chapter 6 - cell signaling

cell signaling

what is the communication between cells of the body called

(1) gap junctions, (2) cell-to-cell binding, and (3) extracellular chemical messengers.

what are the different ways cells can communicate

a way that cells can communicate, basically at gap junctions there are membrane proteins called connexins that form tunnels called connexons that connect neighboring cells

what are gap junctions

these are the tunnels that connect neighboring cells - thru these, ions and small molecules can diffuse from the cytosol of one cell to the cytosol of antoher cell

what are connexons

in a variety of tissues including nervouse tissue between some neurons, cardiac muscle, and some types of smooth muscle

where are gap junctions found

when gap junctions are present between neurons, the movement of ions through the connexons electrically couples the cells which facilitates and synchronizes the neural communication

How do gap junctions facilitate communication between neurons?

Gap junctions are present between muscle cells and electrically couple them. This coupling allows muscle cells to contract simultaneously as a single unit.

Where can gap junctions be found in muscle tissue, and what is their role there?

surface molecule of one cell binds to a surface molecule on another cell - this is important during development and for leukocytes to recognize and respond to dangerous cells

What is cell-to-cell binding, and when is it important for cells?

using an extracellylar chemical messenger

what is the most common type of communication between cells

basically, a cell secretes a chemical messenger into ECF, the chemical messenger then diffuses through the ecf and comes in contact with a bunch of cells but it only has an effect on specific target cells

how does using an ECM work

a cell that can respond to the extracellular messenger

what is a target cell

Receptors are specific proteins that bind to extracellular chemical messengers, initiating the signal transduction process.

What is the role of a receptor in cell communication?

a molecule that binds to a particular site on a protein

what is a ligand

an extracellular messenger

what acts as a ligand

in the target cell's plasma membrane or inside the target cell

where are receptors found

signal transduction is the process by which the signal molecule (ECM) is transduce (converted) into a response by the target cell - binding of the ecm to the receptor causes it

what is signal transduction? what causes it?

A signal transduction pathway is the sequence of events that occurs during signal transduction, involving multiple molecules that each trigger changes in the next molecule in the pathway.

What is a signal transduction pathway?

a cellular response by the target cell (examples of cellular responses cell growth, protein synthesis, secretion, muscle contraction)

what happens at the end of a signal transduction pathway

a molecule that is released by a cell, enters the extracellular fluid and then binds to a receptor on or in its target cell to cause a response

what is an extracellular chemical messenger

horomones and neurotransmitters and local mediators

what are the types of extracellular chemical messengers

extracellular transmitters that are carried by the blood to distant target cells.

what are horomones

1) hormone is secreted by sell into institiual fluid

2) hormone diffuses into blood stream

3) bloodstream carries hormone everywhere in body - but only target cells have the correct receptors to respond to the hormone

describe how a hormone is used to send a message

cell signaling that is mediated through hormones

what is endocrine signaling

an endocrine cells

what is an epithileal cell that secretes a hormone called

extracellular chemical messengers that are released from a neuron into a synapse in order to reach a nearby target cell

what are nuerotransmitters

a junction between a neuron and its target cell (which can be another neuron, muscle cell or gland cell)

what is a synapse

presynaptic neuron

what is the nueron that releases the neurotransmitter called

postsynaptic cell

what is the neuron that receives neurotransmitter called

synpatic cleft (it is filled with interstitial fluid)

What separates the plasma membranes of a presynaptic neuron and a postsynaptic cell in synaptic communication?

electrical and chemical signals

What are the two main types of signals used by the nervous system for communication?

A graded potential is an electrical signal produced in the dendrites or cell body of a neuron.

What is a graded potential, and where is it produced in a neuron?

An action potential is triggered when a graded potential in a neuron is strong enough and spreads to the beginning of the neuron's axon.

What triggers the formation of an action potential in a neuron?

An action potential travels along the axon in the direction of the synapse.

Describe the path of an action potential in a neuron.

Neurotransmitters are chemical signals that are released by the presynaptic neuron into the interstitial fluid of the synaptic cleft. The neurotransmitters are produced when the action potential travels in the direction of the synapse

What is the role of neurotransmitters in cell communication, and where are they released?

Dopamine is an example of a neurotransmitter. It is involved in generating emotional responses, forming addictive behaviors and pleasurable experiences, and regulating skeletal muscle tone and some aspects of movement in the brain.

