Michael Levin Bioelectricity 101 Crash Course Lesson 24: Microtubules and Bioelectricity: The Cytoskeleton’s Role in Signaling Summary

• The cytoskeleton is a dynamic network of protein filaments inside cells, providing structure, support, and the ability to move and change shape.
• Microtubules are one of the major types of cytoskeletal filaments, forming long, hollow tubes.
• Microtubules are not just static structural elements; they are dynamic, constantly growing and shrinking. This dynamism is crucial for their function.
• Microtubules serve as “tracks” for motor proteins (kinesins and dyneins) that transport materials (cargo) within the cell.
• The organization of microtubules within a cell can influence the distribution of ions and, therefore, the cell’s bioelectric state (membrane potential and voltage gradients).
• There is evidence for bidirectional communication between microtubules and bioelectric signals: microtubules can influence bioelectricity, and bioelectricity can influence microtubule organization.
• Specific microtubule-associated proteins (MAPs) and tubulin modifications can modulate the interaction between microtubules and the bioelectric environment.
• Disruptions in microtubule organization can contribute to developmental defects, regeneration problems, and even cancer, partly through their effects on bioelectric signaling.
• Microtubules exhibit properties consistent with them conducting electrical signals, and may act as “biological wires”.
• The cytoskeleton as a whole (not just microtubules) is intimately linked to bioelectricity.

Michael Levin Bioelectricity 101 Crash Course Lesson 24: Microtubules and Bioelectricity: The Cytoskeleton’s Role in Signaling

So far in this course, we’ve explored the amazing world of bioelectricity – how cells generate and respond to electrical signals, and how these signals control fundamental processes like development, regeneration, and even cancer. We’ve talked about ion channels, membrane potential, voltage gradients, and how these electrical patterns act as a kind of “software” guiding the construction of the body. But there’s a crucial question we haven’t fully addressed: how do these electrical signals actually exert their effects on cells? How do they translate into physical changes in cell behavior, like cell migration, division, and differentiation?

The answer, to a large extent, lies in the cytoskeleton. The cytoskeleton is the cell’s internal scaffolding – a dynamic network of protein filaments that gives the cell its shape, allows it to move, and organizes its internal components. It’s like the frame of a building, but much more dynamic and adaptable. Think of it as a constantly shifting system of girders, cables, and motors, allowing the cell to remodel itself in response to signals from its environment.

There are three main types of cytoskeletal filaments:

1. Actin filaments (microfilaments): These are thin, flexible filaments involved in cell movement, cell shape changes, and muscle contraction.
2. Intermediate filaments: These are rope-like fibers that provide mechanical strength and stability to cells.
3. Microtubules: These are long, hollow tubes, and they’re the focus of this lesson.

Microtubules are built from subunits of a protein called tubulin. Tubulin comes in two main forms, α-tubulin and β-tubulin, which bind together to form a dimer. These dimers then assemble into long chains called protofilaments. Thirteen protofilaments arrange themselves side-by-side to form the hollow tube of the microtubule.

It’s important to understand that microtubules are not static structures. They are constantly growing and shrinking in a process called dynamic instability. This dynamic behavior is crucial for their function. Imagine a construction site where the scaffolding is constantly being assembled and disassembled, allowing workers to move materials and build different parts of the structure. Microtubules are like that dynamic scaffolding, constantly adapting to the needs of the cell.

One of the most important roles of microtubules is to serve as “tracks” for motor proteins. These are like tiny molecular machines that “walk” along the microtubules, carrying cargo. There are two main families of microtubule motor proteins:

• Kinesins: Most kinesins move towards the plus end of the microtubule (the end where new tubulin dimers are added).
• Dyneins: Dyneins move towards the minus end of the microtubule (the end where tubulin dimers are removed).

These motor proteins can carry a wide variety of cargo, including:

• Vesicles: Small, membrane-bound sacs that contain proteins, lipids, or other molecules.
• Organelles: Structures within the cell, like mitochondria (the powerhouses of the cell) or the Golgi apparatus (which processes proteins).
• mRNA: The molecules that carry genetic information from the DNA to the ribosomes, where proteins are made.
• Ion channels: Critical regulators of resting potential and other ions, directly impacting the cell’s bioelectric state.

So, microtubules, along with their associated motor proteins, form a complex intracellular transport system. This system is essential for delivering materials to the right place at the right time, allowing the cell to function properly. Think of it like a city’s railway network, with trains (motor proteins) carrying goods (cargo) along tracks (microtubules) to different destinations.

