Parts Of Eukaryotic Cell And Its Function – Eukaryotic organisms include protozoa, algae, fungi, plants, and animals. Some eukaryotic cells are independent, single-celled microorganisms, while others belong to multicellular organisms. The cells of eukaryotic organisms have several distinguishing characteristics. Above all, eukaryotic cells are defined by the presence of a nucleus surrounded by a complex nuclear membrane. Also, eukaryotic cells are characterized by the presence of membrane-bound organelles in the cytoplasm. Organelles such as mitochondria, endoplasmic reticulum (ER), Golgi apparatus, lysosomes, and peroxisomes are held in place by the cytoskeleton, an internal network that supports the transport of intracellular components and helps maintain cell shape (Figure 1). The genomes of eukaryotic cells are packaged into multiple rod-shaped chromosomes in contrast to the single, circular chromosome that characterizes most prokaryotic cells. Table 1 compares the structural features of eukaryotic cells with those of bacteria and archaea.

Figure 1. Click for a larger image. An illustration of a generalized, single-celled eukaryotic organism. Note that the cells of eukaryotic organisms vary widely in terms of structure and function, and a particular cell may not contain all of the structures shown here.

Parts Of Eukaryotic Cell And Its Function

Parts Of Eukaryotic Cell And Its Function

Eukaryotic cells exhibit a wide variety of different cell morphologies. Possible shapes include spheroid, ovoid, cube, cylindrical, flat, lenticular, fusiform, discoidal, crescent, stellate ring, and polygonal ( Figure 2 ). Some eukaryotic cells are irregular in shape, and some can change shape. The shape of a particular type of eukaryotic cell can be influenced by factors such as its primary function, its cytoskeletal organization, the viscosity of its cytoplasm, the rigidity of its cell membrane or cell wall (if it has one), and the physical pressure exerted on it by the surrounding environment and/or neighboring cells.

Ultrastructure Of Cells 1.2

. (credit a: work modification by NOAA; credit b, e: work modification by Centers for Disease Control and Prevention)

Figure 3. Eukaryotic cells have a well-defined nucleus. The nucleus of this mammalian lung cell is the large, dark, oval-shaped structure in the lower half of the image.

Unlike prokaryotic cells, where the DNA is in the nucleoid region, eukaryotic cells possess a nucleus, surrounded by a complex nuclear membrane that houses the DNA genome (Figure 3). By containing the cell’s DNA, the nucleus ultimately controls all of the cell’s activities and also serves an essential role in reproduction and heredity. Eukaryotic cells usually have their DNA organized into several linear chromosomes. The DNA in the nucleus is highly organized and condensed to fit inside the nucleus, which is accomplished by wrapping the DNA around proteins called histones.

Although most eukaryotic cells have a single nucleus, exceptions exist. For example, protozoa in the genus Paramecium typically have two complete nuclei: a small nucleus used for reproduction (micronucleus) and a large nucleus that directs cellular metabolism (macronucleus). In addition, some fungi temporarily form cells with two nuclei, called heterokaryotic cells, during sexual reproduction. Cells with a divided nucleus, but no cytoplasm, are called coenocytes.

Draw The Structure Of The Eukaryotic Cell Animal Cell

Figure 4. In this fluorescence microscope image, all intermediate filaments were stained with a bright green fluorescent stain. The nuclear plume is the intense bright green ring around the faint red nuclei.

The nucleus is bound by a complex nuclear membrane, often called the nuclear envelope, which consists of two distinct lipid layers adjacent to each other (Figure 4). Despite these connections between inner and outer membranes, each membrane has unique lipids and proteins on its inner and outer surfaces. The nuclear envelope contains nuclear pores, which are large rosette-shaped protein complexes that control the movement of material into and out of the nucleus. The overall shape of the nucleus is determined by the nuclear lamina, a mesh of intermediate filaments found just inside the nuclear envelope membrane. Outside the nucleus, more intermediate filaments form a looser mesh and serve to anchor the nucleus in position in the cell.

The nucleolus is a dense region of the nucleus where ribosomal RNA (rRNA) biosynthesis occurs. In addition, the nucleolus is also the site where ribosome assembly begins. Preribosomal complexes are assembled from rRNA and proteins in the nucleolus; They are then transported out of the cytoplasm, where ribosome assembly is completed ( Figure 5 ).

Parts Of Eukaryotic Cell And Its Function

Figure 5. (a) The nucleolus is the dark, dense area of ​​the nucleus. It is the site of rRNA synthesis and preribosomal assembly. (b) Electron micrograph showing the nucleolus.

Structure Of Prokaryotic Cells (a Level Biology)

Ribosomes found in eukaryotic organelles such as mitochondria or chloroplasts contain 70S ribosomes—the same size as prokaryotic ribosomes. However, the non-organelle-associated ribosomes in eukaryotic cells are the 80S ribosomes, which are composed of a small 40S subunit and a large 60S subunit. In terms of size and composition, this makes them different from the ribosomes of prokaryotic cells.

