Cellular Communication---Cell Biology | Study notes Biology

Cellular communication

Cellular communication is an umbrella term used in biology and more in depth in biophysics and

biochemistry to identify different types of communication methods between living cells. Some of the

methods include cell signaling among others. This process allows millions of cells to communicate and

work together to perform important bodily processes that are necessary to survival. Both multicellular

and unicellular organisms heavily rely on cell-cell communication

Intercellular communication

Intercellular communication refers to the communication between cells. Membrane vesicle trafficking

has an important role in intercellular communications in humans and animals, e.g., in synaptic

transmission, hormone secretion via vesicular exocytosis. Inter-species and interkingdom signaling is the

latest field of research for microbe-microbe and microbe-animal/plant interactions for variety of

purposes at the host-pathogen interface.

Three stages of cell communication

Reception

A G Protein-coupled receptor within the plasma membrane.

Reception occurs when the target cell (any cell with a receptor protein specific to the signal molecule)

detects a signal, usually in the form of a small, water-soluble molecule, via binding to receptor protein.

Reception is the target cell's detection of a signal via binding of a signaling molecule, or ligand. Receptor

proteins span the cell’s plasma membrane and provide specific sites for water-soluble signaling

molecules to bind to. These trans-membrane receptors are able to transmit information from outside

the cell to the inside because they change conformation when a specific ligand binds to it. By looking at

three major types of receptors, (G protein coupled receptors, receptor tyrosine kinases, and ion channel

receptors) scientists are able to see how trans-membrane receptors contribute to the complexity of cells

and the work that these cells do. Cell surface receptors play an essential role in the biological systems of

single- and multi-cellular organisms and malfunction or damage to these proteins is associated with

cancer, heart disease, and asthma.

Transduction

When binding to the signaling molecule, the receptor protein changes in some way and starts the

process of transduction. A specific cellular response is the result of the newly converted signal. Usually,

transduction requires a series of changes in a sequence of different molecules (called a signal

transduction pathway) but sometimes can occur in a single step. The molecules that compose these

pathways are known as relay molecules. The multistep process of the transduction stage is often

composed of the activation of proteins by addition or removal of phosphate groups or even the release

of other small molecules or ions that can act as messengers. The amplifying of a signal is one of the

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Cellular communication Cellular communication is an umbrella term used in biology and more in depth in biophysics and biochemistry to identify different types of communication methods between living cells. Some of the methods include cell signaling among others. This process allows millions of cells to communicate and work together to perform important bodily processes that are necessary to survival. Both multicellular and unicellular organisms heavily rely on cell-cell communication Intercellular communication Intercellular communication refers to the communication between cells. Membrane vesicle trafficking has an important role in intercellular communications in humans and animals, e.g., in synaptic transmission, hormone secretion via vesicular exocytosis. Inter-species and interkingdom signaling is the latest field of research for microbe-microbe and microbe-animal/plant interactions for variety of purposes at the host-pathogen interface. Three stages of cell communication Reception A G Protein-coupled receptor within the plasma membrane. Reception occurs when the target cell (any cell with a receptor protein specific to the signal molecule) detects a signal, usually in the form of a small, water-soluble molecule, via binding to receptor protein. Reception is the target cell's detection of a signal via binding of a signaling molecule, or ligand. Receptor proteins span the cell’s plasma membrane and provide specific sites for water-soluble signaling molecules to bind to. These trans-membrane receptors are able to transmit information from outside the cell to the inside because they change conformation when a specific ligand binds to it. By looking at three major types of receptors, (G protein coupled receptors, receptor tyrosine kinases, and ion channel receptors) scientists are able to see how trans-membrane receptors contribute to the complexity of cells and the work that these cells do. Cell surface receptors play an essential role in the biological systems of single- and multi-cellular organisms and malfunction or damage to these proteins is associated with cancer, heart disease, and asthma. Transduction When binding to the signaling molecule, the receptor protein changes in some way and starts the process of transduction. A specific cellular response is the result of the newly converted signal. Usually, transduction requires a series of changes in a sequence of different molecules (called a signal transduction pathway) but sometimes can occur in a single step. The molecules that compose these pathways are known as relay molecules. The multistep process of the transduction stage is often composed of the activation of proteins by addition or removal of phosphate groups or even the release of other small molecules or ions that can act as messengers. The amplifying of a signal is one of the

benefits to this multiple step sequence. Other benefits include more opportunities for regulation than simpler systems do and the fine- tuning of the response, in both unicellular and multicellular organism. Response A specific cellular response is the result of the transduced signal in the final stage of cell signaling. This response can essentially be any cellular activity that is present in a body. It can spur the rearrangement of the cytoskeleton, or even as catalysis by an enzyme. These three steps of cell signaling all ensure that the right cells are behaving as told, at the right time, and in synchronization with other cells and their own functions within the organism. At the end, the end of a signal pathway leads to the regulation of a cellular activity. This response can take place in the nucleus or in the cytoplasm of the cell. A majority of signaling pathways control protein synthesis by turning certain genes on and off in the nucleus. [4] Local and long distance signaling Local Communicating through direct contact is one form of local signaling for eukaryotic cells. Plant and animal cells possess junctions that connect the cytoplasm of cells adjacent to one another. These connections allow for signaling substances that were dissolved in the cytosol to easily pass between the cells that are connected. Animal cells contain gap junctions and can communicate through these junctions in a process called cell-cell recognition. Plant cells are connected through plasmodesmata. Embryonic development and the immune response rely heavily on this type of local signaling. In other types of local signaling, the signaling cell secretes messenger molecules that only travel short distances. These local regulators influence cells in the vicinity and can stimulate nearby target cells to perform an action. A number of cells can receive messages and respond to another molecule within their vicinity at the same time. This process of local signaling within animal cells is known as paracrine signaling. Long distance Hormones are used by both plant and animal cells for long-distance signaling. In animal cells, specialized cells release these hormones and send them through the circulatory system to other parts of the body. They then reach target cells, which can recognize and respond to the hormones and produce a result. This is also known as endocrine signaling. Plant growth regulators, or plant hormones, move through cells or by diffusing through the air as a gas to reach their targets. Cell signaling and impacts There are three different types of basic cell communication: surface membrane to surface membrane, exterior, which is between receptors on the cell, and direct communication, which means signals pass inside the cell itself. The junctions of these cells are important because they are the means by which cells communicate with one another. Epithelial cells especially rely on these junctions because when one is injured, these junctions provide the means and communication to seal these injuries. These junctions are especially present in the organs of most species.[5] However, it is also through cell signaling that tumors and cancer can also develop. Stem cells and tumor-causing cells, however, do not have gap

