Cell Signalling Concepts PDF

Cell signalling -  **MLO12.**    Describe the various ways in which cells communicate, emphasising the key concept of cell signalling. There are three different types of cell signalling: - Endocrine: when a hormone is released from a gland, travelling through the blood around the body...

Cell signalling -  **MLO12.**    Describe the various ways in which cells communicate, emphasising the key concept of cell signalling. There are three different types of cell signalling: - Endocrine: when a hormone is released from a gland, travelling through the blood around the body and exerting a remote action, slower in comparison to neurons and synapses - Paracrine: chemical being secreted by all cells but only having to travel a short distance, localised effect - Synaptic transmission: nerve cells communicating with each other rapidly, very specific Paracrine signalling: - Synthesis and release from individual cells - Response in individual cells in a particular area - Action is local as it only spreads out by passive diffusion out of source cells - Chemical is not released into the blood - Autocrine: special case where cells will release a chemical which sends a signal to themselves that they need to be doing something (eg inflammation) - Another example is the mast cell signalling pathway Endocrine signalling: - Diffusion long distance signalling - Chemical is distributed through the blood - Controlled by nervous signals, other endocrine signals - Long range signalling - Only specific cells will respond, the cells with receptors for the particular message being released - Message is distributed around the body, slow onset and long lasting Synaptic signalling: - During nerve propagation, information is sent electrically along a cell, delivering a message over a long distance very quickly - When the message reaches the end of the neuron, it causes a secretion of a chemical - Long range electrical component - Very localised as message is directed along a nerve is goes to one specific cell type Synaptic signalling process: - Messaging molecule is synthesised and stored in vesicles which bud off from the golgi body - When needed they can fuse with the plasma membrane then releasing the chemical message - Nerve impulses travels down neuron - When it reaches the synaptic knob, it stimulates the release of prepackaged neurotransmitters into the synaptic cleft - When it travels across the cleft, the neurotransmitters bind to receptors Receptors: - Detects presence of signalling molecule in the environment, causing some form of response - Transduction: refers to whatever process is being used to convert the signal to the molecule for some sort of response - Agonists: molecules which activate the receptors, including artificial molecules such as drugs which mimic the natural ligand by sticking onto the receptors, causing it to open - Antagonists: another type of drug which binds to but doesn't actually activate the receptor, blocking it or jamming it in the closed position instead What determines how the cell responds once it's received a message? - Nothing to do with the chemical nature of the message - Depends on receptor on other side of membrane - Eg. Acetylcholine: released from motor nerve terminal, released after movement causing muscle contraction through nicotinic receptor There are four different ways in which a cell can respond to a message - Ion channels: ligand binds to ion channel, opening the channel gate, resulting in passive diffusion of ions down the electrochemical gradient - Membrane bound enzymes: effector protein embedded directly in plasma membrane, binds to ligand causing direct response - G protein coupled receptors: have a receptor on the CSM, ligand binds to receptor protein, which then signals indirectly through G proteins, which then interact with the ion channel. G protein receptors can also have direct actions through second messengers which can then affect other proteins in the cell - Intracellular receptors: receptors that are located inside the cell, ligand diffuses into cell (must be lipophilic), activating receptor, much longer term Nitric oxide: - Smallest messenger in the body - Controls vasodilation - Produced by nitric oxide synthase Eicosanoids: - 20 carbon compounds - Produced by either cyclooxygenase or lipoxygenase - Play a role in inflammation Moodle recap quiz Q: At the synapse, an -- arrives at the -- terminal. That causes the release of -- which diffuses across the -- to its -- site. Here, it binds to a - , which causes a -- potential A: action potential, presynaptic, neurotransmitter, cleft, postsynaptic, receptor, postsynaptic Q: What are the features of second messenger signalling?\ A: Can involve different pathways even from the same receptor, can mediate long lasting responses, amplifies signal triggered by receptor Q: What does the response evoked by a cell-to-cell signal depend on?\ A: The signalling pathways connected to the receptor that is activated, the type of receptor activated, how much signal arrives at the cell Q: What is autocrine signalling?\ A: acts on the same cell that produced it Q: What is paracrine signalling?\ A: Local effect on the surrounding cells, does not enter bloodstream Q: What is endocrine signalling?\ A: Secreted from glands into bloodstream -- effects on remote bloodstream Q: Neurotransmitters are generally packaged into - , except those such as - , because they are -. A: membrane bound vesicles, nitric oxide, lipophilic