Ribosomes: Definition, Types, Functions, Forms, and Structures

Ribosomes: Definition, Types, Functions, Shapes, and Structures – Ever heard of the term ribosome? On this occasion, we will discuss what is meant by ribosomes? Let's look at the complete explanation below to understand it better.

Ribosomes: Definition, Types, Functions, Forms, and Structures

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A ribosome is a particle, molecule or organelle consisting of protein and ribonucleic acid (RNA) that work together in protein synthesis. In other words, the ribosome is the site for protein synthesis. Ribosomes have small dimensions, where this solid organelle has a diameter of only 20 nanometers. Ribosomes are spherical structures that can be found in the cytoplasm of prokaryotic cells as well as eukaryotic cells. Some types of ribosomes occur freely in the cytosol, and some other types attach to the aggressive endoplasmic reticulum (ER) or what is also known as the nuclear membrane.

The term ribosome comes from the Greek, namely from the word soma which means body, and ribonucleic acid or ribonucleic acid. The scientist who first conducted research on ribosomes was George Emil Palade who was a Romanian scientist. He carried out this research in the 1950s using an electron microscope. Because of the research he did, until 1974, George Emil Palade won the Nobel Prize in Psychology and Health. However, the scientist who first used the name ribosome for this solid molecule was Richard B. Roberts in 1958.

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Features of Ribosomes

Small granules with a diameter of about 20 to 22 nanometers.
Found in all living cells.
The smallest organelle in the cell.
Consists of 65% ribosomal RNA (rRNA) and 35% ribosomal protein.
Can be found in the rough ER and scattered in the cytoplasm.
Produce proteins.

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Types of Ribosomes

• Free Ribosomes are cell structures that are widely distributed in the cytoplasm
• Bound Ribosomes are one of the ribosome structures that are usually attached to the ER (Endoplasmic Reticulum) section or often also called RER (Rough Endoplasmic Reticulum).

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Ribosome Shape and Size

Prokaryotes

Prokaryotic ribosomes are 70S in size and contain 6% RNA and 40% protein. These cell organelles are located freely in the cytoplasm where the size of the 50S and 30S subunits. Has a length of 29 x 21nm with a mass of 2,520,000 Daltons.

Eukaryotes

Whereas in eukaryotic ribosomes the size is 80S with 40% RNA content and 60% protein content.

It has a free location in the cytoplasm and is bound to the endoplasmic reticulum. It measures about 32 x 22nm in length and has a mass of approximately 4,220,000 Daltons.

Ribosome Function

As we already know, ribosomes are small particles that are impermeable to electrons. It is composed of 4 types of ribosomal RNA (rRNA) and 80 different types of proteins. Ribosomes have various functions, including:

Protein synthesis

Ribosome is an example of an organelle that does not have a membrane, where it has a very important role very important in the process of protein synthesis, is a process that translates messege-RNA (mRNA) into proteins.

Ribosomes have a free position in carrying out the process of synthesizing protein enzymes that act as catalysts in the cytosolic fluid. In carrying out these functions, ribosomes are assisted by 3 main components, namely:

• mRNA which is a template for proteins. This molecule is a copy of a gene contained in DNA which is then sent to the cytoplasm to be translated into protein with the help of ribosomes. mRNA consists of a series of codons whose job is to dictate the ribosome sequence of amino acids required in the process of protein synthesis.
• Amino acid
• tRNA which is a special amino acid carrier agent. This molecule has a triplet anticodon that is complementary to a codon located on the mRNA. And with this complementation, the codon sequence of the mRNA will dictate the amino acid sequence.

This chain of protein synthesis processes is called the central dogma. The protein produced in this synthesis process will later be used by the cytoplasm.

