Peroxisomes: Tiny Structures with Big Roles in Eukaryotic Cells - Essay Sample

Introduction

Peroxisomes are membrane-bound organelle of eukaryotic cells. These membranes do not contain protein translation machinery, nor do they have their own DNA (Hu et al., 2012, p.2279). Thus, this means that it is after translation that proteins are transported from the cytosol of eukaryotic cells. Peroxisomes are really small, about 0.1 to 1 μm in diameter and are surrounded by a single lipid bilayer membrane. According to Hu et al. (2012, p.2280), about 50 different types of enzymes have been found and identified in the peroxisomal matrix. Notably, all these enzymes are linked to various biochemical pathways. The amount of peroxisomes in a cell depends on cell type and environmental conditions; the same applies to their size and function. This is why they are called multi-purpose organelles because they can alter their metabolic abilities based on their cellular needs (Hu et al., 2012, p.2282).

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Moreover, Peroxisomes have an important role, and it is to oxidize some specific biomolecules. They also contain enzymes that oxidize known molecules that are in a cell. These include fatty acids and amino acids. Hydrogen peroxide is produced from these oxidation reactions. As stated by John Cooper, hydrogen peroxide is toxic to the living cells; this is because they are able to react with other molecules (Hu et al., 2012, p.2287). Also, they contain catalase, which is an enzyme that is able to convert hydrogen peroxide to oxygen and water. As a result, it neutralizes the toxicity providing a secure location for the oxidative metabolism of some molecules to take place. In a nutshell, the main function of peroxisomes is the oxidation of fatty acids as well as neutralizing hydrogen peroxide (Hu et al., 2012, p.2289).

Peroxisomal Biogenesis

Typically, Peroxisomal Biogenesis entails the process of peroxisome membrane creation, importation of the matrix protein, as well as inheritance and proliferation of the organelle. Notably, the main proteins that are directly responsible for the peroxisome biogenesis have been referred to as proxies. Whereby, the PEX stands for the gene acronym. Moreover, in this particular phase, Arabidopsis proxies are referred to as the AtPEX mainly avoid further confusion, which may be associated with the mammalian and yeast proxies (Waterham et al., 2016, p.922). Furthermore, more than these proteins (proxies) referred to as PEX or Pex in mammals, and yeast respectively are mainly needed for the role of importation of peroxisomal matrix and the remaining are involved in the formation of the peroxisomal membrane proteins, to the peroxisome membrane and later in peroxisome proliferation (Waterham et al., 2016, p.923).

Notably, there are three peroxisome membranes proteins that are important for the early events, particularly in the peroxisome membrane assembly, as well as maintenance in various organisms. These membranes include PEX3, PEX19, and PEX16. The absence of these membranes may lead to incomplete loss, especially in detectable peroxisomes. However, reintroducing the "wild-type proteins" specifically to the mutant cells can significantly help in restoring peroxisome (Waterham et al., 2016, p.922).

Describe in detail the different Protein import Machinery involved in Peroxisomal Biogenesis

PEX2, PEX5, and PEX7 are mainly involved in the peroxisomal matrix protein import types of machinery. Notably, PEX7, together with the PEX5, are the only receptors involved in the protein harboring. However, PTS2 and PTS1 peroxisomal focused sequence as well as the cycle linking the peroxisome and cytoplasm. However, since PEX2 is closely associated with the ring finger complex, it is located particularly at the peroxisomal membrane to enable it to function in the protein importation in a lower direction of PEX7 and PEX5 (Waterham et al., 2016, p.922). Therefore, PEX2 is mainly required for the transportation of both PTS2 and PTS1 proteins.

Notably, since PEX2, PEX5, and PEX7 mainly belongs to the peroxisomal import machinery, PEX5 is the peroxisomal targeting signal 1 (PTS1) receptors that recognize protein harboring a PTS1 signal in the cytoplasm. Moreover, this process of protein importation mainly concerns a number of peroxisomal matrix proteins (Waterham et al., 2016, p.922). Thus, PEX7, which is associated with the PTS2 receptor, represent the next pathway of import. However, the stated pathway is not available in all organisms; hence it is involved in the importation of the few enzymes to peroxisomes (Fujiki et al., 2017, p.302). Typically, in many organisms, receptors are heavily loaded with the cargo routes to the peroxisomal import. This where the peroxisomal membrane will continuously be reduced, translocated and receptors reused back to the cytoplasm.

In addition, the key function of PEX2, particularly in protein importation, is more comprehensive. Moreover, PEX2 is designated as a peroxisomal membrane protein that mainly controls the ring finger domain and enabling the protein to protein interactions. Also, alongside the other two peroxisomal membranes (PEX10 and PEX12), PEX2 creates a ring finger complex that forms part of the importation complex (Fujiki et al., 2017, p.302). Hence, the three proteins get involved subsequently in order to minimize the receptor cargo complexes whereby the PEX2 impairs the importation of peroxisomal targeting signal 1(PTS1) and peroxisomal targeting signal 2 (PTS2) proteins.

