Microtubules and Muscle Contraction: An In-depth Look, Exams of Medicine

Download Microtubules and Muscle Contraction: An In-depth Look and more Exams Medicine in PDF only on Docsity! PCB 3134 Questions with 100% Correct Answers. What is the structure of a microtubule? - Correct answer Straight, hollow tube with a wall consisting of 13 protofilaments. There is a plus end and a minus end Two categories of MTs - Correct answer Cytosolic and axonemal Cytosolic MTs location in cell, function, structure - Correct answer Pervade (diffuse through) the cytosol and are responsible for: maintaining axons, forming mitotic and meiotic spindles, maintaining or altering cell shape Always singlets, or "simple tubes" with 13 protofilaments These also maintain axons - don't get confused with axonemal! Axonemal MTs component of cell made of these, structure - Correct answer Cell motility, an axoneme is a strand of a flagella or cilia, like the strands that cilia and flagella are made of Axonemal MTs are organized and stable MT's found in cilia, flagella, and basal bodies (where cilia and flagella attach) Axoneme: the central shaft of a cilia or flagella which is made of a highly ordered bundle of MT's Some axonemal MTs can form doublets or triplets (refer to picture) What is the monomer of a MT? - Correct answer a-tubulin and B-tubulin. These two monomers bind noncovalently to form an aB heterodimer, which does not normally dissociate What are the "building blocks" of microtubules? - Correct answer Tubulin heterodimers (proteins) (aB heterodimer) When is critical concentration of an MT reached? Why? - Correct answer Critical concentration of an MT is reached when the + end has higher concentration than the - end because tubulin adds to the + end faster than the - end. What is the lag phase of MT assembly? - Correct answer This is the first phase, slow assembly of tubulin dimers What is the elongation phase of MT assembly? - Correct answer This is the second phase, MT structures elongate quickly by adding onto both + and - ends (although elongation is faster at + end) What is the plateau phase of MT assembly? - Correct answer Free tubulin concentration falls and MTs reach structural equilibrium Where do MTs originate within the cell? What is an example of an MTOC? - Correct answer MTOC: microtubule organizing centers Centrosomes are an example (makes sense because this is where spindle fibers come from, and spinde fibers are MTs) What is the (-) end of a MT anchored to? - Correct answer MTOC What is the structure of a centriole? - Correct answer Centriole walls are formed by nine pairs of triplet MTs Two centrioles of a centrosome are oriented at right angles to each other. y-Tubulin shape - Correct answer Large, ring shaped protein complexes Where is y-Tubulin found? - Correct answer only found in centrosomes What is the role of y-Tubulin ring complexes? - Correct answer They assemble new MTs away from centrosome on the - end If there is no y-Tubulin ring complexes then a cell cannot assemble MTs What are antimitotic drugs? - Correct answer Drugs that affect MT function are called antimitotic drugs because they interfere with spindle assembly and disassembly which inhibits cell division What kind of medical treatment are antimitotic drugs used for? - Correct answer Anticancer treatment What do negative regulators of MT assembly do - Correct answer These are a type of antimitotic drug. They prohibit mitotic spindles from assembling How is Rho activated? - Correct answer Activation of Rho occurs when GEF stimulates Rho by converting GDP to GTP This causes Rho to be active so it can engage in actin remodeling How is Rho inactivated? - Correct answer Inactivation of Rho occurs when GAP hydrolyzes GTP to GDP What is keratin an example of? - Correct answer IF What is the most stable and least soluble component of the cytoskeleton? - Correct answer IFs IF polarity - Correct answer No polarity IF substrate - Correct answer No substrate Where do IFs assemble from? - Correct answer Fibrous subunits. IF structure - Correct answer Two IF polypeptides intertwined into a coiled-coil. There is an N terminus (on one end) and a C terminus on the other- these two terminus are globular. Put these IF structures in order: Tetrameric protofilament, protofilament assembly, intermediate filament, dimer - Correct answer dimer, tetrameric protofilament, protofilament assembly, and intermediate filament General purpose of MT - Correct answer resist bending when a cell is being compressed General purpose of MF - Correct answer contractile elements that generate tension. General purpose of IF - Correct answer elasticity Explain how MFs serve as contractile elements - Correct answer Rho GTPases are involved in MFs and have to do with cell growth. Some types of Rho GTPases are Rho which promotes stress fiber formation by utilizing contractile bundles, Cdc42 promotes filopedia growth by utilizing parallel bundles, Rac promotes elongation of lamellipodia by using branched networks of actin. What links the cytoskeleton made up of IF, MF, and Mts together? - Correct answer Spectraplakins (a protein) What is Plectin? - Correct answer