Topic 6: Cell signalling Flashcards

Question

what does Endogenous, Exogenous, Antagonist, Agonist mean

Answer 1

Endogenous ⇒ Normal (normal signalling molecule inside the cell) Exogenous ⇒ From outside Agonist ⇒ signal that activates Antagonist ⇒ binds and inhibits Often in pharmaceuticals we use Exogenous Antagonists, or sometimes Exogenous Agonist

Answer 2

- Cells may receive several signals simultaneously - Signals must be integrated and coordinated 1. One receptor activates multiple pathways 2. Different receptors activate the same pathway 3. Different receptors activate different pathways; one pathway affects the other

Answer 3

An arrow represents and activation event in a diagram “→” Two lines perpendicular represents an inhibition even “-|”

Answer 4

- Signaling pathways will often have several amplification steps - Increased sensitivity - Plays an important role in regulation

Answer 5

1 signal molecule can activate 10 molecules in the next step, which activates 100 in the next, until 100,000,000 of the final molecule are activated. Does not always need to be this large though.

Answer 6

Multiple steps allow two things: - Amplification (going from 1 to 100,000,00 molecules) - Regulation (multiple points to regulate)

Answer 7

The nobel prize in physiology or medicine in 1994 was given to Alfred G Gilman and Martin Rodbell for their discovery of G-proteins and the role of these proteins in signal transduction in cells

Answer 8

The Nobel Prize in Chemistry 2012 was given to Robert J. Lefkowitz G protein → guanine-nucleotide binding protein The GPCR has 7 transmembrane spanning regions. We have more than 8000 GPCRs in the human genome The largest family of signalling receptors estimated that 40-50% of all drugs target GPCR activity.

Answer 9

Henderson and Unwin used electron microscopy in 1975 to make the first model of Bacteriorhodposin The Nobel Prize in Chemistry 2017 was given to Jacques Dubochet, Joachim Frank, and Richard Henderson for work in cryo-electron microscopy.

Answer 10

Has three different proteins An Alpha, Beta, and Gamma subunit Both Alpha and Gamma and lipidated so they embed in the membrane When alpha subunit is bound to GDP it associated with the Beta and gamma subunity and is inactive. Is a Heterotrimeric GTPase Works essentially the same as a monomeric GTPase

Answer 11

G proteins are a form of molecular switch: There are two types of G protein: Monomeric (which have a single subunit) Heterotrimeric (which have three subunits, alpha, beta, and gamma)

Answer 12

1. Resting state: Receptor is not bound to ligand; Ga subunit is bound to GDP and associated with GBy 2. Ligan binds receptor: the receptor binds a G protein; Ga releases GDP and acquires GTP 3. Ga and GBy subunits separate 4. G protein subunits activate or inhibit target proteins, initiating signal transduction events 5. The Ga subunit hydrolyzes its bound GTP to GDP, becoming inactive 6. Subunits recombine to form an inactive G protein

Answer 13

GPCR acts as a GEF when stimulated by its ligand → exchange GDP for GTP on alpha subunit Exchange of GDP for GTP causes the alpha subunit to dissociate from the Beta-Gamma subunit Both the alpha, and Beta-Gamma subunit can potentially act as signalling molecules More commonly the alpha subunit Alpha subunit can hydrolyse its GTP to GDP the rate of hydrolysis can be moderated by other proteins RGS - regulators of G protein signalling → these act as GAPs (GTPase activating proteins)

Answer 14

There are at least 27 alpha subunit, 5 beta sunit, and 13 gamma subunit isoforms that are used combinatorially G(sa) is involved with fight or flight response (G alpha S)

Answer 15

The major families of G protein: Gsα stimulates adenylyl cyclase, cAMP is increased Giα inhibits adenylyl cyclase, cAMP decreased Golfα stimulates adenylyl cyclase, cAMP increased Gqα stimulates phospholipase C (**β**) IP3 increased Goα stimulates phospholipase C (**β**) IP3 increased Gtα stimulates cGMP phosphodiesterase, cGMP decreased

