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Questions and Answers
What are the major structural elements of the cytoskeleton?
What are the major structural elements of the cytoskeleton?
What are the components of microtubules and microfilaments?
What are the components of microtubules and microfilaments?
What are the bacterial cytoskeletal elements involved in DNA segregation and cell shape?
What are the bacterial cytoskeletal elements involved in DNA segregation and cell shape?
Which proteins use ATP to drive vesicle or organelle transport or to generate sliding forces between microtubules?
Which proteins use ATP to drive vesicle or organelle transport or to generate sliding forces between microtubules?
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Which proteins promote depolymerization of microtubules by binding to tubulin heterodimers and preventing their polymerization?
Which proteins promote depolymerization of microtubules by binding to tubulin heterodimers and preventing their polymerization?
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Which proteins act at the ends of microtubules and promote the peeling of subunits from the ends?
Which proteins act at the ends of microtubules and promote the peeling of subunits from the ends?
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Which proteins sever microtubules?
Which proteins sever microtubules?
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What contributes to the dynamic instability of microtubules?
What contributes to the dynamic instability of microtubules?
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What gives microtubules inherent polarity with plus and minus ends?
What gives microtubules inherent polarity with plus and minus ends?
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What nucleates the assembly of new microtubules in microtubule-organizing centers (MTOCs)?
What nucleates the assembly of new microtubules in microtubule-organizing centers (MTOCs)?
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What is the primary function of microfilaments?
What is the primary function of microfilaments?
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What does actin polymerize to form?
What does actin polymerize to form?
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How are F-actin filaments structured?
How are F-actin filaments structured?
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Which protein is found at sites where intermediate filaments connect to microfilaments and microtubules?
Which protein is found at sites where intermediate filaments connect to microfilaments and microtubules?
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What is the fundamental subunit of intermediate filament proteins?
What is the fundamental subunit of intermediate filament proteins?
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What role do intermediate filaments play in neurons?
What role do intermediate filaments play in neurons?
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How do two IF polypeptides align in the basic structural unit of intermediate filaments?
How do two IF polypeptides align in the basic structural unit of intermediate filaments?
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Which protein binds ADP-G-actin and F-actin, increasing turnover at the minus end of microfilaments and severing filaments to create new plus ends?
Which protein binds ADP-G-actin and F-actin, increasing turnover at the minus end of microfilaments and severing filaments to create new plus ends?
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What protein is crucial for the formation of loose networks of crosslinked actin filaments, splicing and joining intersecting microfilaments?
What protein is crucial for the formation of loose networks of crosslinked actin filaments, splicing and joining intersecting microfilaments?
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Which protein facilitates indirect force exertion during cell movement by linking microfilaments to the plasma membrane?
Which protein facilitates indirect force exertion during cell movement by linking microfilaments to the plasma membrane?
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What is the primary function of microfilaments?
What is the primary function of microfilaments?
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What gives microtubules inherent polarity with plus and minus ends?
What gives microtubules inherent polarity with plus and minus ends?
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What are the roads and cars in the context of cellular movement?
What are the roads and cars in the context of cellular movement?
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What gives myofibrils a pattern of alternating dark and light bands in skeletal muscle?
What gives myofibrils a pattern of alternating dark and light bands in skeletal muscle?
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What constitutes a calcium-sensitive switch that activates contraction in striated muscle?
What constitutes a calcium-sensitive switch that activates contraction in striated muscle?
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What model explains muscle contraction as due to thin filaments sliding past thick filaments?
What model explains muscle contraction as due to thin filaments sliding past thick filaments?
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What constitutes the thick filaments in skeletal muscle?
What constitutes the thick filaments in skeletal muscle?
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Which motor protein is involved in ATP-dependent transport towards the plus ends of microtubules?
Which motor protein is involved in ATP-dependent transport towards the plus ends of microtubules?
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What is the structure that consists of an axoneme connected to a basal body and aids in movement through fluid environments?
What is the structure that consists of an axoneme connected to a basal body and aids in movement through fluid environments?
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What is the rate of transporting proteins in fast axonal transport?
What is the rate of transporting proteins in fast axonal transport?
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What did Chargaff observe about the amount of nucleotides in DNA?
What did Chargaff observe about the amount of nucleotides in DNA?
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What did Watson and Crick propose about the structure of DNA?
What did Watson and Crick propose about the structure of DNA?
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What was Erwin Chargaff's significant observation regarding DNA composition?
What was Erwin Chargaff's significant observation regarding DNA composition?
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What did Chargaff's rules reveal about the base composition of DNA?
What did Chargaff's rules reveal about the base composition of DNA?
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What was known about the bases in DNA that allowed Watson and Crick to propose the double-helix model?
What was known about the bases in DNA that allowed Watson and Crick to propose the double-helix model?
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What did X-ray diffraction data from Rosalind Franklin reveal about DNA?
What did X-ray diffraction data from Rosalind Franklin reveal about DNA?
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What is the diameter of the double helix model of DNA?
What is the diameter of the double helix model of DNA?
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What is the primary mechanism suggested for DNA replication by the double helix model?
What is the primary mechanism suggested for DNA replication by the double helix model?
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What is the unit used to measure DNA length?
What is the unit used to measure DNA length?
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What is the role of topoisomerases in DNA?
What is the role of topoisomerases in DNA?
