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Lecture 7

BIOL 130 Lecture 7: Unit 8 Cell communication
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Department
Biology
Course
BIOL 130
Professor
Heidi Engelhardt
Semester
Fall

Description
Unit 8 Cell communication 4. Contact dependent • Why do cells need to communicate with each o Cell to cell contact other? o Big in development o Cells need to work as a team – must listen to o Signal cell hands the signals from all over the body signal molecule to the ▪ Coordinating ‘whole body’ growth and receptor molecules of development with environment – day to the target cell day physiology o When yeast cells have sex – pear shaped cell is Signalling pathways called shmoo • Signalling molecule synthesized and released by signalling cell – regulated secretion Long vs. short range communication (animal cells) • Signal molecule travels to target cell – various • How signals get to their spot means (hop across synapse, diffuse, through blood • Signal producing cell – secretes signals stream) • Signal binds to receptor protein on plasma • Target cell - signal receiving cell membrane in target cell 1. Endocrine o Signal that binds to a receptor is known as a o Using the bloodstream ligand - something that binds to a receptor and heart as a pump o Signal transduction – signal is transformed into o Powerful way to send change as listed bellow signal around the • Change in protein activity (activation/ inactivation entire body in one • Change in gene expression – synthesis of proteins heart beat • Change in cell shape, movement, enzyme activity o Any cell in the body can change metabolism, secretion tht has a receptor for that signal has access to the molecule The same signal molecule can cause different o Very effective – long range communication responses depending on the target cell • Acetylcholine – very common signal molecule in 2. Neuronal mammals o It can be very long • Heart pacemaker cell o Signal molecules that o Acetylcholine binds to the are released to the outside of the 7- synapse (the tiny gap transmembrane receptor and between the synapse never gets inside of the cell – and the target cell. causes receptor in target cell o Great example of a regulated secretion (pacemaker cell in cardiac o Shows that the end of neuron loaded with muscle) to activate neurotransmitters jumps to the receptors ▪ Activation cause heart rate to slow 3. Paracrine • Salivary gland cell o Locally acting o Diffusion – lousy over o Regulated secretion o Target cell is waiting to receive long distances but signal (acetylcholine) to exocytose effective in short the salivary molecules distances • Skeletal muscle cell o Signal is released and o Ion channel is bound to a receptor o Acetylcholine is a great on a neighbouring example of a ligand that target cell binds to the outside (extracellular part of an ion channel) – causes shape change and ions rush in and muscle contracts A cell’s response can be fast or slow • Testosterone • Fast effects can be milliseconds • All derived from cholesterol – cholesterol a major • Enzymes already present – crank up activity – easy component in the lipid bilayer – so easy to move back and forth Steroid hormone mechanism of action • Steroids are evolutionarily related – their receptors are members of nuclear receptor family of transcription factors • Cortisol floats across membrane and binds to a receptor protein in the cytosol • Activated receptor is an active transcription factor • Slow • Escorted into the nucleus o Activate transcription factor – and drive transcription o Goes to nucleus and signals transcription – very slow factor o Slow but powerful o Will drive upstream regulatory sequences o Drive transcription of any cortisol dependent gene The location of the receptor can usually be predicted by the chemistry of the signal molecule • Depends on the chemistry of the signal/ ligand Most signals bind to receptors on plasma membrane • Single ligand/signal molecule binds to receptor • B) have small molecule that likes lipid (hydrophobic) protein which results in many steps – floats through membrane – no special transport • Many possible processes can be affected mechanism – finds receptor often in the cytoplasm intracellular receptor – dependent on the signal o Alter gene expression o An enzyme that is already molecule’s ability to cross the lipid bilayer there can be turned up or o This case the minority down • A) have a signal molecule that is hydrophilic o Many steps gives opportunity (protein, peptides, AAs, AAs derivatives) to modify many processes o Do not cross bilayer but can act as signals by binding to the extracellular side of a membrane Intracellular signalling cascade receptor protein • Single ligand binding o Results in transduction across the bilayer o Through the multiple steps – results in generation of hundreds of downstream messengers ▪ Known as second messengers because first messenger was the one that bound to the receptor protein outside of cell ▪ First messenger never gets into cell ▪ Second messenger – small (non-protien) molecules that are mobile that relay signals from cell surface receptors to Small hydrophobic signal molecules typically enter the cell and regulate gene transcription target molecules • Cortisol within the cell – • Estradiol cause amplification of signal Intracellular signal molecules often act as molecular Protein Phosphorylation - Turning off switch switches • Taking phosphate group off causes protein to revert • 2 very important molecular switches in cell to original inactive shape signalling that involve phosphate groups • Protein phosphatase is used to cleave phosphate • Signalling by protein phosphorylation off from target protein o Power is provided by taking phosphate off ATP and attaching it to another protein Regulation of proteins by phosphorylation o Involves a signal coming in that activates a • Turning off a signal is important as turning it on protein kinase – transfer of a phosphate group o Each activation step in a cascade needs to be onto a target protein inactivated • Signalling by GTP-Binding protein o Activity of a protein regulated by o GTP – guanine triphosphate phosphorylation depends on balance b/w o Target protein is binding the whole GTP activities of its kinases and phosphatases molecule or its bound to its GDP molecule • Many proteins regulated by phosphorylation are (phosphate is taken off) themselves kinases – phosphorylation cascades o Still got an extra phosphate in its active state • Teams of kinases and phosphatases regulating diff o But is acquiring that by trading the diphosphate target proteins and whether the protein is activated form with the triphosphate form depends on the kinase and phosphatases • Phosphorylation of proteins is not random – 2 main classes o Serine/ threonine kinases ▪ Phosphorylate hydroxyl groups of serine and threonine in specific sequences o Tyrosine kinases ▪ Phosphorylate hydroxyl groups of tyrosine Common features • Both activate proteins • Both involve Nucleoside triphosphates (ATP, GTP) – involve them in diff ways • Phosphate is added for activation of protein for both Protein phosphorylation - Turning on switch • Start with target protein – the shape that it is in – not active • Cell signalling is all about proteins changing shape • Signal comes in to the cell and activates an enzyme • All this leads to a protein activated by called a protein kinase – transfers a phosphate onto phosphorylation that triggers a cellular response a protein – and changes shape now activated can do • They are only these AAs that have available its job (transferring a phosphate) hydroxyl groups • Cleave terminal phosphate from ATP and transfer it onto a target protein. GTP binding proteins (G Proteins) – Turning on switch o Goal is to activate the target protein • Start with GTP binding protein – G protein is central o Phosphorylated target protein c
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