Now, how does all of this connect to bioelectricity? There are several crucial links:

1. Microtubules and Ion Channel Localization: As we’ve learned, ion channels are key players in bioelectricity. They control the flow of ions across the cell membrane, creating the membrane potential and voltage gradients. The location of ion channels in the membrane is critical for their function. Microtubules, through their motor proteins, can transport ion channels to specific locations in the cell membrane. This means that the organization of the microtubule network can directly influence the distribution of ion channels, and therefore the cell’s bioelectric state. It’s like directing traffic: by controlling where the “gates” (ion channels) are located, you control the flow of “vehicles” (ions).
2. Microtubules and Voltage Gradients: The organization of the microtubule network can also influence the overall pattern of voltage gradients within a tissue. By controlling the delivery of ion channels and other electrically relevant molecules, microtubules can help shape the “electrical landscape” that guides cell behavior. It’s like setting the topography that rivers and electrical flow will exist upon.
3. Bioelectricity and Microtubule Organization: The relationship between microtubules and bioelectricity is bidirectional. Just as microtubules can influence bioelectricity, bioelectric signals can also influence microtubule organization. Changes in membrane potential, or the presence of electric fields, can affect the stability, growth, and orientation of microtubules. This means that there’s a feedback loop: bioelectric signals can influence the cytoskeleton, which in turn can influence bioelectric signals.
4. Tubulin Modifications and Electrical Properties: The tubulin subunits that make up microtubules can be modified in various ways. These modifications (like acetylation, phosphorylation, and others) can change the properties of the microtubules, including their stability, their interactions with motor proteins, and even their electrical conductivity. This suggests that microtubules might not just be passive tracks, but could also play a more active role in electrical signaling, acting like “biological wires” or tunable electrical components.
5. Microtubule-Associated Proteins (MAPs): Numerous proteins associate with microtubules, regulating their stability, dynamics, and interactions with other cellular components. Some of these MAPs are known to be sensitive to electrical signals, providing another link between bioelectricity and the cytoskeleton. These, too, might have key implications in explaining voltage differences, cell to cell.

Let’s look at some specific examples of how this interplay between microtubules and bioelectricity works:

• Embryonic Development: During early development, microtubules play a crucial role in positioning key molecules, including ion channels, asymmetrically within the embryo. This asymmetric distribution of ion channels helps establish the bioelectric gradients that guide the formation of the body plan, as we saw in the experiments on frog embryos (Lessons 13 & 18, and the research papers discussed previously).
• Wound Healing: When a tissue is injured, electric fields are generated at the wound site. These electric fields can influence the orientation of microtubules, guiding the migration of cells to close the wound.
• Cancer: Disruptions in microtubule organization are common in cancer cells. These disruptions can alter the cell’s bioelectric state, contributing to uncontrolled cell growth and metastasis. Cancer cells also show distinct membrane potentials compared to normal cells.
• Regeneration: In animals that can regenerate lost body parts (like planarians and salamanders), bioelectric signals are crucial for guiding the regrowth of the missing structures. Microtubules are likely involved in translating these bioelectric signals into the physical changes needed for regeneration.

The research we discussed in earlier lessons (Lobikin et al., 2012, and McDowell et al., 2016) provides strong evidence for the role of microtubules in LR asymmetry. The mutations in α-tubulin and γ-tubulin-associated protein disrupted the normal organization of microtubules, leading to mislocalization of key proteins (like cofilin) and randomization of organ placement. These experiments demonstrate the direct link between microtubule function, bioelectric signaling (because the mislocalized proteins included ion channels and transporters), and large-scale anatomical outcomes. The key ability for a cytoskeleton to maintain some organization that can properly transport cell contents across space becomes more difficult to keep when disrupted.

The cytoskeleton as a whole is extremely important, and this includes the relationship of other structures beyond microtubles to bioelectricity:

• Actin Filaments and Bioelectricity: Actin filaments, another major component of the cytoskeleton, are also intimately linked to bioelectricity. They interact with ion channels, influencing their activity and localization. Actin dynamics are also sensitive to electrical fields, contributing to cell migration and wound healing.
• Intermediate Filaments and Bioelectricity: While less directly involved in electrical signaling than microtubules and actin, intermediate filaments can also influence the mechanical properties of cells, which in turn can affect how cells respond to electrical cues.

