Biology Key Terms - Ch. 9: Cell Communication

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1. Insulin
** is an example of...
** how does it work (in simple terms)?

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an example of a hormone that uses chemical signaling to communicate to other cells. Insulin binds to insulin receptors to signal cells to secrete vesicles with glucose transporters to regulate blood sugar.

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2. Local Signaling
** 2 domains included:

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communication or signaling between cells that are near each other. Domains include synaptic signaling and paracrine signaling.

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3. Direct contact signaling
** domains include:

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direct contact or signaling between cells, cells are in direct contact with one another; domains include gap junction and plasmodesmata (signaling molecules sent through cytoplasm, no need to cross membranes), and cell-cell recognition.

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4. Cell-cell recognition signaling

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signaling molecule that is bound on a cell binds to another cells receptor protein in order to communicate.

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5. Paracrine signaling
** example is...

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chemical signal is secreted and influences a cell that is VERY close to it. Signaler is called a local regulator; secretes signal which diffuse through extracellular fluid to surrounding target cells. Ex: growth factor is released by the local regulator causing all surrounding cells to grow and divide.

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6. Chemical signal
** an example is...

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a hormone that travels some distance to signal another cell. An example would be insulin.

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7. Synaptic signaling
** explain fully

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specific cells are targeted by an electrical signal that goes down the length of a neuron releases a neurotransmitter that diffuses across synapse between neuron and cell and causes a chemical signal to be released by a portion of the cell. Usually a neurotransmitter that binds receptors on specific target cell.

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8. Long-distance signaling

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a signaler travels a long distance to signal another cell.
(does not affect nearby cells like local signaling or direct contact like direct signaling.)

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9. Endocrine signaling

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the use of hormones to signal another cell (the endocrine system = hormone secretion).

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10. Ligand

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a molecule that specifically binds to another receptor molecule/protein. The receptor protein usually undergoes a change in shape (conformational change).

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11. Receptor protein

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a protein that is able to bind a specific molecule at a specific site on the protein.

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12. Signal transduction

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the conversion of an extracellular signal to an intracellular response.

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13. Ligand gated ion channel receptor
** allows for...

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ligand binds the ion channel receptor and changes its shape which causes the ion channel to either open or close;
** when it is opened, specific ion can travel into plasma membrane and through the protein channel.

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14. Receptor tyrosine kinase
** domains include (3)...
** how they work/function

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receptors have kinase activity (can phosphorylate substrates).
** three domains include ligand binding domain, dimerization domain, and kinase domain.
** They attach to each other (dimerize) due to shape change from ligands then they phosphorylize each other.

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15. Ligand binding domain

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extracellular portion that binds ligand

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16. Dimerization domain

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intracellular portion that brings two receptors together that have a ligand bound

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17. Kinase

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enzymes that can phosphorylate substrates.

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18. Kinase domain

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intracellular portions that can phosphorylate other proteins (transfer phosphate groups to substrates).

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19. Glucose transporter (GLUT 4)
** how it happens
** allows for...

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secretion of GLUT4 is a response by the cell after insulin binds to insulin receptors, it allows cells to take up glucose from the outside.

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20. G-protein linked receptor
** composed of...
** they are found in... supporting the theory that it ....
** medicine background...
** shape change allows it to ....
** the first step in....

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a receptor that interacts with G-protein.
**This receptor is composed of 7 membrane spanning domains (alpha helices).
** Found in all eukaryotes (evolved early).
** 60% of all medicines in some way influence G-protein pathways. ** The receptor changes shape when bound with its ligand (allows it to interact and therefore activate G-protein).
** This is the first step in signal transduction pathways in the cell.

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21. G-protein
primary or secondary messengers?

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important signal transducing molecules in cells…. Short for “guanine nucleotide-binding proteins”, they are second messenger proteins. A receptor does not activate an enzyme directly; a receptor signal must activate a G-protein for them to stimulate an enzyme.

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22. Alpha-subunit of G-protein:

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one subunit of one of the seven alpha helices that make up the G-protein linked receptor.

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23. Beta-adrenergic receptor:

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a G-protein linked receptor that binds the ligand adrenalin activating the G-protein so it can send a messenger signal.

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24. Adrenalin (epinephrine):

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a hormone secreted by the adrenal gland into the bloodstream when you are frightened

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25. Adenylyl cyclase

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the G-protein that was activated after binding the adrenalin ligand then in turn activated the Adenylyl cyclase to produce cAMP.

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26. cAMP

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(cyclic adenosine monophosphate) …after the G-protein binds to the ligands, they active specific receptors (i.e. Adenylyl cyclase for adrenaline) and then they produce cAMP (using ATP) which binds other kinases and activates them which states a chain reaction of new activity in the cell. cAMP usually activates an enzyme called protein kinase A, which is responsible for phosphorylating other proteins.

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27. Protein kinase A

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activated by cAMP, protein kinase A is an enzyme that phosphorylates other proteins; a serine/threonine protein kinase.

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28. Phosphorylation

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addition of a phosphate group to a protein. This activates many protein enzymes.

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29. Dephosphorylation

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the removal of a phosphate group from a protein. This deactivates many protein enzymes.

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30. Proteins phosphatases

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enzymes that remove phosphate groups from proteins.

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31. Second messenger
** description
** involved in...

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produced in response to the original ligand (first messengers),
** second messengers are small, non-protein, water-soluable molecules or ions.
** They are involved in signal transduction of protein tyrosine kinases and G-protein linked receptors.

