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30 Cards in this Set
- Front
- Back
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In typical cells, actin is the most abundant protein. What does actin need to form a linear polymer?
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ATP
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What is an actin filament composed of?
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Two protofilaments twisting around each other
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This filament has polarity. It has a barbed end and a pointed end. Which side is (+) and (-)?
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barbed = (+)
pointed = (-) |
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At what end is polymerization fastest?
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The barbed (+) end
depolymerization is faster at the (-) end |
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Where do actin filaments often begin?
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The plasma membrane
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What are actoclampins?
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An expansile motor that adds a complex of actin, ATP, and profilin to the growing end of the actin filament.
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What is actin depolymerization factor?
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Has the ability to depolymerize actin filaments from the pointed end.
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What effect do proteins that cap the ends of actin filaments have on actin filaments?
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They slow the turnover of filaments
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What are myosins?
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The actin filament equivalent to kinesins. Myosins are similar to kinesins in that they have two heads, a tail, and ATP hydrolysis powers their movement along actin filaments
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In muscle cells, myosin II aggregates to form these
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Thick filaments
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In skeletal muscle, tropomyosin is wound around the actin/thin filament. During muscle relaxation, when Ca is low, tropomyosin prevents the interaction between actin and myosin. What occurs when the concentration of Ca increases?
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Tropomyosin moves and allows actin myosin interaction
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What is the function of short actin filaments?
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To anchor spectrin to the plasma membrane
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What is spectrin?
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A part of the cytoskeleton in erythrocytes and other cells. It helps give red blood cells their unique biconcave shape.
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What does a mutation in spectrin cause?
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Ellipocytosis or spherocytosis
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How are spherocytic red blood cells distinguishable?
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They do not show a region of central pallor
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How are actin filaments connected to the ECM?
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Via a cell adhesion complex
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What are these cell adhesion complexes composed of?
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They are composed of integrins, and kinases that play a role in signaling cell adhesion.
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What can this signaling affect?
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apoptosis, cell growth, differentiation, and cell division.
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Describe an example of signaling via integrins
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When platelets become activated by thrombin, a change in integrin conformation changes its affinity to fibrin
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How are cells linked by actin filaments?
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By adherens junctions.
They form the bridge actin filament - cadherin - actin filament. Very strong |
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What is the cadherin interaction between two cells dependent on?
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Calcium in the ECM
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How are cadherins linked to actin filaments inside the cell?
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Via a protein complex that includes Beta-catenin
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Besides linking actin filaments with cadherins, what is another function of Beta-catenins?
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They play a role in Wnt Signaling
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How does Wnt signaling work?
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In the absence of extracellular Wnt proteins, free Beta catenin is ubiquitinated and then degraded.
In the presence of extracellular Wnt proteins, they activate frizzled receptors and Beta catenin moves into the nucleus and stimulates transcription. Abnormalities in this pathway can cause cancer |
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What are intermediate filaments composed of?
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Keratin
An acidic and basic keratin form a coiled heterodimer These heterodimers aggregate into intermediate filaments |
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Where is keratin found?
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Epithelial cells
Hair and nails |
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What are desmosomes?
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They are cell-cell linkages that form the bridge keratin-cadherin-keratin
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What is pemphigus vulgaris?
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A disease due to the presence of antibodies against cadherins
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What are hemidesmosomes?
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Cell-matrix linkages that form the bridge, intermediate filaments - integrin - ECM
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In normal cells, signaling from integrins regulate signaling from growth factor. Attached cells induce a large growth factor response. In unattached cells, they do not respond to growth factor. What is different in tumor cells?
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In tumor cells, growth factors often induce a intracellular response even in unattached cells
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