Lecture 3
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Questions and Answers

What term describes the process by which organisms maintain a relatively stable internal environment?

  • Equilibrium
  • Homeostasis (correct)
  • Diffusion
  • Osmosis

Which of the following is NOT a key concept associated with homeostasis?

  • Intracellular fluid (ICF)
  • Dynamic steady state
  • Absolute equilibrium (correct)
  • Extracellular fluid (ECF)

In multicellular organisms, what is essential for maintaining homeostasis at the cellular level?

  • Unregulated cell growth
  • Cellular isolation
  • Random cell migration
  • Intercellular communication (correct)

Which of the following represents the primary role of intercellular communication?

<p>Enabling cell survival, division, differentiation, and death (A)</p> Signup and view all the answers

What are the two basic types of signals cells use for intercellular communication?

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

What happens if an organism's compensatory mechanism is NOT successful when homeostasis is disrupted?

<p>Homeostasis is further disrupted, possibly leading to disease (C)</p> Signup and view all the answers

Which term describes cells that respond to either electrical or chemical signals?

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

What is the extracellular fluid (ECF)'s function in relation to homeostasis?

<p>To serve as a link between cells and the external environment (B)</p> Signup and view all the answers

What is the immediate effect of a ligand binding to a cell-surface receptor?

<p>Change in receptor conformation (A)</p> Signup and view all the answers

Which factor primarily determines the type of ion channel that will be activated?

<p>The type of stimuli present (D)</p> Signup and view all the answers

What property defines the 'selectivity' of an ion channel?

<p>The specific types of ions it allows to pass through (A)</p> Signup and view all the answers

What is the primary function of protein kinases?

<p>To phosphorylate specific proteins. (C)</p> Signup and view all the answers

A voltage-gated ion channel is least likely to be open when:

<p>The cell membrane is polarized. (A)</p> Signup and view all the answers

What is the primary function of ligand-gated ion channels in neural communication?

<p>To convert chemical signals into electrical signals (D)</p> Signup and view all the answers

Which subunit of a G protein is most crucial for determining the specificity of signal transduction?

<p>The alpha (α) subunit (D)</p> Signup and view all the answers

In the inactive state of a G protein, which molecule is bound to the alpha (α) subunit?

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

Which of the following is NOT a typical outcome of ion channel activation following neurotransmitter binding?

<p>Increased synthesis of neurotransmitter molecules. (D)</p> Signup and view all the answers

What two molecules are created after the activation of a G protein when GTP replaces GDP??

<p>The α-subunit linked to GTP and the βγ complex. (B)</p> Signup and view all the answers

How do G protein-coupled receptors (GPCRs) generally differ from ion channel-coupled receptors in their signaling action?

<p>GPCRs transmit signals through secondary signaling molecules. (D)</p> Signup and view all the answers

Which of the following is NOT a typical target of G proteins?

<p>Protein kinase (B)</p> Signup and view all the answers

What is an important characteristic of an ion channel in its role as a cell receptor?

<p>Fast response to stimuli. (D)</p> Signup and view all the answers

What is the second messenger molecule formed by adenylyl cyclase?

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

Which of these ligands can cause the activation of adenylyl cyclase?

<p>Glucagon (D)</p> Signup and view all the answers

What two molecules are produced by the activation of phospholipase C?

<p>IP3 and DAG (C)</p> Signup and view all the answers

Which of the following is NOT a characteristic of ligands that bind to intracellular receptors?

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

In its active state, where are intracellular receptors primarily located?

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

What type of cellular communication involves direct contact between cells for signal transfer?

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

Which domain of a nuclear receptor is responsible for interacting with specific DNA sequences?

<p>DNA binding domain (DBD) (A)</p> Signup and view all the answers

What is the typical length of the hormone response element (HRE) sequence?

<p>15 nucleotides (B)</p> Signup and view all the answers

Which communication method involves molecules released by a cell acting on neighboring cells through the extracellular fluid?

<p>Paracrine (D)</p> Signup and view all the answers

In autocrine communication, where do the released molecules exert their effect?

<p>On the same cell that released them (D)</p> Signup and view all the answers

What term describes a nuclear receptor composed of two different protein subunits?

