Cell Signaling and Communication
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Questions and Answers

What type of signaling involves molecules released by one cell acting on neighboring target cells?

  • Autocrine signaling
  • Paracrine signaling (correct)
  • Endocrine signaling
  • Juxtacrine signaling

Which type of signaling allows cells to respond to signaling molecules that they produce themselves?

  • Autocrine signaling (correct)
  • Exocrine signaling
  • Neurocrine signaling
  • Paracrine signaling

What role does abnormal autocrine signaling play in cancer development?

  • It allows cancer cells to self-stimulate their growth. (correct)
  • It helps to enhance immune response.
  • It reduces the spread of malignant cells.
  • It stabilizes cell proliferation.

Where are intracellular receptors typically located?

<p>Inside the cell (C)</p> Signup and view all the answers

Which hormone is synthesized from cholesterol and classified as a sex steroid?

<p>Testosterone (C)</p> Signup and view all the answers

Which hormone primarily regulates glucose production from the adrenal gland?

<p>Glucocorticoids (C)</p> Signup and view all the answers

What is the primary function of vitamin D3 in the body?

<p>Regulating Ca2+ metabolism and bone growth (C)</p> Signup and view all the answers

What is ecdysone known for in the context of insect physiology?

<p>Triggering metamorphosis in larvae (A)</p> Signup and view all the answers

What happens when signaling molecules bind to receptors on a cell?

<p>They initiate a series of reactions regulating cell behavior. (B)</p> Signup and view all the answers

Which type of signaling involves hormones traveling through the bloodstream to distant target cells?

<p>Endocrine signaling (B)</p> Signup and view all the answers

Which of the following is NOT a characteristic of signaling molecules?

<p>All are transmitted over long distances. (D)</p> Signup and view all the answers

What type of cell signaling is characterized by direct interaction between neighboring cells?

<p>Direct cell-cell signaling (C)</p> Signup and view all the answers

How do many cancers relate to cell signaling pathways?

<p>They can arise from failures in normal signaling pathways. (A)</p> Signup and view all the answers

Which signaling molecules are considered endocrine signals?

<p>Hormones secreted by endocrine cells. (B)</p> Signup and view all the answers

What is the role of receptors in cell signaling?

<p>They bind signaling molecules and initiate cell responses. (A)</p> Signup and view all the answers

Which of the following best describes paracrine signaling?

<p>Signals act on nearby cells in the vicinity. (D)</p> Signup and view all the answers

Which of the following is NOT a peptide hormone?

<p>Epidermal growth factor (EGF) (B)</p> Signup and view all the answers

What is the function of nerve growth factor (NGF)?

<p>Regulates development and survival of neurons (C)</p> Signup and view all the answers

What role do cytokines play in the body?

<p>Regulate development and differentiation of blood cells (C)</p> Signup and view all the answers

Which of the following plant hormones is responsible for stem elongation?

<p>Gibberellins (C)</p> Signup and view all the answers

What type of signaling molecules are enkephalins and endorphins classified as?

<p>Neuropeptides (A)</p> Signup and view all the answers

What process do membrane-anchored growth factors facilitate?

<p>Direct cell-cell interactions (C)</p> Signup and view all the answers

What occurs after ligand binding to a receptor?

<p>Initiation of intracellular reactions (C)</p> Signup and view all the answers

Which growth factor is released during blood clotting and stimulates fibroblast proliferation?

<p>Platelet-derived growth factor (PDGF) (B)</p> Signup and view all the answers

What happens to the glucocorticoid receptor when glucocorticoid binds to it?

<p>It displaces Hsp90 and binds to regulatory DNA sequences. (D)</p> Signup and view all the answers

Which of the following correctly describes the thyroid hormone receptor in the absence of hormone?

<p>It is associated with a corepressor complex and represses transcription. (D)</p> Signup and view all the answers

What defines the action of nitric oxide (NO) as a signaling molecule?

