The Overview of Organelles

Structure

Nucleolus mainly consists of three major components - the dense fibrillar component (DFC), the fibrillar centers (FC) and granular components (GC)^[1]. Nucleolus is a central nuclear location where all the ribosomal RNAs are processed, synthesized and collected with ribosomal proteins. Therefore, nucleolus is also known as the factory for ribosome production. Transcription of the rDNA occurs in the FC domain. The DFC contains the protein fibrillarin, which is important in rRNA processing. The GC contains the protein nucleophosmin, which is also involved in ribosome biogenesis^[2].

Function and Markers

First, nucleolus, a non-membrane bound cellular structure, which is present within the nucleus of the cell and contains ribosomes having ribonucleic acid (RNA) in them, and plays a crucial role in regulating the transactions of proteins and also vitally modulating each and every cellular functions in the cell. Second, the main nucleolus function is to assemble and produce ribosome components within the cell. Besides that, nucleolus mainly acts as a suspension medium for cell-organelles in the nucleus of the cell.

Being one of the main sources of containing chromosomes with DNA present in it, nucleolus is highly rich in RNA and is used for maintaining a sound shape and structure of the nucleus. Other nucleolus functions like transportation of molecules, ions and vital substances for an effectual functioning of cell metabolism is included in the nucleolus functions as well.

In this part, we conclude several markers of nucleolus in the Table 1.

Table 1. The markers of nucleolus

Structure

Fig.2. The Structure of Nucleus

Nucleus, the largest cellular organelle in animal cells, is bound by a double membrane called the nuclear envelope^[3]. This membrane seems to be continuous with the endoplasmic reticulum (introduced in the next section in details) of the cell and has pores, which probably admit large molecules to enter. The average diameter of the nucleus in mammalian cells is approximately 6 micro-meters (µm), which occupies about 10% of the total cell volume. The viscous liquid within it is called nucleoplasm, and is similar in composition to the cytosol found outside the nucleus. It appears as a dense, roughly spherical or irregular organelle. The composition by dry weight of the nucleus is approximately: DNA 9%, RNA 1%, Histone Protein 11%, Residual Protein 14%, acidic Proteins 65%^[4].

In some types of white blood cells specifically most granulocytes the nucleus is lobated and can be present as a bi-lobed, tri-lobed or multi-lobed organelle. As shown in the Fig.2.

Function and Markers

The nucleus provides a site for genetic transcription that is segregated from the location of translation in the cytoplasm, allowing levels of gene regulation that are not available to prokaryotes. The main function of the cell nucleus is to control gene expression and mediate the replication of DNA during the cell cycle.

In this section, we list several markers of nucleus in Table 2.

Table 2. The Markers of Nucleus

Structure

Fig.3. The Structure of Ribosome

Ribosomes are special because they are found in both prokaryotes and eukaryotes. There are two pieces or subunits to every ribosome. In eukaryotes, scientists have identified the 60-S (large) and 40-S (small) subunits. Even though ribosomes have slightly different structures in different species, their functional areas are all very similar. As shown in the Table 3, there are some difference of ribosomes between eukaryote and prokaryote.

Table 3. Compared the ribosome components of eukaryote with prokaryote

Function and Markers

Ribosomes are found in many places around a eukaryotic cell. You might find them floating in the cytosol. Those floating ribosomes make proteins that will be used inside of the cell. Other ribosomes are found on the endoplasmic reticulum. Endoplasmic reticulum with attached ribosomes is called rough ER. It looks bumpy under a microscope. The attached ribosomes make proteins that will be used inside the cell and proteins made for export out of the cell. There are also ribosomes attached to the nuclear envelope. Those ribosomes synthesize proteins that are released into the perinuclear space.

Ribosomes are a cell structure that makes protein. Protein is needed for many cell functions such as repairing damage or directing chemical processes. The location of the ribosomes in a cell determines what kind of protein it makes. If the ribosomes are floating freely throughout the cell, it will make proteins that will be utilized within the cell itself. When ribosomes are attached to endoplasmic reticulum, it is referred to as rough endoplasmic reticulum or rough ER. Proteins made on the rough ER are used for usage inside the cell or outside the cell.

In the following Table 4, we enumerate several markers in the research of ribosome.

Table 4. Markers of ribosome

Structure

The general structure of the endoplasmic reticulum is a network of membranes called cisternae. These sac-like structures are held together by the cytoskeleton. The phospholipid membrane encloses the cisternal space (or lumen), which is continuous with the perinuclear space but separate from the cytosol.