In summary, the cytoskeleton, and particularly microtubules, are not just passive structural elements. They are dynamic, adaptable networks that play a crucial role in implementing bioelectric signals, translating electrical information into physical changes in cell behavior. This connection between bioelectricity and the cytoskeleton is a fundamental aspect of how cells control their growth, shape, and function, and it’s a key to understanding development, regeneration, and disease.

Michael Levin Bioelectricity 101 Crash Course Lesson 24: Microtubules and Bioelectricity: The Cytoskeleton’s Role in Signaling Quiz

1. What is the cytoskeleton?

A) The external skeleton of an insect.
B) A dynamic network of protein filaments inside cells.
C) The rigid cell wall of a plant cell.
D) The bones of a vertebrate animal.

2. Which of the following is NOT a major type of cytoskeletal filament?

A) Actin filaments (microfilaments)
B) Intermediate filaments
C) Microtubules
D) DNA filaments

3. Microtubules are composed of subunits of what protein?

A) Actin
B) Keratin
C) Tubulin
D) Collagen

4. What is “dynamic instability” in the context of microtubules?

A) The constant growing and shrinking of microtubules.
B) The inability of microtubules to maintain their shape.
C) The breakdown of microtubules due to disease.
D) The static, unchanging nature of microtubules.

5. Which motor proteins typically move towards the plus end of a microtubule?

A) Dyneins
B) Kinesins
C) Myosins
D) Actins

6. Which motor proteins typically move towards the minus end of a microtubule?

A) Dyneins
B) Kinesins
C) Myosins
D) Tubulins

7. Which of the following can be transported by microtubule motor proteins?

A) Vesicles
B) Organelles
C) mRNA
D) All of the above

8. How can microtubules influence a cell’s bioelectric state?

A) By providing structural support only
B) They Don’t
C) By transporting ion channels to specific locations in the cell membrane.
D) By degrading cellular proteins

9. True or False: The relationship between microtubules and bioelectricity is unidirectional; microtubules influence bioelectricity, but bioelectricity does not influence microtubules.

A) True
B) False

10. What are MAPs?

A) Maps of the human genome
B) Microtubule-associated proteins that regulate microtubule properties
C) Motor proteins that move along actin filaments
D) Membrane action potentials

11. Which of the following processes is NOT directly linked to the interplay of microtubules and bioelectricity?

A) Embryonic development
B) Wound healing
C) Photosynthesis
D) Cancer

12. Tubulin modifications can affect:

A) microtubule stability
B) interactions with motor proteins
C) electrical conductivity
D) All of the above

13. In the Lobikin et al. (2012) paper discussed in previous lessons, mutations in which proteins were shown to disrupt LR asymmetry?

A) Actin and myosin
B) α-tubulin and a γ-tubulin-associated protein
C) Keratin and collagen
D) DNA polymerase and RNA polymerase

14. What protein discussed showed biased expression that the mutant tubulin messed up in the experiments in the Lobikin paper?

A) Myosin
B) Keratin
C) Kinesin
D) Cofilin-1

15. The cytoskeleton as a whole includes a relationship between the bioelectric landscape and..

A) Actin filaments
B) Microtubules
C) Intermediate Filaments.
D) All of the above.

16. Disruptions in microtubule organization can contribute to:

A) Improved wound healing.
B) Developmental defects and cancer.
C) Stronger bones.
D) Enhanced photosynthesis

17. True/False: It is not important for the dynamic nature of microtubles and their transport capabilities that the microtuble stay “healthy” or organized, because it is the kinesin which really is providing the transportation ability.

A) True
B) False

18. Kinesin Heavy Chain, or KHC, and its relation to bioelectricity, can be said to:

A) Have no relation
B) Transports important ion channels and bioelectrically relevant materials.
C) Affects cancer rates.
D) B and C

19. What are examples of ions that microtubles might transport?

A) Sodium
B) Potassium
C) Chloride
D) All of the Above

20. It may be that microbutles also:

A) Conduct electricity
B) Change voltage across an entire tissue, like wiring.
C) Act in part like electric circuits
D) All of the Above

Michael Levin Bioelectricity 101 Crash Course Lesson 24: Microtubules and Bioelectricity: The Cytoskeleton’s Role in Signaling Answer Sheet

