BIO 131 Cell Signaling Material

What is the role of Protein Kinase A?

(When activated) ; activates another protein, leading to cellular responses. It phosphorylates various other proteins.

What are the roles of the following; 1. Relay Molecule 2. Roles of Enzyme in phosphorylation cascade 3. Signal molecule (first messanger) 4. Does this image involve an intracellular receptor or a Plasma Membrane receptor?

(answers on figure 5.26)

In phosphorylation, the addition of phosphate group often changes the form of a protein from (think of activeness)

Inactive and active)

Phosphorylation Cascade 2. Active protein kinase 1 activates [blank] This is official beginning part of the [blank]

Protein kinase 2 Phosphorylation cascade

Protein phosphatases can also make [blank] available for reuse, enabling the cell to respond to the signal again.

Protein kinases

How/why can the signaling molecules enter the cell?

A number of important signaling molecules can do this because they are hydrophobic enough to cross the hydrophobic interior of the membrane. In order to reach a receptor, the signaling molecule passes through the target cell's plasma membrane.

Phosphorylation cascade

A series of enzyme-catalyzed phosphorylation reactions commonly used in signal transduction pathways to amplify and convey a signal inward from the plasma membrane.

Signal Transduction pathway

A series of steps linking a mechanical, chemical or electrical stimulus to a specific cellular response. - The binding of a specific signaling molecule to a receptor in the plasma membrane triggers the first step in the signal trans. pathway--The chain of molecular interactions that leads to a particular response with the cell

Second messenger

A small, nonprotein, water-soluble molecule or ion, such as Calcium ion or cyclic AMP, that relays a signal to a cell's interior in response to a signal received by a signal receptor protein.

Transduction

A step or series of steps that converts the signal to a form that can bring about a specific cellular response. Transduction usually requires a sequence of changes in a series of different molecules--as a signal transduction pathway.

In Nucleus associated responses, what is a transcription factor?

A transcription factor is a response to the growth factor, the synthesis of one or more specific mRNAs, which will be translated in the cytoplasm into specific proteins.

What does the addition of a phosphate group do to a protein? A. can either activate or inactivate a protein B. always inactivates a protein C. activates G-protein-linked receptors D. is accomplished by protein phosphatases E. always activates a protein

A. can either activate or inactivate a protein The addition of a phosphate often activates a protein, although in other cases phosphorylation decreases the activity of the protein. (dephosphorization)

Lipid-soluble signaling molecules, such as aldosterone, cross the membranes of all cells but affect ONLY target cells because __________. A. intracellular receptors are present only in target cells B. only in target cells is aldosterone able to initiate the phosphorylation cascade that turns genes on C. only target cells retain the appropriate DNA segment D. only target cells have enzymes that break down aldosterone

A. intracellular receptors are present only in target cells

A mutation in the active site of adenylyl cyclase that inactivates it would most likely lead to A. lower activity of protein kinase A B. increased binding of adenylyl cyclase to the G protein that activates it C. reduced binding of adenylyl cyclase to protein kinase A D. higher activity of protein kinase A E. an increase in the amount of cAMP present in the cell

A. lower activity of protein kinase A Protein kinase A is activated by cAMP and if adenylyl cyclase could not make cAMP, then protein kinase A would not be as active as it should.

Pre Test Question: Phosphorylation cascades involving a series of protein kinases are useful for cellular signal transduction because __________. A. they amplify the original signal manyfold B. they counter the harmful effects of phosphatases C. they always lead to the same cellular response D. they are species−−specific

A. they amplify the original signal manyfold

Adenylyl cyclase, an enzyme in the plasma membrane, rapidly converts [blank] to [blank] in response to a number of extracellular signals.

ATP to cAMP

Ion Channel are the [blank] way to make something happen within the cell

Are the fastest way.

