How do our cells build protein?

 Proteins are among the most versatile macromolecules in living systems, as they perform biological functions on a large scale, and this is reflected in their structural diversity.

Proteins consist mainly of (carbon, hydrogen, nitrogen, oxygen, and sulfur), in addition to some other elements that are found in specific specialized proteins, such as iron in hemoglobin protein and phosphorous in casein protein.

All proteins consist of building blocks known as amino acids, which are linked together by bonds called peptide bonds. It is worth noting that there are 22 different amino acids in the proteins of living organisms.

The process of building protein depends on ribosomes along with nucleic acids, which include two types:

First: DNA

And the second: all types of RNA (messenger RNA, tRNA, and rRNA, which is the functional unit of the ribosome).

The process of building proteins in a cell consists of two main steps:

1- The transcription process

2- The translation process

Transcription process: It is a process by which the messenger RNA molecule is transcribed from a specific gene on the DNA through a series of steps that begin with the binding of an enzyme called the RNA polymerase to a site on the DNA called the initiation site, after which the two strands of DNA separate to start the enzyme By adding nucleotides (which are the building blocks in nucleic acids) of the messenger RNA (with the nitrogen base thymine being replaced by the nitrogenous base uracil) from one of the two DNA chains, and when the enzyme polymerase reaches the completion signal (which is a specific region on DNA composed of a specific sequence of nucleotides specified for the end Gene) the resulting messenger RNA is released and the two strands of DNA are rewound.

All three adjacent nucleotides on the messenger RNA are called a codon (which is a code of three nitrogen bases out of four: adenine, guanine, cytosine, and uracil), and the total number of codons is 64 codons, 61 of which are designated to encode 20 amino acids, and the remaining three are not It encodes any amino acid.

As for the translation process, it consists of three steps:

Initiation, Elongation, and Termination

The starting step starts with the association of the two structural units of the ribosome with the messenger RNA and the messenger RNA tRNA, then the messenger RNA begins to pass between the two units of the ribosome until the codons are translated into amino acids by the anti-codon on the tRNA, so the translation begins with the start codon (AUG) on the messenger mRNA. It is encoded for the amino acid methionine (translation cannot begin without the AUG initiation codon).

Then comes the role of the elongation step, where the first vector RNA separates and leaves its amino acid (methionine) behind, and a new vector RNA enters the ribosome carrying an amino acid for the next codon on the messenger RNA, and this process continues until the ribosome reaches the stop codon on the messenger RNA (which is A codon that does not have an anti codon on the tRNA and therefore does not encode an amino acid.)

In the end, the termination step comes as the ribosome reaches one of the stop codons (UAG - UAA - UGA), then the last RNA leaves the ribosome, the two structural units of the ribosome separate from each other and the ribosome moves away from the messenger RNA, and the resulting protein is liberated into the cytoplasm.

(Multiple ribosomes can translate the same copy of messenger RNA.)

This series of biological events that lead to protein building is called other expressions such as the central principle, gene expression, or protein construction.

The process of building proteins in eukaryotic cells can differ from those in prokaryotes, for example: the transcription process takes place inside the nucleus of eukaryotic cells and after it is completed, the translation process begins. As for prokaryotic cells, since they do not contain a nucleus, the transcription process takes place in the cytoplasm because of the presence of DNA in Cytoplasm and thus the translation process can begin before the transcription process is finished and this process is called transcription and translation coupling.

In addition, the messenger RNA in the eukaryotic cell is monocystron, meaning that it encodes a single polypeptide (protein), and the messenger RNA in the prokaryotic cell is polycystron, meaning that it encodes more than one polypeptide.

In addition to the difference of the two ribosome units in the eukaryotic cell from those in the prokaryotic cell, in eukaryotic organisms the messenger RNA ribosomes are distinguished by attaching to its capillary at the 5 end of the messenger RNA molecule, then the ribosome begins with a careful examination of the messenger RNA from the end 5 until the initiation code is reached.

The translation process in eukaryotic cells is more complex than in prokaryotes and requires more translation initiation factors than those in prokaryotes.