Cell Communication Mini-Test Review
Cell Communication Mini-Test Review
Open vs. Closed Junctions
Open Junctions:
Plasmodesmata:
Found in plant cells; functions as channels between adjacent cells allowing for nutrient and signal exchange.
Gap Junctions:
Composed of connexins, forming channels that enhance communication between adjacent animal cells.
Closed Junctions:
Tight Junctions:
Seals adjacent epithelial cells together, preventing leakage of materials between them.
Desmosomes:
Provides mechanical strength by anchoring the cytoskeletal structures of cells together.
Modes of Cell Communication
Juxtacrine:
Cell communication through direct contact between neighboring cells.
Paracrine:
Local signaling where one cell emits signals that influence nearby cells.
Endocrine:
Long-distance signaling often through hormones released into the bloodstream, affecting distant cells.
Autocrine:
Signaling where a cell secretes molecules that bind to receptors on its own surface, influencing its own activity.
Types of Signaling
Cell to Cell Contact:
Utilizes various junctions such as plasmodesmata for direct signaling (notably in the immune system).
Local Signaling:
Example of Paracrine Signaling:
Involved in processes such as mitosis and blood clotting and synaptic signaling at synapses.
Quorum Sensing:
A bacterial communication mechanism that enables collective behavior.
Applications of Quorum Sensing:
Biofilm formation, virulence factor production, and bioluminescence in marine organisms.
Long-Distance Signaling:
Primarily through hormones in the endocrine system, targeting distant cells to regulate bodily functions.
Three Stages of Cell Signaling
Reception:
Detection of signaling molecules by receptors on target cells.
Transduction:
Conversion of the signal into a form that can bring about a cellular response, often involving secondary messengers.
Response:
The final outcome of signaling, which can lead to changes in gene expression or cellular activity.
Types of Messengers
Protein Messengers: (Water-Soluble/Polar)
Receptors located on the cell surface due to inability to cross the lipid bilayer.
Lipid Messengers: (Lipid-Soluble/Nonpolar)
Can easily pass through the membrane and interact with receptors in the cytoplasm or nucleus.
G Protein-Coupled Receptors
Major class of receptors that respond to various signaling molecules such as epinephrine.
Example:
Epinephrine triggers the “fight or flight” response through G protein signaling pathways.
Secondary Messengers
Examples:
cAMP (cyclic adenosine monophosphate) and Ca²⁺ (Calcium ions).
Involved in amplifying the signal initiated by the first messenger (ligand).
Phosphorylation Cascades
Involves a series of protein kinases that add phosphate groups leading to signal amplification.
Mechanism:
Each kinase activates another kinase, creating a cascade effect that vastly strengthens the signal.
Common Responses to Signaling
Transcription of genes:
Can lead to an increase/decrease in gene expression.
Inhibition of transcription:
Prevents genes from being expressed due to signaling events.
Enzymatic reaction in the cytoplasm:
Example: Breaking down glycogen into glucose (glycogenolysis).
Protein synthesis:
Creation of proteins from transcribed mRNA.
The Endocrine System
Antagonistic Hormone Examples:
Hormones that have opposing actions (e.g., insulin lowers blood glucose, glucagon raises blood glucose).
Feedback Loops:
Positive Feedback:
Enhances or exaggerates changes (e.g., childbirth).
Negative Feedback:
Counteracts changes to maintain homeostasis (e.g., regulation of blood glucose).
Multiple Effects from a Single Endocrine Hormone:
Hormones can have diverse effects on different cell types or tissues, resulting in varied biological responses.