1. B

2. D

3. C

4. A

5. B

6. A

7. D

8. C

9. B

10. B

11. C

12. D

13. B

14. D

15. D

16. B

17. B

18. D

19. D

20. D

迈克尔·莱文 生物电 101 速成课程 第24课：微管与生物电：细胞骨架在信号传导中的作用 摘要

• 细胞骨架是细胞内蛋白质丝的动态网络，提供结构、支持以及移动和改变形状的能力。
• 微管是细胞骨架丝的主要类型之一，形成长而中空的管。
• 微管不仅仅是静态的结构元件；它们是动态的，不断地生长和收缩。 这种动态性对其功能至关重要。
• 微管充当运动蛋白（驱动蛋白和动力蛋白）的“轨道”，这些蛋白在细胞内运输物质（货物）。
• 细胞内微管的组织可以影响离子的分布，从而影响细胞的生物电状态（膜电位和电压梯度）。
• 有证据表明微管和生物电信号之间存在双向通信：微管可以影响生物电，生物电也可以影响微管组织。
• 特定的微管相关蛋白 (MAP) 和微管蛋白修饰可以调节微管与生物电环境之间的相互作用。
• 微管组织的破坏会导致发育缺陷、再生问题，甚至癌症，部分原因在于它们对生物电信号传导的影响。
• 微管表现出与其传导电信号一致的特性，并且可能充当“生物电线”。
• 整个细胞骨架（不仅仅是微管）与生物电密切相关。

迈克尔·莱文 生物电 101 速成课程 第24课：微管与生物电：细胞骨架在信号传导中的作用

在本课程中，到目前为止，我们已经探索了生物电的神奇世界——细胞如何产生和响应电信号，以及这些信号如何控制发育、再生甚至癌症等基本过程。 我们已经讨论过离子通道、膜电位、电压梯度，以及这些电模式如何充当一种指导身体构建的“软件”。 但是有一个关键问题我们还没有完全解决：这些电信号实际上是如何对细胞产生影响的？ 它们如何转化为细胞行为的物理变化，如细胞迁移、分裂和分化？

答案在很大程度上取决于细胞骨架。 细胞骨架是细胞的内部支架——一个动态的蛋白质丝网络，赋予细胞形状，允许它移动，并组织其内部成分。 它就像建筑物的框架，但更具活力和适应性。 可以把它想象成一个不断变化的梁、缆索和发动机系统，使细胞能够根据来自其环境的信号进行自我重塑。

细胞骨架丝主要有三种类型：

1. 肌动蛋白丝（微丝）： 这些是细而柔韧的细丝，参与细胞运动、细胞形状变化和肌肉收缩。
2. 中间丝： 这些是绳状纤维，为细胞提供机械强度和稳定性。
3. 微管： 这些是长而中空的管，它们是本课的重点。

微管由称为微管蛋白的蛋白质亚基构成。 微管蛋白主要有两种形式，α-微管蛋白和β-微管蛋白，它们结合在一起形成二聚体。 然后，这些二聚体组装成称为原丝的长链。 13 条原丝并排排列，形成微管的中空管。

重要的是要理解微管不是静态结构。 它们在一个称为动态不稳定性的过程中不断地生长和收缩。 这种动态行为对其功能至关重要。 想象一个建筑工地，脚手架不断地组装和拆卸，允许工人移动材料和建造结构的不同部分。 微管就像那个动态的脚手架，不断地适应细胞的需要。

微管最重要的作用之一是充当运动蛋白的“轨道”。 这些就像微小的分子机器，沿着微管“行走”，携带货物。 微管运动蛋白主要有两大类：

• 驱动蛋白： 大多数驱动蛋白向微管的正极移动（添加新微管蛋白二聚体的一端）。
• 动力蛋白： 动力蛋白向微管的负极移动（去除微管蛋白二聚体的一端）。

这些运动蛋白可以携带各种各样的货物，包括：

• 囊泡： 包含蛋白质、脂质或其他分子的小的膜结合囊。
• 细胞器： 细胞内的结构，如线粒体（细胞的能量工厂）或高尔基体（处理蛋白质）。
• mRNA： 将遗传信息从 DNA 携带到核糖体（蛋白质合成的地方）的分子。
• 离子通道：静息电位和其他离子的关键调节剂,直接影响细胞的生物电状态.

