Exocitosis
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Exocytosis is the process of a biological cell releasing substances into the extra cellular fluid. Extra cellular fluid is the liquid around the cell. Exocytosis is needed by cells for secretion of proteins like enzymes, peptide hormones and antibodies from cells, Turnover of plasma membrane, release of neurotransmitter from presynaptic neurons, placement of integral membrane proteins, acrosome reaction during fertilization, antigen presentation during the immune response and recycling of plasma membrane bound receptors. To release stuff from the cell vessels that contain the substances that need to be released move to the plasma membrane and fuse with it.
The steps to a Membrane Fusion Reaction are:
1. The total surface of the plasma membrane increases. 2. The substances within the vesicle are released into the exterior. This can be waste products or toxins also signalling molecules like hormones or neurotransmitters during synaptic transmission. 3. Proteins that are embedded in the vesicle membrane are now part of the plasma membrane. The side of the protein that was facing the inside of the vesicle is now facing the outside of the cell. Exocytosis is very important in cellular signaling. It is not only involved in digestion, or the breakdown of particles, but also releases neurotransmitters from nerve cells. Both chemical and electrical information needs to be sent throughout the cell. Exocytosis sends and converts the electrical information into chemical information. Within the neural cells, the information is electrical now. In the synapse, after endocytosis has occurred, the neurotransmitters are released and the information is chemical. The release of the neurotransmitter can either be excitatory, causing the cell to do something else, or inhibitory, preventing the cell from doing other activities.
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