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44 Cards in this Set
- Front
- Back
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Cell communication
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- cells must communicate in order to survive as a whole organism
- important in all living organisms unicellular & multicellular - cell need a combination of signals in order to survive, grow, divide and differentiate |
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Saccharomyces cerevisiae - model
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- unicellular
- a budding yeast that secretes mating factor proteins - acts a chemical signal that can be detected by other yeast cells of opposite sex - responsive cells stop cell division and mover toward signal to reproduce sexually |
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Signal Transduction
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- converting the signal that carried that information from one form to another
- begins when receptor on a target cell receives extracellular signal - converts it to a intracellular signal which can then change or modify cell behaviour |
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List types of extracellular molecules ( sending molecules)
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- Proteins - Steroids
-Peptides - fatty acid derivatives -Amino acids - dissolved gases - act as first messengers |
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Types of Extracellular Signals
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- Endocrine
- Paracrine - Autocrine - Neuronal Signalling - Direct Cell Contact |
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Endocrine Signals
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- hormones
- common form of communication - secreted from glands into bloodstream, transported to target cell - includes hormones insulin, glucagon, cortisol, testosterone - long distance signalling, slow & gradual |
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Adrenaline - Endocrine Signal
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- secreted by adrenal medulla of adrenal glands
- tyrosine amino acid based, -causes increase in BP, HR and metabolism |
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Paracrine Signals
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- diffuse locally between extracellular fluid
-DOES NOT ENTER bloodstream - act as local mediators for nearby cells e.g inflammation |
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Histamine - Local Mediator
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- secreted by mast cells of the immune system
- amino acid based ( histidine) - causes blood vessels to dilate and become leaky, - aids inflammation |
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Autocrine
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- a form of paracrine
- cells respond to local mediators that were produced by themselves - the form of cell signalling in cancer cells. |
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Neuronal Signaliing (Neurotransmitters)
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- long distance travelling ( APs), but delivered quick and specific to target cells
- sends AP which convert electrical signals to chemical ones - releases neurotransmitter that can excite or inhibit the postsynaptic cell |
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Acetylcholine - Neurotransmiiter
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- secreted by synaptic end bulbs
- derivative of choline - excitary neurotransmitter at many synapses and in CNS, - leads to muscle contraction in skeletal muscles - inhbitory role in cardiac muscle, causes the rate and contractility of the heart to decrease - different responses in different target cells |
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Direct Cell Contact
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- most short range of all extracellular signals
- signalling cells that contrain signalling molecules on their plasma membrane - interact with receptor proteins in adjacent target cells |
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Contact Cell Signal - Delta
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- developed by prospective neurons
- transmembrane protein - acts to inhibit target cell from becoming specialised like the signalling cell |
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Cell Apoptosis
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- when no signals reach the cell
- causes target cell to undergo programmed cell death |
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Name 2 ways in which Extracellular Signals bind to the target cell
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- cell surface receptors
- intracellular enzymes or receptors |
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Cell Surface Receptors - Water Soluble
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- usually involved binding of hydrophilic ( water soluble) large molecules/ non steroid molecules
- cannot diffuse across plasma membrane - binding to surface receptors initiates intracellular signals inside the cell - passed downstream from one to another until an appropriate response is made |
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Types of Cell Responses
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- metabolic enzymes ----> changes metabolism
- cytoskeletal protein -----> changes cell shape/movement - Transciption regulation ------> altered gene expression - different effector proteins - slow response if response is made in cytosol - long response if it involved entering nucleus, and altering gene expression |
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Intracellular Receptors
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- diffuse across target cell membrane easily e.g lipid soluble steroid hormones
- directly bind to intracellular receptors or bind to active site of enzymes - in either cytosol or nucleus |
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Nitric Oxide
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- act a local mediators in many tissues, due to short half life but turning to nitrate and nitrite
- diffuse out of signal cell and enter target cell - triggers smooth muscle relaxation, which increases blood flow, acts as a local vasolidator |
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Intracellular Signalling Pathways - Function
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- RELAY the signals, helping it to spread
- AMPLIFY, make it stronger - INTEGRATE, process it before relaying it foward - DISTRIBUTE signal to several intracellular pathways or effector proteins - helping to evoke a complex response |
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Phosphorylation Reactions
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- activate/inactivate proteins