因此，微管及其相关的运动蛋白形成了一个复杂的细胞内运输系统。 该系统对于将材料在正确的时间输送到正确的位置至关重要，从而使细胞能够正常运作。 可以把它想象成一个城市的铁路网络，火车（运动蛋白）沿着轨道（微管）将货物（货物）运送到不同的目的地。

现在，所有这些如何与生物电联系起来？ 有几个关键的联系：

1. 微管和离子通道定位：正如我们所了解的，离子通道是生物电的关键参与者。 它们控制离子跨细胞膜的流动，产生膜电位和电压梯度。 离子通道在膜中的位置对其功能至关重要。 微管通过其运动蛋白，可以将离子通道运输到细胞膜中的特定位置。 这意味着微管网络的组织可以直接影响离子通道的分布，从而影响细胞的生物电状态。 这就像指挥交通：通过控制“闸门”（离子通道）的位置，您可以控制“车辆”（离子）的流动。
2. 微管和电压梯度： 微管网络的组织也会影响组织内电压梯度的整体模式。 通过控制离子通道和其他带电相关分子的输送，微管可以帮助塑造引导细胞行为的“电景观”。这就像设置河流和电流将存在的地形。
3. 生物电和微管组织： 微管和生物电之间的关系是双向的。 正如微管可以影响生物电一样，生物电信号也可以影响微管组织。 膜电位的变化或电场的存在会影响微管的稳定性、生长和方向。 这意味着存在一个反馈回路：生物电信号可以影响细胞骨架，而细胞骨架又可以影响生物电信号。
4. 微管蛋白修饰和电学特性：构成微管的微管蛋白亚基可以通过多种方式进行修饰。 这些修饰（如乙酰化、磷酸化等）可以改变微管的特性，包括它们的稳定性、它们与运动蛋白的相互作用，甚至它们的导电性。 这表明微管可能不仅仅是被动轨道，还可能在电信号传导中发挥更积极的作用，充当“生物电线”或可调电组件。
5. 微管相关蛋白 (MAP)： 许多蛋白质与微管结合，调节其稳定性、动力学以及与其他细胞成分的相互作用。 其中一些 MAP 已知对电信号敏感，提供了生物电和细胞骨架之间的另一种联系。 这些也可能对解释细胞之间的电压差异具有重要意义。

让我们看看微管和生物电之间的相互作用是如何发挥作用的一些具体例子：

• 胚胎发育： 在早期发育过程中，微管在将关键分子（包括离子通道）不对称地定位在胚胎内起着至关重要的作用。 离子通道的这种不对称分布有助于建立引导身体形态形成的生物电梯度，正如我们在青蛙胚胎实验中看到的那样（第 13 课和第 18 课，以及之前讨论过的研究论文）。
• 伤口愈合： 当组织受伤时，会在伤口部位产生电场。 这些电场会影响微管的方向，引导细胞迁移以闭合伤口。
• 癌症： 微管组织的破坏在癌细胞中很常见。 这些破坏会改变细胞的生物电状态，导致细胞不受控制地生长和转移。 癌细胞也显示出与正常细胞不同的膜电位。
• 再生： 在可以再生失去的身体部位的动物（如涡虫和蝾螈）中，生物电信号对于引导缺失结构的再生至关重要。 微管可能参与将这些生物电信号转化为再生所需的物理变化。

我们在前面的课程中讨论的研究（Lobikin 等人，2012 年，以及 McDowell 等人，2016 年）为微管在左右不对称中的作用提供了强有力的证据。 α-微管蛋白和 γ-微管蛋白相关蛋白的突变破坏了微管的正常组织，导致关键蛋白（如 cofilin）的错误定位和器官放置的随机化。 这些实验证明了微管功能、生物电信号传导（因为错误定位的蛋白质包括离子通道和转运蛋白）和大规模解剖结果之间的直接联系。 当细胞骨架被破坏时, 维持某种能够正确地在空间中运输细胞内容的组织的关键能力变得更加困难。

整个细胞骨架都极其重要, 其中包括微管以外的其他结构与生物电的关系:

• 肌动蛋白丝和生物电：肌动蛋白丝是细胞骨架的另一个主要组成部分，也与生物电密切相关。 它们与离子通道相互作用，影响它们的活性和定位。 肌动蛋白动力学也对电场敏感，有助于细胞迁移和伤口愈合。
• 中间丝和生物电：虽然中间丝不像微管和肌动蛋白那样直接参与电信号传导，但它们也可以影响细胞的机械性能，进而影响细胞对电信号的反应方式。