Transcription

One of the strands of DNA will process transcription to create RNA. The stretch of DNA that is transcribed into RNA is called a transcription unit. Actually transcription is part of genetic expression. The original interpretation of the transcription is actually a copy or transliteration. So, what is meant by transcription here is the process of copying DNA readings into RNA. In this process, only the nitrogenous base thymine in DNA which is replaced by uracil in RNA encounters change. Transcription consists of 3 stages of the process, namely:

• Initiation (beginning) of the RNA chain
• Elongation (elongation) of the RNA chain
• Termination (termination) of the RNA chain

The transcription process takes place in the cell nucleus or in the mitochondrial matrix and plastids, where this process can be triggered by any stimulus or no stimulus at all. The stimulation that occurs will activate the core prometer which consists of the TATA box, the CCAAT box, and the GC box. This transcription process creates a raw RNA called the primary mRNA, in which there are bundle fragments for proteins that help and control the process of protein synthesis. The next RNA file is post-transcriptional.

translation

This is the process of translating the nucleotide sequence in an mRNA molecule into a sequence of amino acids that make up a protein or polypeptide. This is one of the main processes that can link genes to proteins, not just transcription. This process only occurs in mRNA molecules, whereas other molecules such as rRNA and tRNA do not undergo the translation process. mRNA is a copy of the DNA sequence, in which the molecule arranges the gene in the form of an open reading frame. Not only that, mRNA also conveys amino acid sequence data. Ribosomes are the place where this translation process takes place

The translation process is summarized in 3 sessions, namely:

1. Initiation

This is the first step in the translation process, in which the mRNA, 30S subunit, and formylmethionyl tRNA combine to become the 30S initiation environment. After the 3oS initiation complex is formed, the 50S subunits join to form the 70S subunit.

2. Elongation

This is the process of elongation of polypeptides both in prokaryotes and in eukaryotes. This process is divided into 3 stages, namely:

• Binding of aminoacyl-tRNA to the A side of the ribosome
• Making peptide linkages
• Translocate the ribosome stranded along the mRNA to the next codon position present on the A site

3. Termination

This is the final process of translation, where the three types of termination codons namely UAA, UGA, and UAG found in the mRNA reach position A on the ribosome.

Ribosome Structure and Composition

Ribosomes are components in cells that produce proteins using all types of amino acids. The ribosome itself is composed of 2 significant compounds, namely:

Ribonucleic Acid or Ribonucleic Acid (RNA)

This acid comes from the nucleolus which is the place where the ribosome synthetic process takes place in the cell. Ribonucleic acid is one of the 3 main macromolecules (DNA, protein, RNA) that have an important role for all forms of life. RNA has a structure similar to DNA, in that it is composed of several nucleotides, each of which has a phosphate group, a nitrogenous base group, and a pentose group. Ribonucleic acid also functions in the process of protein synthesis in eukaryotic cells. There are 3 types of RNA in these eukaryotic cells, namely:

• RNA– messenger or what is commonly called messenger– RNA (mRNA). It is a type of RNA that is synthesized with RNA polymerase I
• RNA– Ribosome or known as Ribosomal–RNA (rRNA). It is a type of RNA synthesized with RNA Polymerase II
• RNA– Transfer or what is known as transfer–RNA (tRNA). It is a type of RNA synthesized with RNA Polymerase III

RNA has several main functions, including:

1. As data storage or genetic material

This is especially true for a group of viruses such as bacteriophages, where by the time a virus starts to invade living cells, it can The RNA that it carries into the cytoplasm of the victim cell will be translated by the host cell to create viruses that are new. The results of sophisticated research linked to RNA reported that early in the evolutionary process, RNA was the common genetic material before living organisms used DNA.

2. As an intermediary between DNA and protein in the process of genetic expression that applies to all living organisms

In this case, RNA is a product that acts as a copy of the code for the sequence of nitrogen bases in DNA transcription process, where the sequence code is arranged in 3 sequences of N bases known as codon. Each codon has a bond with one amino acid.

