Term
| How do unicellular organisms like yeast mate? |
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Definition
| There are two sexes: "a" and alpha. "a" cells release "a" mating factors, alpha cells release alpha mating factors. "a" cells are able to bind alpha factors and visa versa. This binding causes the cells to fuse and forms a diploid "a"/alpha cell. |
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Term
| What are the three types of local communication in multicellular organisms? |
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Definition
1. Paracrine signaling is when signals are released into the extracellular fluid and are picked up by cells which have the proper receptors.
2. Synaptic signals are released between neurons in the nervous system.
3. Direct contact of cells (gap junctions in animal cells and plasmodesmata in plant cells) leads to communcation between the two cells. |
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Term
| What is an example of long distance communication in cells? |
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Definition
| Hormonal or endocrine communication is when signals are released into the vascular system or air. Neurotransmitters only go to specific cells. |
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Term
| What are the three stages of cell signaling? |
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Definition
1. The cell recieves a signal on its receptor. The signal is a ligand (small molecule which binds to a larger one) and the receptor only recognizes that signal. Receptors can be internal, although they are mostly transmembrane proteins.
2. The signal triggers biochemical events within the cell (transduction).
3. A response is produced. |
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Term
| What are the four major types of receptors? |
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Definition
1. G protein-linked
2. Enzymes (ex. tyrosine-kinase)
3. Ligand-gated ion channels
3. Internal (ex. steroid hormone receptors) |
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Term
| What happens when a G protein-linked receptor activates? |
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Definition
When a G protein-linked receptor binds to a signal molecule, it attracts a G protein inside of the cell and binds to it. Then, a GDP molecule in the G protein is displaced by GTP, giving it energy to go to the adenylyl cyclase enzyme. After the activated G protein transmits the signal to the enzyme, it detaches from the enzyme and the GTP loses a phosphate group (through hydrolysis), turning to GDP.
The adenylyl cylcase turns ATP into cAMP, which acts a second messenger in transduction.
Cellular amplifcation can occur if the G protein-linked receptoractivates more than one protein. |
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Term
| How are enzyme receptors different than G protein-linked receptors? |
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Definition
Enzyme receptors are different than G protein-linked receptors, because an enzyme can dirrectly activate the relay protein through phosphorylation, which begins the reaction pathway. In G protein-linked receptors, they must send a G protein to activate an enzyme.
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Term
| What happens when a tyrosine kinase receptor is activated? |
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Definition
When two tyrosine kinases bind to a ligand outside of the cell, they dimerize and phosphorylate each other (autophosphorylate). This attracts relay proteins (often more than one at once) which get activated by the TK and begin the transduction pathway. This protein kinase will go until it reaches another protein kinase. At that point, the relay protein phosphorylates the protein kinase and a protein called phosphotases dephosphorylates the relay protein. The active protein kinase then continues until it phosphorylates another protein kinase and gets dephosphorylated by phosphates. This chain continues in a process known as a phosphorylation cascade. Eventually, a different type of protein is activated which triggers the actual cellular response.
Other enzyme receptors that can be activated in the cytosol are serine kinase and threonine kinase. |
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Term
| What happens at ligand-gated ion channels? |
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Definition
| A ligand attaches to an ion channel (a transmembrane protein), which causes it to open and ions to come through. The change in concentration of ions in the cell triggers the cellular response. |
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Term
| Which type of signals can act as internal signals (ligands) which activate internal receptors? What is another name for internal signals? |
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Definition
The signals have to be hydrophobic (non-polar) to be able to go through the plasma membrane on their own.
Because these internal ligands also perform the second step of cellular signaling (transduction), they are also called transducers. |
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Term
| What are second messengers? Give three examples. |
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Definition
Second messengers are the relay proteins which are activated by MEMBRANE receptors. They go on to activate other proteins and continue transduction.
Some common second messengers are Ca2+, cAMP, DAG and IP3. |
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Term
| cAMP is a second messenger involved in trasnduction. How is cAMP activated and how is it deactivated after it has relayed a mesage? What is a major response that cAMP is involved in? |
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Definition
ATP is turned into cAMP by adenylyl cyclase after a G protein-linked receptor sends a G protein to it. When the message has been relayed by cAMP to a protein kinase, it is deactivated by being turned into AMP (-monophosphate) through hydrolysis by phosphodiesterase.
cAMP is a second messenger in epinephrine response. |
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Term
| Ca2+ is the most common second messenger. How many times greater is the concentration of calcium ions outside the cell compared to inside the cell? Where is calcium stored in the cell? What protein binds calcium? |
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Definition
~104
[Ca ions] in cytosol < [Ca ions] in ER < [Ca ions] outside of the cell
Calcium is stored in the ER and the mitochondria as a back up (both via active transport powered by protons, not ATP)
Calmodulin binds calcium. |
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Term
| How are IP3 and DAG (common second messengers) produced? What does IP3 commonly do? |
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Definition
| They are produced through the cleaveage of a phospholipid named PIP2 with the help of the enzyme phospolipase C. IP3 commonly triggers the release of Ca ions from the ER into the cytosol. |
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Term
| What is "cross talk" in cell signaling? |
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Definition
| "Cross talk" is when different signals elicit the same response. |
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Term
True or False?
It is possible for one signal to elicit multiple responses in the cell. |
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Definition
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