TAMU BIOL 213 - Cell Communication Part 1 (6 pages)

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Cell Communication Part 1

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Cell Communication Part 1


Lecture number:
Lecture Note
Texas A&M University
Biol 213 - Molecular Cell Biol
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BIOL 213 1st Edition Lecture 22 Outline of Last Lecture I Cytoskeleton II Intermediate filaments a Structure b Main functions c Two main different kinds i Cytoplasmic and nuclear lamins III Microtubules a Structure i Made of tubulin b Formed from centrosomes c Dynamic instability d Intracellular transport i Motor proteins dynein and kenisin e Mitosis IV Actin filaments a Structure b Growth occurs at both ends c Interaction with myosin to cause muscle contraction These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Outline of Current Lecture I Signal transduction a 5 different kinds of signaling II Response to signaling III Intracellular receptors a Ex nitric oxide and steroid hormones IV Cell surface receptors a 3 main kinds i Ion channels G protein coupled receptors enzyme linked receptors b Molecular switches Current Lecture I Signal transduction a This is the process of converting one form of signal into another b Signal molecules i These can be a lot of different things proteins peptides amino acids steroid hormones fatty acids sugars inorganic compounds gases c Different molecules can mimic or inhibit the signal i Agonist 1 Activates the pathway 2 They mimic the signal ii Antagonist 1 Blocks the pathway 2 They inhibit the signal d These signal molecules bind to receptor proteins to trigger a response e 5 different kinds of signaling i Endocrine 1 The signals travel through the blood all over the body ii Paracrine 1 These signals are released by one cell or a small group of cells and only affect the cells within the immediate vicinity iii Neuronal 1 Neurotransmitters are released by a neuron 2 The target cell is usually a muscle cell or another neuron iv Contact 1 The signal never leaves the signaling cell 2 It s on the surface of the signaling cell and the target cell has to be in direct contact with the signaling cell to get the message 3 The target cell membrane bound receptor has to bind to the signaling cell membrane bound signal v Autocrine 1 This is a specific form of paracrine 2 The signals released also affect the signaling cell 3 This is useful when the cells need to count themselves a A diffusible factor is released by a growing group of cells b The amount of factor represents the number of cells c When the cells detect enough of the signal factor they know that there are enough cells so they stop dividing II Response to signaling a In order to respond to a signal a cell has to have a specific receptor b Cell surface receptors i These are proteins on the surface of the cell that the signal molecule has to bind to 1 This binding will then be translated into a response on the inside of the cell ii The binding of a signal molecule causes movement of the transmembrane domains which initiates the cell s response 1 They can move apart from each other sometimes no more than the distance of the diameter of a hydrogen atom 2 They can shift in opposite directions relative to each other 3 They can cross c Intracellular receptors i The signal molecule actually diffuses across the cell membrane and into the cell to trigger a response 1 Signal molecules are small and hydrophobic so that they can diffuse across the membrane 2 Ex steroid hormones and gas ii Sometimes the signal molecule directly interacts with an enzyme iii Sometimes it binds to intracellular receptors d Can alter protein function or alter protein synthesis III IV i Altering protein function is fast ii Altering protein synthesis is slow 1 The cell has to go through the whole process of transcription and translation iii These both alter the cytoplasmic machinery which changes the cell s behavior e One signal can initiate several different cellular processes i Ex on signal can initiate a pathway that activates metabolic enzymes gene regulatory proteins and cytoskeletal proteins f One signal can initiate different processes in different cells i Ex the signal molecule acetylcholine ii It relaxes heart muscle cells iii It causes the release of amylase in salivary gland cells iv It causes contraction in skeletal muscle cells g Sometimes several signal molecules are needed to initiate one cellular response i If a cell doesn t receive all the necessary signals it usually goes through apoptosis because it means there s something wrong Intracellular receptors a Sometimes the signal molecule directly interacts with an enzyme i This provides a rapid response of only a few seconds to a few minutes ii Ex nitric oxide NO a gas and cGMP signaling to dilate blood vessels and relax heart muscles 1 Acetylcholine binds to a receptor in an endothelial cell membrane 2 This triggers the opening of an ion channel to let Ca2 flow into the cell 3 This activates nitric oxide synthase which turns the amino acid arginine into NO 4 NO binds to and activates the enzyme guanylyl cyclase 5 This enzyme turns GTP into cyclic GMP cGMP a small intracellular signal molecule 6 cGMP ultimately causes the muscle cells to relax b Sometimes it binds to intracellular receptors i These are usually involved in transcriptional regulation ii The receptor in the cytosol or nucleus is inactive until the signal binds to it iii Ex steroid hormones 1 These diffuse through the plasma membrane because they are small and hydrophobic and bind to an intracellular receptor 2 The receptor is activated when the steroid is bonded to it and can diffuse through the nuclear membrane to act as a transcription regulator Cell surface receptors a 3 basic types i Ion channel linked receptor 1 An open channel can let in thousands of ions which leads to amplification 2 These are seen in nerve terminals 3 These are a huge component of action potential ii G protein coupled receptors 1 The receptor protein is activated by the signal 2 This activates the G protein which will activate an enzyme to initiate the response iii Enzyme linked receptors 1 The receptor acts as an enzyme or directly activates an enzyme b Molecular switches i Involved in enzyme linked and G protein coupled receptors ii Molecular switches are protein receptors that are turned on and off by signal molecules iii Signaling by phosphorylation 1 A protein kinase phosphorylates the switch using the phosphate group of an ATP to activate it 2 A protein phosphatase clips off the phosphate group to inactivate the switch 3 The activity of the switch receptor depends on the balance of the activities of the protein kinase and

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