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

What is the primary means of signal distribution in endocrine communication?

<p>The circulatory system via the bloodstream (D)</p> Signup and view all the answers

Which of the following is NOT a family of receptors included in the intracellular receptor category?

<p>Receptors for growth factors (A)</p> Signup and view all the answers

Which of these is a characteristic associated with cell-surface receptors?

<p>Binding of large, hydrophilic or charged molecules (D)</p> Signup and view all the answers

Which system uses a combination of electrical and chemical signals to communicate over long distances?

<p>The nervous system (D)</p> Signup and view all the answers

How do neurotransmitters differ from neurohormones in their mode of action?

<p>Neurotransmitters have a fast, localized effect by diffusing across the synaptic cleft, while neurohormones travel through the bloodstream for a slower effect. (C)</p> Signup and view all the answers

How do ion channel-linked receptors affect the cell membrane?

<p>They cause a change in membrane potential and permeability to specific ions (D)</p> Signup and view all the answers

In neuronal communication, what type of signal is converted into a chemical signal at the end of the neuron?

<p>Electrical signal (D)</p> Signup and view all the answers

What is the function of cellular receptors in cell communication?

<p>To receive, transform, and transmit information from the external environment (D)</p> Signup and view all the answers

Which of the following is a characteristic of enzyme-linked receptors?

<p>Their activation typically involves multiple intracellular transduction steps. (A)</p> Signup and view all the answers

Which of the following is NOT a functional type of enzyme-linked receptor?

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

What process directly follows the binding of a ligand to a tyrosine kinase receptor?

<p>Formation of a receptor dimer. (B)</p> Signup and view all the answers

What is the role of tyrosine residues in the activation of tyrosine kinases?

<p>They are involved in mutual phosphorylation during receptor dimerization. (A)</p> Signup and view all the answers

Which of the following describes the Ras protein in its active state?

<p>Bound to GTP (C)</p> Signup and view all the answers

How is the Ras protein activated?

<p>By an adaptor protein binding a GEF protein, causing GDP to be replaced by GTP. (A)</p> Signup and view all the answers

What is the function of the phosphorylation cascade triggered by activated Ras?

<p>To amplify the signal through phosphorylation of downstream kinases. (D)</p> Signup and view all the answers

What is the role of MAP kinase in the signaling cascade?

<p>It phosphorylates target proteins to produce a cellular response. (B)</p> Signup and view all the answers

Which type of communication requires direct cell-to-cell contact?

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

In which type of communication do signaling molecules act on the same cell that released them?

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

What characterizes endocrine communication?

<p>Signaling molecules are transported via the bloodstream (D)</p> Signup and view all the answers

Which type of molecule does neuronal communication primarily utilize?

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

What defines paracrine communication?

<p>It affects only neighboring cells through the extracellular fluid. (A)</p> Signup and view all the answers

What is the primary effect of neurotransmitters in synaptic communication?

<p>To diffuse across the synaptic cleft rapidly (C)</p> Signup and view all the answers

In which type of communication do signaling molecules travel long distances through the circulatory system?

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

Which cells are primarily affected by hormones in endocrine communication?

<p>Specific target cells with appropriate receptors (D)</p> Signup and view all the answers

What is a characteristic feature of enzyme-linked receptors?

<p>They have effects that may require multiple intracellular transduction steps. (A)</p> Signup and view all the answers

What is the first stage in the action of tyrosine kinases?

<p>Binding of signaling proteins to the receptor. (A)</p> Signup and view all the answers

What characteristic of a signaling molecule determines whether it can pass through the cell membrane?

<p>Hydrophobicity (D)</p> Signup and view all the answers

What is NOT a potential consequence of ligand binding to a receptor?

<p>Day-night cycle change (D)</p> Signup and view all the answers

How does the Ras protein become activated?

<p>By converting GDP to GTP via a GEF protein. (A)</p> Signup and view all the answers

Which type of receptor is responsible for binding hydrophobic signaling molecules?

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

Which of the following best describes the role of MAP kinase in the phosphorylation cascade?

