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Questions and Answers
What is the main function of the centrosome in the cell cycle?
What is the main function of the centrosome in the cell cycle?
What does the M phase of the cell cycle include?
What does the M phase of the cell cycle include?
Which stage comes immediately after prophase during mitosis?
Which stage comes immediately after prophase during mitosis?
What does nucleation of a microtubule begin with?
What does nucleation of a microtubule begin with?
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How long does interphase usually last for mammalian cells?
How long does interphase usually last for mammalian cells?
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Which microtubule is responsible for connecting to chromosomes during mitosis?
Which microtubule is responsible for connecting to chromosomes during mitosis?
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What characterizes the early event of prophase?
What characterizes the early event of prophase?
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What is one consequence of genetic defects in centrosome-associated proteins?
What is one consequence of genetic defects in centrosome-associated proteins?
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What happens to internal membrane systems during prophase?
What happens to internal membrane systems during prophase?
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Which type of microtubule projects toward the cell cortex during division?
Which type of microtubule projects toward the cell cortex during division?
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What role do cytoplasmic microtubules play in nerve cells?
What role do cytoplasmic microtubules play in nerve cells?
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What are the two types of microtubules found in cells?
What are the two types of microtubules found in cells?
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What is the main function of axonemal microtubules?
What is the main function of axonemal microtubules?
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What do microtubules primarily consist of?
What do microtubules primarily consist of?
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What structure do microtubules help form during cell division?
What structure do microtubules help form during cell division?
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What is a key characteristic of microtubules?
What is a key characteristic of microtubules?
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Which proteins are typically associated with microtubules?
Which proteins are typically associated with microtubules?
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What is the structural composition of a protofilament in microtubules?
What is the structural composition of a protofilament in microtubules?
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How does cell polarity impact specialized functions within a cell?
How does cell polarity impact specialized functions within a cell?
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Which of the following is NOT a function of cytoplasmic microtubules?
Which of the following is NOT a function of cytoplasmic microtubules?
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What is the primary role of microtubule-associated proteins (MAPs)?
What is the primary role of microtubule-associated proteins (MAPs)?
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What specific effect does tau phosphorylation have in the context of Alzheimer’s disease?
What specific effect does tau phosphorylation have in the context of Alzheimer’s disease?
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Which proteins make up the building blocks of microtubules?
Which proteins make up the building blocks of microtubules?
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What happens to the Golgi apparatus when cells are treated with nocodazole or colchicine?
What happens to the Golgi apparatus when cells are treated with nocodazole or colchicine?
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How do kinesin and dynein differ in their movement on microtubules?
How do kinesin and dynein differ in their movement on microtubules?
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What is 'dynamic instability' in relation to microtubules?
What is 'dynamic instability' in relation to microtubules?
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What role do microtubule-organizing centers (MTOCs) serve in a cell?
What role do microtubule-organizing centers (MTOCs) serve in a cell?
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Which statement correctly describes the behavior of motor proteins along microtubules?
Which statement correctly describes the behavior of motor proteins along microtubules?
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What type of energy conversion do molecular motors like kinesin and dynein perform?
What type of energy conversion do molecular motors like kinesin and dynein perform?
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What is the main consequence of an excess of phosphorylated tau protein?
What is the main consequence of an excess of phosphorylated tau protein?
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Which nucleotide is the β-tubulin monomer able to bind?
Which nucleotide is the β-tubulin monomer able to bind?
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Which structural characteristic of microtubules contributes to their polarity?
Which structural characteristic of microtubules contributes to their polarity?
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What happens to a motor protein when energy input ceases?
What happens to a motor protein when energy input ceases?
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What occurs to the nuclear envelope at the end of prophase?
What occurs to the nuclear envelope at the end of prophase?
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During prometaphase, how are chromosomes moved into the center of the cell?
During prometaphase, how are chromosomes moved into the center of the cell?
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What is the role of kinetochores during mitosis?
What is the role of kinetochores during mitosis?
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What happens to the sister chromatids during anaphase?
What happens to the sister chromatids during anaphase?
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What structural change occurs to microtubules during anaphase?
What structural change occurs to microtubules during anaphase?
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Which class of microtubules extends toward the cell cortex during mitosis?
Which class of microtubules extends toward the cell cortex during mitosis?
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What marks the transition of a cell from metaphase to anaphase?
What marks the transition of a cell from metaphase to anaphase?
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What is the role of actin microfilaments during cytokinesis?
What is the role of actin microfilaments during cytokinesis?
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How do the nuclear envelopes behave during telophase?
How do the nuclear envelopes behave during telophase?
