BIOL 213 1st Edition Lecture 22 Outline of Last Lecture I. CytoskeletonII. Intermediate filamentsa. Structureb. Main functionsc. Two main different kindsi. Cytoplasmic and nuclear laminsIII. Microtubulesa. Structurei. Made of tubulinb. Formed from centrosomesc. Dynamic instabilityd. Intracellular transporti. Motor proteins: dynein and kenisine. Mitosis IV. Actin filamentsa. Structureb. Growth occurs at both endsc. Interaction with myosin to cause muscle contractionThese 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 transductiona. 5 different kinds of signalingII. Response to signalingIII. Intracellular receptorsa. Ex: nitric oxide and steroid hormonesIV. Cell surface receptorsa. 3 main kindsi. Ion channels, G-protein-coupled receptors, enzyme-linked receptorsb. Molecular switchesCurrent LectureI. Signal transductiona. This is the process of converting one form of signal into anotherb. Signal moleculesi. These can be a lot of different things: proteins, peptides, amino acids, steroid hormones, fatty acids, sugars, inorganic compounds, gasesc. Different molecules can mimic or inhibit the signali. Agonist1. Activates the pathway2. They mimic the signalii. Antagonist1. Blocks the pathway2. They inhibit the signald. These signal molecules bind to receptor proteins to trigger a responsee. 5 different kinds of signalingi. Endocrine1. The signals travel through the blood all over the bodyii. Paracrine1. These signals are released by one cell or a small group of cells and only affect the cells within the immediate vicinityiii. Neuronal 1. Neurotransmitters are released by a neuron2. The target cell is usually a muscle cell or another neuroniv. Contact1. The signal never leaves the signaling cell2. It’s on the surface of the signaling cell and the target cell has to bein direct contact with the signaling cell to get the message3. The target cell membrane-bound receptor has to bind to the signaling cell membrane-bound signalv. Autocrine1. This is a specific form of paracrine2. The signals released also affect the signaling cell3. This is useful when the cells need to count themselvesa. A diffusible factor is released by a growing group of cellsb. The amount of factor represents the number of cellsc. When the cells detect enough of the signal factor, they know that there are enough cells so they stop dividingII. Response to signalinga. In order to respond to a signal, a cell has to have a specific receptorb. Cell-surface receptorsi. These are proteins on the surface of the cell that the signal molecule has to bind to1. This binding will then be translated into a response on the inside of the cellii. The binding of a signal molecule causes movement of the transmembranedomains which initiates the cell’s response1. They can move apart from each other, sometimes no more than the distance of the diameter of a hydrogen atom2. They can shift in opposite directions relative to each other3. They can crossc. Intracellular receptorsi. The signal molecule actually diffuses across the cell membrane and into the cell to trigger a response1. Signal molecules are small and hydrophobic so that they can diffuse across the membrane2. Ex: steroid hormones and gasii. Sometimes the signal molecule directly interacts with an enzymeiii. Sometimes it binds to intracellular receptorsd. Can alter protein function or alter protein synthesisi. Altering protein function is fastii. Altering protein synthesis is slow1. The cell has to go through the whole process of transcription and translationiii. These both alter the cytoplasmic machinery which changes the cell’s behaviore. One signal can initiate several different cellular processesi. Ex: on signal can initiate a pathway that activates metabolic enzymes, gene regulatory proteins, and cytoskeletal proteinsf. One signal can initiate different processes in different cellsi. Ex: the signal molecule acetylcholineii. It relaxes heart muscle cellsiii. It causes the release of amylase in salivary gland cellsiv. It causes contraction in skeletal muscle cellsg. Sometimes several signal molecules are needed to initiate one cellular responsei. If a cell doesn’t receive all the necessary signals, it usually goes through apoptosis because it means there’s something wrongIII. Intracellular receptorsa. Sometimes the signal molecule directly interacts with an enzymei. This provides a rapid response of only a few seconds to a few minutesii. Ex: nitric oxide (NO, a gas) and cGMP signaling to dilate blood vessels and relax heart muscles1. Acetylcholine binds to a receptor in an endothelial cell membrane2. This triggers the opening of an ion channel to let Ca2+ flow into thecell3. This activates nitric oxide synthase, which turns the amino acid arginine into NO4. NO binds to and activates the enzyme guanylyl cyclase5. This enzyme turns GTP into cyclic GMP (cGMP), a small intracellular signal molecule6. cGMP ultimately causes the muscle cells to relaxb. Sometimes it binds to intracellular receptorsi. These are usually involved in transcriptional regulationii. The receptor in the cytosol or nucleus is inactive until the signal binds to itiii. Ex: steroid hormones1. These diffuse through the plasma membrane because they are small and hydrophobic and bind to an intracellular receptor2. The receptor is activated when the steroid is bonded to it and can diffuse through the nuclear membrane to act as a transcription regulatorIV. Cell-surface receptorsa. 3 basic typesi. Ion-channel-linked receptor1. An open channel can let in thousands of ions, which leads to amplification2. These are seen in nerve terminals3. These are a huge component of action potentialii. G-protein coupled receptors1. The receptor protein is activated by the signal2. This activates the G-protein which will activate an enzyme to initiate the responseiii. Enzyme-linked receptors1. The receptor acts as an enzyme or directly activates an enzymeb. Molecular switchesi. Involved in enzyme-linked and G-protein coupled receptorsii. Molecular switches are protein receptors that are turned on and off by signal moleculesiii. Signaling by phosphorylation1. A protein kinase phosphorylates the switch using the phosphate group of an ATP to activate it2. A protein phosphatase clips off the phosphate group to inactivate the switch3. The activity of the switch receptor depends on the balance