Cell Biology Exam III (Chapters 16, 17, 18, 20)

Cell to cell contact stimulus

-Cell 1 comes in contact with cell 2 and that contact will change something in the cell

Signal amplification

-Each GPCR activates multiple G proteins -Each active adenylyl cyclase make many cAMPs -Each active PKA can phosphorylate multiple phosphorylase kinases -Etc.. -using pathways to activate things allows for amplification -enzymes in the amplification pathway may be inhibitory and result in a balance

How do we study DAG?

-We artificially turn DAG on -use something that mimics DAG

GPCR: Signal relay to effector

-activated α subunit changes effector shape ("on") and activates it

IP3 (inositol 1,4,5-trisphosphate)

-small, water soluble (hydrophilic) -binds to a Ca++ channel receptor on smooth endoplasmic reticulum (SER) -releases Ca++ from the SER -after it is cut off and released from the membrane, it goes to the ER to release Ca++

What happens when you add DAG to a cell that does not grow/divide?

-take a cell that does not grow or divide and add something that mimics DAG and the cells start to divide uncontrollably→lose growth control

PLC activation of two signaling pathways:

1. activated alpha and beta-gamma subunits activate PLC 2. activated PLC hydrolyzes inositol phospholipid which produces two small messenger molecules: IP3 and DAG 3. IP3 diffuses through the cytosol and triggers the release of Ca++ from the ER by binding to and opening Ca++ channels in the ER membrane→electrochemical gradient causes Ca++ to rush out of the ER and into the cytosol 4. DAG remains in the plasma membrane and together with the Ca++ help activate PKC 5. PKC phosphorylates and activates its own set of intracellular proteins

G protein subunits and lipid anchors

Both the alpha and gamma subunits of the G protein have covalently attached lipid molecules that help anchor the subunits to the plasma membrane

What controls the activity of monomeric GTP-binding proteins?

They are controlled by two types of regulatory proteins: GAP - GTPase-activating proteins GEF - Guanine nucleotide-exchange factors

Adrenaline and glucose synthesis

1. binding of the signal molecule to the GPCR can activate adenylyl cyclase and increase cAMP 2. increase in cAMP activates PKA 3. PKA moves into the nucleus and phosphorylates specific transcription regulators 4. Once phosphorylated, these proteins stimulate the transcription of a whole set of target genes. **increased cAMP can activate gene transcription Enzymes activated in the target gene are ones needed for gluconeogenesis (generation of glucose)

3 types of stimulus recognized by receptor

1. extracellular ligand 2. cell to cell contact 3. extracellular matrix

GPCR mechanism overview

1. extracellular signal molecule actives receptor 2. inactive G protein gets activated by receptor→GDP of G protein is exchanged for GTP 3. activated alpha subunit and activated beta-gamma subunit of G protein split 4. activated subunits can activate (or inactivate) target proteins 5. activated alpha subunit gets GTP hydrolyzed to GDP and becomes inactive 6. inactive alpha subunit reassociates with beta-gama subunit and reforms an inactive G protein 7. G protein is ready to couple to another activated receptor

cAMP formation

1. glucagon and epinephrine bind to a GPCR 2. G protein gets activated and the alpha subunit will go over and bind to adenylyl cyclase (the effector) 3. activated adenylyl cyclase will turn ATP into cAMP by removing two phosphates 4. cAMP acts as a secondary messenger and activates other things

Ways to increase glucose in the blood

1. increasing the breakdown of glycogen 2. inhibiting the formation of glycogen 3. activating enzymes needed to make glucose from scratch ***This is all done by PKA which is activated by the increase in cAMP which resulted from the activation of glucagon or epinephrine

3 classes of cell surface receptors

1. ion channel coupled receptors 2. G-protein coupled receptors 3. enzyme coupled receptors

Phospholipase C

-GPCR enzyme effector (second example) -membrane bound protein -not active until an activated G protein activates it -releases a second messenger when activated→second messenger is IP3/DAG -enzyme that cuts the bond between the phosphate and the glycerol in the phosphotidylinositol, releasing the phosphate of the headgroup (the glycerol and the two fatty acid tails stay in the membrane)

Animal cells receive multiple signals to:

1. survive: cells need signals to survive; they continuously need signals to tell them to survive 2. grow and divide: additional signals (along with surviving signals) may be needed to grow and divide 3. differentiate: additional signals (along with surviving signals) are needed to differentiate; differentiate means to change which genes are being expressed 4. die: no signals; when a cell receives no signals, it dies

