unit 2 week 3 pt 3 Flashcards
What are gap junctions and plasmodesmata?
Gap junctions are specialized sites of communication between animal cells, while plasmodesmata are specialized communication sites between plant cells. Both structures allow direct communication between adjacent cells.
How do gap junctions work?
Gap junctions consist of connexins, which are integral membrane proteins. These proteins form connexons, creating channels that span the plasma membrane, connecting the cytoplasm of adjacent cells.
What is the structure of connexons?
Connexons are made up of six connexin subunits, arranged in a ring around a central opening of about 1.5 nm in diameter, allowing molecules to pass through.
How do connexons in adjacent cells form a gap junction?
The connexons from the plasma membranes of adjacent cells align and tightly link through noncovalent interactions, forming complete intercellular channels.
What types of molecules can pass through gap junctions?
Gap junctions allow the diffusion of molecules with a molecular mass of less than approximately 1000 daltons, including ions and small molecules.
Can gap junctions be opened or closed?
Yes, gap junctions are gated and can be opened or closed, triggered by stimuli such as phosphorylation of connexin subunits or changes in voltage.
What role do gap junctions play in intercellular communication?
Gap junctions facilitate the direct movement of ions and small molecules between cells, enabling rapid communication crucial for synchronized activities in tissues.
How were gap junctions first discovered to play a role in communication?
In the 1950s, Furshpan and Potter discovered that a subthreshold depolarization in presynaptic neurons caused rapid depolarization in postsynaptic cells, indicating a direct ionic flow attributed to gap junctions.
What did Kanno and Loewenstein discover about gap junctions in the 1960s?
Kanno and Loewenstein found that when ions were injected into the nucleus of one cell, they flowed directly into the cytoplasm of adjacent cells, showing electrical coupling through gap junctions.
What is the significance of gap junctions in different cell types?
Gap junctions are essential for synchronized cellular activities in various tissues, enabling rapid ionic flow crucial for functions like muscle contraction and nerve signaling.
What did electron microscopic studies reveal about animal cells?
Electron microscopic studies showed that animal cells are bounded by a continuous plasma membrane, suggesting that this membrane could be modified at contact sites for direct substance movement.
Who discovered cell junctions containing channels between closely applied cells, and when?
The discovery was made in 1967 by Jean Paul Revel and M. J. Karnovsky, who named these junctions gap junctions.
What did electron micrographs reveal about gap junctions?
Electron micrographs showed a distinct cleft between adjoining cells, helping researchers distinguish gap junctions from other types of junctions.
What did Loewenstein’s laboratory discover about the size of the channels in gap junctions?
Loewenstein’s laboratory found that molecules up to about 1200 daltons could diffuse between insect larval salivary gland cells, estimating the effective diameter of the gap junction channel to be around 1.0 to 1.5 nm.
What did Kanno and Loewenstein investigate after discovering gap junctions?
They studied whether these junctions were present in cancer cells, hypothesizing that a loss of gap junction communication might allow cancer cells to escape growth control.
What did Kanno and Loewenstein find when comparing normal liver tissue to liver tumors?
They found that ionic current flowed easily between cells in normal liver tissue, but no current was detected in liver tumors, indicating a loss of gap junction communication.
What is the relationship between gap junction communication and cancer cells?
Many cancer cells lose the ability to carry out gap junction intercellular communication, which may contribute to escaping growth control mechanisms.
How is the loss of GJIC related to metastatic potential in cancer cells?
The loss of GJIC is correlated with increased metastatic potential, allowing cancer cells to ignore signals from neighboring cells.
What evidence supports a causal relationship between the loss of GJIC and malignancy?
Christian Naus and colleagues showed that forced expression of connexin43 in C6 glioma cells increased GJIC, decreased cell growth, and resulted in smaller tumor sizes.
How do findings with connexin43 in C6 glioma cells relate to other cancer cells?
Similar findings were reported in human cancer cells, where transfection with connexin genes reduced tumor formation, but growth suppression was reversed when the connexin protein was lost.
How are skeletal, cardiac, and smooth muscle cells stimulated differently?
Skeletal muscle cells are stimulated by chemicals from nerve cells, while cardiac and smooth muscle cells are stimulated by electrical impulses through gap junctions.
What is the function of gap junctions in mammalian tissues?
Gap junctions allow the flow of ions and small molecules between adjacent cells, enabling coordinated activity and metabolic cooperation.
What are connexins, and how do they affect gap junction function?
Connexins are proteins forming gap junctions, with about 20 types affecting conductance and permeability. Mutations can lead to disorders like deafness and cardiac arrhythmias.
How do gap junctions contribute to the integration of tissue activity?
Gap junctions allow communication among many cells, enabling coordinated responses to stimuli and sharing of metabolites.
What is the role of plasmodesmata in plant cells?
Plasmodesmata are cytoplasmic channels that pass through plant cell walls, allowing communication and coordination of activities across adjacent plant cells.
How do plasmodesmata differ from gap junctions in terms of permeability?
Plasmodesmata can allow larger molecules (up to 50 kDa) to pass through, while gap junctions typically allow smaller molecules.
How do plant viruses interact with plasmodesmata?
Plant viruses spread by passing through plasmodesmata, using movement proteins to increase pore diameter for cell-to-cell movement.
What are the major differences between animal and plant intercellular communication?
Animal cells use gap junctions for direct communication, while plant cells use plasmodesmata, which allows for coordination of growth and responses.
What are tunneling nanotubes, and what do they do?
Tunneling nanotubes are thin tubules that allow the transfer of proteins, organelles, and signals between cells over long distances.
How do tunneling nanotubes contribute to intercellular communication?
They serve as conduits for cells to communicate over long distances by transferring cellular components.
What are extracellular vesicles, and what role do they play in intercellular communication?
Extracellular vesicles are membrane-bound structures released by cells to communicate with others over long distances, influencing activities like tumor growth.
How were extracellular vesicles initially perceived, and what is the current understanding of their role?
Initially thought to dispose of unnecessary material, they are now understood to play an active role in cell-to-cell communication.
What determines the effects of extracellular vesicles on recipient cells?
The effects depend on the cargo they carry, which can include proteins and RNAs, influencing specific activities in target cells.
How are extracellular vesicles being explored for medical applications?
They are being investigated for targeted drug delivery due to their ability to carry diverse therapeutic agents.
Why are tunneling nanotubes and extracellular vesicles considered important in cellular communication?
They provide new ways for cells to communicate over long distances, expanding the understanding of cellular interaction.
