Cyclic AMP (cAMP) Role in Cell Signaling Quiz and Flashcards

Podcast Beta

Play an AI-generated podcast conversation about this lesson

Questions and Answers

Which of the following is NOT a way that cellular messengers are regulated?

Chemical factors such as calcium levels in the blood

Endocrine factors such as thyroid stimulating hormone

Feedback loops used to maintain homeostasis (correct)

Neural factors such as autonomic stimulation of the pancreas

How do juxtacrine cellular messengers transmit signals between cells?

By binding to receptors on nearby cells

By being secreted and binding to the same cell's receptors

Through the bloodstream to distant target cells

Through direct cell-to-cell contact-dependent signaling (correct)

Which type of cellular messenger is responsible for communication within the immune system?

Hormones

Cytokines (correct)

Second messengers

Neurotransmitters

Which of the following is a key function of feedback loops in regulating cellular messengers?

To maintain a constant level of messengers Signup and view all the answers

What is the primary method by which endocrine cellular messengers, or hormones, are transported to target cells?

Via the bloodstream to distant target cells Signup and view all the answers

Which cellular response to messengers involves activating preexisting proteins through a second messenger system?

Activating preexisting proteins through a second messenger system Signup and view all the answers

What type of messengers are often made on-demand because they cannot be stored?

Lipid-soluble messengers Signup and view all the answers

Which type of messengers are synthesized from cholesterol?

Sex hormones Signup and view all the answers

What do water-soluble 1st messengers interact with to initiate the signaling pathway?

Receptor Signup and view all the answers

In cell-to-cell communication, what is activated by the hormone messenger to produce the primary effector that leads to the creation of the 2nd messenger?

G-protein Signup and view all the answers

What is the primary mechanism by which interstitial fluid and plasma regulate fluid movement and balance?

Capillary hydrostatic pressure (CHP) forces water out from the capillary into the interstitial space Signup and view all the answers

What is the main driving force for movement of water between the interstitial fluid (IF) and intracellular fluid (ICF)?

Osmotic forces Signup and view all the answers

Which electrolyte is the most abundant cation in the extracellular fluid (ECF)?

Sodium Signup and view all the answers

What happens to a cell in a hypertonic solution?

Water moves out of the cell and the cell shrinks Signup and view all the answers

What is the defining characteristic of an isotonic change in total body water (TBW)?

Changes in TBW are accompanied by a proportional change in concentration of electrolytes Signup and view all the answers

Which of the following statements accurately describes the role of G-protein coupled receptors (GPCRs) in cellular signaling?

GPCRs are membrane-bound receptors that activate second messengers like cAMP and calcium upon binding to first messengers. Signup and view all the answers

Which of the following statements accurately describes the role of calcium as a second messenger in cellular signaling?

Calcium is stored in the endoplasmic reticulum and is released into the cytosol to elicit cellular responses like muscle contraction and neuronal activation. Signup and view all the answers

Which of the following statements accurately describes the difference between lipid-soluble and water-soluble messengers in cellular signaling?

Lipid-soluble messengers target intracellular receptors and regulate protein synthesis, while water-soluble messengers interact with membrane-bound receptors and activate second messengers. Signup and view all the answers

Which of the following statements accurately describes the role of proteolytic cascades in cellular signaling?

Proteolytic cascades, such as the coagulation cascade, facilitate signal transduction and amplification through sequential activation of proteolytic enzymes. Signup and view all the answers

Which of the following statements accurately describes the role of feedback loops in cellular signaling?

Feedback loops are mechanisms by which the products or downstream effects of a signaling pathway can regulate the activity of upstream components, providing a means of modulating the signaling response. Signup and view all the answers

Which of the following is a key mechanism by which external/environmental factors can influence cellular processes regulated by the cell membrane?

Modifying the expression of membrane-bound receptor proteins Signup and view all the answers

The sodium-potassium pump is an example of which type of membrane transport mechanism?

Active transport Signup and view all the answers

Which of the following is a key function of feedback loops in regulating cellular messengers?

Decreasing the sensitivity of target cells to cellular messengers Signup and view all the answers

Which type of cellular messenger is responsible for communication between cells that are in direct physical contact?

Juxtacrine messengers Signup and view all the answers

Which of the following is NOT a way that cellular messengers are regulated?

