Cell Structure & Organisation
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Nucleus, mitochondrion & chloroplast
What do the nucleus, mitochondrion and chloroplast have in common?
They are all membrane bound organelles. This means that they are cell structures that are covered membranes; to be precise double membranes.
The more interesting fact is that all three organelles contain genetic material in the form of DNA!
nucleus
The nucleus is an organelle found in most eukaryotic cells. (absent in certain specialised cells like mature red blood cells, xylem vessels)
It contains genetic material in the form of DNA organised into structures known as chromosomes.
mitochondrion
The mitochondrion is a membrane bound organelle found in all eukaryotic cells.
It functions to carry out aerobic respiration which releases energy from food substances.
chloroplast
The chloroplast is also a membrane bound organelle found mainly in plant cells.
It contains chlorophyll and plays an important role in photosynthesis.
Why is DNA present in mitochondria and chloroplasts?
The endosymbiosis theory seeks to explain the presence of DNA (genetic material) in mitochondria and chloroplasts. It is hypothesised mitochondria and chloroplasts were once free-living prokaryotes (bacteria). The ancient eukaryotic cells engulfed these bacterial cells via phagocytosis. Instead of of killing the bacterial cells, they survived and eventually became the modern day mitochondria and chloroplasts.
Overtime, the mitochondria and chloroplasts ancestors lost most of their DNA. The DNA that remains in them currently when sequenced show that they bear some relation to current day prokaryotic (bacteria) DNA.
