Cell-Cell Interactions 2

describe how extracellular signals are received

• signal reception

 extracellular signal molecules bind to and activate a membrane receptor

• signal transduction

 the activated receptor protein activates an intracellular signaling pathway causing the activation of an enzyme

• signal amplification

 an activated enzyme generates multiple intracellular second messenger molecules

• signal response (“switch”)

 second messenger molecules regulate effector proteins

 regulation of effector proteins leads to altered cell function

 typical effector proteins are metabolic enzymes, cytoskeletal and gene regulatory proteins

describe how steroid hormones such as cortisol function

• cortisol is a stress hormone that controls the stress response in vertebrate animals

• signal arrival

 cortisol is a steroid hormone and can pass through the cell membrane into the cytoplasm

• signal reception

 in the cytoplasm cortisol binds to a cortisol receptor protein

 the hormone-receptor complex is translocated into the cell nucleus

• direct signal response (“switch”)

 the hormone-receptor complex acts as gene-regulator and activates transcription of genes

explain why cell signaling pathways amplify the primary transduction

Cell signaling pathways amplify the primary transduction because each step in the cascade activates multiple downstream molecules, creating a chain reaction that magnifies the initial signal. This amplification allows a single external signal to trigger a large and rapid cellular response, often by using second messengers (like cAMP) and phosphorylation cascades, where one kinase phosphorylates and activates many other kinases. 

explain the difference between extracellular and intracellular signal receptors

Extracellular receptors are located on the cell surface and bind hydrophilic (water-soluble) ligands, which are unable to cross the cell membrane. Intracellular receptors are inside the cell and bind hydrophobic (lipid-soluble) ligands that can pass through the membrane. Both types of receptors initiate a cellular response after binding to their specific ligand, but they do so in different ways. 

describe the pathway of G-protein coupled receptor signaling

The G-protein coupled receptor (GPCR) pathway begins with a ligand binding to the GPCR, which activates an associated G-protein by causing it to release GDP and bind GTP. The G-protein then splits into its αalpha and βγbeta gamma subunits, which can each interact with and activate effector proteins (like enzymes or ion channels) to initiate a downstream signaling cascade. This often involves the production of second messengers, which amplify the signal and ultimately lead to a cellular response. 

describe the pathway of enzyme-coupled receptors

The pathway of an enzyme-coupled receptor begins with a signaling molecule binding to the receptor's extracellular domain, causing two receptors to dimerize (come together). This dimerization activates the receptor's intracellular enzymatic domain, often a kinase, which then phosphorylates itself and other intracellular relay proteins. These activated proteins form large signaling complexes that trigger downstream cascades, ultimately leading to cellular responses like changes in gene expression, enzyme activity, or cell growth. 

explain the concept of cross-talk between cell signaling pathways

Cross-talk is the communication between different cell signaling pathways, allowing them to integrate signals and coordinate a cellular response. This interaction can either amplify or inhibit the effects of each other, enabling a cell to fine-tune its response to a complex environment by sharing components or directly influencing one another. Cross-talk is vital for proper cell function, development, and survival, but also plays a role in diseases like cancer when these pathways become miscommunicative. 

explain why cells depend on multiple signal molecules

Cross-talk is the communication between different cell signaling pathways, allowing them to integrate signals and coordinate a cellular response. This interaction can either amplify or inhibit the effects of each other, enabling a cell to fine-tune its response to a complex environment by sharing components or directly influencing one another. Cross-talk is vital for proper cell function, development, and survival, but also plays a role in diseases like cancer when these pathways become miscommunicative. 

describe how extracellular signals are transduced

Extracellular signals are transduced through a process that begins when a signaling molecule (ligand) binds to a cell-surface receptor, causing a conformational change that initiates a cascade of intracellular events. This "signal transduction" converts the external signal into an internal one, often involving second messengers like cyclic AMP and a series of enzyme-catalyzed reactions that amplify the signal. Ultimately, this process triggers a specific cellular response, such as changes in gene expression, metabolic activity, or cell division.