involving hundreds to millions of molecules. As with other signals, the transduction of biological signals is characterised by delay, noise and interference, which can range from negligible to pathological.[5] With the advent of computational biology, the analysis of signalling pathways and networks has become an essential tool to understand cellular functions and disease. STIMULI CAN BE: 1:LIGANDS The majority of signal transduction pathways involve the binding of signalling molecules, known as ligands, to receptors that trigger events inside the cell. The combination of a signaling molecule with a receptor causes a change in the conformation of the receptor, known as receptor activation. Most ligands are soluble molecules from the extracellular medium which bind to cell surface receptors. These include growth factors, cytokines and neurotransmitters. Components of the extracellular matrix such as fibronectin and hyaluronan can also bind to such receptors (integrins and CD44, respectively). In addition, some molecules such as steroid hormones are lipid-soluble and thus cross the plasma membrane to reach nuclear receptors.[8] In the case of steroid hormone receptors, their stimulation leads to binding to the promoter region of steroid-responsive genes.[9] Not all classifications of signalling molecules take into account the molecular nature of each class member. For example, odorants belong to a wide range of molecular classes,[10] as do neurotransmitters, which range in size from small molecules such as dopamine[11] to neuropeptides such as endorphins.[12] Moreover, some molecules may fit into more than one class, e.g. epinephrine is a neurotransmitter when secreted by the central nervous system and a hormone when secreted by the adrenal medulla. 2:OSMOLARITY Cellular and systemic control of osmotic pressure (the difference in osmolarity between the cytosol and the extracellular medium) is critical for homeostasis. There are three ways in which cells can detect osmotic stimuli: as changes in macromolecular crowding, ionic strength, and changes in the properties of the plasma membrane or cytoskeleton (the latter being a form of mechanotransduction).[17] These changes are detected by proteins known as osmosensors or osmoreceptors. In humans, the best characterised osmosensors are transient receptor potential channels present in the primary cilium of human cells.In yeast, the HOG pathway has been extensively characterised 3: MECHANICAL FORCES The prevalence of basement membranes in the tissues of Eumetazoans means that most cell types require attachment to survive. This requirement has led to the development of complex mechanotransduction pathways, allowing cells to sense the stiffness of the substratum. Such signalling is

mainly orchestrated in focal adhesions, regions where the integrin-bound actin cytoskeleton detects changes and transmits them downstream through YAP1.[14] Calcium-dependent cell adhesion molecules such as cadherins and selectins can also mediate mechanotransduction.[15] Specialised forms of mechanotransduction within the nervous system are responsible for mechanosensation: hearing, touch, proprioception and balance 4:TEMPERATURE The sensing of temperature in cells is known as thermoception and is primarily mediated by transient receptor potential channels.[20] Additionally, animal cells contain a conserved mechanism to prevent high temperatures from causing cellular damage, the heat-shock response. Such response is triggered when high temperatures cause the dissociation of inactive HSF1 from complexes with heat shock proteins Hsp40/Hsp70 and Hsp90. With help from the ncRNA hsr1, HSF1 then trimerizes becoming active and upregulating the expression of its target genes.[21] Many other thermosensory mechanisms exist in both prokaryotes and eukaryotes. 5:LIGHT In mammals, light controls the sense of sight and the circadian clock by activating light-sensitive proteins in photoreceptor cells in the eye's retina. In the case of vision, light is detected by rhodopsin in rod and cone cells.[22] In the case of the circadian clock, a different photopigment, melanopsin, is responsible for detecting light in intrinsically photosensitive retinal ganglion cells. RECEPTORS: TWO TYPES EXTRACELLULAR

G-PROTEIN-COUPLED RECEPTOR
TYROSINE AND HISTIDINE KINASE
INTEGRINS
TOLL LIKE RECEPTORS
LIGANDS GATED ION CHANNELS

INTRACELLULAR

1. NUCLEAR RECEPTORS

2. CYTOPLASMIC

Second messengers First messengers are the signaling molecules (hormones, neurotransmitters, and paracrine/autocrine agents) that reach the cell from the extracellular fluid and bind to their specific receptors. Second messengers are the substances that enter the cytoplasm and act within the cell to trigger a response. In essence, second messengers serve as chemical relays from the plasma membrane to the cytoplasm, thus carrying out intracellular signal transduction.

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INTRACELLULAR

1. NUCLEAR RECEPTORS

2. CYTOPLASMIC