Answer 16

“Fight or Flight” - Kinase mediated priming of muscles for action - cAMP is a secondary messenger - cAMP activates a protein kinase called PKA (protein kinase A)

Answer 17

- Glucagon or Beta-adrenergic receptor (depending on ligand) - ultimately results in increased glucose for muscle cells - stimulates α(s) - Signal is Epinephrine - Occurs in muscle cells to get action ready, but also liver cells when blood glucose levels drop. - Produces phosphorylated glucose from glycogen, in liver, the phosphate can be cut off allowing glucose to be released into the blood

Answer 18

The binding of a ligand such as Glucagon or epinephrine that causes G-alpha-S to bind to Adenylyl cyclase G-alpha-S reacts directly with Adenylyl cyclase which uses ATP to produce Cyclic AMP which activates PKA (a SER/THR kinase) PKA activates phosphorylase kinase (with a phosphate group), causing glycogen phosphorylase be activated (with a phosphate group). Which breaks down glycogen to release glucose-1-phosphate PKA also activates transcription regulators which affect the transcription of certain genes PKA also shuts down gluconeogenesis

Answer 19

Cyclic AMP stimulates Protein Kinase A. which then activates CREB (by taking a P from ATP and adding to CREB). CBP then comes in and binds to CREB-P, and recruits RAN polymerase II to start transcription. Long term effects through CRE/CREB

Answer 20

CRE - cAMP Response Element CREB - cAMP Response Element Binding protein - CRE Binding Protein CBP - CREB Binding Protein (Binds to Phosphorylated CREB). This recruits RAN polymerase II to start transcription

Answer 21

- Most effects linked to increased cAMP levels are the results of PKA activity - two regulators and two catalytic subunits - upon binding cAMP, regulatory subunits fall off, allowing catalysis Allosteric Regulation → binding of cAMP is outside of the active site

Answer 22

- V. cholerae adhere to intestinal cells, and secrete choleragen, an AB exotoxin - the A subunit enter intestinal epithelial cells and activates adenylate cyclase via ADP-ribosylation - this results in hyper-secretion of water and chloride ions from the cells - treatment with oral rehydration, sometimes antibiotics, 50% mortality if untreated.

Answer 23

ERAD - Endoplasmic reticulum-associated degradation Used on proteins which are unable to properly fold Pushes proteins out of ER and ubiquinidated, to be degraded in a proteosome. Cholera toxin takes advantage of this to get the A subunit to get into the cytosol, but isn’t ubiquinidated. Does this once its ready to leave to host, infect water, and find a new host. Done at end of infection.

Answer 24

- Both second messengers - inositol-1,4,5-trisphosphate (IP3) - Diacylglycerol (DG) - Breakdown product of phosphatidlyinositol-4,5-bisphosphate (PIP2) - initiated by phospholipase C - referred to as PLC PLC cleaves the head group off phosphatidlyinositol-4,5-bisphosphate (PIP2) leaving Diacylglycerol and the head group (Inositol-1,4,5-trisphosphate)

Answer 25

Receptor can be GPCR or receptor tyrosine kinase (depending on which PLC) G protein is activated by receptor Beta-Gamma bind to PLC which breaks down PIP2 to release IP3 and DAG IP3 opens calcium channels in the smooth ER DAG recruits and activates protein kinase C (C for calcium) PKC is bound by Ca2+

Answer 26

When a Sperm fertilizes an egg cell, there is a wave of calcium that spreads through the egg over several minutes. Calcium causes the fusion of cortical granules to the cell membrane, causes them to release their contents. The contents released cause a “jelly layer” around the egg cell which prevents more sperm from entering, called the fertilization envelope.

Answer 27

- Can be up to about 1% of a cell’s total protein mass - involved in Ca2+ signalling - highly conserved single polypeptide with four high affinity Ca2+ sites - a 10 fold increase in Ca2+ leads to a 50-fold activation of calmodulin - calmodulin does not have its own activity, but rather it binds to and activates other proteins - It is not an enzyme!!! Just a regulatory protein

Answer 28

1. Calmodulin binds to four calcium ions 2. Calmodulin changes conformation, resulting in an active complex 3. The two globular “hands” of the complex wrap around a binding site on a target protein - Changes structure upon calcium binding - when bound to Ca2+, able to regulate a number of different protein targets in the cell

Answer 29

Calmodulin Regulates Activity of many enzymes → Calmodulin has No enzymatic activity

Answer 30

Important family of Calmodulin regulated enzymes = CaMk → Protein Kinases some Calmodulin regulated enzymes are very important for neurology. CaMK2 is essential to forming memories.

