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Cell Bio 2382 Midterm 2 Notes.pdf

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Biology 2382B
Sashko Damjanovski

Topic 1 Microtubules Structure microtubules are 25 nm in diameter and very longmicrotubules make up things such as flagella thats why it is much longer than a cellmade up of tubulin a polymer of alpha and beta tubulinalmost always exist as alphabeta dimer 110 kDa both alpha and beta monomers are 55 kDa eachalphabeta dimer is the basic subunit you build things with itwhen things get taken apart they get taken apart at this dimer levelalphabeta dimers have polaritydimers can polymerize can grow a chainprotofilament dimers that are formed end to endwill have alpha on one end beta on the other hence polarityalphabetaalphabeta etcbunch of protofilaments can come together to form a hollow tube which is 25 nm in diameter up to 100 m long 2nd figure which is the microtubulehollow tube also has polarity they all have protofilaments that have alpha on one end beta on the other endalpha end is called the minus end beta is plus endminus and plus have nothing to do with charge called plus because plus grows faster you add to italphabeta dimer has size of 8 nmyou can predict how steps are occurring from knowing this size of 8 nmex if a molecule takes steps of 4 nm you know it is walking from monomer to monomer since each monomer is 4 nmif it steps every 8 nm then you know it is going from dimer to dimer eg alpha to alphaDimeric Tubulin Subunit tubulin is very abundant as cells have tons of itthus tubulin is easy to isolate and get all kinds of crystal structuresdimer when it is formed is very stable cell almost never breaks it apart into monomersdimer is used to build structures and when the structure is broken apart it will end up with dimers againalpha monomer is permanently bound to GTP cannot hydrolyze GTPbeta monomer can hydrolyze GTP to GDP so can be bound to either GTP or GDPso as protofilament grows by adding alphabeta dimers hydrolysis of the betas GTP occursthus beta can bind to either GTP or GDP depending on if its hydrolyzed Arrangement of MT Protofilaments dimers make protofilaments and protofilaments come together to form a hollow tubein most cells cytoskeleton form asinglet tube of 25 nm diameter with 13 protofilamentsbut there are exceptions but in general it is 13in addition to forming singlets doublets and triplets can also be formedtake a singlet and add more protofilaments onto them in groups of 10singlet protofilament is called the A protofilament then when you add another array of 10 protofilaments you make the B protofilament to form a doubletdoublets are found in cilia and flagellatriplets are found in basal bodies and centriolesno such thing as four ringssinglets are dynamic tend to grow and shrink in sizedoublets and triplets tend to be stablegreen pic a lot of singlet microtubules in cytoplasm2 types to classify singlet microtubules singlets organize interior of cellcytoplasmic microtubule microtubules found in cytoplasmnerve microtubules are still cytoplasmic microtubules which are everywhereaxonemal microtubules microtubules found in axonemeaxonemal means in flagella cilia NOT nerve Microtubule Organization wherever microtubules are they are organized and they have to be nucleatedgrow microtubules on some sort of nucleus which you buildthey are nucleated in the microtubule organizing centre MTOCthere are many diff MTOCs as nucleation can be many diff thingsnucleation analogy start off with snowflakes then build snowball build more snow around it to make a snowmanmicrotubules are dynamic meaning they grow and shrinktheend does the growingshrinkingall microtubules have theirend growing away from the MTOCminusends of microtubules are associated with MTOCin dendrites of nerves however microtubules are organized in a random fashionsome microtubules haveaway from cell body some have but this is not understood they are just not pointing in same direction
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