It works like a micro machine to make proteins. Ribosomes are composed of unique proteins and nucleic acids.
A ribosome is a cellular organ formed from two subunits that join and works to translate information encoded from the cell nucleus provided by the messenger ribonucleic acid (mRNA).
It also works to bind selected and harvested amino acids from the cytoplasm by transferring ribonucleic acid (tRNA). The mRNA determines the order in which the amino acids are bound together. They export the produced polypeptide to the cytoplasm, where it will form a functional protein.
Ribosomes are “free” in the cytoplasm or join the endoplasmic reticulum (ER) to form ER rough. In a mammalian cell, there can be up to 10 million ribosomes.
Several ribosomes can be attached to the same mRNA chain; this structure is called a polysome. Ribosomes only have a temporary existence. When they have synthesized a polypeptide, the two subunits are separated and reused or divided.
Ribosomes can bind amino acids at a rate of 200 per minute. Therefore, small proteins can be prepared relatively quickly, but it takes two to three hours for larger proteins, such as the massive muscle protein titin of 30,000 amino acids.
Ribosomes in prokaryotes use a slightly different process to produce proteins than ribosomes in eukaryotes. Fortunately, this difference presents a window of molecular opportunity for the attack of antibiotic drugs such as streptomycin.
Unfortunately, some bacterial toxins and the poliovirus also use it to allow them to attack the translation mechanism.
Beyond the ribosome
These are organelles composed of ribosomal proteins (lipoproteins) and ribonucleic acids (ribonucleoproteins). The word ribosome is taken from taking ribonucleic acid’s ribs and adding it to ‘soma,’ the Latin word for the body. Ribosomes are joined by a membrane but are not membranous.
A micromachine to make proteins
A ribosome is a very complicated but elegant micro-machine to produces proteins. Each complete ribosome is constructed from two subunits.
A eukaryotic ribosome comprises nucleic acids and approximately 80 proteins and has a molecular mass of roughly 4,200,000 Da. About two-thirds of this mass consists of ribosomal RNA and one-third of around 50+ different ribosomal proteins.
These are found in prokaryotic and eukaryotic cells, mitochondria, chloroplasts, and bacteria. Those found in prokaryotes are generally smaller than those in eukaryotes. Ribosomes in mitochondria and chloroplasts are similar in size to those of bacteria.
There are about 10 billion protein molecules in a mammalian cell, and ribosomes produce most. A rapidly growing mammalian cell can contain around 10 million ribosomes.
A single E. Coli cell contains approximately 20,000 ribosomes, representing about 25% of the total cell mass.
The proteins and nucleic acids that form the ribosome subunits are manufactured in the nucleolus and exported through the nuclear pores into the cytoplasm. The two subunits are unequal in size and exist in this state until their use is required.
The largest subunit is approximately twice as large as the smallest subunit.
The largest subunit has mainly a catalytic function; the smallest subunit is especially decoding. In the large subunit, ribosomal RNA plays the role of an enzyme and is called a ribozyme. The smallest unit connects to the mRNA and binds to a larger subunit.
Once formed, ribosomes are not static organelles. When the production of a specific protein has finished, the two subunits separate and, in general, divide. Ribosomes only have a temporary existence.
Sometimes, the ribosomal subunits admit mRNA as soon as the mRNA emerges from the nucleus. When many ribosomes do this, the structure is called polysome.
Ribosomes can function in a “free” state in the cytoplasm, but they can also “settle” in the endoplasmic reticulum to form a “rough endoplasmic reticulum.”
When there is a rough endoplasmic reticulum, the association between the ribosome and the endoplasmic reticulum (ER) facilitates the subsequent processing and control of the proteins newly created by the ER.
Protein production also needs service requirements. A site that requires the provision of services occurs in a small subunit of ribosomes when one strand of mRNA enters through a selective aperture and one strand of initiator tRNA through another.
This action activates the small subunit to bind to a large subunit of the ribosome to form a complete and active ribosome. The unique process of protein production can now begin.
For the translation and synthesis of proteins, many initiators and release chemicals participate, and many reactions use enzymes. However, there are general requirements, and these must be satisfied.
Main requirements and how they are provided
This installation is provided by the two ribosomal subunits, each protected by a membrane that covers it; when the two subunits form the complete ribosome, the molecules that enter and leave can only do so through selective slits or tunnels molecular structure.
There is a supply of information in a form that the ribosome can translate with a high degree of accuracy. The translation must be accurate so that the correct proteins are produced.
The information is supplied by the nucleus and delivered to the ribosome in the form of an mRNA chain. When the mRNA is formed in the middle, the introns are cut (non-coding sections), and the exons (coding units) are joined by splicing.
A supply of amino acids from which the ribosomal mechanism can obtain the specific amino acids needed.
Amino acids, mainly supplied by food, usually are freely available in the cytoplasm.
A system that can select and fix an amino acid in the cytoplasm and send it to the translation and synthesis site on the ribosome.
The short ribonucleic acid transfer strands (tRNAs) produced in the nucleus and available in the cytoplasm act as “adapter tools.”
When one strand of tRNA has fixed itself to an amino acid, the tRNA is said to be “loaded.” The tRNA diffuses into the smaller ribosome subunit, and each short tRNA chain releases ONE amino acid.
A release medium in the cytoplasm: (a) a newly formed polypeptide, (b) mRNA that has been used in the translation process, and (c) tRNA that has released the amino acid it was carrying and is now “unloaded.” ‘
When a newly formed peptide chain is produced inside the large subunit of the ribosome, it is directed towards the cytoplasm along a tunnel or cleft. (b) The ‘used’ mRNA leaves the smaller ribosomal subunit through a tunnel on the side opposite its entry point.
Movement through the ribosome is produced by an intermittent one-way movement of the ribosome along and in the direction of the incoming mRNA chain. (c) tRNA in the “unloaded” state goes through a tunnel in the molecular architecture of the large ribosome subunit.