<p>It is involved in the phosphorylation of target proteins. (A)</p> Signup and view all the answers

In which way can a single signaling molecule affect different target cells?

<p>Different receptors on different cells (C)</p> Signup and view all the answers

What is a key function of tyrosine kinases?

<p>They induce a change in gene expression. (A)</p> Signup and view all the answers

Which of the following accurately describes antagonists in cellular signaling?

<p>They inhibit receptor activity (A)</p> Signup and view all the answers

Which ligands are known to activate tyrosine kinases?

<p>FGF, EGF, PDGF, and VEGF. (A)</p> Signup and view all the answers

What type of signaling molecules do NOT require the presence of a receptor on the target cell to exert their effect?

<p>Small and hydrophobic molecules (B)</p> Signup and view all the answers

What type of protein is predominantly activated by most tyrosine kinases?

<p>Ras proteins. (A)</p> Signup and view all the answers

Which category includes signaling molecules that are typically unable to cross the cell membrane?

<p>Hydrophilic signaling molecules (A)</p> Signup and view all the answers

What is the state of Ras protein when it is inactive?

<p>It is bound to GDP. (A)</p> Signup and view all the answers

Which of the following definitions correctly describes ligands in terms of their function?

<p>They act as signaling molecules that bind to receptors (C)</p> Signup and view all the answers

What occurs when homeostasis is disrupted and compensation is unsuccessful?

<p>The organism may develop a disease (B)</p> Signup and view all the answers

Which compartment serves as a link between the external environment and cells in the context of homeostasis?

<p>Extracellular fluid (ECF) (B)</p> Signup and view all the answers

How do cells communicate to maintain homeostasis in multicellular organisms?

<p>Through intercellular communication or signaling (B)</p> Signup and view all the answers

What characterizes a dynamic steady state in homeostasis?

<p>Constant movement and imbalance of substances (B)</p> Signup and view all the answers

What is the primary role of electrical signals in cell communication?

<p>To trigger changes in the cell's membrane potential (A)</p> Signup and view all the answers

Which of the following statements about intercellular signaling is true?

<p>Both electrical and chemical signals can initiate a response in target cells (D)</p> Signup and view all the answers

Which level of coordination is essential for maintaining homeostasis in multicellular organisms?

<p>Across cells, tissues, and entire systems (C)</p> Signup and view all the answers

What type of environment do cells within tissues maintain to achieve homeostasis?

<p>A relatively stable internal environment overall (B)</p> Signup and view all the answers

What role does a ligand play in the process of signal transduction?

<p>It binds to a specific receptor on the target cell membrane. (D)</p> Signup and view all the answers

How does the activation of G proteins occur?

<p>By the exchange of GDP for GTP. (D)</p> Signup and view all the answers

What describes the conformational change in 7TM receptors upon ligand binding?

<p>It induces further signaling within the cell. (C)</p> Signup and view all the answers

What mechanism is primarily responsible for the switch-like behavior of molecular switches?

<p>Phosphorylation and dephosphorylation. (C)</p> Signup and view all the answers

Which outcome is part of the signaling cascade within the cell?

<p>Activation or inactivation of an enzyme. (B)</p> Signup and view all the answers

What is the primary characteristic of G protein-coupled receptors (GPCRs)?

<p>They consist of seven transmembrane (7TM) domains. (D)</p> Signup and view all the answers

What is the role of intracellular signaling molecules in the context of a signaling cascade?

<p>They propagate the signal deeper into the cell. (C)</p> Signup and view all the answers

How do molecular switches maintain their active state?

<p>Through prolonged GTP binding. (A)</p> Signup and view all the answers

What is the primary function of intracellular receptors?

<p>Regulate gene expression (D)</p> Signup and view all the answers

Which component is NOT part of the nuclear receptor structure?

<p>Signal transducing domain (C)</p> Signup and view all the answers

What type of dimer is typically formed by most nuclear receptors?

<p>Both B and C (A)</p> Signup and view all the answers

Which of the following ligands can bind to intracellular receptors?

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

In which cellular location do intracellular receptors primarily function when active?

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

Which of these best describes the hormone response element (HRE)?