A G protein is active when __________. A. Ca2+ binds to a G-protein-linked receptor B. GTP is bound to it C. it is phosphorylated by protein kinase D. it is bound by its ligand and transported to the nucleus E. GDP replaces GTP

B. GTP is bound to it When GDP is bound, the G protein is inactive; when GTP is bound, it is active.

The general name for an enzyme that transfers phosphate groups from ATP to a protein is __________ A. protein phosphatase B. protein kinase C. peptidase D. protein dehydrogenase E. protein cyclase Most protein kinases attach phosphate groups to proteins different from themselves. However, some protein kinases phosphorylate other protein kinases of the same type.

B. protein kinase Most protein kinases attach phosphate groups to proteins different from themselves. However, some protein kinases phosphorylate other protein kinases of the same type.

What event would activate a G protein? A. hydrolysis of GTP to GDP B. replacement of GDP with GTP C. phosphorylation of GDP to GTP D. hydrolysis of GDP to GTP E. phosphorylation of GTP to GDP

B. replacement of GDP with GTP Inactive G proteins are bound to GDP. The activated receptor replaces the GDP with GTP, thereby activating the G protein.

In our previous epinephrine example: is the cellular response regulation of gene synthesis or is it regulating the activity of already existing proteins in cytoplasm?

Based on the figure, the cellular response is regulating the activity of existing proteins in the cytoplasm.

In deactivation, the cellular response diminishes rapidly when the hormone is no longer [blank] to its [blank]

Bound Receptor

In eukaryotic cells, which is a second messenger that is produced as a response to an external signal such as a hormone? A. Glucose B. Epinephrine C. Cyclic AMP D. tRNA E. Glycogen

C. Cyclic AMP The first messenger, the hormone, causes a membrane enzyme to synthesize cAMP, which transmits the signal to the cytoplasm.

Pre Test Question: Why are there often so many steps between the original signal event and the cell's response? A. Each transduction is a checkpoint. B. Lengthy pathways provide the opportunity for the initial pathway molecules to recycle back to inactive forms should additional signaling molecules be present. C. Each step in a cascade produces a large number of activated products, causing signal amplification as the cascade progresses. D. Long, highly specific pathways minimize the possibility that a relay molecule could accidentally activate a pathway leading to a secondary response. E. The accumulation of genetic mutations over time has added redundant steps to the pathway.

C. Each step in a cascade produces a large number of activated products, causing signal amplification as the cascade progresses. This amplification permits the signaling molecule to have a widespread effect throughout the cell.

Pre Test Question: Which of the following provides molecular evidence that signal transduction pathways evolved early in the history of life? A. Cell signaling is observed in organisms that do not utilize sexual reproduction. B. Simple forms of life, such as prokaryotic cells, utilize cell signaling C. The molecular details of cell signaling are quite similar in organisms whose last common ancestor was a billion years ago. D. The pathways in primitive organisms, such as bacteria, are short, whereas those in advanced forms, such as mammals, are long. E. Receptor molecules have been identified in preparations of fossilized organisms billions of years old.

C. The molecular details of cell signaling are quite similar in organisms whose last common ancestor was a billion years ago.

ATPgammaS is a form of ATP that cannot be hydrolyzed by enzymes. If this compound was introduced to cells so that it replaced the normal ATP present in the cell, which of the following would you predict? A. an increase in anabolic cellular reactions B. an increase in cell division C. a decrease in phosphorylated proteins in the cell D. an increase in the synthesis of mRNA E. Two of the listed responses would be expected.

C. a decrease in phosphorylated proteins in the cell Protein kinases transfer the gamma phosphate from ATP to a target protein. ATPgammaS cannot be hydrolyzed and has a sulfur protein in the gamma position. This molecule cannot be used by protein kinases.

Steroid hormones can enter a cell by simple diffusion. Therefore steroids __________ A. directly bind to DNA B. do not bind to receptors C. do not initiate cell signaling by interacting with a receptor in the plasma membrane D. act by phosphorylating DNA E. are not an example of signaling molecules

C. do not initiate cell signaling by interacting with a receptor in the plasma membrane Steroid hormones, because of their hydrophobic characteristics, readily cross cell membranes and bind to receptors in the cytoplasm, activating the receptor. The active receptor protein then binds to and turns off genes in the nucleus that control the response. Thus, the receptor carries out the complete transduction of the signal.