Answer 31

- Cytosolic domain has protein kinase activity or the cytosolic domain associated with a protein kinase - generally single-pass transmembrane proteins that multimerize upon ligand binding - two classes: - tyrosine kinase receptors - serine/threonine receptor kinases - often bound by growth factors

Answer 32

Serine, threonine, and Tyrosine can all be phosphorylated Each have an -OH as part of their R group The phosphate group is attached at the site of the -OH group PO3 + HO- → H + PO4-

Answer 33

- unbound, no P-Tyrosines - receptor binding induces multimerization - trans-autophosphorylation activates the receptor. (Phosphorylated across the receptor)

Answer 34

Ras comes from Rat sarcoma, it its a monomeric GTPase Sos = Son of Sevenless is the GEF for Ras, from drosophila Sos can be activated by indirect binding bia GRB2 to the receptor kinase, or through other activation pathways

Answer 35

Signal causes phosphorylation across receptor Grb2 (adaptor) attaches to the phosphate groups Grb2 recruits a protein called Sos (a GEF for Ras (a monomeric GTPase) At this point, the process has brought Sos to the membrane where Ras resides (Ras is membrane bound) GTP → GDP occurs, activating Ras

Answer 36

MAP = mitogen activated protein. It is a transcription factor, active when phosphorylated mitogens are growth/proliferation signals three components: - MAPK = MAP kinase - MAPKK = MAP kinase kinase - MAPKKK = MAP kinase kinase kinase - mammalian cells have 12 MAPK, 7 MAPKK and 7 MAPKKK genes

Answer 37

epidermal growth factor (EGF) binds to an EGF receptor The EGF receptor activates GTP bound Raf GTP bound RAS activates MAPK Kinase Kinase(MAPKKK) (not through phosphorylation) MAPKKK phosphorylates MAPK Kinase, (MAPKK), activating it MAPKK phosphorylates MAP Kinase (MAPK) activating it MAPK phosphorylates MAP, activating it

Answer 38

Ex: Ras activates Raf (the MKKK), which activates MEK (the MKK), which activates ERK (the MAPK), which targets cytosolic species to promote growth and division. Leads to phosphorylation of c-Myc which leads to Transcription of genes promoting cell growth and division

Answer 39

Receptor Tyrosine Kinases and Cancer Many receptor tyrosine kinases are important for specific cancers, such as IGFR which is important for cervical cancer

Answer 40

Mutations in signalling pathways can lead to defective heart development or abherant axon pathfinding, etc. It can also lead to Gain of function Transformation: Conversion of normal cells into a cancer like state of uncontrolled cell division Constitutive activation of RTK can lead to transformation

Answer 41

1. When the insulin receptor binds insulin, the activated receptor phosphorylates the IRS-1 protein. IRS-1 can lead to recruitment of GRB2, activating the Ras pathway 2. IRS-1 activates PI 3-kinase, which catalyzes the addition of a phosphate group to the membrane lipid PIP2, thereby converting it to PIP3. PTEN can convert PIP3, back to PIP2 3. PIP3 binds a protein kinase called AKt, which is activated by other protein kinases 4. Akt catalyzes phosphorylation of key proteins, leading to an increase in glycogen synthase activity and recruitment of the glucose transported, GLUT4 to the membrane PI 3-kinase phosphorylates lipids, not proteins

Answer 42

PI(3)P, PI(3,4)P2 and PI(3,4,5)P3 are recognize by specific lipid binding domains (eg: PH domain) used to mark membranes

Answer 43

AKT can also prevent apoptosis via phosphorylation of a target protein. The target protein is called Bad

Topic 6: Cell signalling Flashcards

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