Altering the distribution of messenger molecules within the cell Signup and view all the answers

Which of the following is a key way that juxtacrine cellular messengers transmit signals between cells?

By directly binding to receptors on the surface of target cells Signup and view all the answers

Which of the following is the primary mechanism by which endocrine cellular messengers, or hormones, are transported to target cells?

Vesicular transport within the bloodstream Signup and view all the answers

Which type of cellular messenger is responsible for communication within the immune system?

Cytokines Signup and view all the answers

Which of the following is a key function of feedback loops in regulating cellular messengers?

Decreasing the sensitivity of target cells to cellular messengers Signup and view all the answers

Which of the following is NOT a way that cellular messengers are regulated?

Altering the distribution of messenger molecules within the cell Signup and view all the answers

What is the main function of cellular messenger receptors in target cells?

Initiate signal transduction upon hormone binding Signup and view all the answers

Which type of hormones can easily diffuse across the plasma membrane?

Lipid-soluble hormones Signup and view all the answers

How do low concentrations of hormones affect cellular messenger receptors?

Increase the number of receptors per cell Signup and view all the answers

Which process is associated with the transport of water-soluble hormones?

Being bound to carrier proteins Signup and view all the answers

What happens when a target cell has more cellular messenger receptors?

The cell becomes more sensitive to hormones Signup and view all the answers

Which of the following processes is primarily responsible for the rapid regulation of blood pH in response to changes in CO2 levels?

Respiratory regulation of CO2 removal through exhalation Signup and view all the answers

What is the primary role of the carbonic acid-bicarbonate buffer system in regulating blood pH?

Maintaining the narrow pH range required for optimal enzyme function Signup and view all the answers

In the context of cell-to-cell communication, which of the following best describes the role of hemoglobin in regulating pH?

It serves as a buffer to maintain pH within red blood cells Signup and view all the answers

What is the primary mechanism by which the kidneys contribute to the regulation of blood pH?

Reabsorbing bicarbonate and excreting hydrogen ions in the urine Signup and view all the answers

Which of the following best describes a feedback loop involved in the regulation of blood pH?

A decrease in bicarbonate levels triggers the kidneys to reabsorb more bicarbonate Signup and view all the answers

Which type of cellular messengers are often synthesized on-demand because they cannot be stored?

Lipid-soluble messengers Signup and view all the answers

What is the primary mechanism by which $G$-protein coupled receptors (GPCRs) transmit signals in cellular communication?

Activating preexisting proteins through a second messenger system Signup and view all the answers

What happens to the number of cellular messenger receptors when hormone concentrations are high?

The number of receptors decreases Signup and view all the answers

Which of the following is a key mechanism by which lipid-soluble messengers, such as hormones, influence cellular processes?

Binding to intracellular receptors and activating RNA polymerase Signup and view all the answers

What is the primary function of second messengers in cellular communication?

To amplify and propagate the signal initiated by the first messenger Signup and view all the answers

Which of the following is NOT a characteristic of water-soluble messengers in cellular signaling?

Target intracellular receptors Signup and view all the answers

What is the primary function of proteolytic cascades in cellular communication?

Amplify signal transduction Signup and view all the answers

In cellular signaling, what initiates the creation of the second messenger within a target cell?

GPCR activation Signup and view all the answers

Which process can be activated by increased concentrations of calcium in the ICF?

Muscle contraction Signup and view all the answers

What is a direct consequence of releasing calcium from endoplasmic reticulum stores?

Increase in ICF calcium levels Signup and view all the answers

What is the primary mechanism by which lipid-soluble hormones initiate cellular signaling in target cells?

Binding to intracellular receptors and directly regulating gene transcription Signup and view all the answers

Which of the following best describes the function of negative feedback loops in the regulation of cellular messengers?

Terminate the signal once a specific threshold is reached Signup and view all the answers

Which of the following processes is primarily responsible for the transport of water-soluble hormones to target cells?

Circulation in free, unbound form through the bloodstream Signup and view all the answers

What is the primary mechanism by which up-regulation of cellular messenger receptors occurs in response to low hormone concentrations?

Increased synthesis of new receptors by ribosomes Signup and view all the answers

Which of the following best describes the role of positive feedback loops in cellular signaling?

Amplify the initial signal to maintain a sustained response Signup and view all the answers

What is the primary mechanism by which external/environmental factors can influence cellular processes regulated by the cell membrane?