<p>A 15-nucleotide sequence within the nucleus (A)</p> Signup and view all the answers

How do cell-surface receptors differ from intracellular receptors in terms of ligand characteristics?

<p>Cell-surface receptors bind large, hydrophilic molecules (B)</p> Signup and view all the answers

Which ion would most likely pass through an opened ion channel linked to a receptor?

<p>Calcium ions (Ca2+) (C)</p> Signup and view all the answers

Intracellular receptors are divided into which of the following categories?

<p>Nuclear receptors and cytoplasmic receptors (B)</p> Signup and view all the answers

Cell surface receptors are divided into which of the following categories?

<p>All of the above (D)</p> Signup and view all the answers

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Flashcards

Homeostasis

The process of maintaining a relatively stable internal environment in an organism despite changes in the external environment.

Extracellular Fluid (ECF)

The fluid surrounding cells, serving as a link between cells and the external environment.

Intracellular Fluid (ICF)

The fluid inside cells, containing all the necessary components for cellular functions.

Dynamic Steady State

A state where the composition of both ECF and ICF remains relatively stable, although substances are constantly moving between them.

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Intercellular Communication

The exchange of information between cells, enabling them to communicate and cooperate.

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Electrical Signals

Signals that involve changes in the electrical potential across the cell membrane.

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Chemical Signals

Signals that involve chemical compounds released by cells into the extracellular space.

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Target Cells

Cells that respond to electrical or chemical signals, receiving and interpreting the message.

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Distant communication

Communication between cells that occurs over long distances.

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Local communication

Communication between cells that occurs over short distances.

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Paracrine communication

A type of local communication where a cell releases a signaling molecule that acts on neighboring cells.

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Autocrine communication

A type of local communication where a cell releases a signaling molecule that acts on the same cell that secreted it.

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Juxtacrine communication

A type of local communication where cells communicate through direct contact.

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Endocrine communication

A type of distant communication where the signal travels through the bloodstream.

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Neuronal communication

A type of distant communication where the signal travels along specialized cells called neurons.

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Neurocrine molecules

Chemical messengers used by neurons to communicate with each other at synapses.

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What are intracellular receptor ligands?

Small, hydrophobic molecules that can pass through the cell membrane. They include steroid hormones, thyroid hormones, vitamin D, and retinoic acid.

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What are intracellular receptors?

Proteins located inside the cell that bind to specific ligands and regulate gene expression.

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What is the ligand binding domain (LBD)?

The region of an intracellular receptor that binds to a specific ligand.

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What is the DNA binding domain (DBD)?

The region of an intracellular receptor that binds to DNA, allowing it to regulate gene expression.

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What is the hormone response element (HRE)?

A specific DNA sequence that intracellular receptors bind to, often located in the promoter region.

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Where are active intracellular receptors located and what do they do?

The active state of intracellular receptors occurs when they are bound to their ligand and located in the nucleus.

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What are cell-surface receptors?

Proteins located on or within the cell membrane that bind to extracellular signals and transmit information into the cell.

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What kind of ligands do cell-surface receptors bind to?

Large, hydrophilic, or charged molecules that cannot pass through the cell membrane and require cell-surface receptors.

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Ion Channel-Coupled Receptor

A type of membrane-bound receptor that directly opens a channel in the cell membrane upon ligand binding, allowing ions to flow across the membrane.

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Voltage-Gated Ion Channel

A specific type of ion channel that opens or closes in response to changes in the membrane potential, often associated with nerve impulse transmission.

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Ligand-Gated Ion Channel

A specific type of ion channel that opens or closes when a specific molecule binds to it, like a neurotransmitter.

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G Protein-Coupled Receptor (GPCR)

A type of receptor that activates intracellular signaling pathways through a G protein upon ligand binding, resulting in a cascade of events that can alter cell function.

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Signal Transduction

The process by which a cell receives and responds to external signals, often involving a series of steps from reception to cellular response.

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Ligand

A molecule that binds to a receptor, initiating a cellular response. Examples include hormones, neurotransmitters, and growth factors.

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Ion Channel Selectivity

The ability of a channel to selectively allow certain types of ions to pass through while restricting others. This plays a crucial role in maintaining ionic balance and cellular function.

