Special Sub-Topic: The Cellular Internet
|Basically, there are two major participants in every cell communication activity: the "doer" of the communication, and the "receiver" of the communication. They may also communicate through direct and indirect contact, also called local and long-distance signaling, respectively. Which of the following is an example of long-distance signaling occurring in the body?|
Hormonal signaling. Paracrine signaling and synaptic signaling are examples of local signaling, which happen in direct contact, or in the vicinity of the communicator. In paracrine signaling, cells act on nearby cells by discharging molecules called local regulators, special messenger molecules which may be growth factors or other types of messengers. In synaptic signaling, which is usually done by nerve cells, there is a release of neurotransmitters which diffuses across the synapse, the space between two nerve cells, which stimulates the target cell, which is usually another nerve cell. In hormonal signaling, also called endocrine signaling, specialized cells release hormones into the vessels of the circulatory system, which then reaches the target cell. There is no such thing as systematic signaling.
|The receiving end of a cellular conversation can be dissected into three stages. These stages were elucidated by Earl Sutherland, whose research led to a Nobel Prize in 1971. He and his colleagues were investigating how an animal hormone that stimulates the breakdown of the storage polysaccharide glycogen within liver cells and skeletal muscles, which in turn releases the sugar glucose-1-phosphate, which the cell converts to glucose-6-phosphate.
The question is, what was the animal hormone?
Adrenalin. Adrenalin, or better known as epinephrine, aside from stimulating the breakdown of the glycogen within liver cells and skeletal muscles, also stimulates the cells in the heart to contract, leading to a more rapid heartbeat. This accounts for what we feel when we have an adrenalin rush (or adrenaline rush), or that "fight-or-flight" feeling. Oxytocin, insulin, and TSH are hormones too, but we shall not concern them much in our quiz.
|The three stages of "cellular conversation" are reception, transduction, and response. In which of these stages are signal molecules binding to certain proteins in the cell membrane, causing the protein to change shape?|
Reception. Reception is the detection of a target cell of a signal molecule coming from outside the cell. Transduction is the process initiated by the binding of the signal molecule, which in turn changes the receptor protein in some way. What is triggered by the transduced signal will be the response, which could be any cellular activity, such as catalysis by an enzyme, activation of genes, and the like.
|Most water-soluble signal molecules bind to specific sites on receptor proteins embedded in the cell's plasma membrane. Such a receptor transmits information from the extracellular environment to the inside of the cell by changing shape or aggregating when a specific ligand, or the molecule that specifically binds to another molecule, binds to it. There are three major types of such membrane receptors. Which of the following membrane receptors is not one of them?|
Active receptor relay proteins. A G-Protein-linked receptor works with the help of a protein called a G protein in the plasma membrane. The G protein carries with it a special energy carrying molecule, Guanosine triphosphate, or GTP, hence its name. A receptor tyrosine kinase can trigger more than one signal transduction pathway at once. It has three amino acids, which would be tyrosine. An active receptor tyrosine kinase undergoes phosphorylation, which would be the addition of the functional group Phosphate, and dimerization, a combination or fusion of two receptor tyrosine kinase polypeptide structure, thus forming a phosphorylated receptor tyrosine kinase dimer. (That was a mouthful.) An ion channel receptor functions as a gate, wherein when a signal molecule binds as a ligand to the receptor protein, the gate opens or closes, allowing or blocking the flow of specific ions, such as those of sodium and calcium.
|In the second stage, transduction, cascades of molecular interactions relay signals from receptors to target molecules in the cell. The binding of a specific signal molecule to a receptor in the plasma membrane triggers the first step in the chain of molecular interactions that leads to a particular response within the cell. What are these interactions?|
Signal transduction pathways. Signal transduction pathways occur in transduction, which sometimes occurs in a single step but more often requires a sequence of changes in a series of different molecules. In a phosphorylation cascade, a series of different molecules in a pathway are phosphorylated in turn, each molecule adding a phosphate group to the next one in line, forming a cascade. Cellular protein phosphatases are enzymes, not interactions, which can rapidly remove phosphate groups from proteins, a process called dephosphorylation, in phosphorylation cascades.
