Genetic Code: Definition, Function and Types of Mutations

It is the code that our body uses to convert the instructions contained in our DNA into the essential materials of life.

It is normally formed using the “codons” found in the mRNA, since the mRNA is the messenger that transports information from the DNA to the site of protein synthesis.

Everything in our cells is finally built based on the genetic code . Our hereditary information, that is, the information transmitted from parents to children, is stored in the form of DNA.

That DNA is used to build RNA, proteins and finally cells, tissues and organs.

Like the binary code, DNA uses a chemical language with only a few letters to store information in a very efficient way. While the binary uses only ones and zeros, the DNA has four letters that are the four nucleotides:

  • Adenina.
  • Citosina.
  • Guanine.
  • Timina/Uracilo.

Thymine and uracil are very similar to each other, except that “thymine” is a little more stable and is used in DNA. Uracil is used in RNA and has all the same properties as thymine, except that it is a little more prone to mutate.

This does not matter in RNA, since new copies of RNA can be produced from DNA at any time, and most RNA molecules are intentionally destroyed by the cell shortly after production so that the cell does not waste resources producing unnecessary proteins from old RNA molecules.

Together, these four letters of A, C, G and T / U are used to “spell out” coded instructions for each amino acid, as well as other instructions such as “start transcription” and “stop transcription”.

The instructions to “start”, “stop” or for a given amino acid are “read” by the cell in blocks of three letters called “codons”.

When we speak of “codons”, we usually refer to codons in mRNA: the “messenger RNA” that is made by copying the information in the DNA.

For that reason, we talk about codons made of RNA, which uses uracil, instead of the original DNA code that uses thymine.

Each amino acid is represented in our genetic instructions by one or more codons .

One of the most remarkable evidences of the common ancestor of all life on earth of a single ancestor is the fact that all organisms use the same genetic code to translate DNA into amino acids.

There are some small exceptions that are found, but the genetic code is sufficiently similar in all organisms that when a gene from a plant or jellyfish is injected into a mammalian cell, for example, the mammalian cell will read the same gene way and build the same product as the original plant or jellyfish!

Function of the genetic code

The genetic code allows cells to contain a huge amount of information.

Consider this: a microscopically fertilized egg, following the instructions contained in its genetic code, can produce a human being that even has a personality and behaviors similar to those of their parents. There’s a lot of information there!

The development of the genetic code was vital because it allowed living beings to reliably produce the products necessary for their survival, and passed instructions on how to do the same to the next generation.

When a cell tries to reproduce, one of the first things it does is make a copy of its DNA. This is the “S” phase of the cell cycle, which means “Synthesis” of a new copy of the cell’s DNA.

The information encoded in the DNA is conserved by specific pairing of the DNA bases with each other. Adenine will only join with Timina, Citosina, Guanina, etc.

That means that when a cell wants to copy its DNA, all it has to do is separate the two strands of the double helix and align the nucleotides with which the existing DNA bases “want” to pair.

This specific base pairing ensures that the new partner’s strand will contain the same sequence of base pairs, the same “code”, as the previous one. Each resulting double helix contains an old DNA strand paired with a new strand of DNA.

These new double helices will be inherited by two daughter cells. When the time comes for these daughter cells to reproduce, each strand of these new double helixes acts as templates for a new double helix.

When the time comes when a cell “reads” the instructions contained in its DNA, it uses the same principle of peer-specific linking. RNA is very similar to DNA, and each RNA base binds specifically to a DNA base. Uracil binds to adenine, cytosine to guanine, etc.

This means that, like DNA replication, the information in the DNA is transferred precisely to the RNA provided that the resulting RNA chain is composed of the bases that bind specifically to the bases in the DNA.

Sometimes, the RNA chain itself can be the final product. The structures made of RNA play important functions in ourselves, such as the assembly of proteins, the regulation of gene expression and the catalysis of protein formation.

In fact, some scientists think that the first life on earth could have been composed mostly of RNA.

This is because RNA can store information in its base pairs like DNA, but it can also perform some enzymatic and regulatory functions.

In most cases, however, the RNA becomes transcribed into a protein. Using the amino acid “building blocks of life”, our cells can build almost protein machines for almost any purpose, from muscle fibers to neurotransmitters and digestive enzymes.

In protein transcription, the codons of RNA that were transcribed from the DNA are “read” by a ribosome.

The ribosome finds the appropriate transfer RNA (tRNA) with “anti-codons” that are complementary to the codons in the messenger RNA (mRNA) that has been transcribed from the DNA.

