What are caspases and how do they participate in apoptosis process? PDF

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This is a short essay style answer for the 2016/17 past exam question: What are caspases and how do they participate in apoptosis process? ...

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Q. What are caspases and how do they participate in apoptosis process? Apoptosis is the programmed death of a cell it was planned by the cell itself within multicellular organisms and can therefore be described as ‘cell suicide’. Apoptosis has specific morphological features by which it can be identified. All cells live for a different length of time before being replaced by the organism with new cells. For example, red blood cells can live up to 120 days, whereas a skin cell may only live up to two weeks. In a human body, about 50 to 70 billion cells die a day. These cells may die off for a number of reasons, one of which is age, cells have a given lifespan, when exceeded, the are killed. If a cell undergoes irreparable damage it must be killed and replaced. Other cells that may possibly be dangerous to the organism due to the infection of a virus, or cancerous cells are also targeted for apoptosis. The body may also want to remove superfluous cells during development by killing said cells Therefore, there are a number of reasons to which the body wants to control the death of cells. Apoptosis may be described as a natural form of cell death. It functions to remove damaged, superfluous, and dangerous cells from the body, without inducing inflammation. There are a number of steps involved in the process of apoptosis. First, the targeted cell separates from its neighbouring cells. From here, the cell begins to shrink, and undergoes membrane blebbing. Membrane blebbing is a process by which bulges occur in the plasma membrane. The nucleus then begins to fragment whilst the chromatin condense, the remainder of the intracellular organelles, such as mitochondria, ribosomes and lysosomes however, stay intact. These organelles and fragmented parts migrate to the blebs where the entire cell is then broken up into several apoptotic bodies. These apoptotic bodies are then phagocytosed so as to complete the process. Apoptosis consists of a predictable and reproducible sequence of events in which no trace is left of the cell. CED-3 proteins are proteolytic enzymes found in C. elegans. Caspases are CED-3-like proteins. They are essentially the human counterpart of CED-3. They are cysteine-dependant aspartic acid-specific proteases. This means that this proteolytic enzyme which is specific for aspartic acid, has a cysteine residue at the active site and is required for catalytic activity. Therefore aspartic-specific proteases function to cleave substrate proteins at aspartic acid residues. In the case of apoptosis, caspases dismantle most of the cellular structures, this includes the cytoskeleton, cell junction, mitochondria, endoplasmic reticulum, Golgi, and the nucleus. This is a very specific process affecting about 500 proteins in total in an irreversible process. Caspases are formed by a tetramer of 2 small subunits and 2 large subunits. This then forms an active site on either side of the tetramer. Caspases are important to apoptosis and play a central role in inducing almost all features of apoptosis. They play a part in cleavage and rearrangement of cytoskeletal proteins to nuclear fragmentation to membrane blebbing, with multiple other key features in between. Their main roles involve the inactivation of proteins that protect living cells, such as the cleavage of ICAD, Bcl-2 proteins, and the destruction of nuclear lamins....