Two types of non-organelle-associated eukaryotic ribosomes are defined by their location in the cell: free ribosomes and membrane-bound ribosomes. Free ribosomes are found in the cytoplasm and serve to synthesize soluble proteins; ribosomes are found bound to the membrane attached to the rough endoplasmic reticulum and make proteins for insertion into the cell membrane or proteins destined for export from the cell.

The differences between eukaryotic and prokaryotic ribosomes are clinically important because certain antibiotic drugs are designed to target one or the other. For example, cycloheximide targets eukaryotic action, whereas chloramphenicol targets prokaryotic ribosomes.[1] Since human cells are eukaryotic, they are generally not harmed by antibiotics that destroy prokaryotic ribosomes in bacteria. However, sometimes negative side effects can occur because mitochondria in human cells contain prokaryotic ribosomes.

The endomembrane system, unique to eukaryotic cells, is a series of membrane-bound tubules, sacs, and flattened discs that synthesize many cell components and move materials within the cell (Figure 6). Due to their larger cell size, eukaryotic cells require this system to transport materials that cannot be spread by diffusion alone. The endomembrane system contains several organelles and connections between them, such as endoplasmic reticulum, Golgi apparatus, lysosomes and vesicles.

What Is An Animal Cell?

Figure 6. The endomembrane system is composed of a series of intracellular membrane structures that facilitate the movement of materials throughout the cell and across the cell membrane.

The endoplasmic reticulum (ER) is a series of tubules and cisternae (flattened sacs) connected by a single lipid bilayer ( Figure 7 ). The space inside the cistern is called the ER lumen. There are two types of ER, rough endoplasmic reticulum (RER) and smooth endoplasmic reticulum (SER). These two different types of ER are sites for the synthesis of different types of molecules. RER studded with ribosomes bound to the cytoplasmic side of the membrane. These ribosomes make proteins destined for the plasma membrane (Figure 7). After synthesis, these proteins enter the RER membrane. The RER sacs containing these newly synthesized proteins bud as transport vesicles and move either to the Golgi apparatus for further processing, directly to the plasma membrane, to the membrane of another organelle, or out of the cell. Transport vesicles are single-lipid, bilayer, membrane-bound spheres with hollow interiors that carry molecules. SER does not contain ribosomes and, therefore, appears “smooth.” It is involved in lipid biosynthesis, carbohydrate metabolism, and detoxification of toxic compounds in the cell.

Figure 7. The rough endoplasmic reticulum is studded with ribosomes for membrane protein synthesis (which gives it its rough appearance).

Parts Of Eukaryotic Cell And Its Function

The Golgi apparatus was discovered in the endomembrane system in 1898 by an Italian scientist Camillo Golgi (1843–1926), who developed a new staining technique that showed the stacked membrane structures of cells.

Cytoplasm — Structure & Function

, the agent that causes malaria. The Golgi apparatus is composed of a series of membranous disks called dictyosomes, each containing a single lipid bilayer, which are stacked together ( Figure 8 ).

Figure 8. A transmission electron micrograph (left) of a Golgi apparatus in a white blood cell. The illustration (right) shows the cup-shaped disk, stacked with several transport vesicles. The Golgi apparatus modifies lipids and proteins, producing glycolipids and glycoproteins, respectively, which are often embedded in the plasma membrane.

Enzymes in the Golgi apparatus modify lipids and proteins transported from the ER to the Golgi, often adding carbohydrate components, glycolipid products, glycoproteins, or proteoglycans. Glycolipids and glycoproteins are often embedded in the plasma membrane and are important for signal recognition by other cells or infectious particles. Different cell types can be distinguished from each other by the structure and arrangement of the glycolipids and glycoproteins contained in the plasma membrane. These glycolipids and glycoproteins often also serve as cell surface receptors.

, face Proteins are processed in the Golgi apparatus, and then additional transport vesicles containing the modified proteins and lipids are shed from the Golgi apparatus on its exit, or

Eukaryotic Cell: What Is It, Difference From Prokaryotic Cells, And More

, face These outgoing vesicles move and fuse with the plasma membrane or the membranes of other organelles.

Exocytosis is the process by which secretory vesicles (spherical membrane sacs) release these to the exterior of the cell (Figure 8). All cells have constitutive secretory pathways in which secretory vesicles transport soluble proteins that are released into the cell continuously (constitutively). Certain specialized cells also have regulated secretory pathways, which are used to store soluble proteins in secretory vesicles. Regulated secretion involves substances that are released only in response to certain events or signals. For example, certain cells in the human immune system (eg, mast cells) secrete histamine.

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