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Lecture 10

BIO1140 Lecture 10: Signal Transduction I

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University of Ottawa
Caroline Petit- Turcotte

Signal Transduction Reactions between cells and how they communicate with each other/ interpret that message, how it’s received and how the cell deals with it and makes several different messages. Must interpret and create a cellular response. These are more positive outcomes. The foundation for signal transduction and how it will lead us into the next topics. Will stay for the rest of the semester. Mechanisms how cells interpret their environment pick up on different types of molecules and act upon them are mechanisms that are well conserved throughout evolution, between species, different processes (I.e. making sure that organisms and cells can develop and defend against pathogens or react against changes in their environment, etc.) Smart Bio Videos: how cells respond and give off signals in the environment -the message itself: what can we send from one cell to another to elicit a response? The message must be received. If nothing receives that message or interacts with the message, it’s going to be a chemical messenger and the cell will be oblivious to the message that is sent. Once it is read, you must be able to understand, interpret it—deciding what the cell should do and how it should respond to it. Sometimes, the message should be priority number one and other times, it should be simply ignored and an entire gradient of responses between. The cell must act upon what’s interpreted, and what is the best outcome. It should also act on the cell: growing, dividing, dyeing, etc. Neural activity involves transmission of information via ______; in contrast, endocrine activity involves transmission information via _______? A- Electrochemical evens; hormone transport to target tissues B- Hormone transport; hormone release in body fluids C- Electrical events; hormone transport through electrical signals D- Hormone transport; hormone transport to target tissues ANSWER: A We do not transmit neural information through electricity, it is those fluctuations in the electrochemical gradients, difference in flow of ions, how the action potential is sent down the cell. Communication between cells that was direct communication. Exchange of small ions, small molecules from one cell to another (i.e. gap junctions) - Signal transduction: to reach cells that are both near and far o To be done quickly and efficiently - There are different paths where this can be done - Nature of the path depends on the physical properties of the chemical messengers - Look at the paths and match the messengers that can be used for each of them The target tissues for steroids do not have receptors for them on the membrane surface, because steroids… A- Can enter the cell by facilitated diffusion B- Alter the membrane potential of the cell, leading to cellular responses C- Are soluble in the lipid bilayer D- Are transported against their concentration gradient by active transporters in the cell membrane Answer: C - Soluble; They’re able to freely diffuse and go across both layers of the membrane, so they can find the receptors, the structures, proteins that can recognise the steroids, bind to them and help the cell make the decision to make a cellular response. Will find them in the cell—in the cytoplasm or in the nucleus. It’s true for lipophilic messengers. 6 Classes of chemical messengers. - Steroids, lipids, peptides/proteins, purines, amines, gasses - Steroids: lipophilic, derived from cholesterol, should be able to recognise a general structure for steroids. Sorted into 3 classes – Based on the kinds of cellular classes they’re responsible for i.e. sex hormones, glucocorticoids (cholesterol) and mineralocorticoids—such as aldosterone, which helps regulate water and ions in different tissues (i.e. salts, minerals and water content); they are lipophilic and cannot package in vesicles, will be diffused across the membrane forming the vesicle—will be used on demand to anchor and transport in hydrophilic environments, such as the bloodstream. - Steroids vs. other chemical messengers o Steroids enter the cell, which hydrophilic compounds never do and when bound to receptors, the complex is immediately enabled as a transcription factor (initiates the transcription of DNA to mRNA—proteins bind to sequences of the DNA, and it activates or puts a stop of DNA to mRNA) o When steroids bind to receptors, it forms a transcription factor - Eicosanoids: from phospholipids—forms eracodonicacid and it is further modified of 1 of 2 enzymatic pathways, and could get one of 2 families of Eicosanoids—prostaglandins or lupatrians(?), involved in inflammation and pain and they act locally. They are lipophilic and act in an autocrine or paracrine pathway. o Autocrine: cell secretes the messenger, to act upon it o Paracrine: secretes the messenger, diffuses locally and act upon the neighbouring cells. This is a very short distance - - Peptides and proteins o Proteins packaged in vesicle to be ready when cell wishes to secrete the peptide/protein (i.e. glucagon, insulin, etc.) o What proteins would you favour? Needs to be packaged in a vesicle. Needs to be globular, soluble protein. These proteins will have catalytic or enzymatic activity. Do not want to be active when packaged in vesicle—will package in an inactive form, additional process which prevents the activity from being turned on. Will package the enzyme proteases that are responsible for cutting the peptide bond and ridding the pro-sequence. When it’s released, the enzyme is activated, cleaves the pro-portion and the enzyme is active. o Will talk about protein synthesis, sorting, secretion in detail later. o Amines ▪ Need a group on these messengers • Derived or biosynthesised from amino acids, r they are a.a.s • Can package in vesicles • When cell needs to secrete, it is already there—quick response in relaying to next cell • Often NTs • Do have an exception, thyroid hormones are hydrophobic, cannot package in vesicles, must be produced and secreted on demand o Purines o Theobromine—found in chocolate and caffeine ▪ Caffeine exacerbates the effects of the stress hormone, cortisol! o Derived from adenine or guanine o Characteristic rings - Gasses o Direct communication and indirect communication ▪ Cannot travel far, have half-lives, however, they are essential…we survive on gasses ▪ They tend to passively diffuse across the membrane due to their size ▪ No need to have specific transport molecules and won’t need specific receptors as they can act directly on their targets. Receptors Cell must be
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