Cell Structure and function test 4 extra textbook notes Lecture 32 1 MT organization in cilia and flagella Flagellar motility in sperm tail and chamydomonas algae o Chlamydomonas reinhardtii revealed particles moving a constant speed toward tip anterograde movement and others moving from the tip of the base retrograde intraflagellar transport occurs in both flagella and cilia o Anterograde movement powered by kinesin 2 o Retrograde movement powered by cytoplasmic dynein o Cilia and flagella related microtubule based and membrane bound extensions that project o Abundant motile cilia found on surface of specific epithelia wavelike fashion movement o Animal cell flagella propel cell through liquid o 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 flagella o Contain long doublet microtubules bridged by dynein mot ors o 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 PM o Central bundle of microtubules axoneme 9 2 arrangement of 9 doublet microtubules surrounding a central pair of single ultrastructurally distinct microtubules o Each of the 9 outer doublets consists of A microtubule filament with 13 protofilaments and B microtubule with 10 protofilaments Axoneme structure o Held together by 3 sets of protein cross links o Central pair of singlet microtubules connected by periodic bridges o Second set of linkers nexin joins adjacent outer doublet microtubules Radial strokes project from each A tubule of outer doublets toward central pair o Major motor protein present in cilia and flagella protein related to cytoplasmic dynein axonemal dynein large multisubunit o 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 o ATP dependent sliding of outer doublets generates force for motility o Cilia and flagella motile structures because the axonemal dynein motors bending o Bend starts base of cilium flagellum propagates along structure o 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 doublet microtubule doublets connected to one another action of dynein induces flagellar bending as o Axoneme with intact nexin links Axonemal dynein mediated bending trying to move to the 0 end o Axonemal dynein attached to A tubule of outer doublet pulls on B tubule of adjacent tubule o Because adjacent tubules tethered by nexin force generated by dynein bends cilium o Experimental evidence flagellum induce dynein activity microtubule doublets slide past each other 2 doublet microtubules incubated with ATP o Protease treated axoneme when nexin links are cleaved with protease and ATP added to In absence of cross linking proteins dynein arms project from A tubules interacting with B tubules of left microtubule doublet doublet microtubules slide excessively Primary cilium is assembled by centrosome o Assembled from basal body o Built around 9 linked triplet microtubules o Continuous with A and B tubules of axoneme membrane bound core of cilium flagellum o Between basal body and axonome transition zone Iclicker Question The force for axoneme bending is derived from the C sliding movement of outer doublet microtubules Lecture 31 Key characteristics of IFs o Extend throughout cytoplasm o Line inner nuclear envelope of interphase animal cells o Biochemically much more heterogenous o Have great tensile strength o Don t have intrinsic polarity o No known motors that use them as tracks o Dynamic in terms of subunit exchange much more stable than microfilaments and microtubules because the exchange rate is much slower o Not found in all eukaryotes only animals IF filaments o Nonpolar structure o Presence of conserved helical domain o Coiled coil motif o flanking the rod domain nonhelical N and C terminal domains of different sizes characteristic of each IF class o primary building block dimmer held together through the rod domains that associate as a coiled coil then make tetramers where 2 dimers are in opposite orientations o tetramers assembled end to end and interlock in long protofilaments o 4 protofilaments protofibril o 4 protofibrils associate side by side 10 nm filament o 1 filament 16 protofilaments in it o tetramer symmetric no polarity o filament based on its structure rather than its mechanism of assembly Nuclear lamins nucleus nuclear structure and organization 2 Nuclear lamin basic structure and function 3 Nucleolus structure and function sub nuclear organelle w o membrane association Nuclear lamins line the nucleus of all animal tissue o Network of lamin intermediate filaments meshwork extending over inner surface of nuclear envelope o Cytoplasmic filaments extend from cytoplasmic side of NPC into cytosol o Phosphorylation of lamins causes nuclear envelope breakdown in mitosis Nuclear lamins building blocks of nuclear architecture o Lamins structural support and chromosome organization Function in replication transcription in DNA metabolism Interact with proteins located at inner nuclear envelope As cells enter mitosis lamins become hyperphosphorylated and disassemble In telophase they reassemble with the reassembling nuclear membrane Nuclear lamin protein Emerin Integral protein of the inner nuclear membrane Mediates membrane anchorage to the cytoskeleton X linked muscle dystrophy results from mutation of emerin gene Compartmentalization within the nucleus o Nuclear envelope o Nucleolus euchromatin heterochromatin o Chromatin Nucleus contains a variety of subnuclear structures There are domains in nuclei in addition to chromosome territories and nucleoli Nuclear domains Nuclear bodies NOT surrounded by membranes Regions of high concentrations of specific proteins and RNA s that form distinct roughly spherical structures within the nucleus o Nucleolus A sub organelle inside of the nucleus The ribosome producing factory contains most of cell s rRNA synthesized here Subcompartment not bound by phospholipid membrane o Ribosomal proteins