Cell Communication Quiz

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Questions and Answers

Which type of cell communication involves the direct transfer of molecules through gap junctions?

Endocrine

Juxtacrine (correct)

Paracrine

Autocrine

What distinguishes neurohormones from neurotransmitters?

Neurohormones diffuse into the bloodstream, while neurotransmitters diffuse across the synaptic cleft. (correct)

Neurotransmitters utilize electrical signals, while neurohormones use chemical signals.

Neurotransmitters travel through the bloodstream, while neurohormones diffuse across the synaptic cleft.

Neurohormones have more localized effects compared to the faster effects of neurotransmitters.

In which type of communication does a cell release molecules that act on itself?

Paracrine

Autocrine (correct)

Endocrine

Juxtacrine

What is the primary mode of signal transmission in endocrine communication?

Release of chemicals into the bloodstream Signup and view all the answers

Which of the following best describes paracrine signaling?

Signaling where a cell releases molecules into the extracellular fluid that affect neighboring cells. Signup and view all the answers

Which type of cellular communication relies on both electrical and chemical signals?

Neuronal Signup and view all the answers

Which type of cellular communication requires a signaling molecule on the cell membrane of one cell binding to a receptor on the cell membrane surface of another cell?

Juxtacrine Signup and view all the answers

Why do neurohormones have a relatively slower effect compared to neurotransmitters?

Because they must travel through the bloodstream to reach their target. Signup and view all the answers

What is a characteristic of ligands that interact with intracellular receptors?

They are small and hydrophobic, allowing them to diffuse through the cell membrane. Signup and view all the answers

When an intracellular receptor is in its active state, where is it primarily located and what is its function?

In the nucleus, where it regulates gene expression. Signup and view all the answers

Which of the following components is NOT a characteristic element of a nuclear receptor?

A transmembrane domain (TMD). Signup and view all the answers

What is the primary function of the HRE sequence in a target gene?

To serve as a binding site for intracellular receptors. Signup and view all the answers

Most nuclear receptors form dimers. Which type of dimer is formed by two identical receptor molecules?

A homodimer Signup and view all the answers

Which of the following is an example of a ligand that would bind to a cell-surface receptor?

A large, hydrophilic protein. Signup and view all the answers

What is the immediate effect of a ligand binding to an ion channel-linked receptor?

Change in the configuration of the proteins that make up the ion channel. Signup and view all the answers

How do ions pass through an open ion channel after a ligand binds to an ion channel-linked receptor?

According to the concentration gradient. Signup and view all the answers

What characterizes the response mechanism of most receptors for neurotransmitters?

Fast response Signup and view all the answers

Which type of ion channel is activated by the electrical charge across the membrane?

Voltage-gated Signup and view all the answers

During which phase is a voltage-gated ion channel inactivated and cannot open?

After depolarization and before repolarization Signup and view all the answers

What is the primary function of ligand-gated ion channels activated by neurotransmitters?

Convert chemical signals into electrical signals Signup and view all the answers

Which of the following is NOT a feature of ion channels?

They operate independently of the membrane potential Signup and view all the answers

How do G protein-coupled receptors differ from ion channel-coupled receptors in signal transduction?

They transmit signals slower and more complexly Signup and view all the answers

What element of ion channels determines the types of ions that can pass through?

Selective permeability characteristics Signup and view all the answers

What is the consequence of a neurotransmitter binding to a ligand-gated ion channel?

Change in membrane potential leading to depolarization Signup and view all the answers

What occurs immediately after a ligand binds to its receptor in signal transduction?

Intracellular signaling molecules are produced. Signup and view all the answers

Which of the following is NOT a role of molecular switches in cell signaling?

Directly binding to DNA sequences. Signup and view all the answers

What characterizes the structure of a G protein-coupled receptor (GPCR)?

It consists of seven transmembrane alpha-helices. Signup and view all the answers

What happens to G proteins when they are activated?

They switch GDP for GTP. Signup and view all the answers

In signal transduction, what term describes the series of reactions triggered after a ligand binds to a receptor?

Cascading amplification. Signup and view all the answers

Which mechanism is involved in turning off molecular switches that rely on phosphorylation?

Dephosphorylation. Signup and view all the answers

What initiates the signal transduction cascade in a cell?

Binding of a ligand to a receptor. Signup and view all the answers

Which statement about G protein-coupled receptors (GPCRs) is correct?

They possess an extracellular ligand-binding domain. Signup and view all the answers

What are the three subunits that compose G proteins?

Alpha, beta, gamma Signup and view all the answers

Which of the following is a primary role of protein kinases in the cell?

Phosphorylation of specific proteins Signup and view all the answers

What is the role of GDP in the inactive state of G proteins?

