Biology Chapter 9 - Cytoskeleton and Cell Cycle

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Questions and Answers

What phase of the cell cycle does mitosis occur in?

G2 phase

Interphase

M phase (correct)

G1 phase

What is the average duration of interphase for mammalian cells?

90% of the cell cycle

1 week

1 hour

24 hours (correct)

What initiates the nucleation of a microtubule at the centrosome?

γ-tubulin (correct)

Centrioles

αβ-tubulin dimers

Kinetochore

Which class of microtubules is connected to chromosomes during mitosis?

Kinetochore microtubules Signup and view all the answers

What occurs during prophase in mitosis?

Internal membrane systems disperse Signup and view all the answers

What is the primary role of astral microtubules during mitosis?

Orient the spindle of division Signup and view all the answers

Which structures are a complex of proteins that make up the centrosome?

γTURCs and centrioles Signup and view all the answers

What percentage of the cell cycle does interphase constitute?

90% Signup and view all the answers

What happens to endocytosis and exocytosis during prophase?

Both processes stop Signup and view all the answers

What is the role of polar microtubules during mitosis?

Anchor the spindle poles Signup and view all the answers

What are microtubules primarily responsible for in nerve cells?

Maintaining axons Signup and view all the answers

Which type of microtubule is associated with motility structures like cilia and flagella?

Axonemal microtubules Signup and view all the answers

What is the basic subunit of a protofilament in microtubules?

αβ-heterodimer of tubulin Signup and view all the answers

Which of the following accurately describes the structure of microtubules?

Hollow, straight cylinders made of polymers called protofilaments Signup and view all the answers

What role do microtubules play during cell division?

They form mitotic and meiotic spindles. Signup and view all the answers

What defines cell polarity?

Asymmetrical distribution of cellular components Signup and view all the answers

What is a characteristic of microtubule-associated proteins (MAPs)?

They enhance microtubule rigidity. Signup and view all the answers

What happens to the cytoskeleton during cell division?

It undergoes significant reorganization. Signup and view all the answers

What is the primary role of microtubule-associated proteins (MAPs)?

Stabilize and promote assembly of microtubules Signup and view all the answers

Which statement is true regarding the composition of microtubules?

They form when α-tubulin and β-tubulin combine. Signup and view all the answers

How does the phosphorylation status of tau protein affect its function?

Abnormal phosphorylation levels are linked to Alzheimer's disease Signup and view all the answers

Which of the following is NOT a function of cytoplasmic microtubules?

Movement of water Signup and view all the answers

Which statement accurately describes the structure of a microtubule?

Microtubules consist of dimers of alpha and beta tubulin Signup and view all the answers

What is indicated by the polarity of microtubules?

Microtubules have distinct plus and minus ends Signup and view all the answers

What happens to the Golgi apparatus when cells are treated with nocodazole?

Golgi elements disperse into separate stacks throughout the cytoplasm Signup and view all the answers

What defines the mechanism of kinesin movement along microtubules?

Kinesin walks in a hand-over-hand mechanism, powered by ATP hydrolysis Signup and view all the answers

What is the role of microtubule-organizing centers (MTOCs) in a cell?

MTOCs control the assembly location and number of microtubules Signup and view all the answers

Kinesin and dynein motor proteins are responsible for what type of movement?

Unidirectional movement along microtubule tracks Signup and view all the answers

What process describes the alternating growth and shrinkage of microtubules?

Dynamic instability Signup and view all the answers

What is the typical length of one kinesin step during movement?

8 nm Signup and view all the answers

Which factor influences the rate of kinesin movement along microtubules?

Concentration of ATP Signup and view all the answers

In what form can the nucleotide bound to the beta tubulin monomer exist?

Either GTP or GDP form Signup and view all the answers

What primarily regulates movement along microtubules?

Intrinsic properties of motor proteins Signup and view all the answers

What happens to motor proteins when energy input ceases?

They stop almost immediately Signup and view all the answers

What event occurs at the end of prophase involving the nuclear envelope?

The nuclear membrane undergoes mechanical disruption. Signup and view all the answers

Which microtubules are responsible for connecting to chromosomes during cell division?

Kinetochore microtubules Signup and view all the answers

During which phase are chromosomes aligned at the metaphase plate?

Metaphase Signup and view all the answers

What is the role of the contractile ring during cytokinesis?

To tighten and divide the cytoplasm Signup and view all the answers

What type of motor protein is primarily involved in separating polar microtubules during anaphase?

Kinesin Signup and view all the answers

Which process marks the completion of telophase?

Reassembly of the nuclear envelope Signup and view all the answers

What is the effect of phosphorylation on lamin proteins during prophase?

It causes de-polymerization of intermediate filaments. Signup and view all the answers

What maintains the structural integrity of the mitotic spindle?

