Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
83 Cards in this Set
- Front
- Back
|
What two types of receptors receive signals at the cell surface?
|
- G-protein couple receptors
- Enzyme coupled receptors |
|
|
What is the difference between small intracellular mediators/second messengers and large intracellular signaling proteins?
|
Small:
- generated in large numbers in response to receptor activation - diffuse away from source and spread signals to other cell parts - alter conformation and behaviour of selected signaling proteins or effector proteins Large: - generate small intracellular mediators OR activate next signaling/effector protein |
|
|
What are the 8 types of signal transduction?
|
1. Relay - from one signaling component to the next
2. Scaffold - bring 2 or more signaling proteins together so that they can interact more quickly and efficiently 3. Transduce - transform the signal into a different form 4. Amplify - by producing large amounts of a small intracellular mediator or by activating many copies of a downstream signaling protein, small number of extracellular signal molecules can evoke a large intracellular response 5. Integrate - receive signals from 2 or more signaling pathways and integrate them before relaying a signal onward 6. Spread - from one signaling pathway to another 7. Anchor - insures one or more signaling proteins in a particular structure of the cell where they are needed 8. - regulate other signaling proteins and therefore the strength of signals along the pathway |
|
|
What are molecular switches? What are the two main groups?
|
- switch between active and inactive conformation
1. activated or inactivated by phosphorylation 2. activated or inactivated by GTP binding |
|
|
How do molecular switches work that are (in)activated by phosphorylation?
|
- switch thrown in one direction by a protein kinase which adds phosphate groups
- switch thrown in the other direction by a protein phosphatase which removes a phosphate group |
|
|
What is a phosphorylation cascade?
|
- one protein kinase, activated by phosphorylation, phosphorylates the next protein kinase and so on to amplify or spread the signal
|
|
|
What are the two main types of protein kinases?
|
1. Serine/Threonine kinases - majority, phosphorylate proteins on serines and threonines
2. Tyrosine kinase - phosphorylate proteins on tyrosines - occasionally a kinase can do both |
|
|
How many protein kinases and protein phosphatases does the humane genome have?
|
- 520 protein kinases
- 150 protein phosphatases |
|
|
What percentage of human proteins can be activated or inactivated by phosphorylation?
|
30 %
|
|
|
How do molecular switches that are (in)activated by GTP binding work? And what are the two main types?
|
- on when GTP is bound, off when GDP is bound
- GAP drives protein into "off" state, GEF drives protein into "on" state 1. G-Proteins/Trimeric GTP binding proteins - help relay signals from G-protein coupled receptors that activate them 2. Monomeric GTP binding domains/Monomeric GTPases - help relays signals from many classes of cell-surface receptors |
|
|
How does the intracellular signaling cascade work for the animal fibroblast growth factor?
|
- growth factor binds to fibroblast growth factor receptor on kinase domains after ADP is phosphorylated to ATP
- kinase domains lead to MAP kinase cascade: Raf-->MEK-->MAPK are all phosphorylated in turn - this then activates transcription factor which transcribes genes |
|
|
How does the intracellular signaling cascade work for the plant brassinosteroid pathway?
|
- phosphorylation causes kinase domains of brassinosteroid to come together in dimerization
- this leads to signaling cascade until BIN2 kinase enters nucleus - this leads to phosphorylation of the negative regulator that inhibits the transcription factor and forces it to leave the nucleus so transcription can begin |
|
|
How does the intracellular signaling cascade work for the auxin pathway in plants?
|
- AUX/IAA repressor protein inhibits Arf transcription factor preventing transcription
- Auxin and E3 ligase complex are added to AUX/IAA repressor and this is then ligated with ubiquitin for protein degradation in the proteasome, allowing transcription factor to be activated |
|
|
What are scaffold proteins and what do they do?
|
- bind together groups of interacting signaling proteins into signaling complexes
- allows components to interact at high local concentrations and be sequentially activated speedily, efficiently and selectively |
|
|
What are transient signaling complexes and what do they do?