<p>It is extremely unstable, with a half-life of only a few seconds. (A)</p> Signup and view all the answers

How do hydrophobic signaling molecules typically regulate gene expression?

<p>By influencing transcription factors that bind to DNA. (C)</p> Signup and view all the answers

What role do nuclear receptors play as transcription factors?

<p>They have multiple domains for ligand binding and DNA binding. (A)</p> Signup and view all the answers

Which of the following is NOT a type of signaling molecule mentioned?

<p>Myokines (C)</p> Signup and view all the answers

What is the primary function of paracrine signaling molecules like nitric oxide?

<p>To alter the activity of enzymes locally. (B)</p> Signup and view all the answers

Which component is associated with the glucocorticoid receptor in the absence of hormone?

<p>Hsp90 chaperones (C)</p> Signup and view all the answers

What is the primary function of cAMP in signaling pathways?

<p>To mediate effects via protein kinase A (B)</p> Signup and view all the answers

How does the Gi protein affect heart muscle contraction?

<p>It opens K+ channels and slows contraction (A)</p> Signup and view all the answers

What is the role of protein kinase A in glycogen metabolism?

<p>To phosphorylate and activate glycogen phosphorylase (A)</p> Signup and view all the answers

What triggers the formation of cAMP from ATP?

<p>Adenylyl cyclase (B)</p> Signup and view all the answers

What is a consequence of cAMP binding to the regulatory subunits of protein kinase A?

<p>Activation of the catalytic subunits (C)</p> Signup and view all the answers

What effect does cAMP have on glycogen synthase?

<p>It inhibits glycogen synthase activity (A)</p> Signup and view all the answers

Who discovered the role of cAMP as a second messenger, and in what year?

<p>Sutherland in 1958 (D)</p> Signup and view all the answers

What are the products of cAMP degradation?

<p>AMP and phosphates (B)</p> Signup and view all the answers

What is the primary role of ligand binding to receptor tyrosine kinases?

<p>To activate cytosolic kinase domains (A)</p> Signup and view all the answers

What is the consequence of receptor dimerization?

<p>Autophosphorylation of the receptors (C)</p> Signup and view all the answers

What role does autophosphorylation play in receptor tyrosine kinases?

<p>It creates binding sites for other signaling proteins (C)</p> Signup and view all the answers

Which domain is recognized for binding to phosphotyrosine-containing peptides?

<p>SH2 (Src homology 2) (A)</p> Signup and view all the answers

What is an immediate effect of the phosphorylation of tyrosine in the catalytic domain of a receptor?

<p>Increased protein kinase activity (C)</p> Signup and view all the answers

What is a key characteristic of nonreceptor tyrosine kinases?

<p>They stimulate intracellular tyrosine kinases (A)</p> Signup and view all the answers

Which statement is true regarding the structure of receptor tyrosine kinases?

<p>They possess a cytosolic domain with protein-tyrosine kinase activity (A)</p> Signup and view all the answers

How do growth factors interact with receptor tyrosine kinases?

<p>They bind to extracellular domains and activate the receptors (C)</p> Signup and view all the answers

Flashcards

Cell Signaling

The process by which cells receive and respond to signals from their environment, regulating their behavior.

Signaling Molecules

Substances secreted or expressed on cells' surfaces; they bind to receptors and initiate cellular responses.

Endocrine Signaling

Hormones are secreted by endocrine cells, carried in the bloodstream, and affect distant target cells.

Direct Cell-Cell Signaling

Cells interact directly with each other via surface proteins like integrins and cadherins.

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Receptors

Protein molecules on the cell surface or inside cells that bind to signaling molecules, initiating intracellular responses.

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Cell-cell signaling types

Signaling methods classified by distance the signal travels, such as Endocrine, Direct

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Signal Complexity

Signaling molecules range from gases to proteins, acting locally or over long distances based on function.

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Cancer and Signaling

Problems in signaling pathways can lead to uncontrolled cell growth and cancer development.