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Study Notes
Microtubules: Structure, Assembly, and Function
- Microtubules are the largest structural elements of the cytoskeleton, involved in various cellular functions.
- There are two types of microtubules: cytoplasmic and nuclear, responsible for different functions such as maintaining axons and cell shape, and forming spindles.
- Microtubules are composed of tubulin heterodimers, forming straight, hollow cylinders of varied lengths.
- Protofilaments, made of α and β tubulin heterodimers, give microtubules inherent polarity with plus and minus ends.
- Microtubules form through the reversible polymerization of tubulin dimers in the presence of GTP and Mg2+, with distinct lag and elongation phases.
- Microtubule assembly depends on the concentration of tubulin dimers and the critical concentration, leading to growth or disassembly.
- The plus end of microtubules grows faster due to the addition of tubulin dimers, while treadmilling occurs when free tubulin concentration varies at the plus and minus ends.
- GTP hydrolysis contributes to the dynamic instability of microtubules, leading to periods of growth, shrinkage, catastrophe, and rescue.
- Microtubules originate from microtubule-organizing centers (MTOCs) containing γ-tubulin, which nucleates the assembly of new microtubules.
- MTOCs organize and polarize microtubules within cells, with the minus ends anchored in the MTOC, leading to dynamic growth and shrinkage at the plus ends.
- Centrosomes, containing γ-tubulin ring complexes, are MTOCs that nucleate the assembly of new microtubules away from the centrosome.
- Loss of γ-TuRCs prevents a cell from nucleating microtubules, impacting cellular functions.
Actin and Intermediate Filaments: Structure and Function
- Myosin subfragment 1 (S1) binds and decorates actin microfilaments in a distinctive arrowhead pattern, defining the plus and minus ends.
- Actin monomers in the cytosol bind ATP, which is converted to ADP upon complex formation, reflecting the polarity of microfilaments.
- Actin-binding proteins regulate the polymerization, length, and organization of actin, controlling nucleation, elongation, severing, and network association.
- Thymosin β4 and profilin compete for G-actin binding, regulating the availability of ATP-bound G-actin for microfilament assembly.
- ADF/cofilin binds ADP-G-actin and F-actin, increasing turnover at the minus end of microfilaments and severing filaments to create new plus ends.
- Capping proteins like CapZ and tropomodulins bind to the plus and minus ends of microfilaments, respectively, regulating filament growth.
- Filamin, a protein, is crucial for the formation of loose networks of crosslinked actin filaments, splicing and joining intersecting microfilaments.
- Actin can be bundled into highly ordered arrays like focal contacts or focal adhesions, with proteins like α-actinin and fascin playing prominent roles.
- Microfilaments are connected to the plasma membrane by crosslinks made of myosin I, calmodulin, fimbrin, and villin, exerting force during cell movement.
- Proteins like band 4.1, ezrin, radixin, moesin, spectrin, and ankyrin link microfilaments to the plasma membrane, facilitating indirect force exertion during cell movement.
- Actin forms dendritic networks with the help of the Arp2/3 complex, nucleated by proteins like WASP and WAVE/Scar.
- Intermediate filaments (IFs) are abundant in many animal cells, with keratin being an important IF in structures growing from animal skin, supporting the entire cytoskeleton.
Microtubule-Based and Microfilament-Based Movement Inside Cells
- Microtubules act as tracks for organelle and vesicle transport, with inbound and outbound traffic
- Kinesins and dyneins are microtubule-associated motor proteins that enable movement
- Fast axonal transport involves transporting proteins at a rate of about 2 μm/sec
- Kinesin is involved in ATP-dependent transport towards the plus ends of microtubules
- Kinesins are a large family of proteins classified based on amino acid sequence
- Cytoplasmic dynein moves cargo towards the minus ends, aided by protein complexes called dynactin
- Microtubule motors shape the endomembrane system and facilitate vesicle transport
- Cilia and flagella are structures that aid in movement through fluid environments
- Cilia and flagella consist of an axoneme connected to a basal body
- Doublet sliding within the axoneme causes cilia and flagella to bend
- Myosins, a large superfamily, interact with actin microfilaments and are involved in various cellular events
- Muscle contraction is mediated by intracellular filaments, such as thin and thick filaments in skeletal muscle cells
DNA Structure and Packaging
- X-ray diffraction data from Rosalind Franklin revealed DNA's long thin helical structure
- Watson and Crick produced the double helix model based on Franklin's data
- The double helix model has 10 base pairs per turn and a diameter of 2 nm
- Purine-pyrimidine pairing in the double helix is consistent with Chargaff’s rules
- The double helix model suggested a mechanism for DNA replication
- DNA length is measured in base pairs (bp) with larger stretches in kilobases (kb)
- DNA can exist in right-handed (BDNA) and left-handed (Z-DNA) helical forms
- DNA can be interconverted between relaxed and supercoiled forms
- Supercoiling helps make chromosomal DNA more compact
- Topoisomerases induce and relax supercoils in DNA
- Strand separation (DNA denaturation) can be induced by raising temperature or pH
- Very long DNA molecules must be packaged into the cell's nucleus in eukaryotes
Studying That Suits You
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Description
Test your knowledge of microtubules with this quiz on their structure, assembly, and function. Explore the composition of microtubules, their polymerization process, and the impact of GTP hydrolysis. Dive into the role of microtubule-organizing centers (MTOCs) and centrosomes in nucleating and organizing microtubules within cells.
