why can DNA transcription and translation processes be ‘wrong’ and make mistakes?
In: Biology
DNA/RNA are built out of smaller units called nucleotides, which are a bit like the links in a chain – a strand of DNA/RNA is made up of many individual nucleotides stuck together. To produce a new strand, you need to get a bunch of nucleotides and put them in the right order, so your main job as a protein designed to do this is to figure out what the right order is.
There are four DNA nucleotides – T, A, C and G. There’s also a fifth nucleotide, U, which is the RNA version of T for an interesting but irrelevant reason. These nucleotides are the links you see in graphics of a DNA helix, like [this one](https://external-content.duckduckgo.com/iu/?u=https%3A%2F%2Fd2noibkeom3qqq.cloudfront.net%2Fwp-content%2Fuploads%2F2017%2F02%2FDNA-helix-molecule-genetic.jpg&f=1&nofb=1). Notice how each of these links is split in the middle into two different colours. These are a visual representation of the DNA structure. See, DNA has two different strands each with its own nucleotides, that stick together a bit like a zip – the nucleotides on one strand of the DNA stick to the nucleotides on the other strand to form this stable helix structure.
The fact they stick together like this is how proteins know what the right order of nucleotides is when replicating the DNA. Nucleotides exist in matching pairs that preferentially stick together. T and A are a pair, and C and G are a pair. To produce more DNA/RNA, proteins unzip the DNA to expose the nucleotides on one of the strands, and then free floating nucleotides come into the protein complex and if they stick to the next exposed nucleotide in the line, the protein glues them onto the end of the emerging strand. So if the exposed DNA strand says TTCAGACGA, then the proteins will produce an RNA strand of AAGUCUGCU, because those are the RNA nucleotides that stick to the DNA strand (noting that U here is substituting in for T).
However, this stickiness is not particularly strong. It’s done using interactions called hydrogen bonds, and the number of these bonds formed between a pair determines its stickiness. T and A pairs form 2 hydrogen bonds, while C and G pairs form 3. These have positive and negative ends, a bit like magnets, so TG and AC pairings aren’t going to happen, but you can get TC and AG pairings, they’ll just be uncomfortable and not fit properly. There are other proteins that check for these uncomfortable pairings and replace them with the right nucleotide, but they’re not super reliable and there’s a good chance they replace the wrong one and cause a mutation.
Transcription errors occur then when the wrong nucleotides stick together. This isn’t a big deal for RNA cos RNA lasts for such a short time, but the fixing proteins can permanently establish these mistakes as mutations in DNA, occasionally.
Translation errors follow a similar process, but due to a mis-stickying between the nucleotides of the mRNA and the nucleotides of the already built tRNA molecules.
im no expert but i know that its easy to think that our cells seem so incredible that they must be perfect. the mechanisms work most of the time but they ocassionally make mistakes. when dna gets replicated i believe mistakes are made every 10,000 base pairs on average. there are proteins that correct those but even they can be wrong
i think a good analogy to cells would be a factory. factories are efficient because they have many distincts parts that are designed to only do a single task. they call this an assembly line. it works well and mistakes are rare but they still happen. these mistakes are best thought of as random with the cause generally being unimportant. although, if you get a surge in mistakes then that would require further investigation
Just due to the random nature of genes and that processes just go wrong (assuming no allogenic, or outside, factors, like alcohol, radiation, etc.).
Have you ever gone somewhere repeatedly, done by the same person and asked for the same thing (think fast food restaurants)? When you have gone there, have there been times where they get the order wrong? That’s exactly how it goes wrong – just random chance (again, assuming no outside influence or underlying conditions that make mutation more common). This is cornerstone that drives traits to be placed under selective forces for evolution.
Edit: removed redundant words
Just randomness. It’s millions of DNA strands, somethings bound to go wrong with one of them.
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