Contact dependent communication

-a cell surface bound signal molecule binds to a receptor protein on an adjacent cell -two cells actually touch each other -nothing is released, it is just simply cell 1 touching cell 2

protein kinase C (PKC)

-activated by DAG -a serine/threonine kinase (kinase that phosphorylates other things on serine or threonine) -important in many cellular events (e.g ., cell growth, differentiation, metabolism and transcriptional activation)

Similarities between extracellular ligand, cell to cell contact, and extracellular matrix stimulus

-all need receptors to pick up signals -signals change something inside the cells -eventually the change has to be reversed

Reversal of signal: glucose pathway

-ways to reverse glucose production pathway: 1. phosphatase-1 removes all of the phosphates that were added by PKA in every step of the pathway (phosphatase→enzyme that removes phosphates; dephosphorylates enzymes, turning off pathways) 2. cAMP is destroyed by cAMP phosphodiesterase (cAMP becomes AMP). cAMP can no longer turn on PKA 3. GPCR can get turned off by a kinase and then arrestin will bind to the receptor, keeping it from being able to activate more G proteins. Inactive G proteins will not be able to activate the effector so the effector will be turned off as well

Ca++ as an intracellular messenger

-low Ca++ in the cytosol; high Ca++ in the ER -when Ca++ levels are high in the cytosol, other things will be activated -Ca++ release from intracellular stores acts as a second messenger -can act as the first messenger for hormones, neurotransmitters, electrical activation (muscle)

Specificity of G protein-coupled responses

-not all parts of signal transduction machinery identical in all cells -multiple forms of receptors ( e.g., 9 different isoforms of epinephrine receptors) with different ligand and G protein affinities -multiple G proteins ( 20 Gα; 5 Gβ; 11 Gγ ); various combinations -can be stimulatory or inhibitory→Gαs stimulatory and Gαi inhibitory **In the cell there are different forms and specificity of G proteins

Reversal of signal

-pathways do not stay on forever and must be turned off

Protein phosphorylation

-phosphates are highly charged. The charge can change the shape of the protein making it active or inactive -some proteins are active until they get phosphorlyated. Other proteins are inactive until they get phosphorylated. -may increase or decrease protein's activity -may cause a conformational change in the protein→ temporarily changing the shape of the protein -may be part of a protein binding site -may be added to serine, tyrosine, or threonine amino acids (these amino acids all have OH groups in side chain. OH group will be part of phosphorylation) -most substrates in pathway are other enzymes

Phosphatidylinositol (PI)- mediated responses

-phospholipase C cleaves PIP2 into DAG (diacylglycerol) and IP3 -DAG (glycerol + 2 fatty acid tails)→hydrophobic and stays in the membrane (diffuses around in the membrane) which will signal some things; secondary messenger -IP3 (Inositol head and the phosphate)→hydrophillic and moves further into the cell for signalling; secondary messenger

phorbol esters

-plant compounds that mimic DAG and activate PKC; cells lose growth control and behave as malignant cells

G-protein coupled receptors

-receptor binds its extracellular signal molecule. The activated receptor signals to a G protein on the opposite side of the plasma membrane, which then turns on (or off) an enzyme (or ion channel) in the same membrane -protein will change shape (depending on whether it is GTP or GDP) and that activated G protein will then activate an enzyme -G protein acts as a link between the receptor and the enzyme (effector) -receptor changes its shape when it binds its ligand which activates the G protein. The G protein binds to the effector which will create the secondary messenger -ex: receptors in eye

G-protein coupled receptors (GPCR)

-receptor binds its ligand which causes effector to release a secondary messenger -largest superfamily of proteins in animal genome (e.g., nematode worm has 19,000 genes of which 1000 are GPCRs) -Target of ~40% of modern medicinal drugs

Extracellular matrix stimulus

-receptor binds to an extracellular matrix protein (provides structural and biochemical support to the surrounding cells) -when that binds to receptor, cytolsolic tail will change and changes inside the cell will take place -ex: collagen

glucagon and epinephrine

-regulate glucose levels and phosphorylase and glycogen synthase -increase blood glucose by inhibiting glycogen synthase and activating phosphorylase -glucagon is released by the pancreas -epinephrine (adrenaline) released by the adrenal glands