Nitric oxide is unusual among animal signal molecules in that it __________ A. enters the cell via a protein channel B. acts by directly binding to DNA C. is a gas D. binds to membrane receptors and cytoplasm receptors E. activates proteins by removing phosphate

C. is a gas Chemical messengers with intracellular receptors include the steroid hormones and even the

Receptors for signal molecules __________. A. all work via protein kinases B. are only found associated with the plasma membrane C. may be found embedded in the plasma membrane, or found within the cytoplasm or nucleus D. all work by opening ion channels E. are never found in the nucleus of a cell

C. may be found embedded in the plasma membrane, or found within the cytoplasm or nucleus Not all signal receptors are membrane proteins. Some are located in the cytoplasm of target cells.

Second messengers tend to be water-soluble and small. This accounts for their ability to __________. A. move from substrate to substrate during a phosphorylation cascade B. cross the nuclear membrane and interact with DNA C. rapidly move throughout the cell by diffusion D. rapidly cross the plasma membrane E. pass quickly from cell to cell

C. rapidly move throughout the cell by diffusion Diffusion permits a wide dispersal of the molecules from the site of their entry or production at a membrane.

Common Second Messengers?

Ca and cAMP

What Ion binds to calmodulin?

Ca+2

Neurotransmitters (more specialized type of paracrine signal)

Chemical messengers that cross the synaptic gaps between neurons

The source of phosphate for a phosphorylation cascade is __________. A. protein kinase B. GTP C. protein phosphatase D. ATP E. cAMP

D. ATP The general name for an enzyme that transfers phosphate groups from ATP to a protein is a protein kinase.

Testosterone and estrogen are lipid-soluble signal molecules that cross the plasma membrane by simple diffusion. If these molecules can enter all cells, why do only specific cells respond to their presence? A. In nontarget cells, these signal molecules cross the membranes of the endoplasmic reticulum and are captured by vesicles. B. The signal molecules diffuse from the cell before an effective concentration can be achieved. C. Nontarget cells possess enzymes that immediately degrade the molecules as they enter the cell. D. Nontarget cells lack the intracellular receptors that, when activated by the signal molecule, can interact with genes in the cell's nucleus. E. Nontarget cells lack the inactive enzymes that the signal molecules activate.

D. Nontarget cells lack the intracellular receptors that, when activated by the signal molecule, can interact with genes in the cell's nucleus. Nonpolar signal molecules easily enter cells, but only those cells with functional intracellular receptors respond.

What did Sutherland discover about glycogen metabolism in liver cells? A. Glucose is produced from glycogen when epinephrine binds to a cytoplasmic protein. B. Glucagon breaks down glycogen to glucose in liver cells. C. A cytoplasmic receptor triggers the signal transduction pathway that produces glucose from glycogen. D. The hormone epinephrine binds to a specific receptor on the plasma membrane of the liver cell. E. The hormone that breaks down glycogen into glucose enters the liver cell.

D. The hormone epinephrine binds to a specific receptor on the plasma membrane of the liver cell. Epinephrine activates the receptor to carry out the breakdown of glycogen into glucose.

Steroid hormones can enter a cell by simple diffusion. Therefore steroids __________. A. move up a concentration and are polar B. move up a concentration gradient and are nonpolar C. move through a channel, down a gradient, and are nonpolar D. move down a concentration gradient and are polar E. None of the choices is correct.

E. None of the choices is correct. Simple diffusion must occur down a gradient, and as the molecule moving must pass through the membrane, that molecule must be nonpolar; no membrane protein is required for passive diffusion.

cAMP usually directly activates __________ A. phosphodiesterase B. G proteins C. adenylyl cyclase D. receptor tyrosine kinases E. protein kinase A

E. Protein Kinase A The relay molecule immediately after cAMP in a signaling cascade is usually protein kinase A, a serine/threonine kinase, which is activated by cAMP.