*I just made up the transductory voltage-gated ion channel receptor routes, for "multiple choice confusion tactics" purposes. Although there are voltage-gated ion channels. These are gated ion channels that are controlled by electrical signals instead of ligands, and they are crucial to the functioning of the nervous system.
|Many signaling pathways involve small, nonprotein, water-soluble molecules or ions called messengers. One such messenger, which transmits signals from the plasma membrane to the metabolic machinery of the cytoplasm, is found by Earl Sutherland in his research. What are these messengers?|
cAMP. cAMP, or cyclic Adenosine monophosphate, was found by Sutherland to be increasing in concentration in the cytosol when epinephrine binds to the plasma membrane of a liver cell. An enzyme embedded in the plasma membrane, adenylyl cyclase, not only adenylyl, converts ATP to cAMP in response to an extracellular signal, well, in this case, epinephrine. Calcium ions are also messengers, and their concentration is usually much lower in the cytosol than in the extracellular fluid.
|Our understanding of signaling pathways involving messengers has allowed us to develop treatments for certain conditions in humans. One such "technology" is the compound/are the compounds that inhibits/inhibit the hydrolysis of a messenger to another. What is this compound/ these compounds that prolong/prolongs such signal and was originally prescribed for chest pains?|
Viagra. Maybe it's difficult for you to believe, but it's true. Viagra causes dilation of blood vessels, which allows increased blood flow to the penis, optimizing physiological conditions for penile erections. I am not sure about the existence of Lavitra, but I heard it somehow. I also don't know about Inositol, but there is inositol triphosphate, a second messenger that is involved in the pathways leading to calcium release.
|What is a protein kinase, and what is its role in routes of transduction of chemical signals?|
It transfers a phosphate group from ATP to a protein, usually activating that protein.. The statement "It is an enzyme that is embedded in the plasma membrane which converts ATP in response to an extracellular signal." refers to adenylyl cyclase, which convertys ATP to cyclic AMP. The statement "It removes phosphate groups from proteins in a process called dephosphorylation, which in turn provides the mechanism for turning off the signal transduction pathway when the initial signal is no longer present." refers to protein phosphatases, the enzyme that counteracts the action of protein kinases. The statement "It cleaves sugar molecules into two different three-carbon sugars: dihydroxyacetone phosphate and glyceraldehydes-3-phosphate." refers to aldolase, and enzyme working in glycolysis, a process in cellular respiration.
|The third and last stage is response, where cell signaling leads to regulation of cytoplasmic activities or transcription. Also, scaffolding proteins are large relay proteins increase the efficiency of signal transduction in many cases. How can two cells with different scaffolding proteins behave differently in response to the same signaling molecule?|
They hold molecular components of signaling pathways in a complex with each other.. Different scaffolding proteins would assemble different collections of proteins, leading to different responses in the two cells. Signal amplification and specificity of cell signaling are important benefits in response, not really scaffolding proteins.
|Here's a trivia question for you, to top it all off. Research has discovered that cells of this organism identify their mates by chemical signaling. They have two mating types, called a and α (alpha). This organism is also used for making wine, bread, and beer. What is the scientific name of this organism?|
Saccharomyces cerevisiae. The real trivia I wanted to give to you is the scientific name of yeast, and this too. Cells of mating type a secrete a chemical signal called a factor, which can bind to receptors on nearby α (alpha) cells. The same goes to α (alpha) cells. They secrete α (alpha) factor, which binds to receptors on a cells.
Zea mays is the scientific name for corn, Oriza sativum for rice, and Thiomargarita namibiensis is an organism, possessing the largest cells, visible even with the naked eye.
Well, I hope you enjoyed taking this quiz! And I hope you learned a lot in the cellular internet!
Did you find these entries particularly interesting, or do you have comments / corrections to make? Let the author know!
Send the author a thank you or
Submit a correction