Calcium

-secondary messenger -low in the cytosol because it is being concentrated in the ER and mitochondria -calcium levels can go up in the cytosol which will act as a signal to activate other things

Lipid-derived

-secondary messenger -specialized phospholipids that get activated -enzyme cuts the phospholipids into pieces which can act as messengers inside cell

Cyclic AMP (cAMP)

-secondary messenger that is released inside the cell and will go around and bind to targets -can activate gene transcription

Signal pathways

-series of distinct proteins that alter the conformation of the "downstream" protein -ex: when signal binds to receptor, receptor does not directly alter gene expression. It alters gene expression through a series of events -one thing in the pathway affects the next which affects the next, etc -proteins changing the shape of another protein

Molecular switches: signalling by protein phosphorylation

-shape change by phosphorylation -phosphorylation→protein kinase takes off a phosphate from ATP and puts it on its target -signal→ receptor binds to a ligand which leads to a series of events. One of the things that happens is that kinase in the cytosol will be activated and will take a gamma phosphate off of ATP and covalently put it on the target protein. -protein gets phosphorylated and changes its shape and is now active -to deactivate protein, phosphate must be taken off by protein phosphatase

Signal transduction

-signal conversion -process in which one type of signal is converted into another -ex: a target cell converts an extracellular signal molecule into an intercellular signalling molecule. Extracellular signal can increase or decrease something inside the cell, but the signal molecule itself does not enter cell

Paracrine communication

-signals are released by cells into extracellular fluid in their neighborhood and act locally -short distance -does not go through the bloodstream -cell releases the signal and it reaches another "local" cell that's close to the signalling cell

Synaptic/neuronal communication

-signals are transmitted electrically along a nerve cell axon. When this signal reaches the nerve terminal, it causes the release of neurotransmitters onto adjacent target cells -can be long distance -one cell stimulating directly another cell. Signal is not released to just any cell that's around with a receptor. The signal is going directly to a specific cell.

GPCR and enzymes

-some G proteins activate membrane bound enzymes -Enzymes activated by G proteins catalyze production of small intracellular signaling molecules -effector is an enzyme -ligand binds to the receptor and the G protein will activate an enzyme

GTPase-activating proteins (GAP)

-stimulate the hydrolysis of GTP to GDP, switching the GTP-binding protein off -causes the protein to rapidly hydrolyze GTP back to GDP

signal transduction

-stimulus received by cell-surface receptor is different than signal released in cell interior -the first messenger is now converted into a second messenger -the first type of the messenger becomes another type of messenger

Animal cells have several PI and PIP kinases and phosphatases

-there are many different ways, orders, and sequences to phosphorylate the PI -kinases will add the phosphates and the phosphatases will remove them -kinases that add the phosphates will be activated by the cell signalling pathway

Glucagon and epinephrine bind to different receptors but lead to the same intracellular response. How?

-they both activate adenylyl cyclase -Both use the same secondary messenger cAMP→both merge in the same downstream pathway

What are the ways that animal cells use extracellular signal molecules to communicate with each other?

1. Endocrine 2. Paracrine 3. Synaptic/neuronal 4. Contact dependent

Alternate types of signal transduction pathways

1. G protein-linked receptor or G-protein coupled receptors (links receptor to the effector which will lead to a series of events) 2. Protein kinase receptor (enzyme will phosphorylate itself leading to a series of events)

Protein kinase example pathway

1. Protein kinase (PK) 1 was inactive. Receptor of PK1 bound to its ligand so it causes it to be active. 2. Now that PK1 is active, it will add a phosphate to PK2, activating it 3. activated PK2 will phosphorylate PK3 and activate it 4. activated PK3 may activate a transcription factor 5. active transcription factor binds to the DNA and turns on gene expression *series of proteins modifying another protein

Overview of signal initiation and responses

1. Receptor recognizes stimulus 2. Signal transferred to cytoplasmic surface of receptor 3. Signal transmitted to effector molecule 4. Cessation of response

Ion channel coupled receptors

-transmembrane receptor that opens in response to binding an extracellular signal molecule. These channels are also called transmitter-gated ion channels -gate is closed, extracellular signal molecule binds, gate opens to let ions in -signal molecule is different than ion -ex: neurotransmitter and target cell receptors → neurotransmitters bind to receptors and gate opens to allow ions in which depolarize the target cell -ex: acetylcholine and muscle receptors

Molecular switches

-way to turn on a protein -Many intracellular signaling molecules act as "molecular switches" -protein is "off" and then it gets something modified so now it is "on" → happens rapidly -signalling proteins can be activated (or in some cases inhibited) by the addition or removal of a phosphate group or a GTP -two types: signalling by protein phosphorylation and signalling by GTP binding proteins

Where does the cAMP that is used in glucose regulation come from? How is it degraded?

