What is the relationship between DNA, genes, chromosomes, etc?
In: Biology
At a simple level, think of DNA, genes, and chromosomes like the alphabet.
Genes are like sentences. Chromosomes are like paragraphs, or long texts.
DNA is all the letters that make these up. Except there are only 4 letters, making up many, many words, sentences , paragraphs and texts.
On a slightly more chemical level: DNA is a complex chemical structure. There are 4 “types”, to which we assign a letter, A,TC or G.
DNA exists in loooooong strands. A number of different letters in a row forms a gene.
A loooooong number of genes together forms a chromosome. Humans have 23 pairs of chromosomes.
You can imagine DNA as a really long string made up of the same four elements repeated over and over again. For simplicity, we can call those elements A, G, C, or T. These longs strands are a code which tells our body how to make the proteins that make our body work. So while we would just see a long list of four letters, our body sees a clear set of instructions.
In your cells, you have 46 of these strands: 23 from each parent. Each individual strand is called a chromosome. Each chromosome holds the instructions for thousands of different proteins. The instructions for a specific protein is called a gene. Everyone has the same basic set of genes, but every individual has specific “versions” of each gene. For example, you and I both have a gene for eye color, but my version of that gene may give me blue eyes, while yours gives you brown eyes.
Specific genes are found on specific chromosomes. Since you get one copy of each chromosome from each parent, you get two versions of each gene. The unique combination of these versions is what makes us similar but different from each of our parents.
TLDR: Chromosomes are long strings of DNA which each hold thousands of genes
*DNA* — a chemical substance that life uses to store genetic information. It is a polymer — long chain consisting of a lot of connected parts.
*nucleotide* — a single part of that chain.
*base* — the part of the nucleotide that differs between nucleotides (that’s why from the information point of view the words nucleotide and base are sometimes used interchangingly).
*gene* — a fragment of DNA that encodes a single protein
*chromosome* — a DNA molecule in eucaryotic (not bacteria) cell with some proteins that “manage” it. They contain multiple genes.
Your entire genome (or a whole cell nucleus) is the library.
Each chromosome is a cookbook. Books consist of paper (the DNA) and binding/cover (the histones). The nitrogen bases are the letters on the paper. In the language of DNA there are only four letters, A, C, G and T.
The letters combine to make words, which we call codons. In the genetic language all the words are three letters long.
Put together a string of codons(words) and you make a recipe(gene), which is the instructions for how to make something. One of the codon-words is ATG which is called the initiator codon, and it does the same job as a capital letter, which tells you a new sentence is starting. There are also three codons called terminator codons (TAA, TAG, TGA), which do the same job as a period; they tell you where a sequence ends.
The big important part of a recipe is the ingredients and how to put them together, which we call a structural gene. The other thing you find in a cookbook is *when* to use the recipe – “this is a good drink for a hot day”, “pour this over pasta or fish”, that kind of thing. Information about when to use a gene/recipe is called a regulator.
So the purpose of all that is your cells have to make proteins (insulin, titin, acetyl coenzyme A, MTOR kinase, many, many others) for you to survive, and your DNA is the ‘cookbook’ that stores how to do all that. Instructions from the cookbook are relayed to your ribosomes (kitchens), where proteins are put together. The relaying is done by messenger RNA. Each of your cells only has one copy of each cookbook so you aren’t allowed to take them out, but you can use a notebook (mRNA) to make a copy of the recipe and then take that copy to the kitchen. Amino acids are the ingredients you cook with. Transfer RNA is the kids who hang around the kitchen and help you by fetching ingredients. The metaphor just keeps on going. 🙂
**DNA** – type of polymer (material made up of many small sub-units) that are composed of a sort of “alphabet” (nucleotides, A/T/C/G), with and without additional modifications at each location to also influence how it’s read (epigenetics). They store not only information, but also sequences that can just modify how the DNA surrounding it is read and transcribed into protein, and how fast.
**Genes** are specific segments of DNA that code for a specific thing. You can have a very long sequence of DNA, but there will be, essentially, functional sub-units/spans within that that actually code for a specific protein. These regions are labelled as specific genes, and usually you have two of each, one for each parent.
**Chromosomes** are specific, separate molecules of DNA. All the DNA in your cells aren’t connected into a single very long molecule, but potentially dozens of very long molecules that become a sort of spaghetti-soup in the nucleus, with distinct regions that are read or not-read/condensed/blocked. These chromosomes can condense to become more readily seperable during cell division.
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