Why can a signaling molecule cause different responses in different cells? A. Different cells have membrane receptors that bind to different sides of the signaling molecule. B. Different cells possess different enzymes, which modify the signaling molecule into different molecules after it has arrived. C. The transduction pathway in cells has a variable length. D.All of the listed responses are correct. E. The transduction process is unique to each cell type; to respond to a signal, different cells require only a similar membrane receptor.

E. The transduction process is unique to each cell type; to respond to a signal, different cells require only a similar membrane receptor. The signal simply initiates a process by binding to and activating a membrane receptor. How transduction proceeds may be quite different for different cells.

Testosterone does not affect all cells of the body because __________ A. it is a local regulator B. testosterone cannot cross the plasma membrane C. not all cells in the body have membrane receptors for testosterone D. it affects only cells that have ion-channel receptors E. not all cells have cytoplasmic receptors for testosterone

E. not all cells have cytoplasmic receptors for testosterone Steroid hormones, such as testosterone, readily enter cells all over the body, but they stimulate a response only in target cells--those with receptor molecules in the cytoplasm.

Long Distance signaling can be also known as

Endrocrine (hormonal) signaling

Protein Kinases and Protein Phosphatases are both [blank]

Enzymes

protein phosphatases

Enzymes that can rapidly remove phosphate groups from proteins. Referred to as Dephosphorylation. They provide the mechanism for turning OFF the signal transduction pathway when the initial signal isn't present.

Examples of signaling molecules which use GPCRs

Epinephrine, other hormones and neurotransmitters.

Paracrine signaling

when a signaling cell acts on nearby target cells by secreting molecules of a local regulator (a growth factor, for ex)

Is every cell in our body going to respond to the same hormone?

No Depends if the cell has the CORRECT receptor for the CORRECT signal!

Do first messengers enter the cell?

No!

Examples of Common "cellular responses"?

1. Catalysis by an enzyme (for example: glycogen phosphorylase) 2. Rearrangement of the cytoskeleton 3. Activation of specific genes in the nucleus

Cytoplasmic Response: Glycogen Breakdown (Signal transduction) 1. Epinephrine (signal molecule) binds to [blank] triggering signal transduction pathway in the cytoplasm. 2. G protein is activated (blank--> blank) 3. The G protein the activates [blank] converting (blank --> blank) 4. Second messenger [blank] activates series of [2 blank blank]. 5. Final [blank] activates the enzyme [blank] 6. This enzyme cleaves glycogen molecules releasing [blank] monomers which enter the bloodstream... providing quick energy from fighting or fleeing from a threat

1. G protein coupled receptors. 2. GDP --> GTP 3. Adenylyl Cyclase ATP to cAMP 4. cAMP 2 Protein Kinases 5. Kinase The enzyme glycogen phosphorylase 6. Releases glucose monomers

Where are signal receptors located? (2 locations)

1. IN the plasma membrane ---where they can bind to signaling molecules that cannot or do not cross the membrane. Their ligands are water-soluble and generally too large to pass freely through the plasma membrane. 2.INSIDE the cytoplasm ---where they respond to lipid-soluble signaling molecules that readily diffuse w/ the plasma membrane

Identify the components of: 1. GPCR signaling pathway (insert epinephrine example components into this pathway)

1. The binding of epinephrine to a GPCR (receptor) leads, via a G protein meaning that it releases a G protein (GDP) to exchange for a GTP molecule) , then it activates adenylyl cyclase, an enzyme embedded in the plasma membrane that converts ATP to cAMP. cAMP, a second messenger, activates another protein, leading to cellular responses.

Besides GPCR and Ligand-gated ion channels, what is a 3rd type of receptor in the plasma membrane?

3rd type of receptor in the Plasma membrane: [Receptor Enzyme]

RTK (receptor tyrosine kinase)

3rd type of receptor in the Plasma membrane: [Receptor Enzyme] Enzyme-coupled receptor in which the intracellular domain has a tyrosine kinase activity, which is activated by ligand binding to the receptor's extracellular domain.

