B. The Cytoskeletal System and Adhesion ______

• Red = ______• Green = ______

______

______

______Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings ______

______3 Fibrous Components and Motors ______• Thin Filaments: Actin family of ______• Microtubules: Tubulin family of proteins ______• Intermediate Filaments: Very ‐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 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 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 ______• found in nucleus, cytosolic IF’s found in some cells and not others ______• IF’s found only in some animals, including vertebrates, nematodes, molluscs ______• Plants and single‐celled organisms have no IF’s ______

______

______

______

______

______

______

______Figure 16-19 Molecular Biology of the Cell (© Garland Science 2008) ______

______

Keratins in the ______cytosol ______

______

______

______Figure 16-20 Molecular Biology of the Cell (© Garland Science 2008) ______

Lamins in the Nucleus ______

______

______

______

______

______

______Sarcomere Support ______

______

______

______

______

______

______The Key Structural Elements ______1. Apolar – very stable, not structurally nor functionally ______oriented towards one end or the other ______2. No motors ______

______

______4. Bacterial Homologs and Analogs ______• Homologs are genes and proteins that share common sequence ______

• Analogs are proteins that share common function ______

______

______

______

______Actin homologs: MreB and Mbl ______

______

______

Mbl+ Mbl‐

Helical proteins give cell its shape by distributing themselves ______throughout the cell and directing sites of cell wall synthesis. Analogous to plant tubulin! ______Figure 16-26 Molecular Biology of the Cell (© Garland Science 2008) ______

______Actin homolog: ParM ______

______Analogous to tubulin! ______

______

______Figure 16-27a Molecular Biology of the Cell (© Garland Science 2008) ______Tubulin homolog: FtsZ ______

______

______As a bacterium divides: after the two chromosome copies have been segregated, the Z‐ring forms and then contracts to split the daughter cells. Two rings reform in the daughters. ______

This is analogous to actin! ______Figure 16-25a Molecular Biology of the Cell (© Garland Science 2008)

______

______Intermediate filament homolog: ______

______

______

______

Creates the curved shape by forming a cortical band ______Figure 16-28 Molecular Biology of the Cell (© Garland Science 2008)

______

______b. Molecular motors allow filament‐ based intracellular transport ______The three basic types

1. : move along microfilaments towards the ______positive end (mostly), Some gene products move toward negative end ______2. : move along microtubules towards the positive end (away from the MTOC)

3. : move along microtubules towards the negative ______end (toward the MTOC) ______

______Molecular Motors are ATPases that Couple Hydrolysis with Movement ______

______

______

Globular heads on fibrous tails: ______a. Heads have ATPase activity, dictate filament track, direction and speed b. Tails have “cargo” binding and myosin thick filament organizing activity ______Figure 16-54a Molecular Biology of the Cell (© Garland Science 2008)

______

______

Kinesins and Myosins are Evolutionarily Related ______1. Both have single head (type I ) and double head (type II) designs 2. Little sequence similarity but remarkable similarities in tertiary structures ______

Dyneins are Something Else ______1. They are an ancient family of proteins found in all eukaryotes

a. Cytosolic dyneins move most structures, ciliar dyneins move cilia and flagella ______2. Generally similar structure to the others –can have trimer heads ______

______

______

______

______The motor cargo complex grabs onto ______meshwork and transmembrane proteins. ______

______Figure 16-67 Molecular Biology of the Cell (© Garland Science 2008)

______“Power Stroke” mechanism to couple movement to ATP metabolism ______1. At the end of one cycle the motor is bound to actin at 45o

2. ATP binding Filament Release ______

3. ATP Hydrolysis Conformational Relaxation to 90o ______4. Release of Pi Filament Binding 5. Release of ADP Conformational Stroke to 45o ______6. The shift in the motor back to 45o moves the cargo forward ______

______

______

______2. Regulation of Cell Function via Control of the ______

______

______

______

______

______a. Actin filaments are assembled and disassembled rapidly and thus are able to help regulate long‐term activities, change and movement ______

Assembly of specific actin structures and cellular functions is dependent on the expression and activity of ______associated proteins (MFAP’s) in specific cellular locations ______

______

______

______Actin fiber assembly is spontaneous if only actin and ATP are present and the bonds between subunits are non‐covalent ______

______

______

______Nucleation is the rate‐limiting step in assembly and the first control ______Figure 16-10 Molecular Biology of the Cell (© Garland Science 2008) ______

______To make a dense actin network, or gel, the cell must express ______and activate ARP complexes at that site ______

______

______

Activating factor can follow internal or external signals ______Figure 16-34c Molecular Biology of the Cell (© Garland Science 2008) ______

______Formin facilitates nucleation and causes rapid extension ______

______

______

______Expressed with ARP complexes, leads to very rapid assemblage and branching ______Figure 16-36 Molecular Biology of the Cell (© Garland Science 2008) ______Thymosin and Regulate Speed ______

______

______

______

______

______

______Caps mean slow growth and stabilized fibers ______

______

______

______

______Figure 16-43 Molecular Biology of the Cell (© Garland Science 2008)

______

______Lateral association of double helical fibers by bundling proteins ______

______

______

______

______Figure 16-49a Molecular Biology of the Cell (© Garland Science 2008)

______Stabilization of gel structures ______

______

______

______

______Figure 16-51 Molecular Biology of the Cell (© Garland Science 2008)

______

______Microvilli assemblage ______

______

______

______

______Figure 16-50a Molecular Biology of the Cell (© Garland Science 2008)

______

______

Many changing cell functions are regulated by ______actin fiber reorganization, which requires coordinated disassembly of existing fibers ______followed by nucleation and polymerization at a new location ______