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What is the function of myosin during cytokinesis?
What is the function of myosin during cytokinesis?
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Which of the following components is NOT part of the nuclear envelope?
Which of the following components is NOT part of the nuclear envelope?
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What regulates the cell cycle during mitosis?
What regulates the cell cycle during mitosis?
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What processes govern the dynamics of microtubules during mitosis?
What processes govern the dynamics of microtubules during mitosis?
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Which stage of mitosis is characterized by fully condensed chromosomes aligned at the metaphase plate?
Which stage of mitosis is characterized by fully condensed chromosomes aligned at the metaphase plate?
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What describes the movement of chromatids during the progression of prometaphase?
What describes the movement of chromatids during the progression of prometaphase?
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Study Notes
Chapter 9 - Part 1: The Cytoskeleton, Cell Cycle, and Microtubules
- This chapter covers the cytoskeleton, cell cycle, and microtubules.
- Required reading includes sections of Chapter 9 and Chapter 14.
Cytoskeletal Component Properties
- Table 13-1 outlines properties of microtubules, microfilaments, and intermediate filaments.
- Microtubules: Polymer subunit is αβ-tubulin heterodimers. Structure is a hollow tube with 13 protofilaments. Diameter is 25 nm. Polarity: plus and minus ends. Nucleotide substrate: GTP.
- Microfilaments: Polymer subunit is G-actin monomers. Structure is two intertwined F-actin chains. Diameter is 7 nm. Polarity: plus and minus ends. Nucleotide substrate: ATP.
- Intermediate Filaments: Polymer subunit is IF dimers. Structure is eight protofilaments staggered. Diameter is 8-12 nm. Polarity: none. Nucleotide substrate: none.
Table 9.1: Properties of Microtubules, Intermediate Filaments, and Actin Filaments
- Microtubules: Subunits: GTP-αβ-tubulin heterodimer; Preferential site of incorporation: + end (β-tubulin); Polarity: Yes; Enzymatic activity: GTPase; Motor proteins: Kinesins, dyneins; Major associated proteins: MAPS; Structure: Stiff, hollow, inextensible tube; Dimensions: 25 nm outer diameter; Distribution: All eukaryotes
- Intermediate filaments: Subunits ~70 different proteins; likely incorporated as tetramers; Preferential site of incorporation: Internal; Polarity: No; Enzymatic activity: None; Motor proteins: None; Major associated proteins: Plakins; Structure: Tough, flexible, extensible filament; Dimensions: 10-12 nm diameter; Distribution: Animals
- Actin filaments: Subunits: ATP-actin monomers; Preferential site of incorporation: + end (barbed); Polarity: Yes; Enzymatic activity: ATPase; Motor proteins: Myosins; Major associated proteins: Actin-binding proteins; Structure: Flexible, inextensible helical filament; Dimensions: 8 nm diameter; Distribution: All eukaryotes
Roles of Cytoskeletal Components:
- Cytoskeletal components provide structural support, intracellular transport, cell organization, and contribute to various cellular activities.
Cytoskeletal component roles in different cell types
- **Epithelial cells: **Microfilaments, microtubules, and intermediate filaments provide support, and intracellular transport mechanisms.
- Nerve cells (neurons): Microtubules play a crucial role in maintaining the axon structure, which is essential for neuronal signaling.
- Dividing cell: Microtubules are involved in the cell division process. Motor proteins facilitate these cellular functions.
Cytoskeleton and Signaling
- Cytoskeleton plays a key role in cellular signaling.
- Disassembly and reassembly of filaments within the cytoskeleton can occur rapidly due to a signal like a nutrient.
- Cytoskeleton organization and movement are linked to signal transduction pathways.
Chapter 9 - Section 9.2: Structure and Function of Microtubules
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Microtubules are the largest of the cytoskeletal components in cells.
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There are two main types: cytoplasmic and axonemal.
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Cytoplasmic microtubules are involved in many cellular functions like maintaining axons, forming mitotic/meiotic spindles for cell division, and moving vesicles.
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Axonemal microtubules are organized structures like cilia and flagella, crucial for cell movement.
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Microtubules are hollow cylindrical polymers of α-tubulin and β-tubulin heterodimers. Protofilaments (typically 13) run longitudinally, forming the microtubule wall. The two ends of a microtubule have distinctive chemical and structural properties (minus and plus).
Section 9.2: Microtubule-Associated Proteins (MAPs)
- Microtubules typically have additional proteins associated called microtubule-associated proteins (MAPs).
- MAPs increase microtubule stability and promote their assembly.