The functions of the endoplasmic reticulum can be summarized as the synthesis and export of proteins and membrane lipids, but varies between ER and cell type and cell function. The quantity of both rough and smooth endoplasmic reticulum in a cell can slowly interchange from one type to the other, depending on the changing metabolic activities of the cell. Transformation can include embedding of new proteins in membrane as well as structural changes. Changes in protein content may occur without noticeable structural changes.

Function and Markers

The rough endoplasmic reticulum manufactures membranes and secretory proteins. The ribosomes attached to the rough ER synthesize proteins by the process of translation. In certain leukocytes (white blood cells), the rough ER produces antibodies. In pancreatic cells, the rough ER produces insulin. The rough and smooth ER are usually interconnected and the proteins and membranes made by the rough ER move into the smooth ER to be transferred to other locations. Some proteins are sent to the Golgi apparatus by special transport vesicles. After the proteins have been modified in the Golgi, they are transported to their proper destinations within the cell or exported from the cell by exocytosis.

The smooth ER has a wide range of functions including carbohydrate and lipid synthesis. Lipids such as phospholipids and cholesterol are necessary for the construction of cell membranes. Smooth ER also serves as a transitional area for vesicles that transport ER products to various destinations. In liver cells the smooth ER produces enzymes that help to detoxify certain compounds. In muscles the smooth ER assists in the contraction of muscle cells, and in brain cells it synthesizes male and female hormones.

In the following Table 5, we enumerate several markers in the research of endoplasmic reticulum.

Table 5. Markers of Endoplasmic Reticulum

Structure

The Golgi apparatus has a structure that is made up of cisternae, which are flattened stacks of membrane usually found in a series of five to eight, or until they fill up the cytoplasm. These cisternae help proteins and cytoplasmic components.

Function and Markers

The Golgi complex works closely with the rough ER. When a protein is made in the ER, something called a transition vesicle is made. This vesicle or sac floats through the cytoplasm to the Golgi apparatus and is absorbed. After the Golgi does its work on the molecules inside the sac, a secretory vesicle is created and released into the cytoplasm. From there, the vesicle moves to the cell membrane and the molecules are released out of the cell.

In the following Table 6, we enumerate several markers in the research of Golgi apparatus.

Table 6. Markers of Golgi Apparatus

Structure

The cytoskeleton is composed of at least three different types of fibers: microtubules, microfilaments, and intermediate filaments. These fibers are distinguished by their size with microtubules being the thickest and microfilaments being the thinnest. In the Table 7 below, the difference among these three types of cytoskeleton are presented.

Table 7. Comparison of Three Types of Cytoskeleton

*the content of Table 7 is derived from Wikipedia.

Function and Markers

The cytoskeleton extends throughout the cell's cytoplasm and directs a number of important functions, involving the maintenance of cell shape, held variety of cellular organelles in their place, and assistance of vacuoles formation. Note that, the cytoskeleton is not a static structure, but is able to disassemble and reassemble its parts in order to enable internal and overall cell mobility.

In the following Table 8, we enumerate several markers in the research of cytoskeleton.

Table 8. Markers of Cytoskeleton

Structure

Fig.4. The Structure of Mitochondria

Mitochondria are typically round to oval in shape and range in size from 0.5 to 10 μm, and contains outer and inner membranes composed of phospholipid bilayers and proteins. Due to the different properties of outer and inner membranes, there are five distinct sections to a mitochondrion- the outer mitochondrial membrane, the inter-membrane space (the space between the outer and inner membranes), the inner mitochondrial membrane, the cristae space (formed by infoldings of the inner membrane), and the matrix (space within the inner membrane).

Function and Markers

The primary function of which is to generate large quantities of energy in the form of adenosine triphosphate (ATP), which is a series of reactions (also known as the citric acid cycle, or the Krebs cycle). In addition to producing energy, mitochondria store calcium for cell signaling activities, generate heat, and mediate cell growth and death. The number of mitochondria per cell varies widely; for example, in humans, erythrocytes (red blood cells) do not contain any mitochondria, whereas liver cells and muscle cells may contain hundreds or even thousands. The only eukaryotic organism known to lack mitochondria is the oxymonad Monocercomonoides species.

In the following Table 9, we enumerate several markers in the research of mitochondrion.

Table 9. Markers of Mitochondrion

Structure and function

Each lysosome is surrounded by a membrane that maintains an acidic environment within the interior via a proton pump. Lysosomes contain a wide variety of hydrolytic enzymes (acid hydrolases) that break down various macromolecules it engulfs, invovling nucleic acids, proteins, and polysaccharides. These enzymes are active only in the lysosome's acidic interior; their acid-dependent activity protects the cell from self-degradation in case of lysosomal leakage or rupture, since the pH of the cell is neutral to slightly alkaline. In addition to being able to break down polymers, lysosomes are capable of fusing with other organelles & digesting large structures or cellular debris; through cooperation with phagosomes, they are able to conduct autophagy, clearing out damaged structures. Similarly, they are able to break-down virus particles or bacteria in phagocytosis of macrophages.