It comes from the effector Adenylyl cyclase: cyclic AMP is synthesized by adenylyl cyclase and degraded by cyclic AMP phosphodiesterase. cAMP is formed from ATP by a cyclization reaction that removes two phosphate groups from ATP and joins the free end of the remaining phosphate group to the sugar of the AMP molecule. The degradation reaction breaks the bond between the phosphate and the sugar of the AMP, forming AMP

Signal transduction pathway

Primary transduction → relay → transduce and amplify → integrate → distribute Most steps in these pathways are something binding to a target and that target changing shape. The changing shape in the target will cause the target to change something on the next target and so on (domino effect).

Cell communication type analogy

Radio announcement: 1. Announcement can be put out on the radio so that people who live far away can still here it. Everyone in the city can receive the announcement (signal) as long as they have a radio (receptor): Endocrine 2. Flyers with the announcement (signal) are put up around close neighborhoods. Everyone locally can read the flyers and receive the announcement: Paracrine 3. Writing a letter to someone to tell them the announcement. The announcement can go a really long way (another state) but the destination is specific to one person: Synaptic/neuronal 4. You are walking down the street and you see a friend. You tell them the announcement face to face: Contact dependent

G-proteins

proteins that when bound to GTP have a certain shape and activity and when bound to GDP have another shape and another activity

What do Extracellular signals bind to?

They bind to cell-surface receptors or intracellular receptors. Most extracellular signal molecules are large and hydrophilic and are unable to cross the plasma membrane directly. Instead, they bind to cell surface receptors, which in turn generates one or more intracellular signaling molecules in the target cell. Small hydrophobic extracellular signal molecules (carried in carrier proteins) can pass the target cell's membrane and either activate intracellular enzymes directly or bind to intracellular receptors that then regulate gene transcription or other functions (ex: estrogen, cortisol, testosterone)

Cancer cells and signals

cancer cells do not need continuous survive signals to survive. Cancer cells have a lot of mutations that tell them to continue to divide and do not need the signaling to survive.

GPCR structure

All GPCRs have a similar structure: 1. all have 7 transmembrane alpha helices 2. ligand binds to external face which will change the shape of the cytosolic tail 3. cytosolic side of receptor binds to a G protein inside the cell

Adenylyl cyclase

-integral membrane protein that makes cAMP -an "effector"

Molecular switches: signalling by GTP binding proteins

-GTP binding protein is activated when it exchanges its bound GDP for GTP (which adds a phosphate to the protein). Protein switches itself off by hydrolyzing its bound GTP to GDP -GDP is always inactive form and GTP is always active form (different than phosphorylation) -there is something that pulls off GDP and now that the GDP spot is empty, GTP will come in and bind (there are lots of GTP in the cytosol) and activate the protein -there is a signal receptor that tells when GDP has to be exchanged for GTP -eventually the GTP will be hydrolyzed back to GDP. This is done by the protein entirely on its own→ protein is a GTPase -when protein is going from GTP to GDP, it actually loses a phosphate to become GDP ***G proteins are not kinases. G proteins will not phosphorylate other proteins ***this is an entire exchange of GDP to GTP. This is NOT an addition of phosphate to GDP to make GTP

GPCR: ending the response

-GTP of α subunit is hydrolyzed to GDP and α subunit changes shape and becomes inactive (When α subunit is bound to GDP, it dissociates from the target protein) -G protein no longer binds effector, but reforms trimer with beta-gamma subunit -Effector changes shape and becomes inactive -receptor desensitization

