Codesonne ➤ Reading genetic code and examples of use

the code sun is a tool to easily convert a sequence of bases into a amino acid can translate. The scheme allows, if the DNA sequence is known, to infer the composition of the protein synthesized on its basis.

The protein biosynthesis

As you probably know, the genetic information of living beings is stored in their DNA. More precisely, the expression of various characteristics of a living being (such as the color of your eyes) are determined by certain sections of DNA. These sections of DNA are called genes. The sequence of bases in this section of DNA forms a kind of “blueprint” for a very specific one protein. This protein then drives various reactions in the body that lead to the expression of a trait.

The process by which a protein is formed based on the sequence of bases in the DNA is called protein biosynthesis. It consists of two phases: transcription and translation.

Would you like to refresh your knowledge of protein biosynthesis? Then have a look at articles on the topic!

transcription

In the transcription, the gene is read and its base sequence in so-called mRNA rewritten.

mRNA stands for messenger ribonucleic acid. As the name suggests, it assumes a messenger function in the cell. The genetic information of the DNA is temporarily stored on it before it is translated into a protein.

The mRNA is also single-stranded.

Four different bases occur in double-stranded DNA: adenine (A), guanine (G), Thymine (T) and Cytosine (C). To each of these bases is a different one complementary. This means that base pairs are formed which z. B. in the DNA double strand opposite and interact with each other. Specifically, it is always adenine and thymine, as well as guanine and cytosine.

Base pairing is also important for transcription. If, for example, the base guanine is found on the DNA segment, then cytosine, rather than guanine, is built into the mRNA.

Danger! The mRNA contains the base instead of thymine uracil (U). It then also corresponds to the complementary base to adenine.

With DNA, a distinction is made between codogenic strand (template strand) and the coding strand. During transcription, the codogenic strand is read so that the resulting mRNA is complementary to it. In the end, the sequence on the mRNA corresponds to the coding strand, apart from the presence of uracil.

translation

In translation, the mRNA serves as a template for linking different amino acids to form a protein. The properties of the amino acids contained then determine the folding and specific function of the protein.

How exactly the sequence of bases determines the structure of a protein and how you use the code sun, you will find out shortly afterwards.

The Genetic Code

Three consecutive bases of DNA or mRNA, too triplet or codon called, code for an amino acid. This means that a certain sequence of three bases can be assigned to exactly one amino acid. Since there are four different bases in the mRNA (adenine, uracil, guanine and cytosine), there are 64 different possible combinations (43).

In addition to normal codons that code for a specific amino acid in the protein, there are also some triplets with special functions.

stop codons

Three of the codons are so-called stop codons.

stop codons do not code for any amino acid, but form a signal for the end of translation.

The stop codons are:

The remaining 61 codons code for the 20 different amino acids. So almost every amino acid is encoded by more than one codon, which is genetic code degenerate.

start codon

Besides, there’s this start codon AUG.

That start codon marks the beginning of translation and codes for the amino acid methionine.

Codons line up directly between the start and stop codons, which is the genetic code comma free. This means that there are no characters separating codons from each other. Since there is also no overlap between codons, this is not necessary. Bases 1-3 code for the first amino acid of the protein, bases 4-6 for the next, and so on.

Also, the genetic code universal. This means that each codon codes for the same amino acid in all living things (with a few exceptions). Therefore, the code sun, which you will learn about later, is almost universally applicable.

read code sun

How exactly do you read amino acid sequences from the code sun? To do this, it is helpful to recall that transcription and translation have taken place beforehand. Here is a brief summary of the processes of protein biosynthesis:

  1. transcription: The DNA section (gene), specifically the codogenic strand, is read. The respective complementary bases are combined to form mRNA. The base sequence of the mRNA corresponds to the coding strand.
  2. Translation: The mRNA is also read. It consists of codons with three bases each. Each base triplet (except for the stop codons) corresponds to an amino acid.

In the code sun you can now read which codons on the mRNA code for which amino acid. Likewise, start and stop codons are also marked.

You can tell from the base uracil that the code sun is about bases of the mRNA. It only occurs in RNA but not in DNA.

Figure 1: Code sun. Source: wikipedia.de

The code sun is to be read from the inside out. Since the translation always takes place in the 5′ –> 3′ direction, the code sun is also shown in the 5′ –> 3′ direction from the inside to the outside. You can use the code sun to easily check which amino acid a specific codon encodes.

We want to translate the following base sequence of the codogenic strand of DNA into the corresponding amino acid sequence of a protein. We assume that reading begins on the left.

Codogenic strand: TAC AGG TCT ATA AAC GCC ACTThe coding strand of the DNA is complementary to the base sequence of the codogenic strand.Coding strand: ATG TCC AGA TAT TTG CGG TGABecause the codogenic strand is read, the mRNA sequence corresponds to the coding strand, but it must contain thymine be replaced by uracil.mRNA: AUG UCC AGA UAU UUG CGG UGAUsing the code sun you can now read the amino acid sequence: Amino acid sequence: Met – Ser – Arg – Tyr – Leu – Arg – Stop

You can see which amino acids these abbreviations stand for in the following table:

shortcut

amino acid

shortcut

amino acid

mead

methionine

Gly

glycine

Thr

threonine

Phe

phenylalanine

asn

asparagine

leu

leucine

Lys

lysine

Tyr

tyrosine

ser

serine

Cys

cysteine

argument

arginine

trp

tryptophan

Val

valine

Per

proline

Ala

alanine

His

histidine

asp

aspartic acid

equation

glutamine

glue

glutamic acid

Ile

isoleucine

When doing tasks, always pay close attention to which strand of DNA is given (codogenic or coding strand).

Codesonne – The most important thing

  • With the Codeson, base triplets/codons on mRNA can be translated into amino acids.
  • The base sequence of the mRNA is complementary to the codogenic strand, its sequence corresponds to the coding strand (thymine replaced by uracil).
  • A base triplet or codon, i.e. a sequence of three bases, encodes an amino acid.
  • The genetic code is comma-free, there are no separators between codons and codons do not overlap.
  • The genetic code is degenerate, multiple codons can encode the same amino acid.
  • The genetic code is universal, i.e. identical in almost all living beings.