Terms 94 and onward will be questions along the study area in Mastering Biology When a platelet contacts a damaged blood vessel, it is stimulated to release thromboxane A2. Thromboxane A2 in turn stimulates vascular spasm and attracts additional platelets to the injured site. In this example thromboxane A2 is acting as a __________. (Section 5.6) A. local regulator B. transcription factor C. protein kinase D. G protein E. neurotransmitter

A (Local Regulator) A transmitting cell can secrete molecules of a local regulator, a substance that influences cells in the vicinity.

What are the differences between G-protein coupled-receptors (GPCR) vs. ion channel receptors

A GPCR is a signal receptor protein in the plasma membrane that responds to the binding of a signaling molecule by activating a G protein. GPCRs are all remarkably similar in structure, as are G proteins suggesting they these signaling systems evolved very early in the history of life. Ion Channel Receptors act as a "gate" for ions.. contains a pore that opens or closes as it changes shape in response to a signaling molecule (ligand) allowing or blocking the flow of specific ions; also called an ionotropic receptor.

calmodulin

A calcium-binding protein; triggers the assembly of microtubules that alter the shape of the cell.

Ligand

A molecule that binds specifically to another molecule, usually a larger one. LDLs, or low density lipoproteins act as ligands when they bind to their receptors, as do the molecules that bind to enzymes.

2nd messengers will rapidly

Amplify and distribute the information of a signal (they bind noncovalently)

Protein Kinase

An enzyme that transfers phosphate groups from ATP to a protein, thus phosphorylating the protein. Recall: These enzymes are widely involved in signaling pathways in animals, plants and fungi.

Ras, a small G protein located at the plasma membrane, is often mutated in different types of cancer. Ras normally signals to a cell that it should divide. Cancer cells divide uncontrollably. Which change to Ras would you expect in a cancer cell? A. a mutation that means Ras cannot bind to GTP B. a mutation that leads to Ras being sent to the endomembrane system C. a mutation that means Ras cannot hydrolyze GTP to GDP D. a mutation that means GDP is constantly bound to Ras E. a mutation in which Ras cannot bind to its GPCR

C. a mutation that means Ras cannot hydrolyze GTP to GDP Such a mutation would mean that Ras would always be turned on, and would thus signal to the cell to divide continuously. Such division could lead to cancer.

Multistep pathways pathways provide more opportunities for [blank] and [blank] than do simpler systems.

Coordination and control

Early work on signal transduction and glycogen metabolism by Sutherland indicated that __________. A. The signal molecule worked equally well with intact or disrupted cells B. The signal molecule combined directly with a cytosolic enzyme to form an active quaternary structure C. epinephrine is involved in response to stress D. The signal molecule did not interact directly with the cytosolic enzyme, but required an intact plasma membrane before the enzyme could be activated E. the cell-signaling pathway involves two separate steps: transduction and response

D. The signal molecule did not interact directly with the cytosolic enzyme, but required an intact plasma membrane before the enzyme could be activated Enzyme activation could proceed only when the plasma membrane was intact.

The cellular response of a signal pathway that terminates at a transcription factor would be __________. A. a change in the chemical composition of the cytosolic environment B. the activation of a metabolic pathway C. the activation of an inactive enzyme D. the synthesis of mRNA E. alteration of the cytoskeleton

D. The synthesis of mRNA Transcription factors are proteins that regulate the transcription of DNA into mRNA.

Let's say what if? How can a target cell's response to a single hormone molecule result in a response that affects a million other molecules?

During each step in a cascade of sequential activations, one molecule or ion may activate numerous molecules functioning in the next step. This causes the response to be amplified at each such step and results in a LARGE amplification of the original cell.

True false: Hormones are present in only animal cells?

False, they can ALSO in plant cells

Example of G protein-coupled receptor:

Figure 5.23

EXAMPLE of Ion Channel Receptor:

Figure 5.24

Based on figures 5.27 and 5.28, which of these has their cellular response occurring in the cytoplasm v the nucleus?

