All cells of living organisms consist of a plasma membrane, nucleus, and cytoplasm. The latter contains organoids and inclusions.
Organoids are permanent formations in the cell, each of which performs certain functions. Inclusions are temporary structures that mainly consist of glycogen in animals and starch in plants. They perform a spare function. Inclusions can be found both in the cytoplasm and in the matrix of individual organelles, such as chloroplasts.
Organoid classification
Depending on the structure, they are divided into two large groups. In cytology, membrane and non-membrane organoids are isolated. The first can be divided into two subgroups: single-membrane and double-membrane.
Single-membrane organoids include the endoplasmic reticulum (reticulum), Golgi apparatus, lysosomes, vacuoles, vesicles, melanosomes.
Mitochondria and plastids (chloroplasts, chromoplasts, leukoplasts) are classified as two-membrane organoids. They have the most complex structure, and not only due to the presence of two membranes. They may also include inclusions and even whole organelles and DNA. For example, ribosomes and mitochondrial DNA (mtDNA) can be observed in the mitochondrial matrix.
Non-membrane organoids include ribosomes, the cell center (centriole), microtubules, and microfilaments.
Non-membrane organoids: functions
Ribosomes are needed in order to synthesize protein. They are responsible for the translation process, that is, the decoding of information that is on the mRNA, and the formation of the polypeptide chain of individual amino acids.
The cell center is involved in the formation of the spindle division. It is formed both in the process of meiosis and mitosis.
Non-membrane organoids such as microtubules form the cytoskeleton. It performs structural and transport functions. On the surface of microtubules, both individual substances and entire organoids, for example, mitochondria, can move. The transport process occurs with the help of special proteins called motor proteins. The center of microtubule organization is centriole.
Microfilaments can participate in the process of changing the shape of the cell, and are also needed for the movement of some unicellular organisms, such as amoeba. In addition, various structures can form from them, the functions of which are not fully understood.
Structure
As the name implies, non-membrane organoids do not have membranes. They are made up of proteins. Some of them also contain nucleic acids.
Ribosome structure
These non-membrane organoids are located on the walls of the endoplasmic reticulum. The ribosome has a spherical shape, its diameter is 100-200 angstroms. These non-membrane organoids consist of two parts (subunits) - small and large. When the ribosome is not functioning, they are separated. In order for them to combine, the presence of magnesium or calcium ions in the cytoplasm is mandatory.
Sometimes, in the synthesis of large protein molecules, ribosomes can combine into groups called polyribosomes or polysomes. The number of ribosomes in them can range from 4-5 to 70-80, depending on the size of the protein molecule that they synthesize.
Ribosomes are composed of proteins and rRNA (ribosomal ribonucleic acid), as well as water molecules and metal ions (magnesium or calcium).
The structure of the cell center
In eukaryotes, these non-membrane organoids are made up of two parts, called centrosomes, and the centrosphere, the lighter region of the cytoplasm that surrounds the centrioles. Unlike the case with ribosomes, parts of this organoid are usually combined. The combination of two centrosomes is called the diplosome.
Each centrosome consists of microtubules, which are twisted in the form of a cylinder.
The structure of microfilaments and microtubules
The former consist of actin and other contractile proteins, such as myosin, tropomyosin, etc.
Microtubules represent long cylinders, empty inside, that grow from centriole to the edges of the cell. Their diameter is 25 nm, and the length can be from several nanometers to several millimeters, depending on the size and function of the cell. These non-membrane organoids are primarily composed of tubulin protein.
Microtubules are unstable organoids that are constantly changing. They have a plus-end and a minus-end. The first constantly attaches to itself tubulin molecules, and from the second they are constantly split off.
The formation of non-membrane organoids
The nucleolus is responsible for the formation of ribosomes. In it, the formation of ribosomal RNA occurs, the structure of which is encoded by ribosomal DNA located on special sections of chromosomes. The proteins that make up these organoids are synthesized in the cytoplasm. After that, they are transported to the nucleolus, where they combine with ribosomal RNA, forming a small and large subunit. Then, the finished organelles move to the cytoplasm, and then to the walls of the granular endoplasmic reticulum.
The cell center is present in the cell from the moment of its formation. It is formed during the division of the mother cell.
Conclusion
As a conclusion, we give a brief table.
General Information on Non-Membrane Organoids| Organoid | Localization | Functions | Structure |
| Ribosome | the outer side of the membranes of granular endoplasmic reticulum; cytoplasm | protein synthesis (translation) | two subunits consisting of rRNA and proteins |
| Cell center | the central region of the cell cytoplasm | participation in the process of formation of the spindle division, the organization of microtubules | two centrioles, consisting of microtubules, and a centrosphere |
| Microtubules | cytoplasm | maintaining cell shape, transport of substances and certain organelles | long cylinders of proteins (primarily tubulin) |
| Microfilaments | cytoplasm | cell shape change, etc. | proteins (most often actin, myosin) |
So, now you know everything about non-membrane organoids that are found in both plant and animal and fungal cells.