|
- form only in response to an extracellular signal and rapidly disassemble when the signal is gone
- activated receptor often phosphorylates itself at multiple sites which then act as docking sites for intracellular signaling proteins |
|
|
What are the four main functions of scaffold proteins according to Good et al?
|
1. Specify linear pathway
2. Pathway branching 3. Target for external regulation 4. Mediate feedback, shape response dynamics (can phosphorylate themselves for negative feedback) |
|
|
How do pathogens use scaffolds? Ex. HIV
|
- pathogens bring together 2 proteins or kinases that would never interact naturally, or make new scaffolds or rewire existing ones to lead to improper activity
Ex. HIV makes unnatural scaffold and ligates anti-viral enzyme causing it to degrade and thereby inactivating the host's defense |
|
|
What are the five ways a cell can become desensitized to a signal?
|
1. Receptor sequestration - binding of signal molecules to receptors may induce the endocytosis and temporary sequestration of the receptors in endosomes
2. Receptor down-regulation - destruction of receptors in lysosomes 3. Receptor inactivation - receptor on cell surface is desensitized by phosphorylation or some similar method 4. Inactivation of signaling protein 5. Production of inhibitory protein that blocks signal transduction |
|
|
What are GPCRs?
|
G-Protein Coupled Receptors
- largest family of cell-surface receptors, all use G-protein to relay signal to cell interior - exist in all eukaryotes - responsible for sense of smell, sight, taste, etc - all have a very similar structure of 7 transmembrane domains which shift toward each other to activate - mediates the interaction between activated receptor and target protein/enzyme to begin signal transduction in cell - more than 700 GPCRs in humans |
|
|
What is the structure of the G-protein?
|
- has alpha and gamma subunits with beta in between
- alpha and gamma both have lipid anchors attaching them to plasma membrane - in inactive form alpha has GDP attached |
|
|
How is the G-protein activated?
|
- binding of an extracellular signal to a GPCR changes the conformation of the receptor, which in turn alters the conformation of the G Protein
- the alpha subunit exchanges GDP for GTP activating both the alpha subunit and the beta-gamma complex - usually followed by dissociation of alpha from beta-gamma but not always |
|
|
What is RGS?
|
Regulator of G-Protein Signaling
- same function as GAP, help shut off G-protein mediated responses by exchanging GTP for GDP |
|
|
What can the alpha complex and beta-gamma complex of the G-protein do once they are activated?
|
- regulate the activity of target proteins
- regulate the activity of RGS in the plasma membrane - catalyze the activation of many other G-Proteins |
|
|
What is cAMP?
|
Cyclic AMP
- small intracellular mediator in all prokaryotic and animal cells - normal concentration in the cytosol is very low (about 10^-7 M) but an extracellular signal can increase the concentration dramatically in seconds |
|
|
How can changes in the concentration of cAMP be monitored?
|
- load a cell with a fluorescent protein that changes colour when it binds cAMP so you can watch the dramatic increase
|
|
|
How is cAMP synthesized and destroyed?
|
- cAMP is synthesized from ATP by adenylyl cyclase
- it is also rapidly and continually destroyed by cyclic AMP phosphodiesterases that hydrolyze cAMP to 5'-AMP |
|
|
How is cAMP concentration inside a cell increased?
|
- adenylyl cyclase must be more active that cAMP phosphodiesterase
|
|
|
How does the cholera toxin work?
|
- enzyme that catalyzes transfer of ADP ribose to alpha subunit of stimulatory G protein (Gs) so that it can no longer hydrolyze GTP
- this causes the Gs to remain active and continually stimulate adenylyl cyclase production leading to an increase in cAMP - the increase in cAMP causes an efflux of chloride and water to the gut causing diarrhea |
|
|
How many forms of adenylyl cyclase are there in mammals?
|
at least 8
|
|
|
What does Gs do?
|
It is the stimulatory G protein that activates adenylyl cyclase
|
|
|
What is the whole process for increasing cAMP in the cytosol, starting with the extracellular signal?