______

______

______Rapid disassembly of fibers ______

______

______

______Severing Depolymerization ______

______

______Combine disassembly with localized assembly ______

______

______

______

Profilin promotes ATP exchange and ARP nucleation ______

______

______

______

______

______

______

______Figure 16-90 Molecular Biology of the Cell (© Garland Science 2008)

______Lamellipodia ______

______

______

______

______

______

______Assembly of the contractile ring followed by severing is required in ______

______

______

______

______

______

______Pseudopod‐Driven Phagocytosis in Neutrophils ______

______

______

______

______Figure 13-46 Molecular Biology of the Cell (© Garland Science 2008)

______Actin polymerization is required to extend pseudopods ______

______

______

Actin depolymerization is required to seal off the ______phagosome ______Figure 13-47a Molecular Biology of the Cell (© Garland Science 2008)

______

Regulation of the active actin structure is associated ______with known Rho‐family signaling pathways ______

stress fibers ______

______

microspikes lamellipodia or ______filopodia

______

______

______

______

______

______

______

______Figure 16-98b Molecular Biology of the Cell (© Garland Science 2008)

______

______

______

______

______

______Figure 16-98a Molecular Biology of the Cell (© Garland Science 2008)

______

______

______b. Microtubules are also assembled and disassembled rapidly and are used to ______regulate movement and positioning of materials, including the cell ______

______

______

______

______

______

______

______γ‐Tubulin ring complex (γ‐TuRC) nucleates assembly from the ______MTOC and remains associated with the minus end ______Figure 16-30a Molecular Biology of the Cell (© Garland Science 2008)

______A high concentration of free tubulin subunits is required ______for assembly and elongation ______

______

______

______Figure 16-30b Molecular Biology of the Cell (© Garland Science 2008) ______

______MAP2, Tau and Plus‐end tracking proteins (TIPs) bind and stabilize microtubules ______

______

______

______

______Figure 16-41 Molecular Biology of the Cell (© Garland Science 2008) ______

______

Green = MT ______

Red = +Tip protein ______

______

Long‐term stable ______structures ______Figure 16-45a Molecular Biology of the Cell (© Garland Science 2008) ______Expression of protein will bind free tubulin subunits and inhibit assembly and elongation ______

______

Each stathmin protein binds two dimers ______

______

Phosphorylation of stathmin will inactivate it ______

______

______Microtubule Severing ______

______

______

______

______

______

______

______

______

______

______

______Figure 16-44 Molecular Biology of the Cell (© Garland Science 2008) ______Disassembly and Reassembly in Mitosis ______

______

______

______

______

______

c. Intermediate filaments are the most stable element in the ______cytoskeleton but their structure can be regulated to facilitate specific cell activities ______

Remember.... ______

______

______

______Figure 16-19 Molecular Biology of the Cell (© Garland Science 2008) ______

______The aminoterminal head and carboxyterminal tail appear to be key points of regulatory control ______

______

______

______

______

______Glycosylation and phosphorylation of intermediate filaments.

______

______

______

______

Hyder C L et al. J Cell Sci 2011;124:1363-1372 ______©2011 by The Company of Biologists Ltd ______

______Disassembly of nucleus in mitosis ______

______

______

______

______

______

______Nuclear Envelope Fragmentation ______

______

______

______

______

______

______

______CELLULAR ______ADHESION ______

______

______

______

______

______

Hemidesmosomes bind ______intermediate filaments to anchor proteins to integrins to ECM fibrous ______proteins Very stable ______Figure 19-46 Molecular Biology of the Cell (© Garland Science 2008) ______

______

______Focal adhesions bind microfilaments to anchor proteins ______to integrins to ECM fibrous proteins ______

______

Can be stable or used for migration ______Figure 19‐45 Molecular Biology of the Cell (© Garland Science 2008) ______Internal binding and external binding are linked ______

______

______

______

______Figure 19-48b Molecular Biology of the Cell (© Garland Science 2008) ______

______

______

Desmosomes bind ______intermediate filaments to anchor proteins to their ______own cadherins which bind to the adjacent cell’s ______cadherins Very stable ______Figure 19‐17a Molecular Biology of the Cell (© Garland Science 2008) ______

______

______

______Adherens junctions bind microfilaments ______to anchor proteins to their own cadherins which bind to the ______adjacent cell’s cadherins ______

______A fairly large protein family, all have homophillic ______binding and are Ca++‐dependent ______

______

______

______Figure 19‐7 Molecular Biology of the Cell (© Garland Science 2008) ______

______Tight Junctions can block molecules as small as ions from passing between cells ______

______

______

______

______Figure 19-24 Molecular Biology of the Cell (© Garland Science 2008) ______

______

______

______

______

______

______Figure 19-26a Molecular Biology of the Cell (© Garland Science 2008) ______

______

______

______When there is an infection or inflammation, endothelial cells will express selectins on their surface that specifically bind WBC. ______

WBC also express integrins that bind strongly, stop their rolling and aid in escape ______

______

______Ig superfamily cell adhesion molecules

______NCAM is found on a variety of cell types and ______mediates homo‐ philic binding. ICAM is found on endothelial ______cells and binds heterophilically to integrins on ______white blood cells. ______Figure 19‐20 Molecular Biology of the Cell (© Garland Science 2008) ______

______This is a large gene family ______

______

______

______

______

______