This essay is dedicated to the topic of eukaryotic cells – the most structurally advanced of the major cell types. The aim of the essay includes describing the structure and functions of each of the eukaryotic organelles; distinguishing membranous and non-membranous eukaryotic cells; and explaining the importance of membrane structure and function in the organization of living processes within cells. In order to achieve this particular aim, different study methods and approaches will be implemented. The paper will contain information about cells in general, definition of eukaryotic cells, their structural differences and specific functions. Moreover, definitions of membranous and membranous free eukaryotic cells will be provided as well as the dissimilarity between these two types. In addition, the essay presupposes sophisticated explanation of the membrane structure and function importance in the life span and processes within cells. Every definition will be grounded on scientific literary sources.
Keywords: eukaryotic cells, cell structure, membrane, nucleus, organelles
Eukaryotic Cells and the Many Functions
The first scientist who became well-known for cell discovery was Robert Hooke. In 1665, Hook used his microscope and saw something new: an abundance of tiny structures. He decided to propose a name for these living structures – the cells. Later, the scientist had described them in his articles. He wrote, “The cell is the smallest unit of a living system and fall in the microscopic range of 1 to 100 µm”. Cells have the possibility to take various sizes and shapes, and, therefore, carry out multiple functions. It is necessary to understand the function of a single cell as a living organism of the unique structure. The most important characteristic features of cells are their ability to divide. Theodor Schwann states that a single cell exists because it evolved from another one already, and, what is quite amazing, it can produce a completely new cell. Cells are the common features of all living beings, and they carry the information about these living life forms. By learning about the structure and functions of cells, humanity comes closer to getting to know every type of living form on the Earth.
Like all living beings, cells fall under specific classification categories. There are organisms formed from only one cell – unicellular (for example, different bacteria and algae), and organisms which have more cells – multicellular (for instance, plants, animals, and fungi). Basing on the number of cells containing in the organism, scientists distinguish between Prokaryotic or Eukaryotic types of cells. The given terms were applied in 1960s by Hans Ris, famous researcher. The aim of the paper is to investigate the Eukaryotic type of cells, their structure, and functions.
A eukaryotic cell is comprised of “membrane-bound organelles”. Organism species, which are averagely large and complex in their structure, are eukaryotes (animals, plants, fungi, and others). Eukaryotes are essentially monophyletic. These organisms make up one domain of life by forming a clade. Prokaryotes are the two other domains. Eukaryotes have a significantly smaller number of cells present in all living beings. There are dozen times more microbes within a human body than human cells. Dissimilar to prokaryotes, the eukaryotic genome is located in the nucleus, surrounded by a nuclear membrane. Cell cytoplasm enumerates many other membrane bound organelles besides the nucleus. The cell is divided by separation of the genome structure of which is relatively tight, packed, and condensed (the chromosomes).
There are such eukaryotic organelles as: nucleus, chromosomes, endoplasmic reticulum, ribosomes, lysosomes, mitochondria, Golgi body, cytoplasm, vesicles, vacuole, as well as pores and cell membrane. Eukaryotic cells are relatively larger than prokaryotic ones. They range from10 to 100 micrometers and have a lot of membranes and structures – organelles (see fig. 1), and cytoskeleton made of microtubules, microfilaments, and intermediate filaments which are the characteristic features in the cell’s shape and organization. Eukaryotic DNA is divided into several chromosomes which are separated during nuclear division by a microtubular spindle.
The cell’s membrane work lies in separating the inner structural features of all the cells from outer influences posed by environment and other factors. This membrane is “selectively-permeable to ions and organic molecules and controls the movement of substances in and out of cells”. Cell membranes take part in adhesion, signaling, and ion conductivity. They also serve as “an attachment for the extracellular glycocalyx and the intracellular cytoskeleton cell wall”.
Cell membrane looks like a mosaic. Thus it has a particular structure, including macromolecules. There are two building factors within the cell membrane:
- Blocks, including integral proteins, peripheral proteins, and glycoproteins. These protein molecules occupy 60% of the membrane while fat covers only 40%;
- Phospholipids which are produced from the phospholipid double layer.
Functions of Cell Membrane
There are several functional characteristics of a cell membrane. They include:
- The protoplasm of a cell which is surrounded by the cell membrane. In animal cells, it carries out the mission of separating the extracellular components from the intracellular ones. Fungi, bacteria, and plants also possess a wall from the cells which supports them mechanically and prevents from the passage of larger molecules;
- The cell membrane anchors cytoskeleton to provide shape to the cell and helps to group cells together to form tissues in attaching to the extracellular matrix and other cells;
- The barrier is permeable and able to regulate what enters and exits the cell, thus facilitating the transport of materials needed for survival;
- The membrane also plays a role of cell potential manager and maintainer;
- Being a selective barrier, a membrane supports and retains the cytoplasm;
- Proteins in the membrane function to carry out selective transport;
- Communication with the help of receptors.
There are two general types of membranes: apical membrane and basolateral membrane of a cell. The first membrane is “the surface plasma membrane that faces the lumen” (School of science and technology, 2014, p. 21). The second membrane “is the surface of the plasma membrane that forms its basal and lateral surfaces. It faces towards the interstitium and away from the lumen” (School of science and technology, 2014, p. 21).
The first of the organelles is a nucleus. It is the most notable, as the nucleus appears to be the number one characteristic which defines the eukaryotes. It is an oval organelle containing the DNA. The membrane of a nucleus is of a double-membrane structure. This structure also contains pores and connections to a membrane-bound network channel such as an endoplasmic reticulum. This might be either Smooth ER (with no ribosomes) or Rough ER (ribosomes associated with membranes of ER). Here, ribosomes function as protein synthesis that is transported through ER channels to different parts of the cell.
ER system produces a derivative – the Golgi body. This organelle was named after Camillo Golgi, the scientist who was the first scientist managed to describe it (Nicholl, 2001). Golgi body’s function is to modify and package polysaccharides and proteins.
Mitochondria are the organelles whose inner membrane is arranged in series of folds – cristae. Its outer membrane is smooth. The matrix is a semifluid center in the mitochondrion. Cristae also locate ATP formed enzymes.
A lot of functions carried out by cells require much energy. Chloroplasts and mitochondria are responsible for energy conversion in eukaryotic cells. In plants chloroplasts containing chlorophyll carry out the mission of photosynthesis. The membranes they have are complex (thylakoids), arranged in stacks and called grana. These membranes attempt to increase the surface area inside the chloroplast and provide other membranes to maintain electron transport of proteins.
Lysosomes are the white blood cells which are used to bacteria destruction with the help of phagocytosis. These are the membrane-enclosed spheres containing powerful enzymes of digestive character.
Vacuoles are the space cavities within the cytoplasm that are used mostly as storage places.
Peroxisomes are also the organelles of a cell that are structurally similar to lysosomes, but are smaller. Enzymes, which are located in peroxisomes, oxide various organic substances.
Centrosomes are the organelles consisting of a peri centriolar area which organizes the mitotic spindle (cell division). This area also contains centrioles – arrays of microtubules that form or regenerate cilia and flagella. Centrioles, in their turn, play an important role in cell division.
To conclude, the aim of the paper was achieved. Information about cells in general, definition of eukaryotic cells, their structural difference and specific functions were presented, as well as the definitions of membranous and membranous free eukaryotic cells and the dissimilarity between these two types. In addition, the essay explained the membrane structure and function importance in the life span and processes within cells