an example of a linker protein that is found where IFs connect to MFs and MTs. Cell motility (movement of cell and components) is done by _ - Correct answer microtubules Cell contractility (shortening of muscles) is done by _ - Correct answer microfilaments Microtubule based motility examples (2) - Correct answer 1. fast axonal transport in neurons 2. sliding of MTs in cilia and flagella Microfilament based motility example - Correct answer muscle contraction What motor protein is associated with MT motility? (2) - Correct answer Dyneins (cytoplasmic and axonemal) Kinesins What motor protein is associated with MF motility? - Correct answer Myosin What is fast axonal transport? and is it MT or MF motility? - Correct answer MT, and it is when proteins are transported to nerve endings What are 2 proteins responsible for fast axonal transport? - Correct answer *remember it is MT so the two motor proteins are kinesin and dynein (in this case cytoplasmic dynein) Kinesin I in fast axonal transport: does what, and is called what? - Correct answer Transports ATP to plus end (away from centrosome) Called anterograde axonal transport Cytoplasmic dynein in fast axonal transport: does what, and is called what? - Correct answer Moves cargo in opposite direction Called retrograde axonal transport Kinesin structure (remember kinesin is a motor protein associated with MT motility) - Correct answer two dimerized heavy chains and two light chains Heavy chains have globular domains, they have ATP binding sites The tail is the light chains, where cargo binds What is dynactin? - Correct answer A protein that links dynein to cargo What direction are dyneins directed - or +? What is their movement dependent on? - Correct answer Dyneins are - end directed and their movement is ATP dependent What carries the vesicles to and from the golgi complex? - Correct answer MT motors carry vesicles to golgi on little Microtubule tracks Also: think about why this would be MT, MTs deal with movement in a cell so this would fall under that definition What is longer, cilia or flagella? - Correct answer Flagella What is a common structure in both cilia and flagella? (you already know this) - Correct answer axoneme What is an axoneme connected to in cilia and flagella? - Correct answer basal body Between the axoneme and basal body is a _____ zone - Correct answer transition in picture: basal body has triplets, axoneme has doublets Axoneme structure (MTs) - Correct answer outer edge is 9 doublets around a central pair of MTs Basal body structure (MTs) - Correct answer outer edge is triplet MTs around a central hub, nine sets of triplets (like a centriole) Primary cilia structure - Correct answer 9 + 0 structure Meaning they lack a central pair Primary cilia are actually not motile but important in cell signaling pathways regions of overlap between thin and thick filaments are associated with the presence of ___ - Correct answer cross-bridges What are cross bridges formed between - Correct answer F actin of thin filaments and myosin heads of thick filaments Do cross bridges form and dissociate rapidly or slowly? - Correct answer rapidly Put these muscle contraction steps in order: ATP binds to myosin Myosin is released from thin filaments Myosin power stroke is accompanied by release of ADP Myosin binds to thin filament and releases P ATP hydrolysis alters shape of myosin - Correct answer ATP binds to myosin ATP hydrolysis alters shape of myosin Myosin binds to thin filament and releases P Myosin power stroke is accompanied by release of ADP Myosin is released from thin filaments What do regulatory proteins tropomyosin and troponin regulate? - Correct answer the availability of myosin binding sites on actin filaments Myosin binding sites on actin are normally blocked by ____ which must be removed if cross-bridges are to form - Correct answer tropomyosin Troponin has two shapes. Shape 1: low Ca2+ concentrations - Correct answer When the Ca2+ concentration is low, tropomyosin blocks the myosin-binding sites on actin filaments which prevents myosin interaction with actin Myosin is prevented from binding- myosin binding sites blocked by tropomyosin Myosin wants to bind with __ - Correct answer actin Shape 2 of troponin: high Ca2+ concentrations - Correct answer At high Ca2+ concentrations, calcium binds TnC causing tropomyosin to shift and allows myosin to bind Myosin can bind, contraction state What happens when nerve impulses to the muscle stop? - Correct answer Ca2+ levels drop, causing the muscle to relax (and) when Ca+ levels drop then it is in the relaxed state with myosin binding site blocked by tropomyosin What is sarcoplasm - Correct answer muscle relaxation, you can expect to find high levels of Ca2+ in the sarcoplasm when the muscle is relaxed Is smooth muscle more similar to nonmuscle cells or skeletal muscle? - Correct answer nonmuscle cells What types of actions/movement is smooth muscle responsible for - Correct answer involuntary contractions these are slow and last longer than contractions in skeletal or cardiac muscle Smooth muscle structure - Correct answer long, no striations, pointed ends Instead of Z