It is linked to the alpha subunit Signup and view all the answers

Which of the following molecules is formed by the action of adenylyl cyclase?

Cyclic adenosine-3′,5′-monophosphate (cAMP) Signup and view all the answers

What happens to the G protein upon activation?

The G protein splits into α-subunit linked to GTP and G βγ complex Signup and view all the answers

Which ligands are known to activate adenylyl cyclase?

Adrenaline, acetylcholine, glucagon Signup and view all the answers

What is the primary function of second messenger molecules formed by the targets of G proteins?

Transmitting signals within the cell Signup and view all the answers

What type of G protein is primarily associated with stimulating pathways?

Gs (stimulating) G protein Signup and view all the answers

Which of the following steps is the first in the action of adenylyl cyclase?

The ligand binds to the 7TM receptor Signup and view all the answers

What is the role of the α-subunit of the G protein in the adenylyl cyclase pathway?

It binds to adenylyl cyclase Signup and view all the answers

Which second messenger is produced by the activation of phospholipase C?

Inositol triphosphate (IP3) Signup and view all the answers

What happens after inositol triphosphate (IP3) binds to the Ca2+ channel in the endoplasmic reticulum (ER)?

It causes the efflux of Ca2+ ions into the cytosol Signup and view all the answers

Which factor is crucial for the activation of protein kinase C (PKC)?

Diacylglycerol (DAG) and Ca2+ ions Signup and view all the answers

What do ligands like acetylcholine, vasopressin, and thrombin activate?

Phospholipase C Signup and view all the answers

Which of the following statements best describes enzyme-linked receptors?

They bind to ligands on the outside of the membrane and have an enzymatic site inside. Signup and view all the answers

What is the primary function of cyclic adenosine monophosphate (cAMP) in cellular signaling?

It activates protein kinase A (PKA) Signup and view all the answers

Study Notes

Cell Signaling Lecture Notes

Dr. Michelle Kuzma lectured on cell signaling, adapting slides from Dr. Danuta Mielżyńska-Švach
The lecture covered molecular biology in 2024/2025 academic year

Homeostasis

Organisms maintain a relatively stable internal environment.
Homeostasis is the process of maintaining a stable internal environment.
Homeostasis is disrupted when compensation is unsuccessful, which can lead to disease.
If compensation is successful, homeostasis is restored.
The slides demonstrate how external changes affect the internal environment and how organisms attempt to maintain internal stability.

Homeostasis Concepts

Extracellular fluid (ECF): Acts as a link between the external environment and cells.
Intracellular fluid (ICF): Found inside the cell or within the cell.

Imbalance in Homeostasis

The composition of both compartments (ECF and ICF) in homeostasis is relatively stable.
There's a dynamic, not a static equilibrium between substances moving constantly between compartments.
Despite constant movement, concentrations in ECF and ICF differ.
This leads to an established state of imbalance.
A graph illustrates the differing concentrations of Na+, Cl-, and K+ between ECF and ICF.

Role of Homeostasis in Multicellular Organisms

Coordination is crucial at the cellular, tissue, organ, and systemic levels.
Cells must cooperate to maintain homeostasis.
Intercellular communication (cell signaling) is essential for this cooperation.

Intercellular Communication

Essential for cell survival, division, differentiation, and death.
Coordination between cells involves signal transmission.
Two basic types of signals: electrical (related to membrane potential) and chemical (secreted molecules).
Target cells respond to these signals.

Methods of Local Communication

Juxtacrine: direct contact between cells via gap junctions, transferring molecules.
Paracrine: signaling molecules released into the extracellular fluid act on neighboring cells.
Autocrine: molecules released into the extracellular fluid act on the same cell that secreted them.

Methods of Distant Communication

Endocrine: hormones travel through the circulatory system to target cells throughout the body.
Neuronal: nervous system uses a combination of electrical and chemical signals for long-distance communication to signal cells.

Neurocrine Molecules (specifically, neurotransmitters and neurohormones)

Neurotransmitters diffuse across the synaptic cleft for fast effects.
Neurohormones diffuse into the blood for slower effects and act on cells throughout the body.

Types of Signaling Molecules

Divided by their ability to pass through the cell membrane:
those that pass through the cell membrane (small, hydrophobic). They require intracellular receptors within the cell.
those that do not pass through the membrane (large, hydrophilic). They require cell-surface receptors.

Types of Receptors

Intracellular receptors:
- cytoplasmic or nuclear located.
- Respond to small, hydrophobic signaling molecules.
Cell-surface receptors:
- located on or within the cell membrane.
- Respond to large, hydrophilic signaling molecules.