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Paracrine signaling

Signaling where molecules released by one cell act on nearby target cells.

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Intracellular receptors

Receptors located inside the cell, responding to small, hydrophobic molecules that cross the plasma membrane.

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Steroid hormones

Group of hormones synthesized from cholesterol, including testosterone, estrogen, progesterone.

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Corticosteroids

Hormones from the adrenal gland, with types including glucocorticoids (glucose production) and mineralocorticoids (salt/water balance).

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Thyroid hormone

Hormone synthesized from tyrosine, crucial for development and metabolism.

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Vitamin D3

Regulates calcium metabolism, important for bone growth.

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Insulin & Glucagon

Peptide hormones produced by the pancreas, regulating blood sugar levels. Insulin lowers blood glucose by promoting glucose uptake by cells, while glucagon raises blood glucose by stimulating glycogen breakdown in the liver.

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Pituitary Hormones

Peptide hormones secreted by the pituitary gland, controlling various bodily functions. Examples include growth hormone for growth, follicle-stimulating hormone (FSH) for reproduction, and prolactin for milk production.

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Neuropeptides

Peptides secreted by neurons that act as neurotransmitters or neurohormones, influencing nerve impulses and other bodily functions. Examples include enkephalins and endorphins, which reduce pain.

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Nerve Growth Factor (NGF)

A protein belonging to the neurotrophin family that plays a crucial role in the development, survival, and maintenance of neurons. It promotes the growth and survival of neurons.

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Epidermal Growth Factor (EGF)

A protein that stimulates cell proliferation and is vital for tissue repair and growth. It is particularly important for skin healing.

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Platelet-Derived Growth Factor (PDGF)

A protein stored in blood platelets that is released during wound healing. It promotes fibroblast proliferation, helping with tissue repair at the wound site.

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Cytokines

Small proteins that regulate immune responses and blood cell development. They act as signaling molecules in the immune system, influencing processes like inflammation and immunity.

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Gibberellins

Plant hormones that promote stem elongation, leading to increased plant growth and development.

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Nuclear receptors

Proteins that act as transcription factors, directly regulating gene expression by binding to DNA and influencing transcription.

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Steroid hormone action

Steroid hormones bind to receptors and influence gene expression by altering transcription factors. These receptors are typically inactive in the absence of the hormone.

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Glucocorticoid receptor activation

Glucocorticoid receptors are bound to chaperone proteins (Hsp90) in the absence of the hormone. Upon binding the hormone, the chaperones are released, allowing the receptor to bind to DNA and regulate gene expression.

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Thyroid hormone receptor action

In the absence of thyroid hormone, the receptor is associated with a corepressor complex, silencing target gene expression. Binding of thyroid hormone activates the receptor, promoting gene transcription.

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Nitric oxide (NO) signaling

NO is a gas that acts as a paracrine signaling molecule, affecting nearby cells by influencing enzyme activities. It is unstable and has a short half-life.

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NO's role in the body

NO plays a role in the nervous, immune, and circulatory systems. It influences processes like blood vessel dilation and immune responses.

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How do signal molecules differ?

Signaling molecules can be hydrophobic (like steroids) or hydrophilic (like peptides and neurotransmitters). Each type interacts with receptors and triggers different signaling pathways.

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Types of hydrophilic signal molecules

These include neurotransmitters, peptide hormones, neuropeptides, and polypeptide growth factors. They bind to receptors on the cell surface and initiate cellular responses.

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What do all receptor tyrosine kinases have?

All receptor tyrosine kinases possess an N-terminal extracellular ligand-binding domain, a single transmembrane α helix, and a cytosolic C-terminal domain exhibiting protein-tyrosine kinase activity.

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What triggers receptor tyrosine kinase activation?

Ligand binding to the extracellular domains of receptor tyrosine kinases activates the cytosolic kinase domains, leading to phosphorylation of both the receptors and intracellular target proteins.

