Cytoskeleton Flashcards
Actin
Globular multi-functional proteins that form microfilaments.
G-actin
Microfilament subunits. Come together to form F-actin. Bound to ATP when in monomer and ADP when in filament. Hydrolysis weakens binding affinity so ADP bound subunits are more likely to dissociate while ATP subunits are more likely to be added.
F-actin
Microfilament. Made of G-actin subunits. Made of 2 filaments in Right-handed helix. Flexible. Barbed Plus End and Pointed Minus End. Plus ends grow/shrink faster. Treadmilling.
Microtubules
Made of alpha/beta tubular dimers. Bound to GTPs (or GDPs). Made of 13 protofilaments that form hollow tube. Alpha is minus end and Beta is plus end. Rigid and and polar. Dynamic Instability. GTP cap allows for rapid growth, but loss of GTP cap leads to shrinkage until GTP cap is regained.
Alpha-tubulin
GTP bound is physically trapped. Not hydrolyzed or exchanged. Integral part of tubulin heterodimer structure.
Beta-tubulin
GTP or GDP can be bound. Hydrolysis weakens binding affinity so GDP bound subunits are more likely too dissociate while GTP subunits are more likely to be added.
Gamma-tubulin
Gamma-tubulin bind accessory proteins to form spiral complexes (13 gamma-tubulins) that serve as nucleating sites that help overcome the nucleation barrier, allowing microtubules to then form from them, especially in the MTOC.
Intermediate Filaments
8 antiparallel tetramers (32 monomers) twisted into helical roselike filament. Flexible and strong with no nucleotide bound and non-polar.
Polymerization
Adding monomers to filament.
Plus End
Plus ends grow/shrink faster in f-actin and microtubules.
Minus End
Grow/shrink faster. Where nucleation occurs.
Protofilament
Linear row of tubulin dimers.
Critical Concentration
Concentration of monomers at steady state where subunits on=subunits off.
Treadmilling
Consequence of ATP/GTP hydrolysis. Net influx of subunits through the polymers as it maintains a constant length. Force generator for cellular motility. For Critical Concentration at Plus end < Current Concentration < Critical Concentration at minus end, treadmilling occurs.
Dynamic Instability
Microtubules depolymerize 100x faster from GDP ends than GTP ends. Elongation and shrinkage. Rapid growth with GTP-cap end, but random loss of GTP cap causes rapid shrinkage. When GTP cap is regained, there is rapid growth with GTP capped end again.
Profilin
Actin binding protein that binds subunit and speeds-elongation. Pulls monomer over and locks it so it can only bind to plus end.
Cofilin
Bind ADP-actin filaments, accelerates disassembly by cleaving actin filaments. Squeezes tight and rotates to add strain to filament.
Arp2/3
Actin related protein. Complex that nucleates actin. When activate, works with other proteins and actin monomers to nucleate at minus end. Nucleates branched F-actin networks.
Formin
Nucleate F-actin bundles. Nucleate straight, unbranched bundles. Formin dimers works with actin monomers, always at the plus end, by “shimmying up” filaments by releasing one monomer and adding new one.
gammaTURC
Nucleates assembly and remains associated with the minus end of microtubules in centrosome.
MTOC, Centrosome
Microtubule organizing center that has gamma-tubulin ring complexes that serve as nucleating sites. Microtubules grow from gamma-ring complexes of the centrosome. The two most important types of MTOCs are 1) the basal bodies associated with cilia and flagella and 2) the centrioles associated with spindle formation.
Myosin II
First motor protein identified. They are found anywhere, not just muscle. Long and flexible. Coiled-coil tail of two alpha-helices on c-terminus and and 2 flexible myosin heads that rotate around n n-terminus. Light chains and neck/hinge region. Myosin connect and contract actin within the cell.
Lamellipodia
Cellular protrusions that are formed at the periphery of a moving or spreading cell. Lamellipodia are enriched with array of branched networks of actin filaments.
Myosin II
First motor protein identified. They are found anywhere, not just muscle. Long and flexible. Coiled-coil tail of two alpha-helices on c-terminus and and 2 flexible myosin heads that rotate around n n-terminus. Light chains and neck/hinge region. Myosin connect and contract actin within the cell. Pull towards plus end of actin filaments (Myosin VI moves towards minus end). Tails dictate role, I and V bind to membranes (vesicles or plasma membrane).
Thick Filaments
Tails of Myosin II interact with one another to form bipolar thick filaments, where both ends are similar. The bare zone in middle is only tails, no heads.
Kinesin
Plus-end microtubule motor (Kinesin-14 moves towards minus end). Walks along microtubules: they are processive. ADP has stronger affinity to grab microtubule.
Dynein- Cytoplamic
Minus-directed microtubule motor transport of cargo. HUGE compared to Myosin and Kinesin. Two motor domains. Processive and functions as a dimer. Tail attaches to cargo, stalk connects to microtubule. AAA domains in motorhead: wheel moves and it walks like kinesin. Bind and pull.
Dynein- Axonemal/Ciliary
Can have one, two, or three motor domains. Power the beating of cilia and flagellum.
Sarcomere
A sarcomere is the basic contractile unit of muscle fiber. Each sarcomere is composed of two main protein filaments—actin and myosin—which are the active structures responsible for muscular contraction. Each actin filament is associated with tropomyosin. The most popular model that describes muscular contraction is called the sliding filament theory.
Sarcoplasmic Reticulum
A form of smooth muscle endoplasmic reticulum (ER) found in skeletal muscle that functions as a regulator of Ca2+ storage and release homeostasis during and after muscle contraction. Rise in Ca2+ concentration initiates muscle contraction.
Sarcomere
A sarcomere is the basic contractile unit of myofibril (muscle fiber). Shortens 10% of length in less than 1/50th of a second. Two parts of light names and a dark band. Each sarcomere is composed of two main protein filaments—actin and myosin—which are the active structures responsible for muscular contraction. Each actin filament is associated with tropomyosin. The most popular model that describes muscular contraction is called the sliding filament theory.
Troponin Complex
A complex of three (I , C, T) regulatory proteins that is a component of thin filament (actin); when calcium ions bind to troponin complex, it changes shape; this conformational change moves tropomyosin away from myosin-binding sites on actin molecules, and muscle contraction subsequently begins as myosin binds to actin.
Z-line (disk)
A sarcomere is defined as the segment between two neighbouring Z-lines (or Z-discs, or Z bodies). i.e. Z-disk to Z-disk is one sarcomere.
CapZ
CapZ is a capping protein that caps the barbed (positive) end of actin filaments in muscle cells.
Cilia
Found on almost all vertebrate cells (non-dividing). Can produce different movements (motile) or serve sensory purposes (non-motile).
Basal Body/Centriole/MTOC
Acts as template for formation of the ciliary or flagellar axoneme (central strand of a cilium or flagellum. It is composed of an array of microtubules). In many cells, basal bodies and centrioles are functionally interconvertible.
Intraflagellar Transport (IFT)
Kinesins and dyneins transport cargo bidirectionally along axonemal microtubules that is essential for the formation and maintenance of most eukaryotic cilia and flagella.