总之，细胞骨架，尤其是微管，不仅仅是被动的结构元素。 它们是动态的、适应性强的网络，在实施生物电信号、将电信息转化为细胞行为的物理变化方面发挥着至关重要的作用。 生物电和细胞骨架之间的这种联系是细胞如何控制其生长、形状和功能的基本方面，也是理解发育、再生和疾病的关键。

迈克尔·莱文 生物电 101 速成课程 第24课：微管与生物电：细胞骨架在信号传导中的作用 小测验

1. 什么是细胞骨架？

A) 昆虫的外骨骼。
B) 细胞内蛋白质丝的动态网络。
C) 植物细胞的刚性细胞壁。
D) 脊椎动物的骨骼。

2. 以下哪一项不是细胞骨架丝的主要类型？

A) 肌动蛋白丝（微丝）
B) 中间丝
C) 微管
D) DNA 丝

3. 微管由什么蛋白质的亚基组成？

A) 肌动蛋白
B) 角蛋白
C) 微管蛋白
D) 胶原蛋白

4. 在微管的背景下，“动态不稳定性”是什么意思？

A) 微管不断地生长和收缩。
B) 微管无法保持其形状。
C) 微管因疾病而分解。
D) 微管的静态、不变的性质。

5. 哪些运动蛋白通常向微管的正极移动？

A) 动力蛋白
B) 驱动蛋白
C) 肌球蛋白
D) 肌动蛋白

6. 哪些运动蛋白通常向微管的负极移动？

A) 动力蛋白
B) 驱动蛋白
C) 肌球蛋白
D) 微管蛋白

7. 以下哪一项可以由微管运动蛋白运输？

A) 囊泡
B) 细胞器
C) mRNA
D) 以上都是

8. 微管如何影响细胞的生物电状态？

A) 仅提供结构支持
B) 它们没有
C) 通过将离子通道运输到细胞膜中的特定位置.
D) 通过降解细胞蛋白质

9. 对或错：微管和生物电之间的关系是单向的； 微管影响生物电，但生物电不影响微管。

A) 对
B) 错

10. 什么是 MAP？

A) 人类基因组图谱
B) 调节微管特性的微管相关蛋白
C) 沿着肌动蛋白丝移动的运动蛋白
D) 膜动作电位

11. 以下哪一项过程不与微管和生物电的相互作用直接相关？

A) 胚胎发育
B) 伤口愈合
C) 光合作用
D) 癌症

12. 微管蛋白修饰会影响：

A) 微管稳定性
B) 与运动蛋白的相互作用
C) 导电性
D) 以上都是

13. 在之前课程中讨论的 Lobikin 等人（2012 年）的论文中，哪些蛋白质的突变被证明会破坏左右不对称？

A) 肌动蛋白和肌球蛋白
B) α-微管蛋白和 γ-微管蛋白相关蛋白
C) 角蛋白和胶原蛋白
D) DNA 聚合酶和 RNA 聚合酶

14. 在 Lobikin 论文的实验中，讨论了哪种蛋白质显示出突变微管蛋白破坏的偏向表达？

A) 肌球蛋白
B) 角蛋白
C) 驱动蛋白
D) Cofilin-1

15. 整个细胞骨架包括生物电景观和…之间的关系

A) 肌动蛋白丝
B) 微管
C) 中间丝.
D) 以上都是。

16. 微管组织的破坏会导致：

A) 改善伤口愈合。
B) 发育缺陷和癌症。
C) 更强壮的骨骼。
D) 增强光合作用

17. 对/错：对于微管的动态性质及其运输能力而言，微管保持“健康”或有组织并不重要，因为真正提供运输能力的是驱动蛋白。

A) 对
B) 错

18. 可以说，驱动蛋白重链 (KHC) 及其与生物电的关系：

A) 没有关系
B) 运输重要的离子通道和生物电相关物质。
C) 影响癌症发病率。
D) B 和 C

19. 微管可能运输哪些离子？

A) 钠
B) 钾
C) 氯
D) 以上都是

20. 微管也可能：

A) 导电
B) 改变整个组织的电压，就像电线一样。
C) 部分充当电路
D) 以上都是

迈克尔·莱文 生物电 101 速成课程 第24课：微管与生物电：细胞骨架在信号传导中的作用 答案表

1. B

2. D

3. C

4. A

5. B

6. A

7. D

8. C

9. B

10. B

11. C

12. D

13. B

14. D

15. D

16. B

17. B

18. D

19. D

20. D