Life’s Meaning

A very romantic beginning, you may think 😏. Well, in this section, we’ll get to define what living things (life) is, by taking into account 7 main characteristics, which are:

1. Cells: they’re the fundamental unit of life. This means that as long as there’s one cell in the universe, there will be life, even if it’s just the tiniest bacteria cell. Every living thing is made of cells. You too! Billions of them
2. Use and need of energy: after you breathe and eat, those substances are transformed into energy that each one of your cells uses so you can do everything you do
3. Adapted to surroundings: change isn’t always comfortable. But it’s necessary to survive. From chameleons changing their color, to humans adapting to food or water scarcity
4. Reproduce: creating more living things at a constant rate is essential for the survival of the species
5. Growth and development: they can be confused. Growth is basically when your cells reproduce/double/make more of them. Development refers to changes in the DNA that lead to different kinds of cells
6. Move: even though we don’t notice very easily, organisms like plants also move. This makes them living things too :)

LIFE = the condition that distinguishes animals and plants from inorganic matter

Cells

Let’s narrow the scope to the microscopic level. We’ve mentioned that 1) The cell is the minimal unit of life 2) Every living thing is made of cells 3) Cells come from cells. This is actually called the “Cell Theory”.

As for humans, there are more than 200 types of cells. Some of them make up your blood so they fight disease and carry oxygen, others are part of your skin and protect your body against the external environment, some others form your heart, brain, lungs, stomach, and more tissues and organs.

But humans aren’t the only living things made out of cells. As the same cell theory says, every living thing is made up of cells. Therefore, we have 2 main types of them, among all living things: eukaryotes and prokaryotes. For all animals, and all other living things, respectively.

What other living things? Well, actually bacteria are widely used in the field of synthetic biology. Other examples of prokaryotes are fungi 🍄

Inside each of those cells, there are many different kinds of tiny things called organelles. Organelles are in charge of various ‘jobs’ to make the cell function. One of these jobs is to produce proteins, a process that we’ll talk about in more detail later in the article.

Central Dogma

I’d describe it as the study of the most important information inside ourselves: the genome. It has to do with DNA, genes, proteins…

🧬 DNA

It stands for Deoxyribonucleic acid. However, what you need to know about it is that it is like an ‘instructions manual’ which has all the information needed to make us who we are.

Going a little bit into more detail, the language in which this instruction manual is written is not English, Spanish or French. It’s rather a ‘chemical language’ in which we can identify 4 letters: A (adenine), C (cytosine), G (guanine)and T (thymine).

In this case, instead of orthographical rules we have chemical rules imposed by nature, which tell us that A will always bind with T, and C will always bind with G. You can memorize this by remembering the phrase: ‘Apples in the Trees and Cars in the Garage’. Even more important, the order of these letters determines the kind of protein that is going to be produced, if a protein is not going to be produced or even if it’s not going to function correctly. Hence, several genetic diseases are a result of one or very few base pairs that are wrong (yes, cells make mistakes).

📄 RNA

So DNA knows how to create proteins that make our bodies work. However, it’s also extremely important, so it cannot go out of the nucleus (like the most protected place of the cell). But don’t worry…

RNA is DNA’s cousin. It’s also thin enough to get into the nucleus and out of it. This means it is a one-helix structure. The other difference is that for RNA, the letter T changes for a U (uracil).

RNA is born as a precise copy of DNA (changing T for U of course). In this case, it’s called mRNA (messenger RNA) because goes out of the nucleus to form a protein. This whole process of copying DNA is called transcription.

🏭 Ribosome

After transcription, comes translation. Just as in any other language, it refers to when mRNA is translated into a protein language. This happens in the ribosome.

You can think of it as the manufacturer inside a company (the cell). It is the organelle in charge of reading As, Cs, Gs and Us in groups of 3, each of which is called a codon. Each codon is translated to amino acid language by tRNA (transfer RNA). A group of 50 or more amino acids forms a protein: the final product.

Almost without noticing it, you’ve now learned the central dogma of biology:

1. Transcription (DNA → mRNA)
2. Translation (mRNA → protein)

Genetics

Now let’s get into the really genetic aspect of this: DNA only. We’ll start from the outside, until getting into concepts that can get a bit abstract, like a gene. Since this is a crash course, I’ll only explain the concepts briefly.

Genome

Think of it, as a collection or series of books. These books contain all the necessary information to make you who you are. The story that each living thing has is different. However, when it comes to humans, the genetic difference between you and me, is only about 1%!

Chromosomes

Simple. Each book in this collection is a chromosome. In humans, there are 46 chromosomes in total. These come in pairs, meaning that we can have 23 pairs of chromosomes.

DNA

I know we’ve defined it earlier. Just to refresh the concept, DNA is the language in which these books are written. Yet, it’s not only an abstract concept. DNA is the ink in these books too. It’s a molecule

Gene

Now, this is where the thing can get a little abstract. Yes, a gene is a physical part of DNA. However, the only thing that determines whether a DNA strand is a gene, is knowing if it has a function; if it codes for a protein.

This is the revelation: not all the DNA in the genome has the instructions to create proteins. Actually, most of the DNA is called junk DNA because it has no apparent function.

Mutations

Mutations are damages to the DNA, like spelling errors in our genetic book. When they occur, even replacing one A for a G, could lead to terrible outcomes, like many genetic diseases.

SNP (Single Nucleotide Polymorphism): variation in the DNA sequence that affects only one base. These are part of 90% of all genomic variations.

Epigenetics

This is the mechanism by which genes are turned on and off. It’s actually a whole topic worth-exploring in more detail. Expect a new article about this topic in a few days ;)

Histones: proteins that wrap the DNA so it can fit into the cells. They control gene expression too by making DNA available or unavailable to transcribe, thus, they are part of the epigenome

Other important concepts

Hereditary: genetic traits transmitted to a descendant

Chromatin: chromosomes + histones

Telomeres: specific DNA sequence at the end of chromosomes that is repeated thousands of times. They protect the coding regions and play an important role in lifespan

Transcription factor (TF): protein that controls the transcription of a gene

Thank you!

I sincerely hope this small and simple guide has been small and simple indeed, and that it has helped you grasp the basics of molecular biology. This is something that would have been very useful for me when I was getting started and hadn’t learned biology of this kind at school.

This may not have been the kind of article that is very interesting and brings a lot of enthusiasm, but if you weren’t very familiar with these concepts already, it will hopefully be very useful to get started in learning about more advanced topics.

Feel free to check out all the articles I’ve written about biotech, which I see as the XXI century application of these basic concepts. Here are my 3 personal favorites:

Hey! I’m Sofi, a 16-year-old girl who’s extremely passionate about biotech, human longevity, and innovation itself 🦄. I’m learning a lot about exponential technologies to start a company that impacts the world positively 🚀. I love writing articles about scientific innovations to show you the amazing future that awaits us!
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