Figure 5.27 has its responses in the cytoplasm while 5.28 has its in the nucleus.

The extracellular signal molecule (ligand) that binds to the receptor is a pathway's

First Messenger

For intracellular receptors, what is aldosterone ?

It's a hormone that can easily pass through the plasma membrane as it is hydrophobic and lipophilic. (fat loving)

During an epinephrine-initiated signal in liver cells, in which of the three stages of cell signaling does glycogen phosphorylase act?

Glycogen phosphorylase acts in the third stage (cellular response) the response to epinephrine signaling.

Receptors that recognize chemical signals will have very specific [blank]?

Have very specific bonding sites.

Diffusion heads from [blank] and [blank] concentrations

High to Low concentrations

In hormonal signaling in animals (endocrine signaling) special cells release [blank] molecules that travel via the [blank]

Hormone molecules Via the Circulatory System

For intracellular receptors, small or [blank] chemical messengers can easily cross the membrane and activate [blank].

Hydrophobic receptors

Amplifying a signal

If each molecule in a specific pathway transmits the signal to numerous molecules at the next step in the series, the result is a geometric increase in the number of molecules by the end of the pathway.

Intracellular receptor proteins are found where in target cells?

In either the cytoplasm or nucleus of target cells.

In deactivation, G proteins hydrolyze GTP their bound GTP to GDP, returning to their [blank] state, dissociate from [blank]. This ends [blank] production.

Inactive Adenylyl Cyclase cAMP

Intracellular receptors vs Plasma Membrane Receptors

Intracellular: Signals are able to pass through the cell rather than plasma membrane receptors because they are hydrophobic enough to cross the hydrophobic interior of the membrane. PM: The information from the signal enters the cell (transmitted within the cell) but the signal molecule CANNOT enter the cell alone!

Is Protein Kinase A specific to the epinephrine pathway or is it involved in many pathways?

It is specific to many pathways because the immediate effect of cAMP is usually activation of Protein Kinase A. Epinephrine is one of MANY hormones and other signaling molecules that trigger the formation of cAMP.

Discuss Shape Change in a Receptor Molecule?

Ligand binding generally causes a receptor protein to undergo a change in shape. Shape change directly activates the receptor, enabling it to interact with other cellular molecules.

Receptors are classified by their...

Location and their functions

What other receptors can we have? (besides on the plasma membrane)

Membrane receptors and intracellular receptors.

signaling molecules

Messengers that are generally involved in the cell signaling process. In other cases, signaling molecules are secreted by the signaling cell.

Are transcription factors the same as growth factors? If not, why?

No! Transcription factors are proteins that bind to DNA (directly, or sometimes indirectly) to encourage transcription of a particular gene or genes. Growth factors however are (typically secreted) that interact with other molecules (receptors) to influence cellular behavior, both through transcription and other molecular messengers. Refer to the figure to examine the behavior of growth factors:

At each step of signal transduction, the signal is transduced into a different form, commonly via a shape change in a protein. For each step, are proteins always going to be involved?

No.

Can hydrophilic molecules cross into chemicals of the same type?

No. Charged atoms or molecules of any size cannot cross the cell membrane via simple diffusion as the charges are repelled by the hydrophobic tails in the interior of the phospholipid bilayer. Hydrophobic molecules can pass directly through the hydrophobic lipid bilayer of the plasma membrane.

Based on Figure 5.24, is the flow of ions through this receptor an example of active or passive transport?

Passive Transport. The ion is moving down its concentration (High to low) gradient, and NO energy is required.

What are some examples of pathways were GPCR proteins are involved?

Pathways include role in embryonic development and the senses of sight, smell and taste. Also involved in MANY human diseases (cholera, pertussis (whooping cough) and botulism, which are caused by bacterial toxins that interfere w G protein function.