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Fast Response of Ion Channels

The property of ion channels to open and close rapidly, allowing for quick and precise signaling between cells, as seen in nerve impulse transmission.

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What are protein kinases?

A group of enzymes that add a phosphate group to proteins, changing their shape and function. This process is crucial in many cellular processes, including signaling.

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What is a G protein?

A type of protein that acts as a molecular switch. It's made up of three subunits (alpha, beta, and gamma) and plays a vital role in transmitting signals within the cell.

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What is a 7TM receptor?

A protein that exists in two forms, active and inactive. It binds to a specific ligand and causes a conformational change, activating the G protein.

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What is a second messenger?

A small molecule that acts as a messenger within the cell, relaying signals from the outside to the inside.

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What is the alpha subunit of a G protein?

The active form of the G protein, which is linked to GTP and can interact with target proteins. It is a key player in transmitting signals within the cell.

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What is a Gs protein?

A type of G protein that activates adenylyl cyclase, leading to the production of cAMP, a second messenger.

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What is a Gi protein?

A type of G protein that inhibits adenylyl cyclase, reducing cAMP production.

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What is adenylyl cyclase?

An enzyme that catalyzes the synthesis of cAMP, a crucial second messenger in cellular signaling.

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Enzyme-linked receptors

Receptors that activate intracellular signaling pathways by triggering a chain of phosphorylation events, often leading to changes in gene expression. They typically respond to low ligand concentrations but have slower responses compared to other receptor types.

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Tyrosine kinase receptors

A class of enzyme-linked receptors that catalyze the addition of phosphate groups to tyrosine residues on target proteins. They are often activated by growth factors and play a vital role in cell growth and development.

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Ras protein

A key protein in the Ras pathway, a monomeric G protein that cycles between an inactive GDP-bound state and an active GTP-bound state. It serves as a molecular switch, relaying signals downstream.

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Ras protein activation

The process of activating Ras protein by exchanging GDP for GTP, which is triggered by the binding of a GEF protein to a specific phosphorylated tyrosine residue on the receptor.

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Phosphorylation cascade (in Ras pathway)

A series of enzymes that sequentially phosphorylate each other, amplifying and transmitting a signal from the activated Ras protein. This process is often triggered by growth factors and leads to changes in gene expression.

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MAP kinase (mitogen-activated protein kinase)

The final kinase in the phosphorylation cascade, activated by the Ras pathway. It plays a crucial role in regulating cell growth, differentiation, and survival.

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Adaptor proteins (in Ras pathway)

Proteins that bind to specific phosphorylated tyrosine residues on activated receptors, acting as adaptors or signal mediators.

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GEF protein (guanine nucleotide exchange factor)

A crucial step in activating Ras protein. The GEF protein binds to a specific phosphorylated tyrosine residue on the receptor and promotes the exchange of GDP for GTP, activating the Ras protein.

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What is Homeostasis?

The process of maintaining a relatively stable internal environment in an organism despite changes in the external environment.

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What is Extracellular Fluid (ECF)?

The fluid surrounding cells, serving as a link between cells and the external environment.

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What is Intracellular Fluid (ICF)?

The fluid inside cells, containing all the necessary components for cellular functions.

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What is Dynamic Steady State?

A state where the composition of both ECF and ICF remains relatively stable, although substances are constantly moving between them.

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What is Intercellular Communication?

The exchange of information between cells, enabling them to communicate and cooperate.

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What are Electrical Signals?

Signals that involve changes in the electrical potential across the cell membrane.

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What are Chemical Signals?

Signals that involve chemical compounds released by cells into the extracellular space.

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What are Target Cells?

Cells that respond to electrical or chemical signals, receiving and interpreting the message.

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Agonists

They bind to a receptor and stimulate it to trigger a cellular response.

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Antagonists

They bind to a receptor and inhibit its activity, preventing it from being activated.

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Intracellular receptors

Receptors located within the cytoplasm or nucleus of a cell. They bind to small, hydrophobic signaling molecules that can pass through the cell membrane.

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Cell-surface receptors

Receptors embedded in the cell membrane that bind to large, hydrophilic signaling molecules unable to cross the membrane.

