# Biochemistry (life chemical science) explained

Life as we understand it uses [DNA](science-life-biochem.png), which stands for deoxyribonucleic acid, with molecules arranged in a double-helix structure.

DNA is made of a very specific chain of nucleotide base pairings of A-T (adenine-thymine) and C-G (cytosine-guanine). This creates 4 permutations (each of the two flipped back-and-forth), which makes [all life information effectively a type of computer](computers-biological.md).

Each DNA strand is arranged into extremely long strands, with 2 strands in a chromosome. Different forms of life have different numbers of chromosomes, with humans having 23 and all life ranging from 1 to 1200 chromosomes, though it's not apparent by looking at any living creature how many chromosomes it has. The very last chromosome determines [gender differences](gender.md) with X and Y chromosomes, and the rest are called autosomes.

- Any location in a gene sequence is called a locus, and variations of those sequences are called alleles. A group of alleles that inherits from a single parent are called haplogroups, which pair together to form chromosomes.
- The very last chromosome of a male is XY and a female's is XX. When they mate, they give one chromosome each, meaning that it can be 4 possible combinations with an approximate 50% chance of a gender (X~m~+X~f1~, X~m~+X~f2~, Y~m~+X~f1~, Y~m~+X~f2~).
- Autosome traits can be dominant or recessive. Some traits (e.g., red hair, sickle cell anemia) require *both* parents to contribute their recessive genes. Others (e.g., blue-yellow color blindness, Marfan syndrome) only require 1 parent to send their autosome.
- On rare occasion, offspring can possess *two* sets of genes (chimerism) and a DNA test that only tests one set won't pick up direct ancestry from the other (especially with bone marrow transplants). This can happen with organ transplants or abnormal events during birth.

DNA has a vastly specific programming. *All* life shares the same ~60% DNA, with the differences arising from the remaining differences.

Beyond DNA, there are several other components necessary for life:

- Proteins, which are chains of amino acids (amino and carboxylate) that form a fixed structure.
- Carbohydrates, which are easily-broken-down chains of carbon/hydrogen/oxygen chemicals.
- Lipids, which include fats, oils, and hormones that aren't soluble in water.

We don't exactly know *how* life formed in the first place. This is contested based on philosophical cosmological beliefs:

1. Biologists say a series of electrochemical reactions formed the existing protein strands that eventually coalesced into what we know as organic life.
2. Religious people say God created organic life fully formed already.

Depending on the belief system, the taxonomy is dramatically different:

1. Kingdom - Plants, Animals, Protists, Fungi, Monids
2. Phylum - a further subdivision into various traits of each (e.g., arthropods)
3. Class - further subdivisions into various broad classifications (e.g., amphibians, reptiles)
4. Order - further subdivisions (e.g., primates, rodents)
5. Family - clearly demarcated subdivisions that *everyone* agrees on irrespective of cosmological values
6. Genus - further classifications that delineate nuances in families
7. Species - the final division that demarcates idiosyncrasies between various organisms

While we've sequenced the genome to measure where various traits are located, we haven't *completely* sequenced it. Instead, as of 2023, we still use the "shotgun method", which involves grabbing chunks of gene sequences and using [statistics](math-stat.md) to model the rest.

Further reading:

- [How does natural selection work?](https://rupertdeese.com/posts/critters/)
- [What is genomics?](https://learngenomics.dev/)

Obvious questions that remain unanswered:

- Will we ever fully cure cancer?
- Why do we have blood types?
- How long can we possibly live?
- What do probiotics do?