Microtubules Signup and view all the answers

What happens to the Golgi apparatus at the end of prophase?

It undergoes fragmentation and partitioning. Signup and view all the answers

What happens to the cytoplasmic organelles during prophase?

Organelles like mitochondria and lysosomes remain intact. Signup and view all the answers

In which phase does the dynamic behavior of microtubules primarily involve both polymerization and depolymerization?

Prometaphase Signup and view all the answers

How do signals from the spindle midzone influence cytokinesis?

They guide the contraction of the contractile ring. Signup and view all the answers

Which of the following components is crucial for the dynamic properties of microtubules?

Tubulin subunits Signup and view all the answers

How do Rho-GTP binding proteins impact the contractile ring during cytokinesis?

They regulate the assembly and activation of the ring. Signup and view all the answers

Study Notes

Chapter 9 - Cytoskeleton, Cell Cycle, and Microtubules

Chapter 9 and 14 contain relevant information
The cytoskeleton, cell cycle, and microtubules are the focus

Cytoskeletal Components

Microtubules:
- Polymer subunit: αβ-tubulin heterodimers
- Structure: Hollow tube, typically 13 protofilaments
- Diameter: 25 nm
- Polarity: Plus and minus ends
- Nucleotide substrate: GTP
Microfilaments:
- Polymer subunit: G-actin monomers
- Structure: Two intertwined chains of F-actin
- Diameter: 7 nm
- Polarity: Plus and minus ends
- Nucleotide substrate: ATP
Intermediate Filaments:
- Polymer subunit: IF dimer
- Structure: Staggered overlaps of eight protofilaments
- Diameter: 8-12 nm
- Polarity: No known polarity
- Nucleotide substrate: None

Cytoskeleton Functions

Support: Provides structural support within cells
Intracellular transport: Facilitates movement of materials within the cell
Cell organization: Maintains and organizes cellular components
Cell shape: Influences cell shape and form
Movement: Enables cellular movement
- Examples: Intracellular transport, contractility, cell motility

Microtubules: Structure and Function

Cytoplasmic microtubules:
- Maintain axons in nerve cells
- Participate in mitotic and meiotic spindle formation
- Facilitate vesicle placement and movement
- Contribute to cell shape maintenance
Axonemal microtubules:
- Essential for ciliary and flagellar movement
- Involved in cilia and flagella structures
- Basal bodies are associated with cilia and flagella, and form connections
- The axoneme is a highly ordered bundle of microtubules that comprise the central shaft

Microtubules: Structure & Composition

Microtubules are hollow cylinders; usually 13 longitudinal arrays of polymers called protofilaments
The basic subunit is a heterodimer composed of α-tubulin and β-tubulin globular proteins
These tubs bind noncovalently to form an αβ-heterodimer

Microtubule-Associated Proteins (MAPs)

MAPs are proteins that interact with microtubules
They increase microtubule stability
They promote microtubule assembly
MAP activity is regulated by the addition/removal of phosphat groups from amino acid residue

Motor Proteins: Kinesins and Dyneins

Molecular motors, utilizing ATP energy to produce mechanical energy
Kinesins and dyneins move unidirectionally along microtubules
Some myosin motors move along microfilaments
Proteins connect microtubules and neurofilaments (e.g. plectin)

Cell Cycle (Chapter 14)

The cell cycle is a series of stages a cell progresses through, including
- A period of growth (interphase)
- A phase of division (mitotic, M phase)
Interphase often comprises the majority of the cell cycle, and extends from days to weeks or more in mammal cells, lasting roughly 24 hours, divided into G1, S, and G2 phases.
G1 (Gap 1): Cells grow and perform normal cellular functions, including the duplication of organelles.
S (Synthesis): DNA replication occurs; The amount of DNA in the cell doubles, and RNA and proteins are also synthesized.
G2 (Gap 2): The cell continues to grow and prepares for mitosis, which is the active process of cellular division.
M phase (Mitosis): The cell divides into two daughter cells.

Overview of M-Phase

Mitosis is divided into 5 phases: prophase, prometaphase, metaphase, anaphase, telophase.
Each phase includes distinct events and transitions

Microtubule Organizing Centers (MTOCs)

MTOCs help regulate the number, polarity, and assembly timing and location of microtubules
The centrosome is the best studied MTOC, a complex of proteins that includes:
- y-tubulin ring complexes that are important nucleation areas
- Two centrioles, which are cylinders of modified microtubules

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Description

This quiz covers the key concepts presented in Chapter 9 regarding the cytoskeleton, cell cycle, and microtubules. Learn about the structures and functions of microtubules, microfilaments, and intermediate filaments, including their polymer subunits and role in cell support and transport.