|
- the binding of an extracellular signal molecules to its GPCR activates adenylyl cyclase via Gs and therefore increases cAMP in the cytosol
|
|
|
Aside from potentially causing diarrhea what else does a rise in cAMP activate?
|
PKA (cAMP dependent protein kinase)
|
|
|
What is the structure of PKA?
|
in inactive state PKA = 2 catalytic subunits and 2 regulatory subunits
|
|
|
How does the binding of cAMP to PKA work?
|
- binding of cAMP to regulatory subunits alters their conformation causing them to dissociate
- the released catalytic subunits are thereby activated to phosphorylate specific target proteins ex. transcription factors for gene expression |
|
|
What is PLC-Beta?
|
Phospholipase C Beta
- plasma membrane bound enzyme |
|
|
How is PLCBeta activated and what does it do?
|
- many GPCRs exert their effects mainly via G proteins that activate PLC-Beta
- the phospholipase then acts on a phosphorylated inositol phospholipid called phosphatidylinositol 4,5- bisphosphate or PIP2 (present in the plasma membrane) by cleaving it into two products: inositol 1,4,5-triphosphate (IP3) and diacylglycerol - this process is activated mostly by a protein called Gq |
|
|
What does IP3 do?
|
- releases calcium from the ER into the cytosol
- it does this by diffusing through the cytosol, and when it reaches the ER it binds to and opens IP3-gated calcium-release channels in the ER membrane - Calcium stored in the ER is then released, this calcium then helps diacylglycerol to activate PKC |
|
|
What does diacylglycerol do?
|
- remains in plasma membrane where it activates protein kinase C (PKC) which in turn phosphorylates target proteins
|
|
|
What does calcium trigger in muscle cells and in secretory cells?
|
- in muscle cells in triggers contraction
- in secretory cells in triggers secretion |
|
|
What is the concentration of calcium inside the cytosol vs. in the ECF?
|
in cytosol: about 10^-7 molar
in ECF: about 10^-3 molar |
|
|
How is the low calcium concentration inside the cytosol maintained?
|
- calcium is pumped out of the cell by a sodium-driven calcium-exchanger and a calcium P-Type ATP driven pump
- it is also pumped into the ER and SR and mitochondria - when in the cytosol calcium is bound to calcium-binding molecules |
|
|
What is calmodulin?
|
- most important calcium binding protein
- can be up to 1% of total eukaryotic protein mass - single polypeptide chain with four high-affinity calcium binding sites connected by an alpha helix - once two or more calcium binds it undergoes a conformational change so it can bind to and activate other target proteins |
|
|
What is Cam-Kinase II? What does it do?
|
- molecular memory device, important for learning and long term memory in vertebrates
- large enzyme made of 12 subunites - becomes active when exposed to calcium or calmodulin, and remains active even after calcium signal decays because it undergoes autophosphorylation |
|
|
How does the ACH receptor reduce heart contraction?
|
- ACH receptor activates inhibitory G protein
- alpha subunit of the G protein inhibits adenylyl cyclase and beta-gamma subunit activate potassium channels - this makes it harder to depolarize the cell and therefore reduces heart contraction |
|
|
How are signals conveyed from the olfactory receptors in the nose to the brain?
|
- receptor is stimulated by odorant binding
- this activates olfactory G-protein - this activates adenylyl cyclase - this activates cAMP - this opens cAMP gated cation channels allowing an influx of sodium to depolarize and send a nerve impulse |
|
|
What did Richard Axel and Linda Buck win the 2004 Nobel Prixe for?
|
- for the discovery that cyclic-nucleotide gated channels are regulated by G-proteins
|
|
|
What are the three ways that GPCRs can be desensitized?
|
1. Receptor inactivation
2. Receptor sequestration 3. Receptor down-regulation - all of these rely on phosphorylation by PKA, PKC or GRK (GPCR kinase) |
|
|
GPCRs and Enzyme-coupled cell-surface receptors activate the same signaling pathways. What, then, makes them different?
|
- they require ligand binding
- they only have one transmembrane domain - they can be directly associated with enzyme |
|
|
What does calcium trigger in muscle cells and in secretory cells?