Ribosome Protein or Ribonucleic Protein (RNP)

Ribosomal protein is a type of protein that works together with rRNA (Ribosome-RNA) to form ribosomal subunits that participate in the cellular process of translation. It is a compound which is a polymer of various monomers linked to one another by peptide linkages. This molecule contains carbon, hydrogen, nitrogen, oxygen, and sometimes also contains sulfur or phosphorus.

Protein has a very important role for living things or viruses, namely in the structure and function of their cells. The process of natural protein biosynthesis is the same as genetic expression. The genetic code carried by DNA is transcribed into RNA, which in turn will serve as a template for translation carried out by ribosomes.

At this stage, the protein is still in its raw state, where it is only composed of proteinogenic amino acids. In order to produce proteins that are biologically able to play a full role, a post-translational mechanism is needed.

Protein structure is divided into 4 levels, namely:

• Primary structure (level one), This is the sequence of amino acids that make up the protein through peptide linkages.
• Secondary structure (level 2), this is the local 3 size structure of the protein amino acid sequence which undergoes a stabilization process via hydrogen acid. There are several forms of the secondary structure, namely: alpha helix (α helix), beta-sheet (β-sheet), Beta-Turn (β-turn), and gamma-turn (y-turn).
• Tertiary structure (level 3), which is a combination of various secondary structures. These structures are generally in the form of agglomerates, whereby the molecules are able to interact physically without covalent bonding to form normal oligomers (such as dimers, trimers, quatonaries), and form structures quaternary.
• Quaternary structures (level 4), for example insulin and rubisco enzymes.

There are also functions of proteins, including:

• As an energy source
• Synthesis of hormones, enzymes and antibodies
• Controls the balance of acid-base content in cells
• Forms and repairs tissues and cells
• as a barn or food reserve

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Division of Ribosomes

The ribosome is divided into 2 large parts which are called sub units, where each sub unit is represented by S units (Svedberg). The unit displays the speed of settling when the sub-unit is centrifuged, where the name of the unit is taken from the name of the inventor. Each ribosome subunit contains RNA and protein. The types of the two sub-units are seen to originate from the level of sedimentation in certain media. There are also two ribosomal subunits, namely:

• 1. Small subunit– The small ribosomal subunit consists of 1 ribosome– RNA (rRNA) and about 21 proteins in bacterial prokaryotes, and about 30 proteins in mammalian eukaryotes.
• 2. Large subunit– In prokaryotes, the large ribosomal subunit contains 2 rRNAs (one large and one small) and approximately 31 proteins. In eukaryotes, on the other hand, the large ribosomal subunit contains 3 rRNAs (one large and 2 small) and approximately 49 proteins.

In eukaryotic cells, the two ribosomal subunits will undergo a process of synthesis in the nucleolus which will then be exported to the cytoplasm before being used.

The structure of the ribosome has the following properties:

• It has a general shape, in which in longitudinal section it is an ellipse
• When the negative coloring method was tried, it appears that there is one transverse groove, perpendicular to the axis, and divided into 2 sub-units, each of which has a different size.
• Each sub-unit is signaled by the presence of a sedimentation coefficient expressed in the S dimension (Svedberg). In prokaryotic cells the sedimentation coefficient is 70S (50S for large subunits, and 30S for small subunits). On the other hand, in eukaryotic cells, the sedimentation coefficient is 80S (60S for the large subunit and 40S for the small sununit).
• Ribosomes come in various sizes and shapes. In prokaryotic cells, ribosomes can be up to 29 nanometers long by 21 nanometers large. In contrast, in eukaryotic cells, ribosomes can reach 32 nanometers in length and 22 nanometers in size.
• In prokaryotic cells, the small subunit is elongated, has a curved shape with 2 symmetries, has 3 digits, and resembles a sofa. On the other hand, in eukaryotic cells, the subunit is the same size as the E ribosome. Colli.

Thus the review from About the knowledge.co.id about Ribosomes,Hope it is useful.