Glucose regulation

-Glucose is stored in animal cells as glycogen (polymer of glucose) -when the body needs glucose, glycogen is broken down back into glucose and your body uses the glucose -glycogen stored in your liver is low→glucagon and epinephrine are released to make more glucose→glucagon and epinephrine release activates enzyme called phosphorylase (glycogen phosphorylase makes more glucose)→ phosphorylase takes an inorganic phosphate and breaks a bond; it essentially carves off one glucose from glycogen and makes it glucose 1 phosphate which will be used for something else in the cell. -When there is too much glucose in the blood, the body releases insulin→insulin causes the glucose to be taken up in the cell and put in the storage form of glycogen→glycogen synthase makes more glycogen

Phosphatidylinositol (PI) and phosphoinositides (PIPs): naming

-Named according to ring position (in parentheses) and number of phosphate groups (in subscript) -phosphate that is part of the phosphotidylinositol does not get included in the numbering of the phosphates→only the phosphates that were added by a kinase are included -ex: PI(3,4)P2 →(3,4) means that carbon 3 and 4 are phosphorylated and the 2 means that only 2 carbons were phosphorylated

PIs and proteins

-PI headgroups are recognized by protein domains that discriminate the different forms -Proteins are recruited to regions of the membrane where these PIs are present -ex: protein was soluble in the cell and as soon as the PI got a specific arrangement (maybe a phosphate on the 4 and 5 carbon), the protein came up and docked on the PI headgroup in the membrane. Another protein will come up to a different PI headgroup and interact with it

G-protein activation of GPCR mechanism

-an activated GPCR activates G proteins by encouraging the alpha subunit to expel its GDP and pick up GTP -in the unstimulated state, the receptor and the G protein are both inactive -binding of an extracellular signal molecule to the receptor changes the conformation of the receptor, which in turn alters the conformation of the bound G-proteins -the alteration of the alpha subunit of the G protein allows it to exchange its GDP for GTP -this exchange triggers an additional conformational change that activates both the alpha subunit and a beta-gamma complex -the beta-gamma complex can dissociate to interact with their preferred target proteins in the plasma membrane or it can remain with the alpha subunit and activate proteins -activated alpha subunit can activate effector or activated beta-gamma can activate effector -receptor stays active as long as external signal molecule is bound to it. Because of this, receptor can catalyze the activation of many molecules of G proteins

receptor desensitization

-another way to end the response of the GPCR -inactivates receptor even if ligand is still bound -Steps: 1. GRK (G protein-coupled receptor kinase) phosphorylates tail of receptor (part of receptor that binds G protein) using ATP 2. arrestin recognizes and binds to the phosphorylated receptor and blocks G protein binding → receptor loses its ability to bind to other G-proteins 3. receptor endocytosed from PM

Extracellular ligand stimulus

-binds to receptor on the surface of target cell -when this binds to the receptor, the receptor will change its shape and the cytosolic side (cytolsolic tail) of that receptor will change and will lead to changes inside the cell (something might be released in cell) -signal is transferred to cytolsolic side of the cell -no channels → ligand does not bind to receptor and then flow into the cell -can move throughout body until a receptor is found -ex: insulin

Protein Kinase and Protein Phosphatase

-change the shape/activities of the proteins they modify -there is a continual balance of kinase and phosphatase activities (phosphates are continuously added and removed; whichever is more active between kinase and phosphatase will decide whether phosphate stays on for a little while) -human genome ~500 different kinases and ~100 different phosphatases (specifically add or remove phosphate)

Phosphatidylinositol (PI) and phosphoinositides (PIPs)

-contain inositol and are used for signalling -PIP results from the phosphorylation of OH in inositol of PI→ usually the 3, 4, or 5 carbon get phosphorylated -cause proteins to come up and dock to the membrane

Protein kinase

-convalently adds a phosphate to target protein during protein phosphorylation to activate the protein -most things in a pathway are kinases→ ex: Kinase 1 activates kinase 2 which activates kinase 3 which maybe activates a transcription factor that changes gene expression

enzyme coupled receptors

-enzyme coupled receptor binds its extracellular signal molecule and an enzyme activity is switched on at the other end of the receptor (inside the cell) -receptor is composed of two monomers that are separated in the membrane and inactive. When ligand comes in, it causes the two receptor monomers to come together and dimerize. The coming together activates the receptor -some enzyme coupled receptors have their own activity (in other words, the tail of the receptor itself is an enzyme→ left in picture) and others rely on an enzyme that becomes associated with the activated receptor (in other words, enzyme inside the cytosol recognizes the dimerized receptor and comes up to receptor to be activated→ right in picture). In this scenario, the binding of the ligand caused the dimerization of the receptor which changed the shape of the receptor so that the associated enzyme can now bind and be activated.