Ribosomes catalyze the formation of peptide bonds between amino acids as they “read” each codon in the mRNA. At the end of the process, it has a chain of amino acids specified by the DNA, that is, a protein

Other building blocks of life, such as sugars and lipids, in turn are created by proteins. In this way, the information contained in the DNA is transformed into all the materials of life, using the genetic code!

Types of genetic mutations

Because the genetic code contains information for life, errors in the DNA of an organism can have catastrophic consequences.

Errors can occur during DNA replication if the wrong base pair is added to a DNA strand, if a base is omitted, or if an additional base is added.

In rare cases, these errors can be useful: the “wrong” version of DNA can work better than the original or have a completely new function! In that case, the new version may be more successful, and your provider may outperform the operators of the previous version in the population.

This extension of new features in an entire population is the way evolution works.

Silent mutations and redundant coding

In some cases, genetic mutations may have no effect on the final product of a protein. This is because, as seen in the previous table, most amino acids are connected to more than one codon.

Glycine, for example, is encoded by the codons GGA, GGC, GGG and GGU. A mutation that results in the wrong nucleotide being used for the last letter of the glycine codon, then, would not matter.

A codon that starts at “GG” will still encode glycine, regardless of which letter was last used.

It is believed that the use of multiple codons for the same amino acid is a mechanism that evolved over time to minimize the possibility of a small mutation causing problems for an organism.

Mutation without meaning

In a nonsense mutation, substituting a base pair for an incorrect base pair during DNA replication results in the use of the wrong amino acid in a protein.

This can have a small effect on an organism, or a large one, depending on how important the amino acid is for the function of its protein and in which it is made.

This can be thought of as furniture construction. How bad would it be if you used the wrong piece to screw the leg of a chair into place?

If you used a screw instead of a nail, the two are probably similar enough so that the leg of the chair stays lit, but if you try to use, for example, a cushion to attach the leg to the chair, your chair will not It will work very well.

A nonsense mutation can result in an enzyme almost as good as the normal version, or an enzyme that does not work at all.

A nonsense mutation occurs when the incorrect base pair is used during DNA replication, but when the resulting codon does not encode an incorrect amino acid.

Instead, this error creates a stop codon or other information that is indecipherable for the cell. As a result, the ribosome stops functioning in that protein and all subsequent codons are not transcribed.

The nonsense mutations lead to incomplete proteins, which can work very badly or not work at all. Imagine if you stopped building a chair in half!

Suppression

In a deletion mutation, one or more DNA bases are not copied during DNA replication. Elimination mutations come in a variety of sizes: a single pair of bases may be missing, or a large piece of a chromosome may be missing!

The smallest mutations are not always less harmful. The loss of only one or two bases can result in a mutation of the reading frame that damages a crucial gene.

Conversely, larger deletion mutations can be fatal, or they can result in a disability, as in DiGeorge syndrome and other conditions that result from the removal of part of a chromosome.

The reason for this is that the DNA looks a lot like the source code of the computer, a piece of code can be crucial for the system to turn on, while other parts of the code could ensure that a website looks good or loads quickly.

Depending on the function of the code fragment that is deleted or modified, a small change can have catastrophic consequences, or a seemingly large alteration of the code one can result in a system that is a bit imprecise.

Insertion

An insertion mutation occurs when one or more nucleotides are mistakenly added to a growing DNA strand during DNA replication. Rarely, long stretches of DNA can be added incorrectly in the middle of a gene.

Like a nonsense mutation, the impact of this may vary. The addition of an unnecessary amino acid in a protein can make the protein only slightly less efficient; or it can paralyze it.

Consider what would happen to your chair if you added a random piece of wood that the instructions did not require. The results can vary greatly depending on the size, shape and location of the extra piece!

Duplication

A duplication mutation occurs when a segment of DNA is accidentally replicated two or more times. Like the other mutations listed above, these may have mild effects, or they may be catastrophic.

Imagine that your chair has two backs, two seats or eight legs. A small duplication and the chair can still be usable, although a bit strange or uncomfortable. But if the chair had, for example, six seats joined together, it could quickly become useless for its intended purpose!

Mutation with scrolling reading pattern

A mutation of the reading frame is a subtype of insertion, deletion and duplication mutations.

In a mutation of the reading frame, one or two amino acids are deleted or inserted, resulting in a displacement of the “frame” used by the ribosome to indicate where a codon stops and the next begins.

This type of error can be especially dangerous because it causes all the codons that occur after the error to be misinterpreted. Typically, each amino acid added to the protein after the mutation of the reading frame is incorrect.

Imagine if you were reading a book, but at some point during the writing, an error occurred, so that each subsequent letter changed one letter later in the alphabet.

A word that was supposed to read “letter” would suddenly become “mfuuft”. This is approximately what happens in a mutation of the reading frame.