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Ion channel-linked receptors

Cell-surface receptors that directly open ion channels in the membrane upon ligand binding, allowing ions to flow across the membrane.

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Signal Transduction Cascade

A series of steps in a signaling pathway where one signaling molecule activates another, relaying information until a response occurs.

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Signal Amplification

The process of amplifying a signal during a signaling pathway, so a small initial signal can produce a large response.

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Molecular Switches

Proteins that act as molecular switches by transitioning between an inactive and active state. They are essential for controlling signaling pathways.

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Phosphorylation/Dephosphorylation

A type of molecular switch that is activated by adding a phosphate group (phosphorylation) or deactivated by removing a phosphate group (dephosphorylation).

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GDP/GTP Exchange

A type of molecular switch that is activated by replacing GDP with GTP and deactivated by replacing GTP with GDP.

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G Proteins

A type of protein located on the cytoplasmic side of the cell membrane, involved in relaying signals from activated GPCRs. They bind to guanosine-5'-diphosphate (GDP) and can be activated by replacing it with guanosine-5'-triphosphate (GTP).

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7TM Receptors

A protein structure composed of seven transmembrane domains that span the cell membrane. They are characteristic of GPCRs and are involved in recognizing and binding to ligands.

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What are enzyme-linked receptors?

Enzyme-linked receptors are a type of cell surface receptor that activate intracellular signaling pathways by triggering a chain of phosphorylation events, often leading to changes in gene expression. They typically respond to low ligand concentrations but have slower responses compared to other receptor types.

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How are tyrosine kinases activated?

Growth factors, like FGF, EGF, PDGF, and VEGF, are the ligands that cause activation of tyrosine kinases. The process involves binding to the receptor, dimerization, phosphorylation, binding of signaling proteins, and finally, phosphorylation of subsequent signaling proteins to transmit the signal.

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What are Ras proteins?

Ras proteins are monomeric G proteins (GTPases) bound to the cell membrane by a membrane lipid. They exist in two states: inactive (bound to GDP) and active (bound to GTP).

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How is Ras protein activated?

Ras protein activation occurs when an adaptor protein binds to a specific phosphorylated tyrosine residue and then interacts with a GEF protein, forming a Ras-GEF complex. This complex forces Ras to exchange GDP for GTP, thus activating it.

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What happens after Ras protein activation?

The activated Ras protein triggers a phosphorylation cascade involving three serine-threonine kinases: MAPKKK, MAPKK, and MAPK. These kinases sequentially phosphorylate each other, amplifying the signal.

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What is MAP kinase and its role?

The final kinase in the phosphorylation cascade is called MAP kinase (mitogen-activated protein kinase). It's involved in the phosphorylation of further signaling or target proteins, affecting processes like cell growth and division.

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What are adaptor proteins?

Adaptor proteins are molecules that bind to specific phosphorylated tyrosine residues on activated receptors, acting as adaptors or signal mediators. They link receptors to other signaling proteins, facilitating signal transmission.

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What is the role of GEF protein?

GEF proteins (guanine nucleotide exchange factors) are essential for activating Ras protein. They bind to a specific phosphorylated tyrosine residue on the receptor and help Ras exchange GDP for GTP, thus switching it to the active state.

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Study Notes

Cell Signaling

  • Lecturer: Dr. Michelle Kuzma
  • Adapted from: Dr. Danuta MielżyÅ„ska-Å vach
  • Course: Molecular Biology
  • Academic Year: 2024/2025

Homeostasis

  • Organism maintains a stable internal environment, despite external variability.
  • Homeostasis is the process of maintaining this stability.
  • Homeostatic disruption triggers compensatory mechanisms.
  • Successful compensation restores homeostasis.
  • Unsuccessful compensation can result in disease.

Homeostasis Overview

  • External change causes internal change.
  • An organism in homeostasis is affected by internal change.
  • Internal change results in a loss of homeostasis.
  • The organism attempts to compensate for the internal changes.
  • Compensation can be successful or unsuccessful.
  • If successful, homeostasis is restored.
  • If unsuccessful, homeostasis remains disrupted and can lead to illness or disease.

