and rbcS very few base pairs linked by hydrogen bond) ) Capable of producing ribosomes that arrange in sequences proteins (RuBisCO) allowing transfer of external energy into the cells and, and inside eukaryotic, genetic material has been transferred to the cell nucleus giving origin to nucleus and the nucleolus of complex cell.

On circular DNA of plant cells there is the first  evidence of metabolic and genetic contingency of animal cells to plant cells because on precholoroplasts there are the genetic tools (rbc genes) and enzymatic (carboxylase) initiating a synthesis chain of nutrients that adapt into animal cells on mirror functions (oxidase) and transfer of genetic material into the nucleus of eukaryotic animals