Cytoskeleton

Question 1

Actin

Answer 1

Globular multi-functional proteins that form microfilaments.

Question 2

G-actin

Answer 2

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.

Question 3

F-actin

Answer 3

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.

Question 4

Microtubules

Answer 4

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.

Question 5

Alpha-tubulin

Answer 5

GTP bound is physically trapped. Not hydrolyzed or exchanged. Integral part of tubulin heterodimer structure.

Question 6

Beta-tubulin

Answer 6

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.

Question 7

Gamma-tubulin

Answer 7

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.

Question 8

Intermediate Filaments

Answer 8

8 antiparallel tetramers (32 monomers) twisted into helical roselike filament. Flexible and strong with no nucleotide bound and non-polar.

Question 9

Polymerization

Answer 9

Adding monomers to filament.

Question 10

Plus End

Answer 10

Plus ends grow/shrink faster in f-actin and microtubules.

Question 11

Minus End

Answer 11

Grow/shrink faster. Where nucleation occurs.

Question 12

Protofilament

Answer 12

Linear row of tubulin dimers.

Question 13

Critical Concentration

Answer 13

Concentration of monomers at steady state where subunits on=subunits off.

Question 14

Treadmilling

Answer 14

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.

Question 15

Dynamic Instability

Answer 15

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.

Question 16

Profilin

Answer 16

Actin binding protein that binds subunit and speeds-elongation. Pulls monomer over and locks it so it can only bind to plus end.

Question 17

Cofilin

Answer 17

Bind ADP-actin filaments, accelerates disassembly by cleaving actin filaments. Squeezes tight and rotates to add strain to filament.

Question 18

Arp2/3

Answer 18

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.

Question 19

Formin

Answer 19

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.

Question 20

gammaTURC

Answer 20

Nucleates assembly and remains associated with the minus end of microtubules in centrosome.

Question 21

MTOC, Centrosome

Answer 21

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.

Question 22

Myosin II

Answer 22

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.

Question 23

Lamellipodia

Answer 23

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.

Question 24

Myosin II

Answer 24

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).

Question 25

Thick Filaments

Answer 25

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.

Question 26

Kinesin

Answer 26

Plus-end microtubule motor (Kinesin-14 moves towards minus end). Walks along microtubules: they are processive. ADP has stronger affinity to grab microtubule.

Question 27

Dynein- Cytoplamic

Answer 27

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.

Question 28

Dynein- Axonemal/Ciliary

Answer 28

Can have one, two, or three motor domains. Power the beating of cilia and flagellum.

Question 29

Sarcomere

Answer 29

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.

Question 30

Sarcoplasmic Reticulum

Answer 30

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.

Question 31

Sarcomere

Answer 31

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.

Question 32

Troponin Complex

Answer 32

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.

Question 33

Z-line (disk)

Answer 33

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.

Question 34

CapZ

Answer 34

CapZ is a capping protein that caps the barbed (positive) end of actin filaments in muscle cells.

Question 35

Cilia

Answer 35

Found on almost all vertebrate cells (non-dividing). Can produce different movements (motile) or serve sensory purposes (non-motile).

Question 36

Basal Body/Centriole/MTOC

Answer 36

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.

Question 37

Intraflagellar Transport (IFT)

Answer 37

Kinesins and dyneins transport cargo bidirectionally along axonemal microtubules that is essential for the formation and maintenance of most eukaryotic cilia and flagella.