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What are the 2 classes of Molecular Switches
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- kinases & G proteins ( GTP binding proteins)
- proteins that turn on other proteins in the signalling pathway - until other process switch them off again - important activation/inactivation mechanism for cell communication |
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Protein Kinase
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- adds a phosphate group to the switch protein
- often involved in phosphorylation cascades, activating more and more -made up of 2 main types - serine/threonine kinases phosphorylates serines or threonine amino acids - tyrosine kinases phosphorylate tyrosine protein |
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Protein Phosphatase
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removal of phosphate group (-de-phosphorylation)
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GTP binding proteins
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- class of switch proteins involved in intracellular signals
- switch between active/inactive state dependant on whether a GTP or GDP is bound |
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Signallng by GTP
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- GTP activates switch protein
- when activated, proteins contain GTPase hydrolyzing activity - they shut themselves off by hydrolyzing bound GTP to GDP ( become dephosphorylated) |
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Ion Channel Coupled Receptors
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- allow inflow of ions (NA2+ or K+) accross the plasma membrane
- changes resting membrane potential - important in the generation of nerve and muscle action potentials - important in neurotransmitters |
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G protein coupled receptors
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- signalling molecule binds to extracellular receptors
- activates membrane bound GTP binding proteins ( G proteins) - in turn activates an enzyme or ion channel, initiates a cascade of other effects - more than 700 types of GPCRS in humans |
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Enzyme Coupled Receptors
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- binds to extracellular signal
- causes intracellular enzymes to switch one on the cytosolic side on plasma membrane - some include own enzyme or associated enzyme that bind also to intracellular receptors |
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G Protein - Subunits
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- 3 subunits ( Alpha, Beta, Upsilon (Y))
- Alpha and upsilon attached to short lipid tails located on plasma membrane |
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G protein - Inactivated State
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- Alpha subunit contains bound GDP
- G protein is idle |
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G protein Activated State
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- extrcellular ligand ( neuroransmitter or hormone) binds to its receptor
- activates a G protein - causes alpha subunits affinity for GDP to decrease - converts it to GTP - Alpha subunits contain intrinsic GTPase which phospylates it back to GDP ( inactivated conformation) - ready to cycle again for next signal |
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Cholera - Homeostatic Imbalances
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- bacteria multiplies in intestines and produces cholera toxin proteins
- which is able to modify the alpha subunit of a particular type of G protein (Gs) - causes the stimulation of adenyl cyclase, remain activated cannot dephosphorylate - causes excessive inflwo of CL- ions and H2O into the gut - causes diarrhoa and dehydration |
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Whooping Cough - Homeostatic Imbalances
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- also known as Pertussis
- respiratory infection - inhbitis alpha subunit of GI protein, inhbits adenyl cyclase - remain inactivated in GDP bound state - leads to inappropriate signals which stimulate coughing |
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Adenylyl Cyclase
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- a membrane bound enzyme
- is activated and binded by the G protein's alpha subunits bound with GTP -it catalyzes the conversion of ATP to cAMP ( cyclic adenosine monophosphate) & inorganic pyrophosphate (PPi) - removes 2 phosphate groups - so produces intracellular signalling molecule |
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Phospolipase C
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- enzyme responsible for production of intracellular signalling molecules
- can also be activated by G proteins like Adenylyl Cyclase - inositol trisphosphate - diaryl glycerol |
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Second Messengers
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-intracellular signals produced in large numbers
- proliferate due to activation of membrane bound enzymes ( Adenylyl Cyclase and Phospolipase C) - rapidely diffuse away from origin, to amplify the signal e.g cAMP |
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cAMP
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- water soluble, diffuse through the cell easily
- interacts with proteins/organelles - important intracellular signalling molecule - activates other molecules such as cAMP protein kinase A (PKA) |
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cAMP phosphodiesterase
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- second enzyme that rapidly breaks down cAMP
- converting cAMP to ordinary AMP |
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Caffeine - Medical Connection
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- acts as stimulant as it inhits cAMP phosphodiesterase enzyme in nervous tissue
- cAMP degradation does not occur, which keep concentration levels high |
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cAMP mediated responses - Examples
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- Adrenaline - causes an increase in HR and contractility in cardiac muscle, causes glycogen breakdown in skeletal muscle
- Adrenaline, ACTH, glucagon - causes fat tissue breakdown |
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cAMP - gene transcription
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- actives PKA, which move into nucleus
- causes phosphorylation transcription regulators - proteins stimulate transcription of target genes - involved in hormone synthesis ( signals themselves) & proteins involved in memory |
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Phospolipase C mediated responses - Examples
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- ADH, in liver tissue results in glycogen breakdown
- Acetylcholine, pancreas cells, secretes amylase enzyme |
