New News Biology #49

DNA Mutations

A mutation is a change in the DNA base sequence.

It happens spontaneously in our cells when DNA is duplicated...

Stuff like carcinogens (which are a group of harmful chemicals, like the ones you find in cigarette smoke) and certain types of radiation (such as X-rays and gamma rays) increase the risk of a mutation happening. Though these things don’t always cause the mutations, they only increase the risk.

To understand how mutations impact the human body, here’s a quick recap on how DNA works:

Every gene in the body is made up of triplets, or codons, which codes for 1 of 20 amino acids.

The amino acids of all the triplets in the gene combined in that specific order will make an protein, which has a particular shape and function.

The mutation... may change one of the triplets, and in turn changing that amino acid in the chain, and in some way affecting the protein.

For example, the mutation might change the shape of the active site of the enzyme, meaning that the enzyme can’t form an enzyme-substrate complex, and unable to catalyze a reaction.

However, most of the time, a mutation wouldn’t have any significant effect. The protein may look different from the original, though it will still work in the same way and carry out the same functions. Also, a huge percentage of all mutations happen in non-coding DNA, which are those stretches of DNA which don’t code for a protein.

Most of this non-coding DNA doesn’t do anything at all, so we’re not sure why we have so much of it in the first place.

But some of it does play an important role in the expression of genes (whether a gene is on or off). This is super important. Take the nerve cell for example. The nerve cell doesn’t need to produce hemoglobin, because those are only needed in red blood cells. So the gene for hemoglobin will be not expressed, or not turned on.

The three types of mutations:

Substitutions: one of the bases is changed for another random base. The problem is it changes the amino acid the codon codes for.

Insertion: an extra base is inserted into the sequence somewhere. The sequence will be messed up, as all the subsequent bases are shifted along by one base, and the amino acid chain will be entirely different.

Deletion: it’s basically the same as insertion, except now a base has been randomly removed from the sequence. In this case, all of the bases will be shifted one space to the left, and it changes the entire sequence as well.

It is important to note here that because the entire sequence is changed in insertion and deletion, it has a much bigger impact than that of substitutions.