|
- in muscle cells in triggers contraction
- in secretory cells in triggers secretion |
|
|
What is the concentration of calcium inside the cytosol vs. in the ECF?
|
in cytosol: about 10^-7 molar
in ECF: about 10^-3 molar |
|
|
How is the low calcium concentration inside the cytosol maintained?
|
- calcium is pumped out of the cell by a sodium-driven calcium-exchanger and a calcium P-Type ATP driven pump
- it is also pumped into the ER and SR and mitochondria - when in the cytosol calcium is bound to calcium-binding molecules |
|
|
What is calmodulin?
|
- most important calcium binding protein
- can be up to 1% of total eukaryotic protein mass - single polypeptide chain with four high-affinity calcium binding sites connected by an alpha helix - once two or more calcium binds it undergoes a conformational change so it can bind to and activate other target proteins |
|
|
What is Cam-Kinase II? What does it do?
|
- molecular memory device, important for learning and long term memory in vertebrates
- large enzyme made of 12 subunites - becomes active when exposed to calcium or calmodulin, and remains active even after calcium signal decays because it undergoes autophosphorylation |
|
|
How does the ACH receptor reduce heart contraction?
|
- ACH receptor activates inhibitory G protein
- alpha subunit of the G protein inhibits adenylyl cyclase and beta-gamma subunit activate potassium channels - this makes it harder to depolarize the cell and therefore reduces heart contraction |
|
|
How are signals conveyed from the olfactory receptors in the nose to the brain?
|
- receptor is stimulated by odorant binding
- this activates olfactory G-protein - this activates adenylyl cyclase - this activates cAMP - this opens cAMP gated cation channels allowing an influx of sodium to depolarize and send a nerve impulse |
|
|
What did Richard Axel and Linda Buck win the 2004 Nobel Prixe for?
|
- for the discovery that cyclic-nucleotide gated channels are regulated by G-proteins
|
|
|
What are the three ways that GPCRs can be desensitized?
|
1. Receptor inactivation
2. Receptor sequestration 3. Receptor down-regulation - all of these rely on phosphorylation by PKA, PKC or GRK (GPCR kinase) |
|
|
GPCRs and Enzyme-coupled cell-surface receptors activate the same signaling pathways. What, then, makes them different?
|
- they require ligand binding
- they only have one transmembrane domain - they can be directly associated with enzyme |
|
|
What are RTKs and what do they do?
|
Receptor Tyrosine Kinase
- one of the enzyme coupled cell surface receptors - can phosphorylate tyrosines on themselves and other target proteins |
|
|
What are tyrosine-kinase-associated-receptors and what do they do?
|
- one of the enzyme coupled cell surface receptors
- recruit cytoplasmic tyrosine kinases to relay signal |
|
|
What are receptor serine/threonine kinases and what do they do?
|
- one of the enzyme coupled cell surface receptors
- phosphorylate serines and threonines on themselves and other proteins |
|
|
What are histidine-kinase-associated receptors and what do they do?
|
- one of the enzyme coupled cell surface receptors
- activate a 2 component signaling pathway in which the kinase phosphorylates itself on histidine and then transfers the phosphate to a second intracellular signaling protein |
|
|
What are receptor guanylyl cyclases and what do they do?
|
- one of the enzyme coupled cell surface receptors
- catalyze production of cyclic GMP |
|
|
What are receptorlike tyrosine phosphatases and what do they do?
|
- one of the enzyme coupled cell surface receptors
- remove phosphate groups from tyrosines or specific intracellular signaling proteins |
|
|
How many genes encode human RTKs and how many subfamilies of RTKs exist?
|
Respectively:
-60 genes -16 subfamilies |
|
|
All RTKs are only a single polypeptide but there is one exception, what is it?
|
Insulin receptor - it is a tetramer bound by disulfide bonds
|
|
|
How are RTKs activated? What happens when they are?
