Question

Dynein is a cytoplasmic motor similar to kinesin, but it travels along microtubules in the opposite direction. A single dynein transports a vesicle \(0.6 \mu \mathrm{m}\) along an axon in \(5 \mathrm{sec}\). Dynein steps use one cycle of ATP hydrolysis that move it \(80 \AA\) along a microtubule filament. Assuming all steps are forward along one filament, what is the ATP hydrolysis rate of dynein?

Short answer

Dynein has an ATP hydrolysis rate of 15 ATP molecules per second.

Step-by-step solution

Determine Total Distance Dynein Travels (in Ångströms)

First, convert the transport distance from micrometers to Ångströms. Since 1 micrometer equals 10,000 Ångströms, the total distance is calculated as follows:\[ 0.6 \, ext{micrometers} \times 10,000 \, ext{Å/micrometer} = 6000 \, ext{Å} \]

Calculate Number of Steps Required

Since each step moves the dynein \(80 \, \text{Å}\), we can calculate the total number of steps required to cover the total distance:\[ \text{Number of Steps} = \frac{6000 \, \text{Å}}{80 \, \text{Å/step}} = 75 \]

Calculate ATP Hydrolysis Rate

To find the rate of ATP hydrolysis, determine how many ATP molecules are used per second. Given that it takes 5 seconds to complete 75 steps:\[ \text{ATP Hydrolysis Rate} = \frac{75 \, \text{steps}}{5 \, \text{seconds}} = 15 \, \text{ATP/s} \]

Key concepts

Dynein Motor Protein

Dynein is a fascinating motor protein that plays a critical role in cellular movement and transport. It is one of the two major motor proteins that navigate microtubules in cells. Unlike kinesin, which typically travels toward the plus end of the microtubule, dynein moves toward the minus end.

Dynein is essential for moving cellular components such as vesicles, organelles, and even chromosomes during cell division. This movement is energy-dependent, utilizing ATP, the cell's energy currency.

• Dynein moves in a processive manner, meaning it can take multiple steps along microtubules without detaching.
• Each step involves the hydrolysis of an ATP molecule, providing the necessary energy for dynein to 'walk' along the microtubule.
• The directionality of dynein's movement is vital for its role in cellular organization and intracellular transport.

Understanding how dynein operates can provide insights into numerous biological processes, including neuronal transport and the immune response.

Microtubule Dynamics

Microtubules are dynamic structures within cells that form part of the cytoskeleton. These cylindrical tubes are made of tubulin protein subunits and are essential for maintaining cell shape, supporting intracellular transport, and facilitating cell division.

Microtubules exhibit dynamic instability, characterized by phases of growth and shrinkage, which are crucial for their cellular functions.

• The plus and minus ends of microtubules have distinct growth rates, influencing motor protein navigation.
• Microtubule dynamics are regulated by various associated proteins that either stabilize or destabilize them.
• In cellular transport, motor proteins like dynein and kinesin use the microtubule network as tracks to carry cargo in opposite directions, integrating transport processes with other cellular activities.

These dynamic properties of microtubules allow cells to rapidly reorganize and adapt to different functional needs.

Molecular Transport Processes

Molecular transport processes are vital for the distribution of molecules and organelles within cells. These processes can be passive or active, with motor proteins playing a central role in active transport.

In eukaryotic cells, the transport of molecular cargo across the microtubule network involves active, energy-dependent mechanisms facilitated by motor proteins like dynein and kinesin.

• Active transport is necessary for moving large or charged molecules across the cell, often against a concentration gradient.
• This transport ensures that cellular components are delivered to specific locations, maintaining cellular functions and homeostasis.
• In neurons, for example, transport processes are crucial for moving neurotransmitter-filled vesicles to synapses, impacting neural communication and response.

Thus, the efficiencies and regulation of these transport processes are fundamental to cell biology and understanding disease mechanisms.