Cell Biology Quiz: Gap Junctions

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Questions and Answers

What is the primary function of tight junctions?

  • To provide structural support to tissues
  • To create a seal to prevent leaks between cells (correct)
  • To allow for the passage of large molecules between cells
  • To facilitate communication between cells

Gap junctions are present only in plant cells.

False (B)

What are the two main families of channel-forming proteins involved in gap junctions?

Connexins and Innexins

The largest functional pore size for gap-junctional channels is about ______ nm.

<p>1.5</p> Signup and view all the answers

Match the following structures with their functions:

<p>Tight junctions = Prevent leakage between cells Gap junctions = Facilitate communication between cells Plasmodesmata = Allow passage of molecules between plant cells Basal lamina = Provides structural support and acts as a filter</p> Signup and view all the answers

Which of the following can pass through gap junctions?

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

Both connexins and innexins are found only in vertebrates.

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

What is the significance of gap junctions in pacemaker cells of the heart?

<p>Gap junctions allow the synchronized electrical activity of pacemaker cells, ensuring coordinated heartbeats.</p> Signup and view all the answers

Which of the following molecules can pass through gap junctions?

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

Gap junctions are formed by the alignment of connexons from two adjacent cells.

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

A connexon is made up of six transmembrane _____ subunits.

<p>connexin</p> Signup and view all the answers

Match the following terms with their descriptions:

<p>Connexon = A hemichannel formed by six connexin subunits Hemichannel = A connexon that does not align with another connexon, opening to the extracellular space Gap junction = A continuous aqueous channel formed by the alignment of two connexons</p> Signup and view all the answers

What is the primary reason why gap junctions in different tissues exhibit varied properties?

<p>The presence of different connexins forming the channels (C)</p> Signup and view all the answers

Unpaired gap junction channels, also known as hemichannels, are typically open, allowing continuous flow of molecules.

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

What is the primary consequence of mutations in connexin-26?

<p>Hearing loss due to cell death in the organ of Corti due to disruption of ions in its sensory epithelium</p> Signup and view all the answers

The neurotransmitter ______ plays a crucial role in regulating gap junction permeability between neurons in the retina, enabling the eye to adapt to varying light intensities.

<p>dopamine</p> Signup and view all the answers

Explain how dopamine contributes to the regulation of gap junction permeability in the retina.

<p>Dopamine reduces gap junction permeability between retinal neurons in response to increased light intensity, facilitating a shift from rod receptors to cone receptors for improved vision in bright light.</p> Signup and view all the answers

Match the following terms with their respective descriptions:

<p>Connexin = A protein that forms gap junctions Hemichannel = An unpaired gap junction channel Lucifer Yellow = A dye used to study gap junction permeability Organ of Corti = The sensory epithelium of the inner ear Dopamine = A neurotransmitter that regulates gap junction permeability</p> Signup and view all the answers

Gap junctions are always open once they are formed.

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

Basal lamina is absent beneath epithelia.

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

Why do certain bacteria secrete enzymes that can digest components of the basal lamina?

<p>To gain access to nutrients or to invade tissues.</p> Signup and view all the answers

What is the main cell type found in connective tissue that secretes extracellular matrix components?

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

The basal lamina provides guidance to cells regarding the location of ______ and the direction of axonal extension.

<p>receptors</p> Signup and view all the answers

What is the neurotransmitter released by the neuron at the neuromuscular junction?

<p>Acetylcholine (ACh)</p> Signup and view all the answers

What happens to dopamine levels in the retina when you wake up in the morning and turn on the light?

<p>Dopamine release is increased. (B)</p> Signup and view all the answers

What role does dopamine play regarding gap junctions?

<p>It closes gap junctions (C)</p> Signup and view all the answers

The basal lamina is a type of extracellular matrix found only in muscle tissues.

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

What is the primary function of the basal lamina?

<p>To provide structural support and anchorage for cells.</p> Signup and view all the answers

The extracellular matrix is primarily composed of __________ and polysaccharides.

<p>proteins</p> Signup and view all the answers

Why does the retina utilize the closure of gap junctions in bright light?

<p>To prevent overwhelming stimuli (D)</p> Signup and view all the answers

The basement membrane is another name for the basal lamina.

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

Match the following tissues with their corresponding extracellular matrix:

<p>Bone = Bulky connective tissue Tendon = Collagen-rich matrix Skin = Dermal layer matrix Muscle = Surrounded by basal lamina</p> Signup and view all the answers

The basal lamina is typically __________ to __________ nm thick.

<p>40</p> Signup and view all the answers

What is the role of the laminin γ-1 chain?

<p>It is crucial for embryonic development in mice. (D)</p> Signup and view all the answers

Type IV collagen only exists in one isoform.

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

What type of protein interacts with the binding sites on laminin?

<p>Integrins</p> Signup and view all the answers

Laminin has binding sites for __________, which help it connect to other extracellular matrix components.

<p>perlecan and dystroglycan</p> Signup and view all the answers

Which of the following is NOT a function of laminin?

<p>Providing tensile strength to the basal lamina (A)</p> Signup and view all the answers

Match the following proteins to their functions:

<p>Laminin = Interacts with integrins and ECM components Type IV Collagen = Provides tensile strength to the basal lamina Integrins = Membrane proteins that connect cells to ECM Nidogen = Fibrous protein that contributes to ECM structure</p> Signup and view all the answers

Both laminin and type IV collagen contribute to the basal lamina's structure.

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

What is the structural composition of type IV collagen?

<p>Three separately synthesized long protein chains</p> Signup and view all the answers

Flashcards

Tight Junctions

Protein complexes that seal cells to prevent leakage.