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What happens during receptor tyrosine kinase dimerization?

Ligand binding induces receptor dimerization, resulting in receptor autophosphorylation as the two polypeptide chains cross-phosphorylate each other.

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What are the two roles of autophosphorylation in receptor tyrosine kinases?

Autophosphorylation increases protein kinase activity by phosphorylating tyrosine within the catalytic domain. It also creates binding sites for downstream signaling proteins by phosphorylating tyrosine outside the catalytic domain.

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What are SH2 domains and their function?

SH2 domains (Src homology 2) are protein domains that bind to specific phosphotyrosine-containing peptides of activated receptors, facilitating downstream signaling.

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How do nonreceptor tyrosine kinases activate signaling?

Nonreceptor tyrosine kinases stimulate intracellular tyrosine kinases through noncovalent association, indirectly contributing to signaling.

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What is the cytokine receptor superfamily?

The cytokine receptor superfamily encompasses receptors for most cytokines and certain polypeptide hormones.

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What is the purpose of the cytosolic C-terminal domain in receptor tyrosine kinases?

The cytosolic C-terminal domain of receptor tyrosine kinases possesses protein-tyrosine kinase activity, enabling phosphorylation of both the receptors and intracellular target proteins, initiating the signaling cascade.

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G protein-coupled receptor

A type of receptor that activates a G protein upon binding to a signaling molecule.

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G protein

A protein that acts as a molecular switch, transmitting signals from a receptor to intracellular targets.

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Adenylyl cyclase

An enzyme that converts ATP to cyclic AMP (cAMP), a second messenger involved in signal transduction.

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Cyclic AMP (cAMP)

A second messenger that relays signals inside the cell, often activating protein kinase A.

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Protein kinase A

An enzyme activated by cAMP, which then phosphorylates other proteins to activate or deactivate them.

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What is cAMP's role in glycogen metabolism?

cAMP activates protein kinase A, which phosphorylates two enzymes involved in glycogen metabolism: phosphorylase kinase (activates glycogen breakdown) and glycogen synthase (inhibits glycogen synthesis).

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What is the role of the Gi protein subunit in regulating heart muscle contraction?

The α subunit of the Gi protein inhibits adenylyl cyclase, while the βγ subunits open K+ channels, both leading to slower heart muscle contraction.

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What is the role of cAMP phosphodiesterase?

This enzyme degrades cAMP, effectively turning off the signal by removing the messenger molecule.

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Study Notes

Cell Signaling

  • Cells respond to signals from their environment.
  • Bacteria and single-celled eukaryotes respond to environmental signals and signals from other cells.
  • In multicellular organisms, cell-cell communication is complex and each cell must be regulated to meet the needs of the whole organism.
  • Signaling molecules, secreted or on the surface of one cell, bind to receptors on other cells.
  • Binding of signaling molecules initiates a series of reactions that regulate cell behavior.
  • Many cancers arise from problems in signaling pathways that control cell proliferation.

Signaling Molecules and Their Receptors

  • Signaling molecules range from simple gases to proteins.
  • Some signals travel long distances, others act locally.
  • Some molecules cross the plasma membrane and bind to intracellular receptors. Others bind to receptors on the cell surface.
  • Modes of cell signaling: Direct cell-cell signaling involves interaction with neighboring cells (e.g., via integrins and cadherins). Signaling by secreted molecules is categorized by the distance the signal travels.

Endocrine Signaling

  • Hormones are secreted molecules carried via the circulatory system to distant target cells.
  • Example: estrogen

Paracrine Signaling

  • Molecules released by one cell act on neighboring target cells.
  • Example: neurotransmitters

Autocrine Signaling

  • Cells respond to signaling molecules they produce themselves.
  • Example: T lymphocytes respond to antigens by producing growth factors that stimulate their own proliferation and strengthen the immune response.
  • Abnormal autocrine signaling contributes to cancer.

