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37 Cards in this Set
- Front
- Back
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Microtubule (MT) subunit
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Tubulin
- Stable dimer of α- and β-subunits - α contains GTP, structural component - β has GTPase activity |
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Tubulin polarity
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Like actin
- β-subunit always towards the + end |
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Tubulin GTPase activity
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Normally VERY slow
- stimulated when assembled into MT |
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Protofilaments
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Linear array of tubulin
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MT assembly
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protofilaments line up to form sheets
- Sheets curl up to make tubes - Cylindrial shape = relative stiffness |
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MT structure
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Mostly singlets - 13 protofilaments
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Doublet structure
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cilia, flagella
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Triplet structure
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Centrioles, basal bodies (cilia)
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MT organization in average, interphase cells
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Single MT organizing center (MTOC) or centrosome
- MTOC contains centrioles - All MTs attach (-) end to MTOC |
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MT organization in neurons
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From body to axon - polarized - (+) extends out
- Dendrite - mixed orientation |
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Cilia
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Motile or sensory function
- Supported by MTs (interphase) |
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Centrosomes
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2 centrioles surrounded by other material
- Other material contains γ-tubulin |
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γ-tubulin ring complex (TURC)
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γ-tubulin and other proteins form circular templates for new MTs to grow
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MT growth
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tubulin subunits add rapidly to + end
- GTP hydrolysis shortly thereafter |
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Critical concentration
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Below this [tubulin], no MTs will form
- Lower critical concentration for GTP-subunits - More net formation at + end |
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Dynamic instability
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Sudden transitions between growing and shrinking
- catastrophe and rescue |
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Dynamic instabiliy purpose
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Allows MT to explore space around it
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GTP cap
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GTP-subunits have lateral stability together
- As long as cap exists, MT will likely grow - No cap - favors depolymerization |
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MT binding protein functions
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either stablize or destabilize MTs
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MAP2 and Tau
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Abundant in neurons
- Stabilize MTs in axons and dendrites |
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Kinesin-13
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Uses ATP hydrolysis to force protofilaments apart
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Stathmin
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Stabilizes curved configuration
- protofilaments stay split, depolymerize |
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Axoneme
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core MT structure of cilia and flagella
- 9 doublets |
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Basal body
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Assembly of triplet MTs from which cilia grow
- like centriole - New basal bodies arise via duplication of existing basal bodies |
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Motile cilia/flagella
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powered by Dynein motor protein
- Sperm motility - Mucus in airways - Egg in fallopian tubes |
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Nexin
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Holds adjacent MTs together
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Dynein motor
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moves towards (-) end of MT
- in cilia/flagella, stem and stalk connected to adjacent MTs - Power stroke causes bending of adjacent MTs |
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Primary cilia
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non-motile - have signalling/sensory functions
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Primary cilia cycle
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They are lost during replication, regrow at G1
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Intraflagellar transport (IFT)
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Transport signal proteins, membrane proteins, and axoneme components to distal end of primary cilia
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Ciliopathies
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Defects in structure/function of primary cilia
- Assembly defects (IFT, etc) - Defects of actual signalling proteins |
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Polycystic kidney disease
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Loss of primary cilia signalling proteins
- Defective regulation of cell division and polarity |
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MT motor proteins
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Dynein and Kinesin
- Dynein moves to (-) end - Kinesin moves to (+) end |
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MT motor protein functions
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- IFT and components to primary cilia
- Organelle distribution/motility |
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Dynein functionality
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- Stem binds something, is fixed
- Stalk angle changes based on ATP hydrolysis |
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Kartagener's Syndrome
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loss of dynein function
- Chronic lung disease - Male/female infertility - Situs inversus (loss of organ asymmetry) - no motors moving organelles! |
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Kinesin
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Moves towards (+) end, out into cytoplasm
- Related to myosin... - ATP-bound state = tightly bound to MT - Coordinated hand over hand motion |