Markers

In the following Table 10, we enumerate several markers in the research of lysosome. We hope that will give some help for you.

Table 10. Markers of Lysosome

Structure

Fig.4. The Structure of Centrosome

The animal centrosome consists of a pair of centrioles linked together with their proximal regions. The centrioles contain cylindrical arrays of triplet MTs organized with nine-fold radial symmetry, and the proximal region is structurally similar to the basal bodies of cilia and flagella^[5][6][7].

In post-mitotic cells, the centrosome contains a mature centriole called the mother centriole and an immature centriole assembled in the previous cell cycle, the daughter centriole, which is about 80% the length of the mother centriole^[8]. Mother centrioles are distinguished by two sets of nine appendages at their distal ends^[9].

Function and Markers

The function of centrosome, during cell division, is to maintain the chromosome number. Replication of DNA is accompanied by the splitting of the centrosome into two, each having one centriole during cell division. The two centrosomes attach themselves to the opposite poles of the nucleus. Sometimes, you may confuse with the concepts of centrosome and chromosome. Actually, as the nouns mentioned, centrosome is an organelle, near the nucleus in the cytoplasm of most organisms that controls the organization of its microtubules. While chromosome is a structure in the cell nucleus that contains DNA, histone protein, and other structural proteins.

In the following Table 11, we list several markers in the research of centrosome. We hope that will give some help for you.

Table 11. The Markers of Centrosome

Structure and function

The cell membrane is primarily composed of a mix of proteins and lipids. Depending on the membrane's location and role in the body, lipids can make up anywhere from 20 to 80 percent of the membrane with the remainder being proteins. Besides that, lipids make membranes flexible, proteins monitor and maintain the cell's chemical climate and assist in the transfer of molecules across the membrane.

The main function of cell membrane is to protect the integrity of the interior of the cell via allowing certain substances into the cell while keeping other substances out. It also serves as a base of attachment for the cytoskeleton in some organisms and the cell wall in others. Thus the cell membrane also serves to help support the cell and help maintain its shape.

Another function of the membrane is to regulate cell growth via the balance of endocytosis and exocytosis. In endocytosis, vesicles containing lipids and proteins fuse with the cell membrane increasing cell size as internalized substances. In exocytosis, vesicles containing lipids and proteins lipids and proteins are removed from the cell membrane. Animal cells, plant cells, prokaryotic cells, and fungal cells have plasma membranes. Internal organelles are also encased by membranes.

Markers

In the following Table 12, we list a number of markers of cell membrane, we hope that will help your research.

Table 12. The Markers of Cell Membrane

Comparison

Concerning the study of chromatin, we always mix the concepts of chromatin and chromosome. In this section, we compare the two things from below aspects (as shown in the Table 13).

Table 13. The Comparison between Chromatin and Chromosome

Function and Markers

The main function of chromatin is to condense the DNA into a compact unit that will be less voluminous and can fit within the nucleus. Chromatin consists of complexes of histones and DNA. Histones help to organize DNA into structures called nucleosomes by providing a base on which the DNA can be wrapped around. A nucleosome consists of a DNA sequence of about 150 base pairs that is wrapped around a set of eight histones called an octamer. The nucleosome is further folded to produce a chromatin fiber. Chromatin fibers are coiled and condensed to form chromosomes. Chromatin makes it possible for a number of cell processes to occur including DNA replication, transcription, DNA repair, genetic recombination, and cell division.

In the following Table 13, we list a number of markers of chromatin, we hope that will help your research.

Table 13. The Markers of Chromatin

Structure and function

The length of a typical cilium is 1~10μm, and the width of that is usually less than 1μm. They are often divided into two different types – motile and non-motile, and these types can work together or separately.

Motile cilia, as named moving, can be found in the respiratory tract, middle ear, and other body systems. Multiple cilia will wave in a rhythmic or pulsating motion, and use that motion to keep sensitive internal passage ways free of mucus or foreign particles, for example. Body cells that have a single moving cilium are sperm cells, which use that cilium to propel the cell.

The non-motile cilia play a key role in many different organs. Some almost act as antenna that receive sensory information for the cell, processing signals from the other cells or the fluids surrounding it. For example, cilia in the kidney are forced to bend as urine flows past, which sends signals to the cells that it is flowing. Non-motile cilia inside the eye are housed in the retina's photoreceptors, allowing important molecules to be transported from one end to the other.

Markers

In the following Table 14, we list a number of markers of cilium, we hope that will help your research.

Table 14. The Markers of Cilium