Provide an example of a neurotransmitter and briefly describe its functions in the brain.

Synaptic signaling is cell signaling mediated through neurotransmitters. It is considered a form of short-distance communication because the presynaptic neuron and postsynaptic cell are close to each other.

What is synaptic signaling, and why is it considered a form of short-distance communication?

Graded potentials and action potentials are essential for cell-to-cell communication because they are required for the release of neurotransmitters by neurons to communicate with target cells.

How do graded potentials and action potentials contribute to cell-to-cell communication?

Graded potentials are a type of short-distance communication as they spread only along small areas of membrane in the dendrites or cell body of the neuron. Action potentials are a form of long-distance communication as they spread along the membrane of the entire length of the axon, which can be very long (a meter or more) in many neurons.

In terms of communication distance, how does a graded potential differ from an action potential?

Local mediators are extracellular chemical messengers that act on nearby target cells without entering the bloodstream. They are also known as local regulators or local agents.

What are local mediators, and what are they also known as?

Local mediators are released from a cell into interstitial fluid and then diffuse through the fluid to act locally on neighboring cells or on the same cell that secreted them.

How do local mediators reach their target cells?

Paracrines are local mediators that act on neighboring cells. They function by affecting nearby cells within close proximity.

What are paracrines, and how do they function in cell signaling?

Autocrines are local mediators that act on the same cell that secreted them. They differ from paracrines in that they affect the cell that produced them.

What are autocrines, and how do they differ from paracrines?

local signaling

What is the term for cell signaling that occurs through local mediators?

Local signaling is short-distance communication because of the close proximity of the local mediator to the target cell.

Why is local signaling considered a type of short-distance communication?

Synaptic signaling is a form of local signaling specifically occurring between a neuron and a postsynaptic cell. It is unique because it involves neurotransmitters as paracrines.

What is synaptic signaling, and why is it considered unique among local signaling?

Cytokines are molecules that regulate various cell functions, including cell growth and differentiation. They play a crucial role in immune responses and help activate nearby immune cells through paracrine effects. They can also act as autocrines by stimulating the same cell that released them.

What are cytokines, and what is their role in the body?

An example of a cytokine is interleukin-2 (IL-2), which is released by helper T cells during immune responses. IL-2 helps activate nearby immune cells through paracrine effects and stimulates the proliferation of the same cell that released it.

Provide an example of a cytokine and describe its function.

Nitric oxide (NO) is a gas released by endothelial cells lining blood vessels.

What is nitric oxide (NO), and where is it released in the body?

Nitric oxide (NO) causes relaxation of nearby smooth muscle fibers in blood vessels, leading to vasodilation or an increase in blood vessel diameter.

What is the effect of nitric oxide (NO) on smooth muscle fibers in blood vessels?

Eicosanoids are molecules released by many cells in response to chemical or mechanical stimuli. They function as local mediators, acting as either paracrines or autocrines on nearby target cells.

What are eicosanoids, and how do they function as local mediators?

The three major types of eicosanoids are prostaglandins, leukotrienes, and thromboxanes.

Name the three major types of eicosanoids.

Eicosanoid synthesis begins when a membrane phospholipid is cleaved by the enzyme phospholipase A2, producing a 20-carbon fatty acid called arachidonic acid.

Describe the synthesis of eicosanoids, including the initial molecule involved.

Arachidonic acid can enter the cyclooxygenase pathway, leading to the production of prostaglandins or thromboxanes, or it can enter the lipoxygenase pathway, resulting in the production of leukotrienes.

What are the two pathways that arachidonic acid can enter during eicosanoid synthesis?

Different cells produce various eicosanoids depending on which set of enzymes (cyclooxygenase or lipoxygenase) is present in those cells.

How are different eicosanoids produced by different cells?

Leukotrienes stimulate chemotaxis (attraction to a chemical stimulus) of leukocytes and mediate inflammation.

What is the role of leukotrienes in the body?

Prostaglandins alter smooth muscle contraction, glandular secretions, blood flow, reproductive processes, platelet function, respiration, action potential transmission, lipid metabolism, and immune responses. They also have roles in promoting inflammation, fever, and intensifying pain.

How do prostaglandins affect various physiological processes in the body?