Phosphorylation Cascade 4. Protein phosphatases catalyze the removal of the [blank] groups from the proteins, making the proteins [blank] again. We don't want the cellular response to go forever! Allows for a recycling of our kinases in order to repeat the next round of signal transduction

Phosphate Inactive

Most signal receptors are [blank]

Plasma Membrane Proteins

When a signal transduction pathway involves a phosphorylation cascade, what turns off the cell's response?

Protein phosphatases reverse the effects of the kinases, and UNLESS the signaling molecule is at a high enough concentration that it is continuously rebinding the receptor, the molecules will all be returned to their inactive states by phosphatases.

Dephosphorylation

Rapid removal of a phosphate group from a molecule

When cellular response is located in the cytoplasm, the pathways can [blank] the activity of already existing [blank] rather than their synthesis, such as the opening of an ion channel or a change in cell metabolism.

Regulate. Proteins/enzymes Reminder: Enzymes are proteins.

In the 3rd stage of cell signaling, the transduced signal finally triggers a specific cellular... ?

Response!

Growth factors (type of paracrine signal)

Stimulate the growth and division of cells

Phosphorylation Cascade 3. Active protein kinase 2 phosphorylates a protein that brings about the cell's [blank] to the signal

The cell's Response

The cell-to-cell communication process usually involves what part of the cell?

The cells' plasma membranes.

protein-protein interactions

The molecules that relay a signal a signal from receptor to response, which we call relay molecules are often proteins. When the signal is passed on, only CERTAIN information is passed on. Each step, the signal is transducer into a different form via a shape change in a protein. Major theme of cell signaling!

If the cellular response is located in the nucleus, what is the response regulating?

The response is regulating protein synthesis (gene expression). The figure shows that the transcription factor stimulates the transcription of a SPECIFIC gene. Result mRNAs direct the synthesis of a particular protein in the cytoplasm.

If the cellular response is located in the cytoplasm, what is the response regulating?

The response is regulating the activity of already existing proteins. cAMP, a second messenger, activates another protein, leading to cellular responses.

Are first messengers *exclusively* extracellular ligands or would a steroid that enters the cell and binds to an intra-cellular receptor also count as a "first messenger"?

The steroid that enters the cell and binds to an intracellular receptor would count as a first messenger. It's not a second messenger because it is the first thing to bind to a receptor!

Reception

The target cell's detection of a signal molecule coming from outside the cell. A chemical signal is "detected" when the signaling molecule binds to a receptor protein located at the cell's surface or, in some cases, inside the cell.

Phosphorlyation

The transfer of a phosphate group on ATP to another molecule, or the addition of phosphate groups to a molecule

Hormone-Receptor complex

They bind to hormones, activating the receptor protein (HR complex), enters the nucleus and binds to specific genes to turn them on.

glycogen phosphorylase

This enzyme cleaves glycogen molecules, releasing sugar in the form of glucose-1 phosphate.

True of False: hormones do not affect other endocrine glands or body systems

True: they affect a specific hormonal gland/receptor

Why are these called second messengers?

While the pathway's "first messenger' is considered to be the extracellular signaling molecule which BIND to a membrane receptor, second messengers can easily spread throughout the cell by diffusion. (higher to lower concentrations)

Ion Channels very specific to the signals they respond to?

Yes (ligand/other signaling molecule fits into an open area on the receptor) *key and lock in order to allow specific ions to flow through the channel before it (ligand) dissociates and leaves the receptor)

Is cell-to-cell signaling also important to unicellular organisms?

Yes, for example Prokaryotes.

Synaptic signaling

a nerve cell releases neurotransmitter molecules into a synapse (SMALL area between the cells), stimulating the target cell (such as a muscle or another nerve cell)

In Figure 5.25, what is the role of mRNA ?

mRNA is a result of the bound protein acting as a transcription factor, stimulating the transcription of a gene (into mRNA). The mRNA assists the translation of a specific protein (which is to be formed).

Examples of local signaling

paracrine signaling and synaptic signaling

Phosphorylation Cascade 1. A relay molecule activates [blank]

protein kinase 1