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The Central Dogma (100th post)

I started this blog last year to showcase life as a Ph. D student in Australia. Most of my Blog is about navigating the world of academic research, and I have many, many posts detailing experiments I’d been doing.

But I do have a few readers who don’t have any background in science, and sometimes, when I talk about stuff I’m doing, it’s missing some basic details. So, I thought I’d write a post outlining what is called the ‘Central Dogma’ in Biology. This is how the cells in our body work, at the core of it.

***

For us humans, we’re made up of billions upon billions of teeny, single cells. We’re what you’d call a ‘multicellular organism’. This is completely different from, say, bacteria, who are made up of a single cell.

Same goes for amoebae and yeast. They’re all ‘unicellular organisms’.

But regardless of how many cells we are made of, every single cell contains genetic material, which is basically an instruction manual on what the cell is supposed to be doing.

Our genetic material is made up of a thing called DNA.

We’ve hopefully all seen this before, the famous double helix, first visualised by the X ray crystallographer Rosalind Franklin.

To put simply, DNA, or Deoxyribonucleic acid, tells our cells what proteins it needs to make. It’s sort of like a recipe book for numerous dishes. The dishes being proteins.

DNA can make up lots of things. Some bits of DNA form things called genes. Genes are the very specific parts of DNA that explicitly instruct the cells what to make. It’s pure information.

But you can also get DNA that make up other things, like the promoter region for a gene.

The promoter region is like a little flag that says ‘please attach here to begin the process of making proteins’. There might be one promoter for one gene (i.e. one flag that says ‘please make protein A’), or maybe a set of genes (‘please make protein A through to D).

Transcription‘ in a mammalian cell involves bringing a team of proteins to a specific segment of DNA. It’ll recognise the promoter region, which tells the team what to make (and how much to make). Then the machinery will make a copy of that segment of DNA, but will do so using a slightly different building material, called RNA, or Ribonucleic acid.

RNA is a little different to DNA (don’t point it out too much or it’ll cry).

Firstly they’re ‘single stranded’, so there’s no double helix.

There’s also a difference in the ‘bases’ (if you can spot the difference from the image, good job!), but we won’t go into that detail here.

Either way, the process of transcription results in the gene (made of DNA) being copied, or ‘transcribed’ into a single strand of RNA.

Transcribed RNA (called mRNA) can slip out of the host cell nucleus through small pores.

3.2 The Cytoplasm and Cellular Organelles – Anatomy and Physiology

The nucleus in a mammalian cell is like the command/brain centre of the cell, because it houses all the genetic material. Once the mRNA gets out of the nucleus, it gets recruited to a different structure in the cell called a ribosome.

The ribosome then begins a process called ‘translation‘, where the mRNA is read, and the ribosome recruits the basic building blocks of proteins, called amino acids, to form a giant chain. The mRNA code literally tells the ribosome what amino acids to bring in, and what order they’re joined together.

Depending on the amino acids that get recruited, the chain will twist and warp in different ways. It comes down to the chemical reactions between each little amino acid, but some will interact with each other and stick close together, while others will hate each other and try to stay away as much as possible. I imagine it would be quite awkward if one amino acid likes sticking close to another amino acid from a different part of the chain, but its next door neighbour hates it… Okay let’s stop making them anthropomorphic.

Regardless, all of these interactions twist the chain of amino acids into all sorts of weird and funky structures, and these structures are what we call ‘proteins’.

So this is what the Central Dogma is.

DNA, gets transcribed in to RNA.

RNA gets translated into proteins.

For us humans, it’s always in that order. It doesn’t go backwards (protein>RNA>DNA).

But that isn’t to say that other things in the world don’t.

For instance, some viruses, like the virus that causes COVID-19 (SARS-CoV-2), or the virus that causes influenza, are RNA viruses. This means that their genetic material is made up entirely of RNA, instead of DNA, like us. They don’t have any DNA on them at all.

Some of these RNA viruses have enzymes that, during infection, will turn the RNA into DNA, which is not something that normally happens in a human cell. Quite funky, if you think about it.

***

Still with me?

So I explained that the Central Dogma is this whole DNA>RNA>protein thing.

But its science, so naturally, there’s more (‘but wait, there’s more!’).

Once a protein is made (‘synthesised’, if you’re feeling fancy), it can still get processed! It’s called ‘post-translational modification‘ (i.e. changes made after translation), but the amino acids that make up the protein serves as a barcode. A barcode on protein A might tell other proteins to come grab it and take it to a specific place. Once there, the protein might work its magic (exact its function) or it could be modified again and have sugars/carbohydrates attached to it- making it a hybrid protein structure made of different components.

Another barcode might tell other proteins to chop protein A into specific segments, and that segment might be what’s required for the protein to ‘work’. It might sound silly that a protein needs to ‘trim off the excess’ in order to work (why not just have it short to begin with?), but this can act as an additional control mechanism. Maybe it only gets trimmed and ‘activated’ under certain conditions? A single protein could have multiple barcodes that do all sorts of things to said protein, all of which serves to control when it’s activated, or ‘expressed‘. Many proteins need the right signal before it gets called into action, and post-translational modifications basically become an additional level of control.

And to think, all of this, is programmed and written in our DNA. I think that’s pretty cool.

Categories: General

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ABugsLife

A former wet-lab based Bacteriology Ph. D student residing in Australia. Now working part time at a secret location as a Communications and Data Officer. 👀 🦠 🧫 🧬

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