Eukaryotic Cells Organelles
The cells that compose the tissues of living organisms may be different in size, shape and content. However, their process of activity, growth, development and the ability to change are usually the same. The paper investigates eukaryotic cells and their organelles.
The cells of all types consist of two main components that are interconnected. They are the cytoplasm and the nucleus. The latter is separated from the cytoplasm with a membrane and contains nuclear juice, chromatin, and nucleolus. The cell is filled with cytoplasm. Outside, it is covered with the membrane. The article “Eukaryotic Cells” states that to the membrane organelles belong the external cytoplasmic membrane, Golgi body, lysosomes, mitochondria, and plastids (n. pag.). Ribosomes, centrosomes, and the organelles of motion that do not possess a personal membrane are the non-membranous ones. All the organelles are based on the biological membrane that has a similar construction and consists of a double layer of phospholipids. The membranes differ only with the content of the proteins (Lodish).
Cytoplasmic membrane is present in all cells of plants, animals, and bacteria. It usually has three layers. The outer and the external layers consist of protein molecules while the middle one is composed majorly of lipid ones. It protects the cytoplasm from the negative influence of the environment, keeps all the organelles in the cells, and, at the same time, is a universal biological unit. Some cells may have several membranes that are interconnected. In such case, the cell may preserve the shape. The majority of plant cells also have the outer layer of cellulose.
The cytoplasm is composed of water, proteins, lipids, hydrocarbons, and mineral connection. All these substances compose colloidal liquid that, depending on the environmental conditions, may have the features both of a liquid and a dense body. The cytoplasm is covered with channels of different size and shape. Their walls are the membranes that contact with all the other organelles and compose a single functional and structural system to carry out the exchange of the nutrients and energy.
Inside the channels, there are the granules named ribosomes. They may be located separately or can compose the complex of five and more ribosomes. This phenomenon is called polysomes. Other channels may not contain the granules and compose the endoplasmic reticulum. On their membranes, there are located the ferments that participate in the synthesis of lipids and hydrocarbons. The inner space of the channels is filled with the products of the vital activity of the cell. The channels regulate the transfer and the concentration of nutritional elements, divide the molecules of the organic substances, and determine the periods of their synthesis. On the internal and external surfaces of membranes, the process of synthesis of proteins, hydrocarbons, and lipids that are either used for the cell vital activity, or are transferred outside is carried out.
Ribosomes are located in all types of cells from bacteria to multicellular organisms. They are majorly composed of ribonucleic acid and proteins. They also contain magnesium that allows saving the ribosome structure. The ribosomes may be connected with the membrane of the endoplasmic reticulum, outside membrane, or may be freely located in the cytoplasm. They carry out the synthesis of proteins. Ribosomes may also be found in the nucleus from where they get to the cytoplasm.
The Golgi body looks like separate bodies limited by membranes. The products of cell secretion come to the membrane channels of the body, from where they are transferred to the cytoplasm, consumed by the cell itself or transferred outside. The Golgi body carries out the synthesis of polysaccharides and the process of their unification with proteins. Due to this connection, there appear glycoproteins.
The article “Eukaryotic Cell” states that mitochondria are the small bodies limited by two membranes (n. pag.). There are located the ferments with the help of which mitochondria are able to produce adenosine triphosphate. Depending on the cellular activity and the conditions of the environment, mitochondria may change their location. They may also transform their physical shape and size.
Lysosomes are the round formations limited by a membrane and located all over the cytoplasm. They may be found in all cells of plants and animals. Lysosomes appear in the endoplasmic reticulum and the Golgi body from where they are transferred to cytoplasm together with ferments. They may also carry out the process of the abolishment of foreign and dying organelles. The products of lysis are transferred to the cytoplasm where they are included in the structure of new molecules. When the lysosome membrane is broken, the ferments start the process of fermentation of the cytoplasm and cause the death of the cell.
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Plastids are located only in plant cells and can be found in the majority of green organisms. They carry out the production and storage of nutritive elements. Plastids may be divided into chloroplasts, chromoplasts and leucoplasts. All of them are formed out of proplastids. They also contain DNA that controls the reproduction of these organelles.
Chloroplasts are the green plastids that contain chlorophyll pigment. They are located in leafs, young stems, and fruits. Chloroplasts are limited by a green membrane. Chromoplasts are the plastids that contain plant pigments (red, yellow, orange). They are located in the cytoplasm of stem cells of flowers, fruits, leaves, and provide them with the coloring. Chromoplasts are formed out of leucoplasts or chloroplasts as a result of carotenoids storage. Leucoplasts are the colorless plastids located in stems or roots. Some of these cells may contain starch, while others include oils and proteins.
The cell center or centrosome plays an important role in the cell coproduction and consists of two centrioles. It may be found almost in all cells of animals and plants. The cell center is the first organelle that is divided. It also controls the division of chromosomes. One centriole is transferred to the daughter cell.
Many cells may have special organelles that may carry out the function of motion. They may also contain the inclusions that are the temporary elements which appear in the cell at a certain stage of its vital activity as a result of the synthetic function. These elements are either used by the cell or transferred out of it. Such elements as organic acids, glycogen, lipid drops, crystals, and pigments among others also belong to the inclusions.
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Vacuoles are the hollows limited by a membrane. They may be found in the cells of plants. They may appear in different parts of endoplasmic reticulum and are constantly separated from it. Vacuoles support the turgor pressure and contain the cellular or vacuolar juice the molecules of which determine its osmotic concentration. The primary products of synthesis such as hydrocarbons, proteins, pectin, and others are considered to be stored in vacuoles.
The cytoskeleton is one of the distinguishing features of a eukaryotic cell. Its elements are interconnected with the external cytoplasmic membrane and the nuclear surface. They determine the shape of the cell, promote the motion of the organelles and the cell in general.
The cell nucleus carries out the primary function for the vital activity of a cell. With its abolishment, a cell stops functioning and dies. The majority of animal cells have one nucleus, but there also exist multinuclear cells (such as those that are located in liver or muscles). Erythrocytes are formed of the cells that contain a nucleus, but they lose it with time. Mature erythrocytes do not live for long without the nucleus.
The nucleus is surrounded by double membrane covered with pores that connect it with the channels of endoplasmic reticulum and the cytoplasm. Inside the nucleus, there is located chromatin – parts of chromosomes. During the period of cell division, they turn into the structures that are complex units of proteins with DNA that is called nucleoprotein.
The functions of the nucleus include the management of the cell activity that is carried out with the help of DNA and RNA. In the process of the preparation to the cell division, the chromosomes are transferred to the daughter cells that provide the inheritance of cell information in each type of organisms.
The nucleolus is the densest part of the nucleus. It is composed of complex proteins and RNA, phosphates of magnesium, calcium, zinc, and ribosomes. The nucleolus disappears in the process of cell division and appears again when the reproduction is completed.
Thus, a cell has a complex structure. The membrane principle of the organelles formation allows different chemical reactions that take place in the same cell. Each of the organelles has a personal structure and a specific function. However, only a harmonic combination of these functions allows the cell to be alive. Due to this interconnection, the substances from the environment come into the cell, and the processed products are transferred outside. The complexity of functions in the cell organization could appear only in a long process of biological evolution. Due to it, the functions carried out by the organelles became more and more complex with time.