It’s that time in the general biology semester where we transfer our attention to cell division. Having already discussed a number of basic principles like the laws of thermodynamics and a touch of chemistry, and cellular functions such as the flow of energy and the flow of information, it’s now time to look at how cells reproduce themselves.
In this chapter we should be recalling all the parts of the cell and accounting for how they get sorted into the developing ‘daughter cells’, and also recall the role of information, in the form of DNA, and how this is apportioned into the daughter. Of course we will spend most of our time focusing on the distribution of DNA, but we should always keep in mind what we know of other structures and organelles.
I previously wrote an essay describing cell division in humans that marries this information with the subject of the next unit, genetics and inheritance. You can find that text here. Therein, I briefly address one of the oddities of eukaryotic cells, the mitochondria. Mitochondria are odd because they live in our cells as strange symbiotes that share their energy with us in exchange for protection and a supply of nutrients. The theory describing this relationship was proposed by Lynn Margulis, and is widely accepted today. A description of her theory can be found here.
Because Mitochondria (and chloroplasts) are pseudo-autonomous cells, they must replicate themselves. A cartoon and some micrographs that illustrate this process have been borrowed from Nature Reviews.
The process involves an interaction with the Endoplasmic Reticulum, that guides an assembly of molecules that constrict around the Mitochondria eventually effecting its division into to smaller organelles. What this image does not include is the replication and separation of the mitochondria’s own circular DNA, a process that necessarily precedes the actual division of the organelle.
Altogether, there’s a lot to keep in mind when examining cell division. Why is this cell dividing? How are the instructions for life (DNA) being distributed between daughter cells? What does the daughter cell need in order to survive on its own? How do these parts / organelles handle their own division between the cells? And what would happen if any of this went wrong along the way?