All living organisms are made up of cells that could comprise the entire animal as in bacteria or which build up their organs and body systems. This has been used as a basis to claim that they must have descended from one source via evolution. Cells are therefore very essential for life to continue and are simply defined as being the basic units of living creatures. Since it takes the collective functioning of the cells to carry out the life-supporting functions, it’s very critical that these cells communicate. Cell communication is the process whereby a cell exchanges basic and essential substances like gases, nutrients, and wastes. Complex communication involves carrying out very complex activities like reproduction, among other physiological reactions. Cell signaling enables this to take place since it’s more advanced than a simple diffusion process. It assists in coordinating the functions of different cells far apart. These actions help to repair damaged tissues, enable the development process, and carry out immunity functions and other homeostatic functions.
The Difference between Cell Communication in Complex and Simple Organisms
The communication in simple cell complex animals is definitely very different. This is simply because complex organisms have millions of cells that are diversely specialized for different functions and are also very far apart in some cases (Alberts 1998). The basic means include cell to cell for those cells that are in contact. Cell membranes are uniquely specialized for communication. The cell membranes contain protein receptors that are able to bind and transfer substances across the cell membrane. Simple processes help to carry out such simple procedures as a simple diffusion process, facilitated diffusion, or osmosis (Alberts 1998).
Complex organism requiredorganismsnals to be transported to distant cells through the circulatory systems so that the message can be conveyed to the recipient. There are specialized transport mechanisms or protein carriers that carry the signals in the vessel (Alberts, 1998). Some chemicals are transported in inactive forms which are activated once they react with the receptors. An example is nor-epinephrine.
Ways of Cell Communication
These simple ways of communication and signalareing is very critical in the reproduction of single-celled organisms like bacteria or yeast cells. The receptors on their membranes are designed in a key and lock manner between the two sexes so that they are able to fit perfectly, fuse, fertilize and begin the process of fission. This produces even more cells (Alberts, 1998). Simple cell communication is more direct and this is described as Juxtacrine signaling. Signaling can be over very short distances in advanced animals and this takes place via a process called paracrine signaling. Long-distance communication is the endocrine signaling. When cells are close, protein receptors enhance the process of communication (Niehoff 2005). However, for a faster communication, cells have evolved some efficient parts of cell communication termed gap junctions. These features enable cells to connect the cytoplasm of neighboring cells. Heart cells enjoy the services of these special features which allow faster propagation of impulses. Notch signaling is a special juxtacrine signaling process that allows specialized cell differentiation during embryonic development (Niehoff 2005).
Complex cell communication requires that signals be carried by another mechanism to its receptors. This is very common in hormone communication. Endocrines glands secrete these chemicals called hormones in order to carry out certain physiological reactions (Niehoff 2005). These chemicals are transferred through blood. However, some chemical only target the neighboring cells. This are termed paracrine signals. Examples of these chemicals are the neurotransmitters like acetylcholine, noradrenalin and dopamine among others.
Adrenaline can act as a hormone and a neurotransmitter. When hormones have traveled to the receptor cells, they have to be recognized for them to be able to elicit any kind of response. The signal or the information carried has to be “translated” or transduced so that the cell can react it the proper manner (Niehoff 2005).
Cell signalizing is very critical for communication to occur. This process takes place in three basic stages namely; Signal reception, Signal transduction and Cell response:
Signal reception: the target cell usually has a membrane protein that forms the signal receptor. This receptor is able to recognize the signal, a process that occurs when the receptor binds the signal. These receptors are also very specific and have a complementary shape to that of the signal (Garther, Hiatt & Strum 2007). The signal is at times referred to as a ligand. Upon binding, the receptor undergoes conformational changes in shape. The change in shape further activated the receptor to interact with other molecules inside the cell. Otherwise, the reaction can result in aggregation of the receptor and thus elicit a series of events inside the cell (Garther et al 2007).
It’s important to note that the receptors could be transmembrane or inside the membrane. Hydrophobic signals pass through the membrane to reach their receptors while hydrophilic molecules have to pass through gates or receptors. Most of the cells have transmembrane and membrane proteins as receptors (Garther et al 2007). The common one is the G – Protein-linked type of receptor. This works in conjunction with another protein in most cases enzymes. The G-protein is usually inactive when there is no signal. It has three protein sub-units and a GDP molecule (Guanosine Di-phosphate). Upon binding the signal, the protein changes in conformation to take up GTP – Guanosine Tri-Phosphate (Garther et al 2007). The free G-protein binds the enzyme which in turn triggers a cascade of events resulting in the response of the cell.
The second group of receptors uses tyrosine- kinase to bring forth a reaction. When not activated by a signal, the tyrosine kinase is a single protein molecule in the cell membrane. The molecule acts as an enzyme and substrate. Upon binding, the molecule phosphorylates and releases the tyrosine residues which can then initiate different reaction pathways (Garther et al 2007).
There are also ion channels that open up once a ligand is bound. As the name indicated, these gates open and let in or out some ions like Na+ or Ca2+. An example of such a mechanism takes place at the neuromuscular junction when acetylcholine binds its receptors and causes calcium channels to open causing an influx of the ions needed for muscle contraction and relaxation (Garther et al 2007).
Signal transduction takes several pathways. They include the enzyme cascade, second messenger signal (cyclic AMP, Cyclic GMP), cholera toxin, and Ca ions signal. The enzyme cascade process activates the respective enzymes by phosphorylation of the protein Kinase. The ATP is then reduced to ADP, therefore, activating it (Friedman & Friedman 2004). The benefit of the transduction stage is the amplification of the signals. Many cycles of activation cause the signal to increase and have a greater impact. This means that a very small signal can translate to a major physiological response. The common process of transduction is protein phosphorylation (Friedman & Friedman 2004).
The process starts by binding a ligand to the specific receptor. The receptor then changes to release the G – protein. Protein kinase is activated to protein kinase 1. This then transfers a phosphate group from ATP and hence activates protein kinase 2, this, in turn, catalyzes further phosphorylation of protein kinase 3. This is the final enzyme that binds to the cell’s reaction to the signal (Friedman & Friedman 2004). The kinases are activated by removing Phosphates that are available for recycling.
Second messengers are very critical in signaling pathways. The signal or ligand is considered the first messenger. Cyclic AMP is the most common second messenger. It’s come to play when the sub-unit of the G-protein binds to GTP and activates an enzyme called adenyl cyclase. This enzyme activates cAMP which in turn binds the inhibitory subunit of an enzyme. The inhibitory unit is then cleaved off by phosphorylase A hence activating the enzyme in question (Friedman & Friedman 2004).
All living things depend on cells for performing various activities. Cell communication is not only necessary but consistent with life. Many of the activities that result from these communications are very essential in sustaining a living organism. Efficient synchronization is an unconditional prerequisite thr the safe functioning of the organism.
Alberts B. 1998. Essential Cell biology- An Introduction to the Molecular Biology of the cell. London: Taylor & Francis. 134 p.
Friedman M & Friedman B. 2004. Cell Communication. Understanding How Information Used in Cells. New York: The Rosen Publishing Group. 89Gatherther L.P, Hiatt J.L, & Strum J.M 2007. Cell Biology and Histology. Philadelphia: Lippincott Williams & Wilkins
Niehoff D. 2008. The Language of Life- How Cells Communicate in health. Washington, D. C.: National Academies Press