{"id":103,"date":"2023-02-17T22:12:45","date_gmt":"2023-02-17T22:12:45","guid":{"rendered":"https:\/\/floydsplace.us\/wpress\/?p=103"},"modified":"2023-02-18T17:20:16","modified_gmt":"2023-02-18T17:20:16","slug":"how-long-is-your-dna","status":"publish","type":"post","link":"https:\/\/floydsplace.us\/wpress\/2023\/02\/17\/how-long-is-your-dna\/","title":{"rendered":"How long is your DNA?"},"content":{"rendered":"\n

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How long would the DNA be from a single human if all of the molecules were lined up end to end? <\/p>\n\n\n\n

\"\"<\/a>
The basic structure of DNA illustrating the double helix backbone and the four types of nucleotides, often abbreviated as A, T, G, and Cs, which are in base pairs between the strands.<\/figcaption><\/figure>\n\n\n\n

Our genome is a little over three billion base pairs (the A,T,G,C sequence of molecular “letters” in our DNA) long (IHGSC 2004). We have two copies per cell, so that puts us at over six billion base pairs of DNA sequence. One complication is the XX versus XY difference between females and males. Women have slightly more DNA than men because the Y chromosome is shorter. This works out to an average of 6.32 billion base pairs per human in our cell’s nucleus (Piovesan et al<\/em>. 2019). (Of course, all of our chromosomes are of slightly different lengths among people because of natural variation, but this is a minimal effect in our calculation.)<\/p>\n\n\n\n

\"\"<\/a>
A schematic of our 25 types of chromosomes in each cell. The banding pattern on the large nuclear chromosomes indicates condensed, highly packed areas of DNA (darker bands corresponding to heterochromatin) versus regions that are more open with more actively expressed genes (light areas called euchromatin). <\/figcaption><\/figure>\n\n\n\n

We also have mitochondria outside of our cell’s nucleus with their own 16,569 bp chromosome (Anderson et al<\/em>. 1981). This is tiny compared to our nuclear genome. However, there are 100s to 1000s of mitochondria per cell, and each contains from one to 10 copies of the mitochondrial chromosome (Cole 2016). These numbers vary widely between cells and over time. Let’s take \"5 \times 500 = 2500\" as a rough working estimate of the number of mitochondrial chromosomes per cell. This comes out to \"2500 \times 16,569 = 41,422,500\" additional base pairs per cell, which brings our average up slightly to approximately 6.36 billion base pairs per cell. <\/p>\n\n\n\n

There are a lot<\/em> of bacteria (and other things such as fungi and viruses) living on and in our bodies that we have coevolved with, and they have a direct effect on our health in both positive and negative ways. The mitochondria originated as a symbiotic bacteria that has now been incorporated into our cells. Here I am not including these additional organisms, our microbiome, because it is highly variable, there are a lot of unknowns, and we generally don’t feel like they are a part of us in terms of DNA sequence. <\/p>\n\n\n\n

Next is the length of a base pair in a DNA strand, which is about 3.4 \u00c5 (an \u00c5ngstron is \"10^{-10}\" meters, about the width of a hydrogen atom). This is<\/p>\n\n\n\n

  <\/span>   <\/span>\"\[3.4 \times 10^{-10} \times 6.36 \times 10^9 \approx 2.2 \mbox{m}\]\"<\/p> <\/p>\n\n\n\n

or 7 feet 2 inches of DNA per cell. This is longer than the height or maximum arm span of the average human. <\/p>\n\n\n\n

It is amazing that a cell is able to pack all of that DNA into such as small space and still function. The longest chromosome, our Chromosome 1, is about 250 million base pairs of DNA long (Piovesan et al<\/em>. 2019). That’s a single molecule<\/em> that is over eight centimeters or over three inches long! <\/p>\n\n\n\n

\"\"<\/a>
When we start adding up the DNA length from multiple cells, we need to start thinking about much longer distances. <\/figcaption><\/figure>\n\n\n\n

That’s just for one cell. How long would the DNA be for all of your cells? How many cells that are in an average human body is hard to answer. They vary widely in size among different tissues and this is a tricky question to answer. However, a reasonable estimate is about \"3.0 \times 10^{13}\" cells (30 trillion with a “t”), which incidentally is about the same as the number of bacterial cells in our microbiome (Sender et al<\/em>. 2016). However, approximately 70% of these are red blood cells, which neither have a nucleus with large chromosomes nor mitochondria, so we need to reduce this number to 30% of the total to estimate the number of DNA-containing cells. (A further complication is that some of our cells, such as some in the liver or heart muscle, have more than two copies of each chromosome, but this is the minority of cells, so we will ignore it in this calculation.) So, <\/p>\n\n\n\n

  <\/span>   <\/span>\"\[0.3 \times 3.0 \times 10^{13} \times 2.2 \mbox{m} \approx 2 \times 10^{13} \mbox{m.}\]\"<\/p><\/p>\n\n\n\n

or 20,000,000,000 km! <\/p>\n\n\n\n

\"\"<\/a>
The Blue Marble<\/em> photo of Earth taken by Apollo 17 in 1972. One of the most iconic images of Earth.<\/figcaption><\/figure>\n\n\n\n

\"2.0 \times 10^{10}\" kilometers, or over 12 billion miles, is a longer distance than we are used to in our daily lives. The Earth’s circumference is a little over 40,000 km. Your DNA would wrap around the Earth 500,000 times. The Moon is 384,400 km away. Your DNA would go to the Moon and back 26,000 times. The Sun is 150,000,000 km away. Your DNA would go to the Sun and back 67 times. However, we don’t want to fold and bend the DNA; we want to stretch it out in a line to see how long it is. <\/p>\n\n\n\n

\"\"<\/a>
The distance from the sun is on a log scale in AU. One AU is \"1.5\times 10^8\" km. On the right side are the closest neighboring stars a few lightyears away.<\/figcaption><\/figure>\n\n\n\n

The diameter of Neptune’s orbit (the planetary solar system) is nine billion kilometers, and your DNA could easily cover twice that distance. The Heliopause, which defines the Heliosphere “bubble” around the Sun, the boundary between the Solar System and interstellar space, is about 17 billion kilometers from the Sun (on its closest edge). Your DNA should be able to just reach that distance to interstellar space. That’s a long way! <\/p>\n\n\n\n

That’s only for one person. Recently we passed eight billion people on Earth. At this point, we are moving to a scale of millions of light years, which would encompass not only our own galaxy but several of our neighboring galaxies, not just interstellar but intergalactic distances! And then there are all of the other species on earth with a huge range of genome sizes and numbers of individuals. Conservative estimates would put it well beyond the diameter of the observable Universe, over 90 billion light years. I honestly don’t know how even to attempt to estimate this more precisely. Landenmark et al<\/em>. (2015) have tried and came up with \"5.3 \times 10^{37}\" base pairs of DNA in Earth’s biosphere with more than \"10^{24}\" operations per second in terms of DNA information processing speed. Numbers this large are hard to think about intuitively. For example, there are only<\/em> about \"10^{80}\" protons in the observable Universe (known as the Eddington number), and since most atoms are hydrogen with one proton, this is close to the number of atoms in the observable Universe. If we view DNA as a way to encode information, it is clear that there is a tremendous amount of biological information on the surface of this planet. <\/p>\n\n\n\n

References<\/p>\n\n\n\n