Module 3.1: Intercellular Communication Flashcards
In what three ways does intercellular communication occur, and which is the most common in the body
Directly through gap junctions, through membrane proteins, and indirectly through extracellular chemical messengers. The most common of these is the indirect extra cellular chemical messengers
What are the four types of extra cellular chemical messengers
Paracrines, Nero transmitters, hormones, and neurohormones
What are paracrines and give one example
Specifically released local messengers, affect only neighbouring cells. Simple diffusion, short distances, rapidly in Aktivated by locally existing enzymes so not much gets into the blood. An example is histamine
What are neurotransmitters
Specifically released from neurons in response to electrical signal, diffuse from site of release and cross very short distance to target cells within nervous, muscular, or endocrine systems. Act locally on adjoining target cell
What are hormones
Specifically released from endocrine cells into circulatory system where they travel to act on target cells. Long range. Respond to appropriate signal
What are neurohormones
Secreted from neurosecretory neurons in response to electrical signals, but are released into the circulatory system where they travel to act on the target cell
What is signal transduction
The process by which incoming signals are conveyed to target cells interior for execution
How does signal transduction happen with lipid soluble messengers and give an example of one
They dissolve and pass through the membrane, binding to receptors inside the target cell. An example is cholesterol derived steroid hormones
How does signal transduction occur with water soluble messengers, and give an example
Messengers bind to receptors in the plasma membrane, which may function as ion channels, enzymes, or may be G-protein linked. Examples are protein hormones delivered by blood, and neurotransmitters released from nerve endings
Describe how receptors act as ion channels
Channel is closed until the messenger binds with the receptor, which opens it to let the ions through, changing the electrical properties of the cell
Describe how receptors work as enzymes
The enzyme is in an inactive state until the messenger binds to the receptor at which time the enzyme becomes active and phosphorylates a specific cellular protein, which will execute a cellular response such as altering cellular metabolism or regulating protein synthesis
Describe how receptors work as G-protein linked
When the messenger is not bound to the receptor, the G protein is inactive in guanosine diphosphate (GDP) bound state. When messenger binds to a receptor the G protein becomes active and guanosine triphosphate (GTP) bound. Activated G protein binds a GTP regulated protein, such as an ion channel or enzyme, and a corresponding cellular response will occur
With what two general means does the first messenger (extra cellular messenger) bring about the desired intracellular response once binding to a receptor
By opening or closing channels as with neurons and Nero transmitters, and muscle contractions, or by activating second messenger systems
How do second messengers work and what is interesting to note about the mechanism used
First messenger binds to membrane receptors, signalling activation for intracellular second messengers. Interesting to note that intracellular pathways activated by second messengers are very similar among different cell types, so variability found in response comes from specialization of the cell, not the mechanism used
How do slow synapses differ from fast synapses, and give an example
Fast synapses utilize chemically gated channels, whereas slow synapses involve activation by second messengers which results in taking longer to achieve the result, but the result also lasts longer. An example is serotonin
Second messenger pathways are one of the key means in which ____________ bring about their effects
Water soluble hormones
What is the main advantage of second messenger systems, and explain how this comes about
Amplification of the initial signal. First Messenger activates multiple G proteins, each of which activate an enzyme in the plasma membrane. Activated enzymes produce hundreds of second messengers, each of which may act on another enzyme, which can then activate hundreds of proteins. I
What is an example of an important secondhand Messenger pathway
cAMP process
Outline the cAMP as a second messenger process
Describe how lipophilic messengers bind to intracellular receptors to alter protein transcription
They diffuse through plasma and nuclear membranes and bind with specified nuclear receptor. This hormone receptor complex then binds with the hormone response element, which is a segment of DNA specific for the hormone receptor complex. Next DNA binding activates specific genes which produce complementary messenger RNA. This mRNA leaves the nucleus and in the cytoplasm directs the synthesis of new proteins. These new proteins will be either enzymatic or structural, and will accomplish the cells ultimate physiologic response to the hormone