- MAP activity is modulated via the addition and removal of phosphate groups from amino acid residues.
- An elevated level of phosphorylation of a specific MAP called tau is associated with Alzheimer's disease.
Section 9.2: Structure and Composition of Microtubules
- Microtubules are straight, hollow cylinders of variable length. Composed of 13 longitudinal polymers called protofilaments.
- The basic unit is a heterodimer of α-tubulin and β-tubulin (globular proteins) bound noncovalently.
- αβ-tubulin heterodimers bind noncovalently to form protofilaments.
Section 9.5: Microtubule Dynamics
- The dissociation rate of a GDP-tubulin dimer is faster than that of a GTP-tubulin dimer.
- Microtubules exhibit dynamic instability, alternating between growing and shrinking phases.
Chapter 9 - Section 9.5: Microtubule Organizing Centers (MTOCs)
- Microtubules' function depends on location and orientation.
- Microtubule organizing centers (MTOCs) control the number, polarity, protofilaments, and assembly time/location of microtubules.
- Centrosomes are the best-studied MTOC.
Chapter 14 - Section 14.1: The Cell Cycle: Phases of the Cell Cycle
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Cell cycle: a series of stages a cell goes through consisting of M phase (including mitosis and cytokinesis) and interphase (G1, S, G2).
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Mitosis lasts approximately an hour and involves nuclear division.
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Interphase (G1, S, G2): constitutes the majority of the cell cycle(~90%), lasting days, weeks or longer (mammalian cells average ~24 hours).
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G1: Cell growth and normal metabolism, organelles duplicate
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S: DNA replication and chromosome duplication
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G2: Cell growth and preparation for mitosis
Chapter 14 - Section 14.2: Overview of M Phase: Mitosis and Cytokinesis
- Mitosis is divided into five distinct stages: prophase, prometaphase, metaphase, anaphase, and telophase. Each stage involves specific changes in chromosomes and cellular structures.
Chapter 14 - Section 14.2: Prophase
- Protein synthesis halts.
- Internal membrane systems (associated with microtubules) disperse.
- Endocytosis and exocytosis stop.
- Each centrosome, formed during S phase, becomes a microtubule organizing center (MTOC) initiating the formation of microtubules.
Chapter 14 - Section 14.2: Prometaphase
- The mitotic spindle is formed, and chromosomes are moved towards the center of the cell.
- A single kinetochore is connected to microtubules from both spindle poles.
- Kinetochores are protein complexes associated with centromeres.
Chapter 14 - Section 14.2: Metaphase
- Cells in metaphase have fully condensed chromosomes aligned at the metaphase plate, equidistant from the spindle poles.
- Chromosomes are aligned in the center of the cell (metaphase plate)
Chapter 14 - Section 14.2: Anaphase
- Tubulin subunits are lost from both ends of kinetochore microtubules.
- Tubulin subunits are added to polar microtubules at their plus end.
- Motor proteins push polar microtubules apart
Chapter 14 - Section 14.2: Telophase and Cytokinesis
- Mitosis ends with telophase, where nuclear envelopes reform around separated chromosomes.
- Cytokinesis is the final step, partitioning the cytoplasm into two daughter cells.
- Cytokinesis involves signals emanating from the spindle midzone and contraction of a belt-like actin microfilament (contractile ring) just below the plasma membrane. This contraction is generated by the interaction of actin protein and myosin motor protein.
Chapter 9 - Section 9.4: Motor Proteins: Kinesins and Dyneins
- Motor proteins use energy from ATP hydrolysis to move unidirectionally along cytoskeletal tracks.
- Three categories of molecular motors: Kinesin and dynein move along microtubules; Myosin moves along microfilaments.
Chapter 9 - Section 9.5: Microtubule Organizing Centers (MTOCs)
- Microtubule organizing centers (MTOCs) control microtubule number, polarity, and assembly.
- Centrosomes are the most well-studied MTOC.
- Centrosomes consist of a complex of proteins that contain nucleating sites for microtubule assembly (γ-tubulin ring complexes).
- Centrioles are short cylinders of modified microtubules.
Chapter 9 - Section 9.5: Nucleation of a microtubule
- Microtubule nucleation begins with y-tubulin at the minus end.
- y-TURC (y-tubulin ring complex) is responsible for initiating nucleation.
- y-tubulin complex is essential for initiating assembly of microtubules.
Section 14.2: Three types of microtubules
- Mitotic spindle includes:
- Kinetochore microtubules: connect to chromosomes
- Astral microtubules: project toward the cell cortex
- Polar microtubules: interact with microtubules from the opposite pole.
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