Gap Junctions

Structures that bridge gaps between cells for communication.

Plasmodesmata

Channels in plant cells that enable direct communication.

Connexins

Channel-forming proteins in gap junctions, mainly in vertebrates.

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Innexins

A family of channel-forming proteins similar to connexins.

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Electrical Coupling

When gap junctions allow electrical signals between cells.

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Metabolic Coupling

Exchange of metabolites and ions through gap junctions.

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Pore Size of Gap Junctions

Largest functional pore size for gap-junctional channels is about 1.5 nm.

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Hemichannels

Single half of a gap junction that can function when unpaired.

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Connexin-26 Mutation

A genetic defect leading to congenital deafness by disrupting ion flow in the ear.

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Gap Junction Permeability Regulation

Cells can adjust how permeable their gap junctions are to ions and molecules.

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Dopamine Role in Retina

Dopamine reduces gap-junction communication in retinal neurons during bright light.

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Rod vs Cone Receptors

Photoreceptors in the retina; rods detect dim light, cones detect color and detail.

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Lucifer Yellow Experiment

Experiment showing how dye can pass through gap junctions to visualize neuron connectivity.

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Small Molecules

Inorganic ions, sugars, amino acids, nucleotides, and vitamins that cells can share.

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Macromolecules

Large biological molecules like proteins, nucleic acids, and polysaccharides that cannot be shared between cells.

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Conformation of Hemichannels

Hemichannels generally remain closed to control ion movement until a stimulus opens them.

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Size Limit of Gap Junctions

Gap junctions typically allow the passage of molecules sized between 500 and 5000 daltons.

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Dopamine's Role

Dopamine can close gap junctions, preventing ion exchange between neurons.

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Retina Function in Bright Light

In bright light, the retina uses dopamine to enhance visual response by closing gap junctions.

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Extracellular Matrix (ECM)

A network of macromolecules providing structural and biochemical support to surrounding cells.

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Basal Lamina

A specialized ECM layer that underpins epithelial tissues and surrounds certain cells.

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Thickness of Basal Lamina

Typically ranges from 40 to 120 nm in thickness.

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Composition of ECM

The extracellular matrix is made up of proteins and polysaccharides secreted by cells.

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Function of Basal Lamina

Provides support and anchorage for various cells such as muscle and fat cells.

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Laminin γ-1 chain

A critical component of most laminin heterotrimers essential for embryogenesis.

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Laminin structure

Laminin is composed of three chains: alpha, beta, and gamma, coiling around each other.

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Binding sites

Regions on laminin that allow interactions with integrins and ECM components.

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Integrins

Membrane proteins on cells that interact with ECM components like laminin.

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Type IV collagen

An essential component of basal lamina providing tensile strength through flexible networks.

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Self-assembly

The process by which laminin molecules bind together while also connecting to cells and ECM.

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Functional domains

Specific regions of laminin that enable binding interactions with various proteins.

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Fibroblasts

Cells in connective tissue that secrete ECM components like collagen.

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Collagen

A protein that provides structural support in tissues.

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Macrophages

Specialized immune cells that can move through tissues.

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Neuromuscular Junction

The synapse between a neuron and a muscle cell.

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ACh Receptors

Nicotinic receptors that respond to acetylcholine at the neuromuscular junction.

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Proteases

Enzymes that break down proteins, allowing cell movement.

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Study Notes

Lecture 6: Passageways from Cell to Cell and Basal Lamina

  • Tight junctions prevent extracellular molecules from leaking between cells. They form a seal between cells.
  • Gap junctions create direct passageways between the cytoplasm of adjacent cells. These are different in animal tissues (gap junctions) and plants (plasmodesmata).
  • Gap junctions and plasmodesmata allow for the exchange of small molecules, but not large macromolecules.
  • Tight junctions are protein complexes, creating a seal between cells to prevent leakage.
  • Gap junctions are protein channels that allow small molecules to pass between cells.
  • Connexins and innexins are channel-forming proteins in gap junctions.
  • Gap junctions are crucial for electrical coupling in tissues like the heart.
  • Gap junction channels have a pore size of roughly 1.5 nm, letting small molecules, but not large ones, pass.
  • Ions can pass easily, complex carbs and proteins cannot.
  • Mutations in connexin-26 are associated with congenital deafness.
  • Gap junctions are gated channels (they close on occasion) in contrast to ion channels that stay open all the time.
  • Dopamine regulates gap junction communication.
  • Basal lamina is not made entirely of cells.
  • Basal lamina is a network of macromolecules.
  • Basal lamina is found in tissues like bone, tendon, and skin.
  • Basal lamina is essential for supporting and organizing tissues.
  • Basal lamina is a filter in kidney glomeruli.
  • Basal lamina is important for cell polarity, metabolism, and differentiation.
  • Defects in basal lamina proteins can cause problems in tissue organization.
  • Basal lamina helps hold tissue components in place.
  • Laminin is a major component of the basal lamina, a network of protein fibers and polysaccharides.
  • Type IV collagen is another main component of the basal lamina, providing strength and structural support.

Laminin

  • Laminin is the primary organizer of the basal lamina structure, crucial in development.
  • Laminin is composed of three polypeptide chains held together by disulfide bonds.
  • Laminin isoforms exist with different properties, and are crucial in cell organization and structure.
  • Laminin is essential for early development.

Type IV Collagen

  • Type IV collagen is a major contributor to the tensile strength of the basal lamina.
  • It consists of three protein chains, assembling into felt-like networks.
  • Type IV collagen and laminin are structured in a way that enables them to interact.

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Lecture 6 2025 (PDF): Passageways from Cell to Cell and Basal Lamina

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