Cell Structure and function test 4 extra textbook notes:Lecture #32 - Flagellar motility in sperm tail and chamydomonas (algae)o Chlamydomonas reinhardtii revealed particles moving @ a constantspeed toward tip (anterograde movement) and others moving from the tip of the base (retrograde) intraflagellar transport occurs in both flagella and ciliao Anterograde movement powered by kinesin 2o Retrograde movement powered by cytoplasmic dyneino Cilia and flagella related microtubule based and membrane-bound extensions that projecto Abundant motile cilia found on surface of specific epithelia wavelike fashion movemento Animal cell flagella propel cell through liquido Both contain many microtubule based motors:  axonemal dyneins beating of flagella kinesin 2 and cytoplasmic dynein are responsible for flagella and cilia assembly and turnover- MT orientation in cilia/ flagellao Contain long doublet microtubules bridged by dynein motorso All microtubules in cilia and flagella have the same polarity (+) ends@ tip attached in the cell axoneme connects with the basal body complicated structure containing 9 triplet microtubules- Cross- section of cilia/flagellum- 9+2 array of MTs inside PMo Central bundle of microtubules axoneme 9+2 arrangement of 9 doublet microtubules surrounding a central pair of single, ultrastructurally distinct microtubuleso Each of the 9 outer doublets consists of A microtubule filament with 13 protofilaments and B microtubule with 10 protofilaments - Axoneme structureo Held together by 3 sets of protein cross-linkso Central pair of singlet microtubules connected by periodic bridgeso Second set of linkers nexinjoins adjacent outer doublet microtubules  Radial strokes project from each A tubule of outer doublets toward central pairo Major motor protein present in cilia and flagella  axonemal dyneinlarge, multisubunit protein related to cytoplasmic dyneino 2 rows of dynein motors attached periodically down the length of each A tubule of the outer doublet microtubules inner arm and outer arm dyneins  interact with adjacent B tubule that bring about cilia and flagella bending- ATP- dependent sliding of outer doublets generates force for motilityo Cilia and flagella motile structures because the axonemal dynein motors= bendingo Bend starts @ base of cilium/ flagellum propagates along structureo Axonemes treated with protease that cleaves nexin links o ATP added to treated axonemes= doublet microtubules slid past one another as dynein attached to A tubule of one doublet “walked” down the B tubule of the adjacent doubleto Axoneme with intact nexin links  action of dynein = induces flagellar bending as microtubule doublets connected to one another - Axonemal dynein mediated bendingo Axonemal dynein attached to A tubule of outer doublet pulls on B tubule of adjacent tubule trying to move to the (-0 end o Because adjacent tubules tethered by nexin= force generated by dynein bends cilium/ flagellumo Experimental evidence  when nexin links are cleaved with protease and ATP added to induce dynein activity= microtubule doublets slide past each other o Protease treated axoneme  2 doublet microtubules incubated with ATP In absence of cross linking proteins  doublet microtubules slide excessively = dynein arms project from A tubules interacting with B tubules of left microtubule doublet- Primary cilium is assembled by centrosomeo Assembled from basal bodyo Built around 9 linked triplet microtubuleso Continuous with A and B tubules of axoneme membrane bound core of cilium/ flagellumo Between basal body and axonome transition zone - Key characteristics of IFso Extend throughout cytoplasm o Line inner nuclear envelope of interphase animal cellso Biochemically much more heterogenous o Have great tensile strength o Don’t have intrinsic polarityo No known motors that use them as trackso Dynamic in terms of subunit exchange much more stable than microfilaments and microtubules because the exchange rate is much slowero Not found in all eukaryotes only animals - IF filamentso Nonpolar structureo Presence of conserved -helical domaino Coiled- coil motifo flanking the rod domain nonhelical N and C- terminal domains of different sizes, characteristic of each IF classo primary building block dimmer held together through the rod domains that associate as a coiled-coilthen make tetramers where 2dimers are in opposite orientationso tetramers assembled end to end and interlock in long protofilamentso 4 protofilaments= protofibrilo 4 protofibrils ( associate side by side) = 10 nm filamento 1 filament= 16 protofilaments in ito tetramer symmetric= no polarityo filament based on its structure rather than its mechanism of assembly - Nuclear laminsnucleus nuclear structure and organizationLecture # 33 Nuclear structure and function- Nuclear laminso Network of lamin intermediate filaments meshwork extending overinner surface of nuclear envelope o Cytoplasmic filaments extend from cytoplasmic side of NPC into cytosol- Nuclear lamins- building blocks of nuclear architectureo Numerous pores perforate the nuclear envelope in all eukaryotic cellso Each nuclear pore formed from elaborate structure nuclear pore complex (NPC) large protein assembly o Made up of multiple copies of 30 different proteins nucleoporins o Lamins= structural support and chromosome organization- Protein synthesis and targeting- nucleuso All proteins found in nucleus histones, transcription factors, and DNA & RNA polymerases synthesized in cytoplasm and imported through nuclear pore complexes- nuclear pore structureo ions, small metabolites, and globular proteins up to 20-40 KDa can passively diffuse through the central aqueous region of the NPCo large proteins and ribonucleoprotein complexes cannot diffuse in and out of nucleus actively transported through NPC with assistance of soluble transporter proteins that bind macromolecules and interact with nuceloporinso contain nuclear localization signal (NLS) and contain fully folded conformation- NLS direct nuclear proteins to the nucleuso Directs proteins to cells nucleus o Cytoplasmic proteins can be localized to the nucleus when fused to a nuclear localization signal- Ran GTPase drives directional transport through nuclear pore complexeso Ran Importin  and  Monomeric G-protein exists as either GTP or GDP bound