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