Altering the activity of membrane transporters and channels Signup and view all the answers

Which type of cellular messenger is responsible for rapid, short-term communication between cells that are in direct physical contact?

Juxtacrine messengers Signup and view all the answers

What is the primary driving force for the movement of water between the intracellular fluid (ICF) and extracellular fluid (ECF)?

Osmotic pressure gradient Signup and view all the answers

Which type of cellular messenger is responsible for long-range communication between cells throughout the body?

Endocrine messengers Signup and view all the answers

Which type of membrane transport mechanism is driven by the electrochemical gradient, rather than directly by ATP hydrolysis?

Secondary active transport Signup and view all the answers

What is the primary mechanism by which lipid-soluble cellular messengers cross the cell membrane to reach their target receptors?

They simply diffuse across the lipid bilayer Signup and view all the answers

Which of the following statements accurately describes the role of proteolytic cascades in cellular signaling?

They amplify the signal by sequentially activating multiple proteins Signup and view all the answers

What is the primary mechanism by which water-soluble messengers initiate cellular responses?

They interact with membrane-bound receptors that activate second messengers Signup and view all the answers

Which of the following best describes the role of desensitization in the regulation of cellular messenger responses?

It reduces the number of active receptors on the cell surface Signup and view all the answers

Which of the following processes is primarily responsible for the rapid regulation of blood pH in response to changes in $CO_2$ levels?

Respiratory regulation of $CO_2$ levels Signup and view all the answers

Which type of cellular messengers are synthesized on-demand because they cannot be stored?

Water-soluble messengers Signup and view all the answers

What is the primary function of second messengers in cellular communication?

Activating preexisting proteins through a second messenger system Signup and view all the answers

Which type of messengers are synthesized from cholesterol?

Lipid-soluble messengers Signup and view all the answers

What is the primary role of the carbonic acid-bicarbonate buffer system in regulating blood pH?

Rapid regulation of blood pH in response to CO2 levels Signup and view all the answers

In cell-to-cell communication, what is activated by the hormone messenger to produce the primary effector for the creation of second messengers?

Extracellular matrix (ECM) Signup and view all the answers

What happens to the number of cellular messenger receptors when hormone concentrations are high?

Increase to enhance cell response Signup and view all the answers

Which type of hormones can easily diffuse across the plasma membrane?

Water-soluble hormones Signup and view all the answers

Which of the following cellular messengers is responsible for communication within the immune system?

Cytokines Signup and view all the answers

What is the primary mechanism by which endocrine cellular messengers, or hormones, are transported to target cells?

Through the bloodstream Signup and view all the answers

Which of the following processes is associated with the creation of ATP, the primary energy currency of the cell?

Glycolysis Signup and view all the answers

Which type of cellular messenger is responsible for local, short-range communication between neighboring cells?

Paracrine messengers Signup and view all the answers

What is a key function of feedback loops in regulating the release of cellular messengers?

To maintain a constant level of messengers in the body Signup and view all the answers

Study Notes

Regulation of Messenger Release

Negative feedback loop: a common mechanism in the endocrine system that prevents overproduction of hormones
Positive feedback loop: an uncommon mechanism that amplifies a response, examples include contractions during childbirth, stimulation of milk production, and trigger of ovulation

Cellular Messenger Transport

Messengers (hormones) are released into the circulatory system by endocrine glands and distributed throughout the body
Water-soluble hormones circulate in free, unbound forms
Lipid-soluble hormones are primarily transported bound to a carrier or transport protein

Cellular Messenger Receptors

Target cells recognize and bind with a high affinity to specific hormones
Receptors initiate a signal, and the more receptors, the more sensitive the cell
Receptors are located in or on the plasma membrane or in the intracellular compartment of the target cell
Water-soluble hormones cannot diffuse across the plasma membrane, while lipid-soluble hormones can diffuse across the plasma membrane and bind to cytosolic or nuclear receptors

Up- and Down-Regulation of Receptors

Up-regulation: low concentrations of hormones increase the number of receptors per cell
Down-regulation: high concentrations of hormones decrease the number of receptors per cell

Effects of Cellular Messengers

Three cellular responses to messengers:
1. Act on preexisting channel-forming proteins to alter membrane channel permeability
2. Activate preexisting proteins through a second messenger system
3. Activate or suppress protein synthesis