Protein Kinase A (PKA)

-enzyme that is activated by cAMP (THINK: PKA→A comes from cAMP) -activates phosphorylase kinase -also phosphorylates glycogen synthase, which inhibits glycogen synthesis (phosphorylation is going to inhibit the glycogen synthase) ***REMEMBER that Kinases phosphorylate their targets

Effector

-enzyme that will activate another messenger in the cell -can be activated by the alpha subunit or the beta-gamma subunits of the G protein -does not directly interact with the receptor→ G protein links them

How does phospholipase C (PLC) get activated?

-gets activated by a signalling molecule: 1. receptor binds its ligand and activates the G protein 2. alpha subunit of G protein activates PLC 3. activated PLC will cut the bond in the PI and will release the IP3 which is soluble and hydrophilic and will go throughout the cell

Diacylglycerol (DAG)

-glycerol with the two fatty acid tails -lipid molecule remains in Plasma Membrane -recruits and activates protein kinase C (PKC)

Endocrine communication

-hormones produced in endocrine glands are secreted into the bloodstream and are distributed widely throughout the body -long distance communication -cell releases the signal, signal goes into the bloodstream, and then reaches a cell

phospholipases

-hydrolytic enzymes that split phospholipids -three types: 1. PLA -- phospholipase A 2. PLD -- phospholipase D 3. PLC -- phospholipase C

Guanine nucleotide-exchange factors (GEF)

-in charge of removing the GDP from the protein -protein that exchanges GDP for GTP and switching the GTP-binding protein on

Adrenaline and glycogen breakdown in skeletal muscle cells

Adrenaline stimulates glycogen breakdown in skeletal muscle cells: 1. adrenaline (hormone) activates a GPCR, which turns on a G protein (Gs→G stimulatory) that activates adenylyl cyclase to boost the the production of cyclic AMP 2. The increase in cyclic AMP activates Protein Kinase A (PKA), which phosphorylates and activates an enzyme called phosphorylase kinase (PKA is activated by cAMP ) 3. phosphorylase kinase activates glycogen phosphorylase (enzyme that breaks down glycogen to release glucose)

Why don't carbons 2 and 6 on inositol usually get phosphorylated when PI is becoming PIP?

Because carbons 2 and 6 are closer to the ring→ so they do not get phosphorylated because of sterol reasons

Speed of extracellular signals: rapid response

Cell signal binds to the receptor and within milliseconds, it can change the protein shape and thus, change its function. Protein level does not change. ex: signalling in the eye

Signal transduction pathway: explanation

Extracellular signal binds to the receptor which will cause a messenger to be released into the cell. Secondary messenger is released by an effector (which is active because the first message was released). Now that the soluble messenger is released, it will go throughout the cell and bind to target protein causing that protein to change shape. The changing shape in the target will cause the target to change something on the next target and so on (domino effect). This is essentially a series of shape changes throughout the pathway.

Speed of extracellular signals

Extracellular signals can act slowly or rapidly. Certain types of cell responses (such as cell differentiation, cell growth and division) involve changes in gene expression and the synthesis of new proteins. They therefore occur relatively slowly. Other responses (such as changes in cell movement, secretion, or metabolism) do not need to involve changes in gene expression and therefore occur more quickly.

True or False: Ca++ is made enzymatically.

False. Ca++ is NOT made enzymatically. Ca++ is not broken down (degraded) or created by enzymes; it only moves location through pumps and channels -Ca++ concentration is controlled by pumps and channels

True or false: A GPCR only activates one G-protein

False. GPCR can bind multiple G-proteins at a time

examples of GPCRs, effector, and secondary messenger

GPCR: glucagon receptor effector: adenylyl cyclase secondary messenger: cAMP

Why doesn't the first messenger bound to the receptor directly change the final target protein? Why go through a pathway of many steps?