Thromboxanes constrict blood vessels and promote platelet activation.

What are the primary functions of thromboxanes in the body?

Growth factors are substances that play important roles in tissue development, growth, and repair. They stimulate cell division and act as mitogenic substances.

What are growth factors, and what roles do they play in the body?

Many growth factors function locally, acting as autocrines or paracrines. Examples of growth factors include epidermal growth factor (EGF), platelet-derived growth factor (PDGF), fibroblast growth factor (FGF), nerve growth factor (NGF), and transforming growth factor (TGF).

How do many growth factors function in cell signaling, and what are the common types of growth factors mentioned in the passage?

Depending on where it is secreted, an extracellular chemical messenger can function as a hormone, neurotransmitter, or local mediator. For example, it functions as a neurotransmitter when released into the synapse between a neuron and its postsynaptic cell, as a hormone when released into the bloodstream, and as a local mediator when acting on nearby cells.

Explain how a given extracellular chemical messenger can function as a hormone, neurotransmitter, or local mediator depending on its secretion location.

Norepinephrine is an example of such a messenger. In the brain, it is released at some synapses, functioning as a neurotransmitter. In the adrenal gland, it is released into the bloodstream, functioning as a hormone.

Provide an example of an extracellular chemical messenger that can function as both a neurotransmitter and a hormone, and describe its roles in each context.

Extracellular messengers can be divided into two broad classes: those that are soluble in water and those that are soluble in lipids.

How can extracellular messengers be divided based on their chemical structure?

Examples of water-soluble extracellular messengers include peptide or protein hormones (such as oxytocin), amine hormones (such as norepinephrine), nearly all neurotransmitters, and most local mediators.

What are some examples of water-soluble extracellular messengers?

Lipid-soluble extracellular messengers include steroid hormones (such as testosterone and estrogens), thyroid hormones, and nitric oxide.

Which types of hormones fall under the category of lipid-soluble extracellular messengers?

The chemical classification of extracellular messengers is useful because it helps explain how the two classes exert their effects differently.

Why is the chemical classification of extracellular messengers useful in understanding their functional differences?

After secretion, an extracellular messenger enters interstitial fluid and then travels to its target cell.

What is the journey that an extracellular messenger takes after being secreted by a cell?

Neurotransmitters and local mediators simply diffuse through interstitial fluid to reach their target cells.

How do neurotransmitters and local mediators reach their target cells?

Hormones initially diffuse through interstitial fluid and then enter the bloodstream to reach their target cells.

What is the initial route of movement for hormones, and how do they ultimately reach their target cells?

Most water-soluble hormones circulate in the watery blood plasma in a "free" form, not attached to other molecules.

What is the typical state of water-soluble hormones in the bloodstream?

most lipid-soluble hormones are bound to transport proteins, which are synthesized by cells in the liver

How are most lipid-soluble hormones transported in the bloodstream?

1. Making lipid-soluble hormones temporarily water-soluble, increasing their solubility in blood.

2. slow down the removal of hormone molecules from the body through urine by preventing them from passing through the kidney's filtering system too quickly.

3) Providing a ready reserve of hormone already present in the bloodstream.

What are the three functions of transport proteins for lipid-soluble hormones?

Extracellular chemical messengers influence target cells by binding to specific protein receptors, triggering a signal transduction pathway and eliciting a cellular response.

What is the role of extracellular chemical messengers in influencing target cells?

When an extracellular messenger binds to its specific receptor, the receptor undergoes a conformational change and is activated.

ow does a receptor in cell signaling respond when an extracellular messenger binds to it?

The binding of the extracellular messenger to the receptor is reversible, meaning that when the messenger leaves the receptor, the cellular response comes to an end.

What is the consequence of the reversible nature of binding between an extracellular messenger and its receptor?

pecificity in messenger-receptor binding means that a given receptor permits binding of only one extracellular messenger or a small group of structurally related extracellular messengers. This specificity is based on the unique three-dimensional shape of the receptor's binding site.

Describe the property of specificity in messenger-receptor binding.

only target cells have the correct receptors with a complementary shape to which the specific extracellular messenger can bind, allowing for a response to occur.

Why do only target cells respond to a specific extracellular messenger even though the messenger may come in contact with many cells in the body?

Receptor affinity refers to the strength with which a messenger binds to a receptor. High affinity results in tight binding, while low affinity leads to loose binding.