Lipid-Soluble Messengers

Lipid-soluble messengers are often made on-demand because they cannot be stored
Synthesized from cholesterol
Examples: sex hormones, steroids, vitamin D, retinoid, thyroxine, and arachidonic acid derivatives
Activate RNA polymerase and DNA transcription

Water-Soluble Messengers

Water-soluble 1st messengers: extracellular molecules that initiate signaling pathways and interact with a receptor
Examples: peptides, glycoproteins, polypeptides, and amines
2nd messengers: intracellular molecules activated by 1st messenger, which in turn activate kinases that lead to cellular response
Activate G-protein to produce primary effector, which leads to the creation of 2nd messenger

G Protein-Coupled Receptor (GPCR)

Image Credit: 2002 Nature Publishing Group, Li, J.

Cellular Metabolism

Cellular metabolism: creation of ATP from chemical energy contained in organic molecules
Two types of cellular metabolism: catabolism (breaks down molecules to create energy) and anabolism (uses energy to synthesize molecules)
Processes: glycolysis, oxidative decarboxylation, citric acid cycle, oxidative phosphorylation
Dysfunction in metabolism can result in profound disease

Cellular Communication

Cellular communication: cells transmit messages to other cells through chemical messengers
Categories of cellular messengers: endocrine (uses bloodstream to send signals), paracrine (local action), autocrine (cell secretes and responds to its own messengers), and juxtacrine (cell-to-cell contact-dependent)
Regulation of messenger release: chemical, endocrine, and neural factors

Effects of Cellular Messengers

Three cellular responses to messengers:
1. Act on preexisting channel-forming proteins to alter membrane channel permeability
2. Activate preexisting proteins through a second messenger system
3. Activate or suppress protein synthesis

Second Messengers

Cyclic AMP (cAMP): a common second messenger
Calcium: a second messenger that can be increased via releasing ER stores or allowing calcium from ECF into the ICF

Proteolytic Cascades

Coagulation cascade: a proteolytic cascade that regulates blood clotting

Cell Membrane

Cell membrane: a phospholipid bilayer that maintains the distinction between internal and external cellular environments
Function: due to the chemical properties of the bilayer (hydrophobic tails and hydrophilic heads)
Important functions: transportation of polar substances, cell adhesion, and cell signaling

Membrane Transport

Types of membrane transport: passive, active, and facilitated diffusion
Passive transport: no energy required, includes diffusion, osmosis, and facilitated diffusion
Active transport: requires energy, includes pumps and co-transport
Facilitated diffusion: uses transport proteins, includes channel-mediated and carrier-mediated transport

Resting Membrane Potential

Resting membrane potential (RMP): an electrochemical gradient across the cell membrane
Established by membrane pumps and channels
Important for neuronal activation and muscle contraction

Buffer Systems

Function: maintain homeostasis within a narrow pH range
Acids: molecules that can donate a proton (H+)
Bases: molecules that can accept a proton (H+)
Buffer systems: prevent large changes in pH, examples include carbonic acid-bicarbonate buffer and phosphate buffer
Importance: enzymes lose efficacy outside of the narrow pH range, and direct cellular injury and death can occur outside of this range### Cell Transport
Cell transport can be either passive or active
Active transport requires energy
Active transporters can fuel other transporters in the form of stored energy
Maintaining the extracellular and intracellular environments through transport mechanisms is vital to a number of biological functions
Potassium gradient (and to a lesser degree sodium) as established by the sodium potassium pump is essential for the resting membrane potential

Cell Adhesion

Cell adhesion mechanisms include:
- Extracellular matrix (ECM)
- Cell-adhesion molecules (CAMs)
- Specialized cell junctions
Extracellular matrix (ECM):
- Molecular network that creates structure and support for cells
- Participates in regulating cell growth
- Comprised of:
  - Basement membrane
  - Glycoproteins/proteoglycans
  - Non-proteoglycan polysaccharides
  - Interstitial proteins
  - Matrix minerals
- Functions:
  - Stores growth factors
  - Hydrates cells
  - Contributes to tensile strength of tendons, ligaments, and cartilage
Cell-adhesion molecules (CAMs):
- Four different families: Cadherins, Selectins, Ig Superfamily, Integrins
- Mechanical attachment between cell and ECM
Specialized cell junctions:
- Desmosomes: physical attachment
- Tight Junctions: barrier
- Gap Junctions: allow cell-to-cell transport