|
- binding of a ligand activates RTK by causing 2 of them to come together in dimerization
- this brings the kinase domains of 2 receptor chains close together so they can become activated and cross-phosphorylate each other on multiple tyrosines (transautophosphorylation) - this triggers assembly of an intracellular signaling complex with many intracellular signaling proteins bound to phosphorylated tyrosines which can then relay a signal |
|
|
What are the SH3 and SH2 domains?
|
- SH3 domains interact with other proteins
- SH2 domains interact with the docking site on the RTK |
|
|
What does the insulin receptor do once it has been activated?
|
- activated receptor phosphorylates itself on tyrosins and one of the phosphotyrosines then recruits a docking protein
- receptor then phosphorylates the docking protein so it can recruit adaptor proteins - these then in turn recruit other poteins like Sos and scaffold proteins |
|
|
What is Ras?
|
- monomeric GTPase that relays signals from cell-surface receptors
- active when GTP is bound, inactive when GDP is bound |
|
|
What does Ras do in a fly eye? And how does it become active?
|
- One cell has already differentiated to become a photoreceptor and expresses this signal on its surface
- that signal activates RTK on the other cell - by way of an adaptor protein RTK leads to the activation of Ras which cuases downstream signals leading the cell to differentiate |
|
|
What signal cascade does Ras use after it is activated?
|
MAP kinase module:
- Ras recruits Raf (MAP kinase kinase kinase) and activates it which then phosphorylates and activates: - Mek (MAP kinase kinase) which then phosphorylates and activates: - Erk (MAP kinase) which in turn phosphorylates a variety of downstream proteins leading to changes in protein activity and gene expression |
|
|
Which of the MAP kinases is the same in almost all pathways?
|
MAP Kinase kinase kinase (or kinase A)
|
|
|
What happens when RTK activates PI 3-kinase? What is the most important product?
|
- PI 3-kinase, once active, catalyzes phosphorylation at the 3' position of the inositol ring of inositol phospholipids to generate several different phosphoinositides
- PI (3,4,5)P3 is most important as it serves as a docking site for many intracellular proteins |
|
|
How does production of PI(3,4,5,)P3 promote cell survival?
|
- it serves as a docking site for 2 serine/threonine kinases with PH domains
- one of these PH domains Akt is phosphorylated and dissociates -it then phosphorylates other target proteins including Bad - Bad then releases the apoptosis inhibitory protein it was holding which then goes on to prevent apoptosis |
|
|
What are tyrosine phosphatases and how many are in the human genome?
|
- dephosphorylate!
- about 100 in human genome |
|
|
What is chemotaxis?
|
- response to chemical stimulus, movement towards or away
|
|
|
How does the flagella of a bacteria move?
|
- flagella is linked to a flexible hook which is attached to a series of protein rings in the inner and outer plasma membrane
- rings form a rotor which rotates the flagellum very rapidly |
|
|
How do bacteria turn away from a repellent?
|
- when flagella rotate counter clockwise (normal) they are drawn together into a single bundle that produces smooth swimming
- if they come in contact with a repellent one or more motors switches direction causing flagella to start going clockwise instead and leading to tumbling and change of direction |
|
|
What receptor mediates chemotaxis?
|
histidine-kinase associated receptors, and then methyl transferace allows activatation of the cascade
|
|
|
What does notch signaling do?
|
- plays a role in controlling cell fate choices and regulating pattern formation during the development of most tissues
|
|
|
What does notch signaling do in Drosophila? How?
|
- produces nerve cells
- when individual cells int he epithelium begin to develop as neural cells they signal to their neighbours not to do the same - this is contact-dependent -- membrane bound inhibitory signal protein (Delta) on neural cell is received by Notch receptor proteins |
|
|
How does notch signaling activate transcription? What is the process?
|
1. Cleavage at site 1 in Golgi
2. Transport to plasma membrane 3. Binding to Delta (complex of Delta and Notch subunit are then taken up by the Delta expressing cell) 4. Cleavage at site 2 and site 3 5. Notch tail migrates to nucleus 6. Notch binds to Rbpsuh and converts it from transcription repressor to transcription activator |