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32. Phosphodiesterase

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the enzyme that destroys cAMP by converting it into AMP.

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33. Phospholipase C
** know how it works/function...

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G-proteins can also stimulate Phospholipase C which converts a lipid called phosphatidyl inositol bisphosphate (PIP2) into two products: -- inositol triphosphate (IP3) which causes calcium ions to release from endoplasmic reticulum into the cytosol & -- diacylglycerol (DAG) which causes Ca2+ + DAG + Protein Kinase C to start different phosphorylation events that result in alteration of gene expression in the nucleus.

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34. Phosphatidyl inositol bisphosphate (PIP2)
** know how it works/function...

Back 34

a lipid called phosphatidyl inositol bisphosphate that is converted by Phospholipase C (after G-protein stimulates it) into two products: -- inositol triphosphate (IP3) which causes calcium ions to release from endoplasmic reticulum into the cytosol & -- diacylglycerol (DAG) which causes Ca2+ + DAG + Protein Kinase C to start different phosphorylation events that result in alteration of gene expression in the nucleus.

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35. Diaclyglycerol (DAG)
** know how it works/function...

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diacylglycerol (DAG) causes Ca2+ + DAG + Protein Kinase C to start different phosphorylation events that result in alteration of gene expression in the nucleus.

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36. Transcription factor
** what are they?

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proteins that bind DNA and alter their expression.

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37. Scaffolding protein
** what do they do?

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crucial regulators in the signaling pathway, they interact or bind with many other pathway components and in doing so, they regulate signal transduction and help confine pathway components to specific areas of the cell (plasma membrane, cytoplasm, nucleus, Golgi apparatus, endosomes and the mitochondria.

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• Stages of cell signaling: (3)

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1. Reception – receiving of the signal (the chemical signal or ligand binds to a receptor protein on or in the target cell).
2. Signal Transduction – shape change allowing things inside the cell to change (the receptor changes its shape in response to binding the ligand, and this shape change can activate it directly if it’s an enzyme or allow it to interact with proteins that it couldn’t before).
3. Cellular Response – response to the information (the activation of enzymes or other proteins cause intracellular change).

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• Types of cell signaling: (3)

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1. Local Signaling: synaptic signaling and paracrine signaling
2. Direct Contact Signaling: gap junction & plasmodesmata and cell-cell recognition
3. Long-Distance Signaling: endocrine signaling/ chemical signaling

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• Receptors can be either (2 types)….

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Membrane bound receptors (have a portion that is shaped to bind specific ligand) or
Intracellular receptors (found either in the cytoplasm or nucleus of a cell)

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• Three types of membrane bound receptors are:

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1. Ligand gated ion channel receptors
2. Receptor tyrosine kinases
3. G-protein linked receptors

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• Lipid Soluble Ligands:
** what they are..
** how they differ...
** examples...

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ligand must cross the plasma membrane and bind to intracellular receptors, ligands are small (usually a cholesterol derivative), induce a slow but long-lasting response; action of the response is in the nucleus (changes gene expression). Ex: steroid hormones – estrogen, testosterone, thyroid hormone, vitamin D, retinoic acid, coritsol

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• Water Soluble Ligands:
** what they are..
** how they differ...
** examples...

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bind surface cell receptors and cannot pass through the membrane (signal must be transduced into the cell by the receptor protein) ligand is broken down rapidly, induces a rapid response that doesn’t last as long. Ex: large polypeptides – insulin, vasopressin, growth factors & small, highly charged molecules – adrenaline (epinephrine), acetylcholine, odors and tastes.

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• Signal transduction can be done by two methods:

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1. Phosphorylation and dephosphorylation by protein kinases (on off switches of protein activity)
2. Second messengers (cAMP [cyclic AMP] , calcium ions [Ca2+] and IP3 and DAG)

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• How do calcium ions work as 2nd messengers

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Ca2+ is released from organelles in response to an extracellular signal, it binds to proteins and changes the proteins shape. (used as 2nd messenger in receptor protein kinase and G-protein linked receptor pathways.

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• How does cyclic AMP work as a 2nd messenger?

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cAMP is produced by the enzyme adenylyl cyclase from ATP, it activates an enzyme called protein Kinase A (PKA) and PKA phosphorylates other proteins. cAMP is destroyed by the enzyme phosphodiesterase (converts cAMP to AMP)

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• How does IP3 and DAG work as second messengers?

Back 47

G-proteins can also stimulate Phospholipase C which converts a lipid called phosphatidyl inositol bisphosphate (P IP2) into two products: -- inositol triphosphate (IP3) which causes calcium ions to release from endoplasmic reticulum into the cytosol & -- diacylglycerol (DAG) which causes Ca2+ + DAG + Protein Kinase C to start different phosphorylation events that result in alteration of gene expression in the nucleus.

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Cellular Response is...?
** two types...

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a response to the signal transduction.

1. cytoplasmic response to transduced signal
2. nuclear response

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Cellular Response: how does the cytoplasmic response to transduced signal work?

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opening-closing of an ion channel, regulation of the activity of enzymes; can result in overall physical responses such as taste, smell, adrenalin release, schmooing (yeast)

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Cellular Response: how does the nuclear response work?

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regulates the synthesis or proteins, involves activation of transcription factors (proteins that can bind DNA and alter its expression)