Cellular Communication

Cellular communication involves ligands binding to receptors on/in a target cell to elicit a response
Types of communication based on distance traveled from signal cell to target cell:
- Lipid-soluble messengers target intracellular receptors
- Water-soluble messengers (1st messengers) interact with membrane-bound receptors on a target cell
- Signal transduction and amplification is an important function of proteolytic cascades

Cell Membrane

Cell membrane is a phospholipid bilayer that maintains the distinction between the internal and external cellular environments
Function is due to the chemical properties of the bilayer (hydrophobic tails and hydrophilic heads) that allow diffusion of non-polar substances but not polar substances
Proteins on/in the membrane perform important functions like:
- Transportation of polar substances
- Cell adhesion
- Cell signaling

Membrane Transport

Passive transport:
- Diffusion: non-polar substances
- Facilitated diffusion: polar substances
- Osmosis: movement of water through a semipermeable membrane
Active transport:
- Pumps: Na/K pump, Cotransport
- Requires energy
- Brings other substances into the cell against their concentration gradients
Secondary active transport:
- Energy derived from “stored” energy as opposed to directly from the breakdown of ATP

Cellular Metabolism

ATP is created from chemical energy contained in organic molecules:
- Carbohydrates
- Lipids
- Proteins
Used in synthesis of organic molecules, muscle contraction, and active transport
Functions as a way to store and transfer energy
Catabolism (breaks down molecules to create energy) and anabolism (uses energy to build molecules)
Processes that create ATP:
- Glycolysis
- Oxidative decarboxylation (pyruvate)
- Citric acid cycle
- Oxidative phosphorylation
Dysfunction in metabolism can result in profound disease, such as phenylketonuria

Cellular Messengers and Receptors

Cellular messengers (also called chemical messengers):
- Created in response to a specific stimulus
- Travel to a target cell to elicit a response
- Categories:
  - Endocrine (uses blood stream to send signals far away)
  - Paracrine (local action, influences nearby cells)
  - Autocrine (cell secretes a chemical messenger that binds to its own receptors)
  - Juxtacrine (cell-to-cell contact-dependent)
Regulation of messenger release:
- Chemical factors (e.g., calcium levels in the blood)
- Endocrine factors (e.g., thyroid-stimulating hormone)
- Neural factors (e.g., autonomic stimulation of pancreas)
- Feedback loops to maintain homeostasis

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

Test your knowledge on second messengers in cell signaling, including cyclic AMP and calcium. Learn how GPCRs activate adenylyl cyclase and the role of calcium in cellular responses.

Cell Signaling Second Messengers Quiz

Podcast Beta

Questions and Answers

Which of the following is NOT a way that cellular messengers are regulated?

How do juxtacrine cellular messengers transmit signals between cells?

Which type of cellular messenger is responsible for communication within the immune system?

Which of the following is a key function of feedback loops in regulating cellular messengers?

What is the primary method by which endocrine cellular messengers, or hormones, are transported to target cells?

Which cellular response to messengers involves activating preexisting proteins through a second messenger system?

What type of messengers are often made on-demand because they cannot be stored?

Which type of messengers are synthesized from cholesterol?

What do water-soluble 1st messengers interact with to initiate the signaling pathway?

In cell-to-cell communication, what is activated by the hormone messenger to produce the primary effector that leads to the creation of the 2nd messenger?

What is the primary mechanism by which interstitial fluid and plasma regulate fluid movement and balance?

What is the main driving force for movement of water between the interstitial fluid (IF) and intracellular fluid (ICF)?

Which electrolyte is the most abundant cation in the extracellular fluid (ECF)?

What happens to a cell in a hypertonic solution?

What is the defining characteristic of an isotonic change in total body water (TBW)?

Which of the following statements accurately describes the role of G-protein coupled receptors (GPCRs) in cellular signaling?

Which of the following statements accurately describes the role of calcium as a second messenger in cellular signaling?

Which of the following statements accurately describes the difference between lipid-soluble and water-soluble messengers in cellular signaling?

Which of the following statements accurately describes the role of proteolytic cascades in cellular signaling?

Which of the following statements accurately describes the role of feedback loops in cellular signaling?

Which of the following is a key mechanism by which external/environmental factors can influence cellular processes regulated by the cell membrane?