Intracellular Receptors

  • Intracellular receptors respond to small, hydrophobic molecules that can diffuse across the plasma membrane.
  • Examples include steroid hormones, thyroid hormone, vitamin D, and retinoic acid.

Steroid Hormones

  • Steroid hormones are synthesized from cholesterol.
  • Testosterone, estrogen, and progesterone are sex steroids produced by the gonads.
  • Other examples: Corticosteroids (glucocorticoids and mineralocorticoids) from the adrenal gland.
    • Glucocorticoids stimulate glucose production.
    • Mineralocorticoids regulate salt and water balance in the kidneys.
  • Other examples: ecdysone (insect hormone) and brassinosteroids (plant hormones).

Thyroid Hormone, Vitamin D3, and Retinoic Acid

  • Thyroid hormone is synthesized from tyrosine in the thyroid gland and plays a role in development and metabolism.
  • Vitamin D3 regulates calcium metabolism and bone growth.
  • Retinoic acid and retinoids are synthesized from vitamin A and are important in vertebrate development.
  • All are members of the nuclear receptor superfamily.
  • These hormones directly regulate gene expression.

Ligand Binding and Receptor Activity

  • Ligand binding affects receptors differently.
  • Some receptors are inactive in the absence of a hormone.
    • Examples include the glucocorticoid receptor, which is bound to Hsp90 chaperones until a hormone binds .
  • Hormone binding changes receptor activity.
    • In the absence of a hormone, the thyroid hormone receptor is associated with a corepressor complex. Binding of a hormone activates transcription.

G Proteins and Cyclic AMP Signaling

  • G protein-coupled receptors are the largest family of cell surface receptors.
  • Signals are transmitted via G proteins (guanine nucleotide-binding proteins).
  • G proteins have three subunits (α, β, γ).
  • In the inactive state, the α subunit is bound to GDP.
  • Hormone binding causes GTP to exchange for GDP, causing the α and βγ subunits to dissociate from the receptor.
  • The separated subunits then interact with their target molecules.
  • A hormone binding to the receptor induces intracellular changes which trigger downstream pathways to reach the nucleus and change gene expression.
  • Cyclic AMP (cAMP) is a second messenger that mediates responses to many hormones.

cAMP-Dependent Signaling

  • cAMP activates protein kinase A (PKA).
  • The inactive PKA consists of two regulatory and two catalytic subunits.
  • cAMP binds to the two regulatory subunits, causing them to dissociate and activate the catalytic subunits.
  • The activated catalytic subunits can then phosphorylate serine on target proteins.

Signal Amplification

  • Binding of a hormone molecule leads to the activation of many intracellular enzymes.
  • In epinephrine signaling, one molecule of epinephrine can activate up to 100 molecules of Gs.

Kinase and Phosphatase Regulation

  • Protein kinases aren’t isolated and require phosphatases to reverse phosphorylation.
  • cAMP can also directly regulate ion channels.
  • Receptor and non-receptor tyrosine kinases are important in cell signaling and are directly linked to intracellular enzymes.
  • Receptor Tyrosine Kinases are the dominant family and includes receptors for most polypeptide growth factors.
  • Receptor tyrosine kinases have an extracellular ligand-binding domain, one transmembrane helix, and a cytosolic C-terminal domain with protein-tyrosine kinase activity.
  • Ligand binding induces receptor dimerization, leading to autophosphorylation.
  • Autophosphorylation creates binding sites for downstream signaling molecules with SH2 domains.
  • Downstream signaling involves activation of intracellular tyrosine kinases.
  • Cytokine receptors are similar to receptor tyrosine kinases structuraly. Differences include the lack of catalytic activity in the cytosolic domains

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This quiz explores the intricate world of cell signaling, focusing on how cells communicate with their environment and each other. It covers the role of signaling molecules, their receptors, and the implications of signaling pathways in health and disease, particularly cancer. Test your understanding of these essential biological processes!

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