Exploring the Intriguing Links Between Your Genome and Astronomy
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Chapter 1: The Riddles of the Universe and Our DNA
In Alice in Wonderland, Lewis Carroll introduces a whimsical riddle through the Mad Hatter: “Why is a raven like a writing desk?” Interestingly, Carroll admitted he had no definitive answer. Yet, this has not hindered others from offering clever interpretations, such as, “Poe wrote on both!” or “There’s a ‘b’ in both and an ‘n’ in neither!”
Now, consider this riddle: how does your genome—the DNA sequence that encodes the blueprint for your existence—relate to a puzzle faced by astronomers gazing into the cosmos? My take is that “most of both are fundamentally dark matter.”
Let’s delve deeper into this intriguing comparison! Along the way, we’ll uncover:
- The distinction between a genome and an exome
- How we perceive the absence of elements in our night sky
- The significance of how we interpret instructions, which may be as crucial as the instructions themselves.
Why is a raven like a writing desk? Because both can produce a few notes! Let’s embark on this journey!
Most of Your DNA is Non-Coding (Surprise!)
To kick things off, let’s revisit the basics of our DNA. Each cell in our body contains an extensive chain composed of pairs of molecules known as bases. These bases come in four varieties: adenine, guanine, cytosine, and thymine (commonly abbreviated as A, G, C, and T). Similar to how a computer program is constructed from 1s and 0s, the arrangement of these four bases—repeated countless times—carries the instructions necessary for creating a human (or any other organism). Notably, a human genome comprises approximately three billion bases!
Within our cells, this DNA is not simply a singular, lengthy chain. There are 23 distinct strands of varying lengths, each paired with a corresponding partner. These strands are referred to as chromosomes.
Zooming in on a specific chromosome reveals that our cells constantly produce copies of various DNA segments. These copies are single-stranded, contrasting the double-stranded DNA, and are termed RNA.
We utilize these ephemeral copies as guidelines for synthesizing different proteins, which are the fundamental building blocks of our cells. The segments of DNA that are transcribed into RNA and subsequently transformed into proteins are known as genes. Depending on the measurement criteria, an individual typically possesses between 21,000 to 30,000 genes.
Now, take a moment to guess: what proportion of our total DNA is composed of genes? How much of our DNA is actually utilized for protein synthesis?
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Have you made your guess?
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The surprising answer is that merely about 1% of our genome consists of protein-coding genes. This means that a staggering 99% of our genome does not hold instructions for constructing and maintaining a human being! Those 21,000-30,000 genes represent only a fraction of the three billion bases that form our genome.
In fact, we utilize different terms when discussing the entire genome versus that small protein-coding segment. The portion that pertains solely to genes is referred to as the exome (derived from “exon” plus “genome”).
Many contemporary companies, when sequencing an individual’s DNA, opt to sequence only the exome. This approach allows them to analyze just about 1% of the total genome, resulting in more manageable datasets while still retaining critical information about the genes!
But what about the remaining 99% of the genome? Is it merely dark matter?
The first video, The Genes that Built You, explores the foundational aspects of genetics and the role our DNA plays in our identity.
Understanding Dark Matter: The Invisible Force in Our Galaxy
When astronomers refer to dark matter, they are acknowledging the existence of a substantial portion (around 85%) of our universe that remains unseen, yet is essential for gravity’s functionality.
Take our galaxy as an example. It presents a vast spiral structure, and while it rotates, we observe no significant portions detaching. This suggests that a certain mass must be present to ensure gravity can hold all stars and solar systems together.
However, when we account for all visible stars and matter, we find it insufficient. For gravity to operate in the manner we observe, there must be a considerable amount of mass hidden from view—this is what we identify as dark matter.
Typically, it is assumed that this matter is non-baryonic, meaning it differs from baryonic matter (the subatomic particles forming the atoms and molecules we commonly understand as matter).
Thus, dark matter represents a substance fundamentally distinct from the tangible matter we can perceive—stars, planets, asteroids, and other celestial bodies account for only about 15% of the overall matter in our universe.
Despite its invisibility, dark matter serves a crucial role, preventing galaxies from disintegrating and maintaining the structure of spiral galaxies. Without it, the universe as we know it would not exist.
What about the “dark matter” in our DNA? What purpose does the 99% of non-coding DNA serve?
In Genetics and Beyond: The Importance of Context
Unlike dark matter, we have a better understanding of the 99% of DNA that lies outside the exome! While it may not specifically encode proteins, it is still of great significance.
This extra DNA is not merely redundant. The non-coding sections of our DNA—our dark matter—encompass features such as:
- Promoters: These are binding sites where molecular machinery can attach to DNA, facilitating easier access to specific genes and promoting greater gene expression.
- Enhancers: Similar to promoters, enhancers attract enzymes to amplify gene activity. While promoters are typically adjacent to the gene's sequence, enhancers can be located much farther away, yet still functionally close in three-dimensional space.
- Silencers: In contrast to promoters and enhancers, silencers inhibit gene expression, whether located nearby or further along the chromosome.
- Non-coding RNA: Certain regions of our genome produce RNA that does not translate into protein but can help form structures for cellular machinery or interact with coding RNAs, providing additional control over gene product levels.
- Centromeres: These regions, located near a chromosome's center, serve as anchor points for the two chromosomal copies (one from each parent), ensuring accurate cell division and genetic material distribution.
- Telomeres: Found at the ends of chromosomes, these repetitive sequences are gradually consumed with each replication, safeguarding crucial information from being lost.
- Epigenetic Sites: Our DNA is tightly coiled for protection, but certain spots regulate when the DNA unwinds for accessibility or coils back up, determining gene expression.
All these components are vital, even if they don’t directly lead to protein synthesis; they establish the context for gene activation and activity levels.
It continues to astonish me that genes constitute merely a small fraction of our genome. Despite biology and genetics curricula often emphasizing genes as the key elements, the remaining 99% is equally integral.
Research into the complexities of our genomic "dark matter" is ongoing. We must also consider additional factors like epigenetics and the three-dimensional arrangement of genomic segments within cells.
One day, astronomers may unravel the mystery of the remaining 85% of dark matter in our universe and its characteristics. Meanwhile, we are already probing into the dark matter of our genome, uncovering the intricate layers that define our complexity.