The sodium-potassium pump is an example of which type of membrane transport mechanism?

Which of the following is a key function of feedback loops in regulating cellular messengers?

Which type of cellular messenger is responsible for communication between cells that are in direct physical contact?

Which of the following is NOT a way that cellular messengers are regulated?

Which of the following is a key way that juxtacrine cellular messengers transmit signals between cells?

Which of the following is the primary mechanism by which endocrine cellular messengers, or hormones, are transported to target cells?

Which type of cellular messenger is responsible for communication within the immune system?

Which of the following is a key function of feedback loops in regulating cellular messengers?

Which of the following is NOT a way that cellular messengers are regulated?

What is the main function of cellular messenger receptors in target cells?

Which type of hormones can easily diffuse across the plasma membrane?

How do low concentrations of hormones affect cellular messenger receptors?

Which process is associated with the transport of water-soluble hormones?

What happens when a target cell has more cellular messenger receptors?

Which of the following processes is primarily responsible for the rapid regulation of blood pH in response to changes in CO2 levels?

What is the primary role of the carbonic acid-bicarbonate buffer system in regulating blood pH?

In the context of cell-to-cell communication, which of the following best describes the role of hemoglobin in regulating pH?

What is the primary mechanism by which the kidneys contribute to the regulation of blood pH?

Which of the following best describes a feedback loop involved in the regulation of blood pH?

Which type of cellular messengers are often synthesized on-demand because they cannot be stored?

What is the primary mechanism by which $G$-protein coupled receptors (GPCRs) transmit signals in cellular communication?

What happens to the number of cellular messenger receptors when hormone concentrations are high?

Which of the following is a key mechanism by which lipid-soluble messengers, such as hormones, influence cellular processes?

What is the primary function of second messengers in cellular communication?

Which of the following is NOT a characteristic of water-soluble messengers in cellular signaling?

What is the primary function of proteolytic cascades in cellular communication?

In cellular signaling, what initiates the creation of the second messenger within a target cell?

Which process can be activated by increased concentrations of calcium in the ICF?

What is a direct consequence of releasing calcium from endoplasmic reticulum stores?

What is the primary mechanism by which lipid-soluble hormones initiate cellular signaling in target cells?

Which of the following best describes the function of negative feedback loops in the regulation of cellular messengers?

Which of the following processes is primarily responsible for the transport of water-soluble hormones to target cells?

What is the primary mechanism by which up-regulation of cellular messenger receptors occurs in response to low hormone concentrations?

Which of the following best describes the role of positive feedback loops in cellular signaling?

What is the primary mechanism by which external/environmental factors can influence cellular processes regulated by the cell membrane?

Which type of cellular messenger is responsible for rapid, short-term communication between cells that are in direct physical contact?

What is the primary driving force for the movement of water between the intracellular fluid (ICF) and extracellular fluid (ECF)?

Which type of cellular messenger is responsible for long-range communication between cells throughout the body?

Which type of membrane transport mechanism is driven by the electrochemical gradient, rather than directly by ATP hydrolysis?

What is the primary mechanism by which lipid-soluble cellular messengers cross the cell membrane to reach their target receptors?

Which of the following statements accurately describes the role of proteolytic cascades in cellular signaling?

What is the primary mechanism by which water-soluble messengers initiate cellular responses?

Which of the following best describes the role of desensitization in the regulation of cellular messenger responses?

Which of the following processes is primarily responsible for the rapid regulation of blood pH in response to changes in $CO_2$ levels?

Which type of cellular messengers are synthesized on-demand because they cannot be stored?

What is the primary function of second messengers in cellular communication?

Which type of messengers are synthesized from cholesterol?

What is the primary role of the carbonic acid-bicarbonate buffer system in regulating blood pH?

In cell-to-cell communication, what is activated by the hormone messenger to produce the primary effector for the creation of second messengers?

What happens to the number of cellular messenger receptors when hormone concentrations are high?

Which type of hormones can easily diffuse across the plasma membrane?

Which of the following cellular messengers is responsible for communication within the immune system?

What is the primary mechanism by which endocrine cellular messengers, or hormones, are transported to target cells?

Which of the following processes is associated with the creation of ATP, the primary energy currency of the cell?

Which type of cellular messenger is responsible for local, short-range communication between neighboring cells?

What is a key function of feedback loops in regulating the release of cellular messengers?