Case 9

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Questions and Answers

Which statement best describes the role of intracellular mediators?

They enable large molecules to transfer between cells without assistance.

They prevent small signaling molecules from diffusing between cells.

They exclusively transmit signals from one cell to the nucleus of another.

They facilitate communication between neighboring cells through diffusion. (correct)

What is the primary function of gap junctions in cardiac muscle cells?

They allow the rapid spread of electrical signals by transporting ions. (correct)

They form a barrier that prevents ion exchange between adjacent cells.

They exclusively transport proteins necessary for muscle contraction.

They hinder the electrical signal from spreading between heart muscle cells.

Which of the following molecules cannot diffuse through the channels formed by gap junctions?

Small ions like Na+

Hydrophilic neurotransmitters

Gases such as CO

Large proteins like antibodies (correct)

What is the structure formed when six connexins align to create a channel between cells?

Connexon Signup and view all the answers

What occurs after neurotransmitters bind to receptors on a receiving cell?

They induce a chemical change inside the cell. Signup and view all the answers

Which of the following is a characteristic of autocrine signaling?

It allows a cell to signal itself using ligands. Signup and view all the answers

Which of the following best describes the role of endocrine signaling?

It involves the distribution of messages through the circulatory system. Signup and view all the answers

The degradation or reuptake of neurotransmitters occurs for which purpose?

To prepare the synapse for future signals. Signup and view all the answers

What type of signaling is primarily involved in the regulation of development and cancer progression?

Autocrine signaling. Signup and view all the answers

Which of the following molecules are typically involved in endocrine signaling?

Hormones produced by endocrine glands. Signup and view all the answers

Which structures are responsible for direct cell-to-cell contact signaling?

Gap junctions and plasmodesmata. Signup and view all the answers

What is true about molecules like cytokines and growth factors?

They are important in both autocrine and paracrine signaling. Signup and view all the answers

What is the primary function of gap junctions in the context of damaged cells?

To immediately close and prevent further damage Signup and view all the answers

What specific role do tight junctions play in cellular structure?

Creating a selective barrier that regulates molecule passage Signup and view all the answers

Which molecules can pass through gap junctions due to their small size?

Amino acids and cyclic AMP Signup and view all the answers

What contributes to the structural integrity provided by anchoring junctions?

Linking the cytoskeleton of cells to each other or to the extracellular matrix Signup and view all the answers

What characterizes the composition of tight junctions between cells?

They are composed of claudins that interact between cell membranes Signup and view all the answers

Which type of junction is chiefly responsible for signaling related to tissue development and repair?

Anchoring junctions Signup and view all the answers

Which junction is important for preventing urine from leaking into the extracellular space?

Tight junctions Signup and view all the answers

What happens to gap junctions when a high influx of Ca2+ occurs?

They rapidly close to prevent damage Signup and view all the answers

What effect does hormone binding have on receptor regions?

It exposes regions of the receptor to bind DNA, influencing transcription. Signup and view all the answers

Which of the following hormones is derived from cholesterol?

Estradiol Signup and view all the answers

Which component of signaling transduction is typically found inside the cell?

Second messenger Signup and view all the answers

What characteristic is true about cell-surface receptors?

They consist of three distinct protein regions. Signup and view all the answers

What happens when a ligand binds to a ligand-gated ion channel?

The channel opens or closes depending on the ligand. Signup and view all the answers

Which of the following best describes orphan receptors?

Receptors without any known ligands. Signup and view all the answers

What type of molecules can act as ligands for cell-surface receptors?

Large and hydrophilic molecules that do not need to cross the membrane. Signup and view all the answers

What role do changes in ion levels play inside the cell?

They influence the activity of enzymes and voltage-sensitive channels. Signup and view all the answers

Which subclass of enzyme-linked receptors is characterized by intrinsic tyrosine kinase activity?

Receptor Tyrosine Kinases Signup and view all the answers

Which types of ligands are typically associated with Receptor Serine/Threonine Kinases?

Transforming growth factor-beta Signup and view all the answers

What is a key difference between Receptor Tyrosine Kinases and Tyrosine Kinase-Associated Receptors?

Tyrosine Kinase-Associated Receptors depend on other intracellular tyrosine kinases. Signup and view all the answers

Which receptor is primarily involved in the regulation of immune cell function?

Receptor Tyrosine Phosphatase Signup and view all the answers

What does the activation of Receptor Tyrosine Kinases lead to following ligand binding?

Dimerization and autophosphorylation on tyrosine residues Signup and view all the answers

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

G protein-coupled receptor Signup and view all the answers

Which of the following statements correctly describes Receptor Serine/Threonine Kinases?

They phosphorylate serine or threonine residues on target proteins. Signup and view all the answers

Study Notes

Synaptic Signaling

Neurotransmitters bind to receptors on the receiving cell, triggering a chemical change.
This change often involves opening ion channels and altering the electrical potential across the membrane.
Neurotransmitters are quickly broken down or reabsorbed by the sending cell, resetting the synapse for the next signal.
Primarily uses neurotransmitters like dopamine, serotonin, and acetylcholine.