lines, they have dense bodies actin and myosin are anchored at both ends What happens when Ca2+ concentration increases in smooth muscle cells - Correct answer 1. Ca2+ binds to and activates calmodulin 2. activated calmodulin can activate myosin light-chain kinase (MLCK) which phosphorylates (switches myosin to active state) a regulatory light chain of myosin what is Myosin light chain phosphorylation - Correct answer this leads to a conformational change in myosin promoting its assembly into filaments it also activates the myosin so that it can interact with actin filaments to undergo the cross-bridge cycle phosphorylation of myosin II by myosin light chain kinase steps - Correct answer Ca2+ outside the cell enters the cytosol 1. an influx of Ca2+ ions is triggered by a nerve impulse or hormonal signal 2. Ca2+ binding activates calmodulin 3. once calmodulin is activated it can bind to MLCK which activates it 4. once MLCK is activated it phosphorylates myosin light chains and myosin is activated nerve impulse--> Ca2+ binds calmodulin --> calmodulin binds MLCK--> MLCK phosphorylates myosin light chains How do the muscle cells relax after contraction? Myosin light chain phosphatase's role - Correct answer As the calcium levels in the muscle cell fall, the MLCK is inactivated Myosin light chain phosphatase removes the phosphate from the myosin light chain which makes the muscle cell relax Contraction of skeletal muscle and smooth muscle cells both involve Ca2+ ions. How does the use of Ca differ between the two cell types? a) the direction of Ca movement b) skeletal muscles require higher concentrations of Ca c) the cells have different binding partners for Ca - Correct answer c Smooth cells binding partner: calmodulin Skeletal cells binding partner: tryponin Name some components of the endomembrane system - Correct answer ER, golgi, plasma membrane, vesicles, vacuoules, lysosomes What components of endomembrane system are sites for protein synthesis? - Correct answer ER and golgi What do endosomes do? - Correct answer carry and sort material brought into cell What do lysosomes do? - Correct answer digest ingested material and unneeded cellular components What component of endomembrane system is a continuous network of flattened sacs, tubules, and vesicles through cytoplasm? - Correct answer ER What are cisternae - Correct answer membrane bound sacs in ER what is the difference between the rough and smooth ER - Correct answer rough: studded with ribosomes (that are bound to membrane), large flattened sheets smooth: no ribosomes, tubular structures each protein has a tag (protein tag) that targets it to a transport vesicle that takes it to the correct location what are protein tags made of? (can be a few things) - Correct answer aa's, hydrophobic domains, oligosaccharide side chains, or other what are protein tags used for? - Correct answer determine movement and final cellular locations of proteins what is the RXR tag attached to? - Correct answer N-methyl-D-aspartate (NMDA) receptor which is important in neurotransmission RXR is a __peptide - Correct answer tripeptide, R "X" means any other aa and then another R amino acid What is the purpose of RXR tag - Correct answer it retains NMDA in the ER until it is completely assembled, the NMDA won't leave ER until RXR is masked ER retrieval tags purpose - Correct answer proteins that are returned from golgi to the ER have retrieval tags what are the tags names short for such as KDEL (Lys-Asp-Glu-Leu) - Correct answer C terminus sequences what do secretory pathways do - Correct answer move proteins from the er through the golgi to secretory vesicles which can secrete the contents to the exterior of the cell process of exocytosis - Correct answer vesicles containing proteins move to the cell surface then the membrane of the vesicles fuses with the plasma membrane then the proteins are discharged and the membrane of the vesicle becomes part of the cell membrane what is it called when the vesicles fuse with the plasma membrane - Correct answer constitutive secretion constitutive secretion is unregulated (automatically fuses) what happens in regulatory secretion - Correct answer secretory vesicles accumulate in the cell and fuse with the plasma membrane only in response to specific signals what is polarized secretion - Correct answer exocytosis of proteins is limited to a specific surface of the cell an example is intestinal cells secreting digestive enzymes only on the side of the cell that faces the intestine Snare proteins role in fusion of vesicles and target membranes in polarized secretion (v snare and t snare) - Correct answer v snare is found on vesicles t snare is found on target membranes what particles are ingesting in phagocytosis - Correct answer solid what particles are ingested in pinocytosis - Correct answer liquid Put these in correct order for the cyclic process by which a myosin head generates force on an actin filament for muscle contraction? crossbridge formation, crossbridge dissociation, cocking of myosin head, power stroke - Correct answer crossbridge formation, power stroke, crossbridge dissociation, cocking of myosin head