Extrait
2
Abstract
Apoptosis refers to a programmed cell death; a biological process in which the body of
an organism destroys its cells for different reasons. In reality, apoptosis and necrosis involve
different mechanisms, and this implies they are different. In addition, the changes that occur in
the process of cell death are differing in terms of morphology and chemical composition.
Evidence indicates that there are various factors that make cells commit suicide. In most
cases, cells commit suicide due to imbalances between positive and negative signals that
determine cell survival. Cells can consider committing suicide upon the recipient of negative
signals.
This research will provide a comprehensive overview of apoptosis. It will discuss
mechanisms of apoptosis and the factors involved in the process. It will also explain the
association between apoptosis.
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Introduction
Apoptosis refers to a biological process in which the body of an organism destroys its
cells for different reasons. Elmore (2007) defines apoptosis as a process that "occurs normally
during development and aging and as a homeostatic mechanism to maintain cell populations in
tissues" (p. 496). On the other hand, apoptosis occurs in other biological processes such as
immune reactions and disease responses. As such, it plays a pivotal role in the body's defense
mechanism. In reality, apoptosis is usually triggered by an array of stimuli and conditions
including pathological and physiological factors. However, it is worth noting that, these stimuli
may not necessarily cause death to all cells that receive the same stimulus owing to other
biological signals that inhibit apoptosis in some cells while exposing others to programmed cell
suicide. Stimuli that trigger apoptosis are diverse, and their mechanisms of cell death are
different too. For instance, some stimuli can trigger cell death by apoptosis, whereas others
trigger cell death by necrosis. These are distinct cell death processes, even though apoptosis is
mostly confused with necrosis. Elmore (2007) states "It is the type of stimuli that determine if
cells die by apoptosis or necrosis; a variety of injurious stimuli such as heat, radiation, hypoxia
and cytotoxic anticancer drugs can induce apoptosis, but these same stimuli can result in necrosis
at higher doses" (p. 497). Ordinarily, stimuli that cause DNA damage in cells trigger the process
of apoptosis in which the cells are programmed to die through a cascade of cell death pathways.
This process is referred to as `programmed cell death' because it is an energy-dependent and
coordinated process that involves "a complex cascade of events that link the initiating stimuli to
the final demise of the cell" (Elmore, 2007 p.497). Therefore, this research paper will provide an
overview on the process of apoptosis.
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Distinguishing Apoptosis from Necrosis
Apoptosis is believed to be an alternative to necrosis; an energy-dependent mode of cell
death involving a toxic process to degrade cells. However, it is worth noting that, apoptosis and
necrosis involve different mechanisms, and this implies they are different. In addition, the
changes that occur in the process of cell death are differing in terms of morphology and chemical
composition.
From a distinctive approach, necrosis can be defined as cell death by injury in which cells
experience mechanical damage or they are exposed to toxic chemicals leading to DNA damage.
In necrosis, cell death exhibits a characteristic array of changes. For instance, the injured cells or
organelles such as the mitochondria swell. This swelling is caused by the disruption of water and
ions passage across the cell membrane. As a result, cytoplasmic cell contents leak out from the
cell leading to a characteristic inflammation of the tissues surrounding the injury. In contrast, cell
death by suicide (apoptosis) exhibits diverse changes in which cells are induced to undergo
suicide. The processes involved in apoptosis are orderly in which the cell shrinks to initiate
apoptotic cascades until the cell exposes the `eat me' signal on the cell membrane to facilitate
binding with phagocytes (Edmonds, 2010). In turn, phagocytes are induced to produce anti-
inflammatory agents such as TGF- and IL-10; thus inflammation does not occur in apoptosis.
Despite the morphological and mechanism differences exhibited by apoptosis and
necrosis, there is a significant overlap between these processes. It is evident that apoptosis and
necrosis "represent morphologic expressions of a shared biochemical network described as the
"apoptosis-necrosis continuum" (Zeiss, 2003 p. 493).
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Factors Leading to Cell Suicide
Evidence indicates that there are various factors that make cells commit suicide. In most
cases, cells commit suicide due to imbalances between positive and negative signals that
determine cell survival. Ordinarily, positive signals control the biological processes of the cells,
whereas negative signals impair cellular activity. Therefore, a transient balance between these
signals is necessary for cell survival or death. In most cases, cells commit suicide when positive
signals are withdrawn implying that some processes that sustain survival are interrupted; thus,
the cell cannot continue with its biological processes. As a result, the cell decides to commit
suicide. Some of the most significant positive signals are growth factors for neurons and
Interleukin-2 (IL-2). IL-2 signal plays a pivotal role in the mitosis of lymphocytes; thus, its
withdrawal disrupts cell functioning.
On the other hand, cells can consider committing suicide upon the recipient of negative
signals. In most cases, negative signals are generated when the synthesis of functional proteins is
impaired leading to the production of defective proteins that lack the tertiary structure. In
addition, negative signals are generated when oxidants accumulate within the cell leading to
DNA damage. As a result, cell death activators including lymphotoxin, Fas ligand (FasL) and
Tumor necrosis factor-alpha (TNF-) initiate the apoptosis program (Elmore, 2007). Some of the
agents that can lead to the generation of negative signals are X-rays, ultraviolet light and
chemotherapeutic drugs.
Fin de l'extrait de 14 pages
- Citation du texte
- Patrick Kimuyu (Auteur), 2018, The Molecular Basis of Apoptosis, Munich, GRIN Verlag, https://www.grin.com/document/388313
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