Lecture 7 Review

A network of protein filaments that provides structural support, shape, and organization to cells.

Hollow tubes made of tubulin protein that form part of the cytoskeleton. They are involved in cell division, organelle transport, and cell shape.

Solid, thin filaments composed of actin protein that form part of the cytoskeleton. They play a role in muscle contraction, cell motility, and maintaining cell shape.

Proteins that use ATP hydrolysis to generate movement along cytoskeletal filaments. They facilitate transport of organelles and other cargo within cells.

The breakdown of ATP, a molecule that serves as the main energy source for cellular processes, into ADP and inorganic phosphate, releasing energy.

A centrosome is a microtubule organizing center (MTOC) that serves as a starting point for microtubule growth.

Microtubules are hollow tubes made of alpha (α) and beta (β) tubulin dimers arranged in 13 protofilaments.

Microtubules have a plus end that favors assembly and a minus end that favors disassembly. They grow by adding tubulin dimers to the plus end.

GTP bound to β-tubulin is important for microtubule stability. It is slowly hydrolyzed to GDP, making the microtubule more prone to disassembly.

Taxol stabilizes microtubules by preventing their disassembly, effectively blocking cell division.

Microtubule motors are proteins that bind to microtubules and move along them using ATP as energy.

Axoplasmic transport is the movement of materials along microtubules in nerve cells. It can be either outward or inward.

Microtubules play a crucial role in cell division by forming spindle fibers that separate chromosomes.

The plus end of a microtubule is where assembly occurs, while the minus end is where disassembly occurs.

Stabilizing the minus end of the microtubule by γ-tubulin complexes ensures its stability and proper function.

When ATP is removed, motor proteins are unable to move cargo, highlighting the crucial role of ATP in their function.

If non-hydrolyzable ATP is used, motor proteins still cannot move cargo. This confirms that ATP hydrolysis, not just ATP binding, is essential for movement.

Motor proteins utilize the energy released from ATP hydrolysis (ATP -> ADP + Pi) to generate movement.

Motor proteins have globular heads that bind to and move along microtubules, using ATP hydrolysis as their fuel source.

Yes, different motor proteins are specialized for transporting specific cargos. Kinesin moves ER tubules, while dynein moves Golgi membranes.

Kinesin motors move ER tubules toward the periphery, or edges, of the cell.

Dynein motors move Golgi membranes towards the center of the cell.

Kinesin has two globular heads, a coiled-coil dimerization region, a cargo-binding tail, and a neck linker. The heads bind ATP, and the tail binds cargo.

Kinesin uses a two-headed 'walking' motion along microtubules. It alternates between binding ATP and ADP on its heads, causing a conformational change that propels it forward.

Kinesin requires ATP hydrolysis for movement. It binds ATP on one head, then hydrolyzes it to ADP+Pi, releasing energy for the 'stepping' motion.

Kinesin's affinity for microtubules changes depending on its nucleotide state. ATP binding increases affinity, while ADP binding decreases it.

The 'neck linker' is a flexible region connecting kinesin's head to its stalk. Its position changes depending on whether ATP or ADP is bound, contributing to the 'walking' movement.

Kinesin is highly processive, meaning it can travel long distances along a microtubule without detaching. This is achieved by having one head always firmly bound.

The 'plus' end of an actin filament is where new actin monomers are added, leading to filament growth. This is the site of polymerization.

ATP bound to actin is slowly hydrolyzed to ADP as the filament grows. This hydrolysis plays a role in filament stability and can impact the rate of monomer dissociation.

Actin nucleator proteins in cells help to initiate and control the formation of new actin filaments. They create a platform where new actin monomers can assemble.

Actin-binding proteins regulate various aspects of actin filament behavior. These proteins can affect filament polymerization, depolymerization, bundling, cross-linking, and interactions with other cellular components.

Myosin filaments are bipolar, meaning they have two distinct ends: one with ATPase head domains that bind to actin and a tail region that interacts with other myosin molecules.

ATP binding to the myosin head causes its detachment from the actin filament. ATP hydrolysis leads to a conformational change that 'cocks' the myosin head, ready for binding to the actin filament. Phosphate release triggers the 'power stroke', moving the actin filament relative to the myosin. ADP release completes the cycle.

The 'power stroke' is the conformational change in the myosin head triggered by phosphate release, resulting in a forceful movement of the actin filament relative to the myosin filament. This movement contributes to muscle contraction.

Myosin is not processive, meaning it doesn't move continuously along the actin filament. Each myosin head works independently. In contrast, processive motor proteins like kinesin and dynein move steadily along microtubules. This difference is due to the way myosin heads interact with ATP and the actin filament.

Muscle contraction is achieved by the sliding of actin filaments relative to myosin filaments. Myosin heads bind to and pull on the actin filaments, shortening the sarcomere, the basic contractile unit of muscle.

Muscle contraction is named 'sliding filament' because the process involves the actual sliding of actin filaments over the myosin filaments. During contraction, the distance between successive Z lines on the sarcomere reduces, which is due to the interdigitation of these filaments.