Going through the steps provides advantages: 1. amplification can occur: a single messenger binding to a receptor which can lead to many downstream proteins being activated (instead of just one); can lead to many copies of a secondary messenger and each secondary messenger can bind to something in the pathway 2. integration: different pathways (different molecules) activating the same target; merging of pathways (some pathways may inhibit the target and others can activate it) 3. Distribution: 1 protein may activate many different targets and distributes the signal

Comparing and contrasting Endocrine, Paracrine, and Synaptic/neuronal, communication

Many of the same types of signal molecules are used for endocrine, paracrine, and neuronal signaling. The crucial differences lie in the speed and selectivity with which the signals are delivered to their targets

Speed of extracellular signals: slow response

Messenger binds to the receptor which leads to a change in gene expression. Transcription factors change shape and go into the nucleus. In the nucleus the transcription factor binds upstream of a gene. RNA polymerase makes the mRNA of that gene which goes out into the cytoplasm to be translated into protein. That protein can now do something. Can take minutes to hours.

GPCR and ion channels

Some G proteins directly regulate ion channels→ the effector of the GPCR is an ion channel A Gαi (inhibitory) protein directly couples receptor activation to the opening of K+ channels in the plasma membrane of the heart pacemaker cells: -Binding of the neutrotransmitter acetylcholine to its GPCR on the heart cells results in the activation of the G protein, Gαi→ activation of alpha changes GDP to GTP and it no longer binds to the beta-gamma complex -beta gamma complex is activated (beta-gamma does not bind GDP or GTP; it seems to be inactivated when associated with the alpha) -The activated beta-gamma complex directly opens the K+ channel in the plasma membrane, increasing its permeability to K+ and thereby making the membrane harder to activate and slowing the heart rate (when K+ channels open, K+ leaves the heart and the heart is hyperpolarized→becomes more negative, slowing down the heart rate) -inactivation of the alpha subunit by hydrolysis of its bound GTP returns the G protein to its inactive state, allowing the K+ channel to close

True or False: The same signal molecule can induce different responses to different target cells.

True. ex: acetylcholine Different cell types (heart pacemaker cell, salivary gland cell, and skeletal muscle cell) are configured to respond to the neurotransmitter acetylcholine. Acetylcholine can bind to the same receptors on different cells (all receptors for acetylcholine on these cells are same-same protein), but evokes different responses in each cell type. When acetylcholine binds to: 1. heart pacemaker cell- it causes heart rate to slow down 2. salivary gland cell- it releases enzymes like salivary amylase 3. skeletal muscle cell- it causes the muscle to contract by controlling the open and closing of ion channels

Signal transduction: cell phones

When a mobile telephone receives a radio signal, it converts it into a sound signal. When transmitting a signal, it does the reverse

GPCR and enzymes examples

enzyme effector example: Adenyl cyclase and phospholipase C secondary messengers: cAMP; IP3/DAG 1. G protein will activate enzyme effector adenyl cyclase which will make lots of cAMP (cyclic AMP). cAMP will diffuse throughout the cell and activate other things

Signalling pathway: first and second messengers

first messenger→ messenger/signal outside cell; generally hydrophilic second messenger→ inside the cell; they are small nonprotein intermediaries acting in signal transduction (will be made and bind to something to activate it so that that something can do something else); levels of second messenger change because first messenger was binded; examples include cAMP, calcium, lipid derived ex: gene expression first messenger→ signal from the outside to change gene expression second messenger→ does not directly alter gene expression, it binds to a protein or a series of proteins and eventually, using transcription factors, they can activate gene and change gene expression

GPCR first messenger and second messenger

first: ligand that binds to receptor second: effector that gets activated

Muscle cells and glucose

muscle cells need sugar and lots of energy so they will go into glycolysis instead to produce ATP

phosphorylase and glycogen synthase

phosphorylase→enzyme that breaks down glycogen making more glucose glycogen synthase→enzyme that takes excess glucose and stores it as glycogen

In a signalling pathway, signaling proteins can:

relay, amplify, integrate, and distribute incoming signals. relay→ relay signal into the cell amplify→ 1 upstream protein can modify and activate many copies of a downstream protein integrate→ convergence in pathway; many different proteins in the cell that can modify 1 protein. ex: 3 proteins can modify 1 protein. 1 can inhibit the protein and another can activate that protein. distribute→ distribution of signal to other proteins ** some proteins in the pathway may be held together in proximity by a scaffold protein, which allows them to be activated at a specific location in the cell and with greater speed and efficiency

Protein phosphatase

removes phosphate off of other proteins during the deactivation or dephosphorylation of the activated protein

Function of molecules are dependent on:

shape

GTPase

takes the GTP bound to protein and cleaves off the gamma phosphate and now the protein is bound to GDP