Kaplan Full length 4 Q. 174

[Axis8Mundi]

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In post-phrasing Kaplan Full length 4, I came upon an explanation I just don't seem to understand. I was hoping someone might clarify.

The by-products of neurotransmitters released into the synapse are taken up by the axon terminal for processing in the cell body. A researcher wishes to purify these by-products from a neuron cytoplasm extract. Microtubules are aligned on a glass surface with their plus-ends towards the right. The extract is placed on the middle of the surface. In order to collect the desired components, the researcher should collect components that:

A. remained in the center of the glass surface.
B. were enclosed in membrane bound vesicles.
C. flowed to the right side of the glass surface.
D. flowed to the left side of the glass surface.

Kaplan provides the following explanation:

Answer D.

A neuron cell extract will contain kinesins, dyneins, and all of the materials that are trans- ported in the axon. It will also contain microtubules, but these microtubules are not attached to the glass surface and will be arranged in a random fashion after extraction. We can ignore their contribution to the movement of the materials because they should not contribute to any overall movement (due to their random arrangement). The passage states that dyneins utilize micro- tubules to transport recycled components back towards the cell body. We are also told that microtubules are arranged with their plus ends towards the synapse. Putting these two pieces together we can deduce that dyneins move materials towards the minus end of microtubules. The dyneins will transport the recycled components towards the left (minus end) of the glass surface.

Choice A is incorrect because these recycled components will be transported by dyneins.
Choice B is incorrect because both the recycled components and the neurotransmitters trans- ported towards the synapse by kinesins will be in membrane bound vesicles.

My question is why is it that the microtubules are not attached to the glass surface and will be arranged in a random fashion after extraction.

 

[monkeyvokes]

My question is why is it that the microtubules are not attached to the glass surface and will be arranged in a random fashion after extraction.

You're wondering why the microtubules aren't just arranged in a random fashion on the glass surface?
Seems like they probably would be normally, just treat the passage information like a thought experiment.

 

[sps27]

In post-phrasing Kaplan Full length 4, I came upon an explanation I just don't seem to understand. I was hoping someone might clarify.

The by-products of neurotransmitters released into the synapse are taken up by the axon terminal for processing in the cell body. A researcher wishes to purify these by-products from a neuron cytoplasm extract. Microtubules are aligned on a glass surface with their plus-ends towards the right. The extract is placed on the middle of the surface. In order to collect the desired components, the researcher should collect components that:

A. remained in the center of the glass surface.
B. were enclosed in membrane bound vesicles.
C. flowed to the right side of the glass surface.
D. flowed to the left side of the glass surface.

Kaplan provides the following explanation:

Answer D.

A neuron cell extract will contain kinesins, dyneins, and all of the materials that are trans- ported in the axon. It will also contain microtubules, but these microtubules are not attached to the glass surface and will be arranged in a random fashion after extraction. We can ignore their contribution to the movement of the materials because they should not contribute to any overall movement (due to their random arrangement). The passage states that dyneins utilize micro- tubules to transport recycled components back towards the cell body. We are also told that microtubules are arranged with their plus ends towards the synapse. Putting these two pieces together we can deduce that dyneins move materials towards the minus end of microtubules. The dyneins will transport the recycled components towards the left (minus end) of the glass surface.

Choice A is incorrect because these recycled components will be transported by dyneins.
Choice B is incorrect because both the recycled components and the neurotransmitters trans- ported towards the synapse by kinesins will be in membrane bound vesicles.

My question is why is it that the microtubules are not attached to the glass surface and will be arranged in a random fashion after extraction.

This blew my mind. God! I have no clue how to even understand this. So they say the microtubules are aligned on the glass surface with their + ends towards the right. But the ans says microtubles are not attached to the glass surface and are oriented randomly?? So how can that be if the question specifically says they are arranged with their + ends towards their right on the glass surface??

The only way I can make any sense of this question is if the microtubules are aligned with their + ends towards the right on the glass surface (and inside the cell this orientation is towards a synapse) and we know from the passage that dynesins use that alignment to transport recycled products towards the cell body, i.e., away from the + end, then any movement of dynesins will be opposite to right, since the + ends are towards the right, so the dynesins will move towards the left. I don't see how the random alignment of microtubules and not attaching to the glass surface has anything to do with this experiment, when it states specifically that the + ends of microtubules are aligned together on the glass surface.

 

[monkeyvokes]

This blew my mind. God! I have no clue how to even understand this. So they say the microtubules are aligned on the glass surface with their + ends towards the right. But the ans says microtubles are not attached to the glass surface and are oriented randomly?? So how can that be if the question specifically says they are arranged with their + ends towards their right on the glass surface??

The only way I can make any sense of this question is if the microtubules are aligned with their + ends towards the right on the glass surface (and inside the cell this orientation is towards a synapse) and we know from the passage that dynesins use that alignment to transport recycled products towards the cell body, i.e., away from the + end, then any movement of dynesins will be opposite to right, since the + ends are towards the right, so the dynesins will move towards the left. I don't see how the random alignment of microtubules and not attaching to the glass surface has anything to do with this experiment, when it states specifically that the + ends of microtubules are aligned together on the glass surface.

yeah the explanation sure is contradictory