# Microbiology (small life science) explained

Cells are the simplest expression of life, and they all have at least most of the same characteristics:

- A nucleus that contains the DNA of the cell.
- Ribosomes that read the nucleus' DNA and make corresponding copies of that DNA with RNA (with uracil instead of thymine).
- A semi-porous cell membrane with a lipid bilayer that lets stuff in and out of the cell, often shaped in a way to only let certain chemicals in that it may need.
- Cytoplasm, a fluid made of mostly water that fills up cells.
- Mitochondria that use ATP (adenosine triphosphate) or photosynthesis to give energy to the rest of the cell.
- Lysosomes that break down unwanted things in the cell.
- Endoplasmic reticulum, a framework for processing chemicals, which are either "rough" (with ribosomes on it) or "smooth" (for processing hormones and lipids).
- Golgi apparatus, an "outbox" where the endoplasmic reticulum sends everything into the cell wall or out of the cell.

Further, plants have a few components of their own:

- A cell wall with a cellulose layer that gives extra structure to the organism.
- Chloroplasts that help with photosynthesis (using photon energy for metabolism).
- Vacuole that serves as a storage space for the cell (often filled with mostly water).

On the cellular level, reproducing life asexually (mitosis) is a relatively straightforward process:

1. The nucleus sends "messenger RNA" (mRNA) to the ribosome.
2. The ribosome uses stuff like "transfer RNA" (tRNA) and "ribosomal RNA" (rRNA) to gather proteins to build more DNA.
3. Once the second DNA is built, the cell lines up everything together, then creates a new cell membrane to split it cleanly in half.

By contrast, more complex life reproduces sexually (meiosis) with another relatively straightforward process:

1. A male sperm (which has all the DNA of the male) penetrates the cell membrane of a female egg (which has all the DNA of the female).
2. The egg splits and lines up the chromosomes of each, then takes half of them.
3. That one half-of-each DNA hybrid is the basis of the new cells, which rapidly keep splitting according to their instructions, a bit like mitosis.

It's worth noting that sexual reproduction requires similar-enough animals. While cross-species mating isn't uncommon and cross-genus mating is sometimes possible, cross-family mating isn't.

Further reading:

- [How do viruses assemble?](http://viruspatterns.com/)

Obvious questions that remain unanswered:

- Can, and how can we beat bacteria?
- How do mitochondria work?