What is receptor affinity in the context of messenger-receptor binding?

if a receptor has high affinity for a messenger, a relatively low concentration of the messenger is needed to cause a cellular response. Conversely, low affinity receptors require a relatively high concentration of messenger for a response.

How does receptor affinity affect the concentration of messenger required for a cellular response?

Adrenergic receptors, including alpha (α), beta (β), and subtypes like α1, α2, β1, β2, and β3, have varying affinities for norepinephrine and epinephrine.

Provide an example of receptors with different affinities for structurally similar messengers.

alpha 1 = alpha 2 = norepinphrine (alpha has no e)

For the alpha receptors, what do they favor

norepinephrine =epinephrine

what does the beta1 receptor favor

epinephrine >norepinephrine

what does the beta2 receptor favor

noreprinephrine> epinephrine

what does the beta 3 receptor favor

Receptor saturation is a property of messenger-receptor binding that occurs when 100% of the receptors in a target cell are bound by the messenger.

What is receptor saturation?

Receptor saturation occurs when all available receptors in a target cell are bound by the messenger. This happens as the concentration of the extracellular messenger increases.

How does receptor saturation relate to the concentration of extracellular messenger?

The cellular response does not increase beyond a certain point because when all receptors are fully saturated (bound by the messenger), there are no more available receptors to bind additional messengers, regardless of the messenger concentration.

Why does the cellular response not become greater beyond a certain point, even with increased messenger concentration?

fully saturated receptors are receptors in a target cell that have all their binding sites occupied by messenger molecules, resulting in a maximal response.

Define "fully saturated" receptors in the context of messenger-receptor binding.

Competition is a property of messenger-receptor binding in which two or more structurally similar messengers compete with each other to bind to the same receptor.

What is competition in the context of messenger-receptor binding?

Norepinephrine and epinephrine compete with each other to bind to adrenergic receptors, such as the beta-1 (β1) receptor which has an equal affinity for both of them

Provide an example of two extracellular messengers that compete with each other to bind to adrenergic receptors.

The relative concentrations of competing messengers influence which one is more likely to bind to receptors. Increasing the concentration of one messenger reduces the competitive effect of the other because more molecules of that messenger are available to bind to the receptors.

How do the relative concentrations of competing messengers affect which one is more likely to bind to receptors?

an agonist is a substance that binds to and activates a receptor, effectively mimicking the effect of the real messenger.

What is an agonist in the context of receptor binding?

Phenylephrine is an agonist to alpha-1 (α1) receptors that typically bind norepinephrine or epinephrine. Phenylephrine constricts blood vessels in the nasal mucosa, reducing mucus production and relieving nasal congestion.

Can you provide an example of an agonist and its action on receptors?

An antagonist is a substance that binds to and blocks a receptor, preventing the endogenous messenger from exerting its effect.

What is an antagonist in the context of receptor binding?

Propranolol (Inderal®) is an example of an antagonist. It binds to beta receptors, preventing their activation by norepinephrine or epinephrine, ultimately leading to a reduction in blood pressure.

Can you provide an example of an antagonist and its action on receptors?

Whether a receptor is located in the plasma membrane or inside the target cell depends on the solubility of the extracellular messenger. Water-soluble messengers have receptors in the plasma membrane, while lipid-soluble messengers have receptors inside the target cell.

What determines whether a receptor for an extracellular chemical messenger is located in the plasma membrane or inside the target cell?

Water-soluble messengers have receptors in the plasma membrane because they cannot pass through the hydrophobic interior of the plasma membrane.

Why do water-soluble extracellular messengers have receptors in the plasma membrane?

The receptors for lipid-soluble extracellular messengers are typically located inside the target cell, either in the cytosol or in the nucleus.

Where are the receptors for lipid-soluble extracellular messengers typically located?

Receptor down-regulation is a process where the number of receptors on a target cell decreases, making the cell less sensitive to an extracellular messenger.

What is receptor down-regulation?

Receptors can be removed from the plasma membrane through endocytosis, followed by degradation in lysosomes.

How can receptors be removed from the plasma membrane during down-regulation?

another mechanism of receptor down-regulation involves chemically modifying the receptor to disrupt its function.

What is another mechanism involved in receptor down-regulation besides removal from the plasma membrane?