6 Cytoskeletal Component

What are the three major types of filaments in the cytoskeleton?

Microtubules, intermediate filaments, and actin filaments

What is the basic building block of microtubules?

αβ-tubulin heterodimer

What determines the polarity of a microtubule?

γ-TuRC determines polarity, with α-tubulin at the minus end and β-tubulin at the plus end

What promotes microtubule assembly and stability?

GTP promotes assembly and stability

What promotes microtubule disassembly and instability?

GDP promotes disassembly and instability

What is dynamic instability in microtubules?

The ability of microtubules to switch between periods of growth and shrinkage

Give examples of stabilizing MAPs.

Tau and MAP2

Give an example of a destabilizing MAP.

Kinesin-13

What is the major site of microtubule initiation in animal cells?

The centrosome

What are the key components of the centrosome?

Centrioles and pericentriolar material (PCM)

What do kinesin and dynein do?

They are motor proteins that use ATP hydrolysis to generate movement along microtubules

Which end of the microtubules do conventional kinesins move toward?

Plus end

Which end of the microtubules does cytoplasmic dynein move toward?

Minus end

What is the structure of cilia and flagella?

9 + 2 array of microtubules

What generates the force for movement in cilia and flagella?

Dynein arms

What is the structure of the primary cilium?

Typically has a 9 + 0 arrangement of microtubules

What is the primary function of the primary cilium?

Sensory

What are ciliopathies?

Human genetic disorders caused by defects in cilia structure or function

Where are intermediate filaments found?

Only in animal cells

How do IFs assemble?

By forming strong lateral contacts between α-helical coiled-coils

What is the nuclear lamina made of?

Lamins

What are keratins?

The primary structural proteins of epithelial cells

Where are neurofilaments found?

In the cytoplasm of neurons

What connects IFs to other cytoskeletal elements?

Plectin

Where are actin filaments highly concentrated?

In the cortex, just beneath the plasma membrane

What are actin filaments made of?

Helical polymers of the protein actin

Which end of an actin filament grows faster?

The plus end

How is actin polymerization controlled?

By the concentration of actin, pH, and the concentrations of salts and ATP

What do actin-binding proteins do?

Regulate actin filament dynamics

What does the Arp2/3 complex do?

Promotes the formation of branched filaments, nucleates actin at the minus end

What do formins do?

Promote the formation of parallel filaments, nucleate actin at the plus end

What do capping proteins do?

Bind to filament ends, regulating filament length

What do thymosin and profilin do?

Thymosin binds to actin monomers to prevent them from adding to the ends of actin filaments, profilin promotes the addition of monomers to the plus end of filaments

What does cofilin do?

Severs actin filaments and accelerates their disassembly

What do myosins do?

Move along actin filaments

How do myosin heads move along actin filaments?

By binding and hydrolyzing ATP

What causes muscle contraction?

The sliding of myosin filaments past the actin thin filaments

What triggers muscle contraction?

A signal from a nerve that triggers an action potential in the muscle cell plasma membrane, leading to an increase in Ca2+ concentration

What is the role of Myosin II?

Primary motor for muscle contraction

What is the sarcomere?

The basic contractile unit of a muscle cell

What proteins are the actin filament plus ends anchored in, in the Z disc?

CapZ and α-actinin

What is the neuromuscular junction?

The point of contact of a terminus of an axon with a muscle fiber

What role does calcium play in muscle contraction?

When the level of Ca2+ is raised, troponin C causes troponin I to release its hold on actin, allowing tropomyosin to return to its normal position so that the myosin heads can walk along the actin filaments