Regulation and development
Genetic information (DNA) of the organisms stays more or slightly less the same during whole life or organism. But cell are behaving differently in different environment and in different stages of life. Multicellular organisms have the same DNA in each cell and we know that we can find many very different cells these organisms (as ourselves). There are multiple mechanisms in cell taking care of this behaviour.
Regulation
There are many types of cells with many different functions in multicellular organisms (just thinks about skin cells, red blood cells or neurone cell), but all these cells share the same DNA. There are multiple layers how DNA is guarding function of cell.
Sequence of DNA is the base layer. But on top of DNA there are layers of regulation that says what parts of DNA should be active, which parts should be suppressed and how to decide in any point in time. This regulatory mechanism is big part of what biology and science is trying to figure out.
Example of one layer of regulation might be accessibility of DNA. We can imagine DNA as a book. And you could have some pages that are glued together and they’re really hard to open and there’s some pages that are almost half open. The pages that are almost half open are much easier to be copied.
Another layer is regulation after part of DNA is copied. Some part of DNA is half open so it can be copied, but later there is a level of regulation that can identify a specific signals and can destroy them or it can regulate how long they will exist.
Development of multicellular organisms
Every multicellular organism starts from one single cell. Cells are programmed to copy themselves to as much as possible perfect copies. There is a whole program of regulation of this process - which part of genome will be more accessible and which part will be almost hidden. This program is called development. It will bring the single cell to copy into 2 - 4 - 8 - etc. Their DNA will not change, but accessibility of DNA will start changing. Eventually, some of these cells will become head, other cells will become skin etc. They will all have different developmental programs.
When we’re talking about multicellular organisms, like plants or humans, we will have many developmental programs that need regulated in a very complex ways to function in a proper way and not cause harm.
Development in singe-cell organisms
In single-cell organisms (like bacteria), processes of development and evolution have not so clear boundaries. This organisms are also trying to make perfect copy of themselves. In simple terms it means, that they will:
- absorb energy and chemical from environment,
- copy their tools (parts of their cell),
- copy their genetic information (DNA),
- they will split into two (hopefully) exact copies.
This two copies will continue in this process: absorbing - duplicating - splitting. It is similar to processes in multicellular organisms, but here new cells are not part of the same organism.
Simple cells have less regulation. They still do have complex regulation, but they have less programs how their cell should behave. When we were talking about bacteria, they need programs for absorbing energy and chemicals, for copying tools and genetic information and for splitting into two cells. But they also might have programs for behaviour for times when there is not enough food.