B. The Cytoskeletal System and Adhesion ___________________________________ • Red = Actin Microfilaments ___________________________________ • Green = Tubulin Microtubules ___________________________________ ___________________________________ ___________________________________ ___________________________________ Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings ___________________________________ ___________________________________ 3 Fibrous Components and Motors ___________________________________ • Thin Filaments: Actin family of proteins ___________________________________ • Microtubules: Tubulin family of proteins ___________________________________ • Intermediate Filaments: Very cell‐specific family of proteins ___________________________________ • The first two have molecular motors ___________________________________ ___________________________________ ___________________________________ 1. Actin Microfilaments ___________________________________ • Chains of few to many 42kDa monomers • Found in all eukaryotic cells (except nematode worm sperm) ___________________________________ • Highly Conserved: Genes vary <20% from algae to humans; human primary protein sequence <5% ___________________________________ • Three main isoforms: alpha, beta, gamma • Alpha is muscle actin, beta and gamma are found ___________________________________ in nearly all cells ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ATP Binding ADP Binding ___________________________________ Figure 16-12 Molecular Biology of the Cell (© Garland Science 2008) ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Figure 16-74c,d Molecular Biology of the Cell (© Garland Science 2008) ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Figure 16-47 Molecular Biology of the Cell (© Garland Science 2008) ___________________________________ Fig. 6‐26 ___________________________________ Microvillus ___________________________________ Plasma membrane ___________________________________ Microfilaments (actin filaments) ___________________________________ ___________________________________ Intermediate filaments 0.25 µm ___________________________________ ___________________________________ ___________________________________ Actin tracks allow specific movement between two points ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Figure 16-69a Molecular Biology of the Cell (© Garland Science 2008) ___________________________________ ___________________________________ Remember..... ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Figure 17-49a Molecular Biology of the Cell (© Garland Science 2008) ___________________________________ ___________________________________ The Key Structural Elements ___________________________________ 1. 70 Å filaments (f‐actin) ‐ polymers of globular monomers (g‐actin) formed as double helix ___________________________________ 2. Structural polarity –sequences and structures ___________________________________ unequally directed towards each of the ends ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ “Dynamic instability” ___________________________________ a. Can form, crosslink, breakdown and reform rapidly b. The cell can build new structures as its needs change ___________________________________ ___________________________________ Figure 16-7 Molecular Biology of the Cell (© Garland Science 2008) ___________________________________ ___________________________________ 2. Tubulin Microtubules ___________________________________ • Large hollow tubes of many 110kDa dimers • Three main isoforms: alpha, beta, gamma ___________________________________ • Found in all eukaryotic cells • Alpha and beta found in microtubules, gamma ___________________________________ found in microtubule organizing center (MTOC) • Highly Conserved: Primary sequences vary ___________________________________ <10% from algae to humans ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ GTP Binding GDP Binding ___________________________________ Figure 16-11 Molecular Biology of the Cell (© Garland Science 2008) ___________________________________ ___________________________________ Large‐scale, long distance ___________________________________ movement of cellular components, ___________________________________ including organelles ___________________________________ ___________________________________ ___________________________________ Figure 16-30c Molecular Biology of the Cell (© Garland Science 2008) ___________________________________ Fig. 6‐22 Centrosome ___________________________________ Microtubule ___________________________________ Centrioles 0.25 µm ___________________________________ ___________________________________ ___________________________________ Longitudinal section of Microtubules Cross section one centriole of the other centriole ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Figure 16-30b Molecular Biology of the Cell (© Garland Science 2008) ___________________________________ ___________________________________ Projections of ___________________________________ asters to move the chromosomes ___________________________________ in cell division ___________________________________ ___________________________________ ___________________________________ Figure 16-85c Molecular Biology of the Cell (© Garland Science 2008) ___________________________________ ___________________________________ Directed transport along the neuronal axon ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Figure 16-104 Molecular Biology of the Cell (© Garland Science 2008) ___________________________________ ___________________________________ ___________________________________ Cilia and flagella ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Give direction ___________________________________ to plant cell division and growth and ___________________________________ dictate sites of plant wall synthesis ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Plant microtubules have no obvious MTOC ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ The Key Structural Elements ___________________________________ 1. These are also polar – unequally directed towards each end a. most: (–) end toward nucleus and (+) end to cell membrane ___________________________________ 2. 250 Å filaments formed as a hollow bundle of 13 protofilaments a. protofilaments are long polymers of tubulin dimers ___________________________________ b. dimers are one alpha and one beta globular monomers c. gamma tubulin makes up the MTOC: centriole or basal body ___________________________________ ___________________________________ ___________________________________ ___________________________________ Like actin, microtubules can be changed as the cells needs change ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Figure 16-16c Molecular Biology of the Cell (© Garland Science 2008) ___________________________________ ___________________________________ 3. Intermediate Filaments ___________________________________ • Rope‐like filament structures formed from 8 protofilaments twisted together ___________________________________