Intracellular Receptors

Transcription factors in the cytoplasm or nucleus.
These receptors bind to small, hydrophobic ligands, such as steroid hormones, thyroid hormones, vitamin D, and retinoic acid, which diffuse easily across cell membranes.
Upon binding, they regulate gene expression.
Their structure includes a ligand-binding domain, DNA-binding domain, hinge region, and a transcription-activating domain.
They bind to the hormone response elements (HRE) within target genes.
Some nuclear receptors are monomeric, while most are dimeric.

Intracellular Receptor Families

Include receptors for:
- lipophilic hormones
- active vitamin A (retinol)
- active vitamin D3
- un-identified ligands ("orphan" receptors)

Steroid Hormones

Such as cortisol (involved in stress response), activate target gene transcription regulators.

Cell-Surface Receptors

Located on or within the cell membrane which regulate cell behavior.
Large, hydrophilic, and/or charged molecules bind to cell-surface receptors.

###Types of Cell-Surface Receptors

Ion channel-linked receptors
G protein-coupled receptors (GPCRs)
Enzyme-linked receptors, such as tyrosine kinase and serine-threonine kinase.
Guanylate cyclase

Ion Channel-Linked Receptors

Binding alters the receptor's conformation and changes the membrane's potential.
Ions (Na+, K+, Ca2+, Cl-) flow through the channel based on the concentration gradient.
These receptors frequently respond to neurotransmitters.

G Protein-Coupled Receptors (GPCRs)

Receptors that link to cytoplasmic G proteins and transmit signals to secondary messenger molecules.
Signal transduction triggers a cascade of reactions with slower and more complex effects than ion-channel receptors.
GPCRs are associated with signaling pathways involving protein kinase activities.

Signal Transduction

Processes where intracellular signaling molecules result from the activation of a specific receptor.
The process involves signal molecules, receptors, and intracellular signaling molecules that transmit the final signal to the effector proteins.

Cascade and Amplification

Cascades involve sequential activation of proteins, amplifying the initial signal.
Receptor-ligand complexes activate amplifier enzymes (AEs).
One ligand can trigger many intracellular molecules.

Molecular Relay Race

The signaling process inside a cell often involves a chain of successive signals or activation. It is like a relay race where information is passed from one signaling molecule to another until a desired response is elicited.

Molecular Switches

Signaling molecules act as molecular switches, changing from inactive to active states to regulate the signaling pathway.

Two Types of Molecular Switches

Protein switches: Phosphate groups are added or removed.
G protein switches: GDP is exchanged for GTP.

Protein Kinases

Specific enzymes that phosphorylate proteins, changing their activity, binding properties, and cellular locations.
~30% of proteins in the cell are regulated this way.

G Proteins

Intermediaries that carry signals from the receptor to the effector such as an enzyme.
Two main types of G proteins based on the alpha (a) subunit: stimulating (Gs) and inhibitory (Gi), acting on effector molecules.

7TM Proteins (GPCRs)

The largest family of cell-surface receptors (over 700 in humans).
They span the cell membrane seven times.
Have extracellular ligand-binding domain and intracellular G protein binding domain.
Ligand binding induces conformational changes.

Types of Second Messenger Molecules

cAMP (cyclic adenosine monophosphate)
IP3 (inositol triphosphate)
DAG (diacylglycerol)

Adenylyl Cyclase

Enzyme that catalyzes the formation of cAMP from ATP.
Activated by specific ligands (like adrenaline, acetylcholine, and glucagon).

Protein Kinase A (PKA)

Enzyme activated by cAMP.
Involved in glycogen breakdown, gene expression regulation, and other cellular processes.

Phospholipase C

Enzyme activated by specific ligands and catalyzes the breakdown of phosphatidylinositol.
Leads to the formation of IP3 and DAG, which trigger Ca2+ release and activation of protein kinase C (PKC) respectively to trigger protein related activities.

Tyrosine Kinases and Ras Protein

Tyrosine kinase activity leads to Ras activation.
Ras is a monomeric G protein, regulates the cellular signals cascade further.

Phosphorylation Cascade

A series of phosphorylations involving kinases (like MAP kinases) that continue the signal from Ras.

PI3K/Akt/mTor Pathway

Plays a crucial role in cell growth, survival, and metabolism by phosphorylating proteins like Akt.

Cell Signal Response

Can result in fast (e.g., changes in protein function) or slow (e.g., protein synthesis) responses.

Signal Integration

Multiple signals can converge on a cell to generate a complex response.

Additional Information

The lecture provided diagrams and examples to illustrate molecular processes.
These notes contain condensed information from the lecture materials.
References were noted as from the "Essential of Cell Biology", Volume 2, Chapter 16.

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Description

Test your knowledge on various types of cell communication, including gap junctions, neurohormones, and paracrine signaling. This quiz will challenge your understanding of how cells interact and transmit signals both chemically and electrically. Perfect for students studying cell biology or related disciplines.