Moreover, in addition to the key function in PTS2 and PTS1 protein import, PEX2 is as well involved in the developmental processes. Typically, PEX2 being one of the proxins, is critically needed for the movement, especially from the cellular state towards the mycelial form. In a nutshell, in the plan referred to as the Arabidopsis theliana, peroxisomal targeting signal 2 has a key role in photomorphogenesis (Fujiki et al., 2017, p.302).

Discuss in detail the connection between peroxisomes and aging

The intracellular storage of the damaged components such as proteins, nucleic acids, and lipids can significantly lead to aging through a process known as deterioration of cells. During this process, there exists a massive loss of cell viability. Of late mitochondria are mainly considered as the key players in the reactive of oxygen species production as well as in the aging process of eukaryotic cells (Fujiki et al., 2017, p.302). It has also been indicated that peroxisomes do produce a massive amount of reactive of oxygen species (ROS)

As a result of this, peroxisomal dysfunction and mitochondrial dysfunction can significantly contribute to cell aging and death. Notably, the significance of peroxisomes membrane in these processes is less understood as compared to the function of mitochondria in cell death pathways, which is well established. Just like mitochondria, peroxisomes have the ability to multiply by typically dividing of the pre-existing ones (Fujiki et al., 2017, p.302). The primary stage of the peroxisomes fusion is known as an organelle elongation intervened by the peroxisomal membrane protein.

However, the Dynamin-related proteins (DRPs) are typically responsible for the final scission event, whereas the Dynamin-related proteins are involved in peroxisome(Fujiki et al., 2017, p.309). Moreover, the yeast Hansenula polymorpha peroxisome fission fully depends on DRPs.

Discuss in detail the connection between peroxisomal biogenesis and peroxisomal disorders; provide relevant examples.

Peroxisomal biogenesis disorder

Genetic Heterogeneity

Typically, the inborn errors of the peroxisomes are mainly grouped into two categories. These include the single enzymes as well as the PBDs. Moreover, the PBD comprises of neonatal adrenoleukodystrophy (NALD), the severe phenotype, the intermediate and infantile Refsum disease (IRD), the cerebrohepatorenal Zellweger syndrome (ZS), and the least severe phenotype (Waterham et al., 2016, p.929). Notably, Rhizomelic chondrodysplasia punctata is characterized as a partial PBD, whereas Genetic heterogeneity is classified as subjects with PBDs. On the contrary, cells from patients categorized as CG14, CG12, and CG9 are empty of peroxisomal remnant structures. Thus this implies that the genes defective in these CGs are needed for peroxisome membrane biogenesis.

Notably, Genetic phenotype complementation of peroxisome collections, defective mutants of mammalian somatic cells, for instance, Chinese hamster ovary cells as well as many yeast species such as Hansenula polymorpha, Yarrowialipolytica, Pichia pastoris and Saccharomyces cerevisiae have led to characterization and identification of several genes, referred as encoding proxies and PEXs that are vital for peroxisome biogenesis (Ma et al., 2011, p. 7).

Peroxisomal Disorders

Due to genes mutations, Peroxisomal disorders are formed by that results in peroxisome biogenesis. These peroxisomes disorders help in the transportation of proteins as well as encoding the enzymes(Ma et al., 2011, p. 8). This process is characterized by taking up the enzymes from the cytoplasm of the peroxisome. Since Peroxisomal disorders are characterized as cognitive disorders, they vary from moderate to severe in nature. For instance, the Zellweger spectrum comprises of neonatal adrenoleukodystrophy (NALD), infantile Refsum disease, and Zellweger syndrome (Ma et al., 2011, p. 9). However, Zellweger syndrome is characterized by a reduction in the number of peroxisomes. Thus it becomes one of the most severe conditions within the Zellweger syndrome. In a nutshell, Mutations that give rise to Zellweger syndrome causes iron, copper as well as other substances referred to as long-chain fatty acids to accumulate in tissues such as kidneys, and liver(Ma et al., 2011, p.12).

Conclusion

In a nutshell, Peroxisomes are membrane-bound organelle of eukaryotic cells. These membranes do not contain protein translation machinery, nor do they have their own DNA. Thus, this means that it is after translation that proteins are transported from the cytosol of eukaryotic cells. Peroxisomes are really small, about 0.1 to 1 μm in diameter and are surrounded by a single lipid bilayer membrane. Moreover, Peroxisomes have an important role, and it is to oxidize some specific biomolecules. They also contain enzymes that oxidize known molecules that are in a cell. These include fatty acids and amino acids. Hydrogen peroxide is produced from these oxidation reactions. Also, Peroxisomal Biogenesis entails the process of peroxisome membrane creation, importation of the matrix protein, as well as inheritance and proliferation of the organelle. Notably, the main proteins that are directly responsible for the peroxisome biogenesis have been referred to as proxies. Whereby, the PEX stands for the gene acronym. Moreover, in this particular phase, Arabidopsis proxies are referred to as the AtPEX mainly avoid further confusion, which may be associated with the mammalian and yeast proxies. PEX2, PEX5, and PEX7 are main protein machinery involved in the peroxisomal matrix protein import types of machinery. Notably, PEX7, together with the PEX5, are the only receptors involved in the protein harboring. However, PTS2 and PTS1 peroxisomal focused sequence as well as the cycle linking the peroxisome and cytoplasm.