Components Associated with Homeostasis

  • Extracellular Fluid (ECF): A fluid environment that surrounds cells and connects the external environment to cells.
  • Intracellular Fluid (ICF): Fluid inside the cells.
  • Intracellular Fluid (ICF): Includes fluid within the cell (intracellular) and fluid within the blood vessels (intravascular).
  • ECF and ICF maintain relatively stable composition, but have dynamic steady states, not equilibrium.
  • Imbalances exist in concentrations of certain substances (e.g., Na+, Cl-, K+) between ECF and ICF.

Role of Homeostasis in Multicellular Organisms

  • Coordination is necessary between cells, tissues, and organs to maintain homeostasis.
  • Intercellular communication is crucial for this coordination and is achieved through cell signaling.

Intercellular Communication

  • Essential for cell survival, division, differentiation, and death.
  • Involves transmission of signals.

Types of Signals

  • Electrical signals: Related to changes in the cell's membrane potential.
  • Chemical signals: Chemical compounds (molecules) secreted into the extracellular space.
  • Target cells respond to these signals.

Methods of Communication

  • Local communication:
    • Juxtacrine communication: Direct contact between cells via gap junctions.
    • Paracrine communication: Signals act on neighboring cells.
    • Autocrine communication: Signals act on the same cell that secreted them.
  • Distant communication:
    • Endocrine communication: Hormones travel via the circulatory system to affect target cells throughout the body.
    • Neuronal communication: Combination of electrical and chemical signals used to communicate over long distances.

Types of Cell Communication (Detailed)

  • Juxtacrine: Direct cell-cell contact; Molecules are transferred across gap junctions in adjacent cells.
  • Paracrine: Signals act on nearby cells.
  • Autocrine: Signals act on the same cell that released them.
  • Endocrine: Signals circulate through the bloodstream to affect distant target cells.
  • Synaptic/Neuronal: Signal released across a synapse, a specialized junction between two nerve cells, for short-distance communication between neurons.

Types of Cell Signaling (Specific Definitions)

  • Juxtacrine: Signaling molecule on one cell binds to receptor on a neighboring cell (in contact).
  • Paracrine: A cell releases a molecule to act on a neighboring cell.
  • Autocrine: A cell releases a molecule to act on itself.
  • Endocrine: A hormone is released into the bloodstream to affect distant cells.
  • Synaptic/Neuronal: Neurotransmitters released across a synapse.

Signal Molecules (Examples)

  • Hormones: (Epinephrine, cortisol, estradiol, insulin, testosterone, thyroid hormone)
  • Neurotransmitters: (Acetylcholine, γ-aminobutyric acid (GABA))

Cell Communication Principles

  • Only cells with receptors respond to signals (selective response).
  • The cell's response depends on the cell's specialization and receptor type.
  • One signal molecule can have different effects on different cells.
  • One signal molecule can produce multiple effects in a single cell.

Intercellular Communication principles

  • Signaling molecules (ligands) bind to receptors.
  • Binding of ligand to receptor can upregulate, downregulate, or activate the receptor.
  • The activated receptor triggers intracellular signaling.
  • The final signaling molecule triggers the final response (e.g., protein modification, synthesis).

Types of Signaling Molecules

  • Pass through the cell membrane: Small, hydrophobic molecules. Intracellular receptors are required.
  • Do not pass through the cell membrane: Large, hydrophilic molecules. Cell surface receptors are needed.

Types of Receptors

  • Intracellular: Located in the cytoplasm or nucleus. Small, hydrophobic ligands.
    • Cytoplasmic receptors
    • Nuclear receptors
  • Cell-surface: Located in the cell membrane. Large, hydrophilic ligands.
    • Ion channel-linked receptors
    • G protein-coupled receptors (GPCRs)
    • Enzyme-linked receptors -Tyrosine kinase -Serine-threonine kinase -Guanylate cyclase
  • (The remaining sections are identical to the original notes.)*

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Test your understanding of homeostasis with this quiz covering key concepts and mechanisms. Explore intercellular communication, cellular responses, and the importance of maintaining stability in multicellular organisms. Ideal for biology students looking to reinforce their knowledge on the topic.

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