Autocrine Signaling

A cell signals to itself by releasing a ligand that binds to receptors on its own surface.
Plays a role in cell development, helping cells maintain their identities.
Important in cancer, possibly contributing to metastasis.
Many signals have both autocrine and paracrine effects.
Commonly uses signaling molecules like cytokines and growth factors.

Endocrine Signaling

Cells use the circulatory system to transmit signals over long distances.
Specialized cells produce hormones and release them into the bloodstream.
Hormones travel to target cells in distant parts of the body.
Endocrine glands, such as the thyroid, hypothalamus, pituitary, gonads, and pancreas, release hormones.
Hormones are master regulators of development and physiology.
Uses hormones like insulin, estrogen, and adrenaline.

Signaling Through Cell-Cell Contact

Gap junctions (in animals) and plasmodesmata (in plants) connect neighboring cells.
These channels permit small signaling molecules (intracellular mediators) to diffuse between cells.
Allows for coordinated responses to signals received by only one cell in a group.
Uses membrane-bound signals like ligands and their corresponding receptors on adjacent cells.

Molecules Used in Cell Signaling

Hydrophobic:
- Steroid hormones
- Fatty acid derivatives
- Gasses
Hydrophilic:
- Neurotransmitters
Gasses:
- NO (Nitric oxide)
- CO (Carbon monoxide)
Ions:
- K+ (Potassium)
- Na+ (Sodium)
- Ca2+ (Calcium)
Amino acids
Peptides
Proteins
Nucleotides:
- miRNA (microRNA)

Protein Secretion

Exocytosis
Shaving (releasing portions of a protein)

MicroRNA

Single-stranded RNA
Requires protection from degradation:
- Connecting to a protein (HDL, RBP)
- Packing into a vesicle

Direct Connections and Communication

Gap junctions:
- Channels between cells that allow transport of ions, water, and other substances.
- Formed by connexins forming connexons.
- Crucial in cardiac muscle, allowing synchronized contraction.
- Allow passage of small molecules like Ca2+, cyclic AMP, nucleotides, and amino acids.
- Highly responsive to changes, opening and closing within seconds.
Tight junctions:
- Create a watertight seal between cells.
- Composed of claudins, forming strands that contribute to a tight seal.
- Prevent leakage of fluids between cells.
Anchoring junctions:
- Provide mechanical stability by linking cytoskeletons of cells or cells to extracellular matrix.
- Important for structural integrity, especially in tissues exposed to stress.
- Adherens junctions: Link actin cytoskeletons of adjacent cells, maintaining tissue architecture and cell shape.

Nuclear Receptors

Ligand binding exposes DNA-binding domains, allowing them to alter gene transcription.
Found in the promoter region of genes, influencing gene expression.
Ligands include:
- Cholesterol-derived hormones (cortisol, estradiol, testosterone, vitamin D3)
- Tyrosine-derived hormones (thyroxine)
- Vitamin A derivative (retinoic acid)
Orphan receptors are receptors with unknown ligands.

Signal Transduction:

First messenger: Signal originating outside the cell.
Second messenger: Signal inside the cell.
Can be water-soluble or lipid-soluble.
Signal amplification often occurs, such as autophosphorylation.

Cell-Surface Receptors:

Extracellular domain: Binds to ligands on the cell surface.
Hydrophobic domain: Spans the cell membrane.
Intracellular domain: Transmits signals inside the cell.
Ligand-gated ion channels:
- Open in response to ligand binding.
- Channel allows specific ions to pass through the membrane.
Enzyme-linked receptors: (catalytic receptors)
- Have an extracellular ligand-binding domain and an intracellular domain with enzymatic activity.
- Ligand binding activates the enzyme, leading to intracellular signaling.

Enzyme-Linked Receptor Subclasses:

1. Receptor Tyrosine Kinases (RTKs):
- Have intrinsic tyrosine kinase activity.
- Upon ligand binding, dimerize and autophosphorylate on tyrosine residues, activating downstream signaling pathways.
- Examples: EGFR, Insulin receptor, VEGFR
- Ligands: Growth factors, insulin
2. Receptor Serine/Threonine Kinases:
- Phosphorylate serine or threonine residues on target proteins.
- Examples: TGF-β receptors
- Ligands: TGF-β, BMPs
3. Tyrosine Kinase-Associated Receptors:
- Associate with intracellular tyrosine kinases (like JAKs) for phosphorylation.
- Examples: Cytokine receptors (interleukin receptors, erythropoietin receptors)
- Ligands: Cytokines, growth hormones
4. Receptor Guanylyl Cyclases:
- Possess guanylyl cyclase activity, generating cGMP from GTP.
- Example: ANP receptor
- Ligands: ANP, BNP
5. Receptor Tyrosine Phosphatases:
- Have phosphatase activity, removing phosphate groups from tyrosine residues.
- Typically regulate signaling pathways.
- Example: CD45
- Ligands: Involved in immune regulation.

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Explore the different types of cell signaling mechanisms including synaptic, autocrine, and endocrine signaling. Understand how neurotransmitters and hormones function in communication between cells and the implications on processes like cell development and cancer. Test your knowledge with this quiz!