Microtubules by Jessica Belliveau: Difference between revisions
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MT are used as a transportation network to transport membrane vesicles through the cell. One example of using MT for transport is in nerve cell axons. The axons can be over a meter long, however, ribosomes are only located in the cell body and dendrites. Using the MT network, proteins, membrane vesicles, and mitochondria are transported from the cell body and dendrites to the axons. MT also transport cellular stress responses throughout the cell. The two main types of motor proteins are dyneins and kinesins. Dyneins consist of light and intermediate chains that are ATP-binding domain that provide the energy necessary to move the protein towards the negative end. Kinesins consist of two heavy chains and two light chains. The head domains of the heavy chains bind to ATP, providing energy for movement along the MT. The other end of the kinesin is used to attach and carry other molecules to the positive end of the MT. | MT are used as a transportation network to transport membrane vesicles through the cell. One example of using MT for transport is in nerve cell axons. The axons can be over a meter long, however, ribosomes are only located in the cell body and dendrites. Using the MT network, proteins, membrane vesicles, and mitochondria are transported from the cell body and dendrites to the axons. MT also transport cellular stress responses throughout the cell. The two main types of motor proteins are dyneins and kinesins. Dyneins consist of light and intermediate chains that are ATP-binding domain that provide the energy necessary to move the protein towards the negative end. Kinesins consist of two heavy chains and two light chains. The head domains of the heavy chains bind to ATP, providing energy for movement along the MT. The other end of the kinesin is used to attach and carry other molecules to the positive end of the MT. | ||
[[Image: | [[Image:MotorProteins.jpg|frame|Figure 3. Dyneins and Kinesins moving along a microtubule.]] |
Revision as of 22:38, 22 March 2017
Introduction
Microtubules, along with actin and intermediate filaments, compose the cytoskeleton of eukaryotic cell. Microtubules are involved with mitosis, cell movement, intracellular transport, and cell structure. Microtubules (MT) are made up of the globular protein, tubulin. The two main forms of tubulin found in MT are α-tubulin and β-tubulin. α-tubulin and β-tubulin spontaneously bind to form a dimer and many tubulin dimers form together into protofilaments. The protofilaments assemble into MT. Microtubules are polar structures with a fast-growing positive end and a slow-growing negative end. The structure and dynamics of MT are shown in Figure 1. At the site of MT attachment to a cellular unit at the slow-growing negative end are γ-tubulin rings, responsible for the nucleation of MT.
Mitosis
Mitosis is the process of nuclear division represented in four stages: prophase, metaphase, anaphase, telophase, followed by cytokinesis. MT, also called spindle fibers, are responsible for establishing cell polarity and pulling the sister chromatids apart into daughter chromatids on opposite sides of the cells. MT attach to the chromosomes at the centrosome and through depolymerazation, pull the daughter chromosome. The centrosome has been traditionally thought as the MT assembly initiation site, however, it is now know MT attach to organelles such as the endoplasmic reticulum (ER).
Through the transition from interphase to mitotic phases, the MT structure completely restructures as shown in Figure 2. First, the rates of MT disassembly increase leading to a decrease in cell polarity. Second, the rate of MT growth starting from the centosomes increase, reestablishing cell polarity in the direction the MT will eventually pull the daughter chromatids.
Intracellular Transport and Cell Movement
Intracellular Transport
MT are used as a transportation network to transport membrane vesicles through the cell. One example of using MT for transport is in nerve cell axons. The axons can be over a meter long, however, ribosomes are only located in the cell body and dendrites. Using the MT network, proteins, membrane vesicles, and mitochondria are transported from the cell body and dendrites to the axons. MT also transport cellular stress responses throughout the cell. The two main types of motor proteins are dyneins and kinesins. Dyneins consist of light and intermediate chains that are ATP-binding domain that provide the energy necessary to move the protein towards the negative end. Kinesins consist of two heavy chains and two light chains. The head domains of the heavy chains bind to ATP, providing energy for movement along the MT. The other end of the kinesin is used to attach and carry other molecules to the positive end of the MT.