Retta - L4 part 2

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Questions and Answers

What characteristic distinguishes actin filaments from microtubules?

Actin filaments are composed of tubulin.

Actin filaments have a smaller diameter. (correct)

Actin filaments have a larger diameter.

Actin filaments are hollow structures.

Which of the following correctly describes the formation of microtubules?

Microtubules consist of a single type of monomer.

Microtubules are built from alpha and beta tubulin dimers. (correct)

Microtubules are formed exclusively from microfilaments.

Microtubules do not have any associated subunits.

What is the approximate diameter of a microtubule?

10 nm

25 nm (correct)

20 nm

7 nm

Which statement correctly describes the proteins forming actin filaments?

Actin filaments consist of globular subunits of actin. Signup and view all the answers

Why are intermediate filaments called 'intermediate'?

Their diameter is between microfilaments and microtubules. Signup and view all the answers

How are microtubules structurally oriented?

Microtubules have a hollow cylindrical structure formed by subunits disposed in an ordered manner. Signup and view all the answers

What type of structure do actin filaments exhibit?

Twisted chains of filaments Signup and view all the answers

What are the basic building blocks of actin filaments?

Globular proteins Signup and view all the answers

How do actin filaments influence cellular morphology?

By mediating the intracellular distribution of filaments Signup and view all the answers

What role do focal adhesions play in cellular attachment?

They anchor the cell to the extracellular matrix through actin filaments. Signup and view all the answers

What structural characteristic differentiates microtubules from actin filaments?

Microtubules are hollow cylindrical structures. Signup and view all the answers

What is the function of microtubules in neurons?

They facilitate the movement of vesicles along the axon. Signup and view all the answers

What happens to a filament when monomers are removed?

The filament shortens. Signup and view all the answers

Where do microtubules emanate from within the cell?

From the MicroTubule Organization Centre (MTOC). Signup and view all the answers

Which component plays a significant role in muscle contraction?

Actin filaments Signup and view all the answers

What is a key function of the actin cytoskeleton?

Promoting and shaping cellular protrusions. Signup and view all the answers

Which statement correctly describes the differences between actin filaments, microtubules, and intermediate filaments?

Actin filaments and microtubules possess polarity while intermediate filaments do not. Signup and view all the answers

What role do accessory proteins play in regulating cytoskeletal dynamics?

They facilitate the initial formation of filaments and influence polymerization. Signup and view all the answers

How do cells respond to environmental changes via their cytoskeleton?

By rapidly assembling and disassembling components to adapt movement. Signup and view all the answers

What is the structure and composition of microtubules?

They consist of cylindrical structures made from dimers of alpha and beta tubulin. Signup and view all the answers

Why are intermediate filaments described as having mechanical resistance?

They have a rope-like structure formed from elongated proteins. Signup and view all the answers

What is the primary role of actin and myosin interactions within the sarcomere?

To facilitate the contraction and relaxation of the muscle cell Signup and view all the answers

Which type of intermediate filament is specifically found in muscle cells?

Desmin Signup and view all the answers

What is the consequence of the absence of intermediate filaments in stressed cells?

Cells can detach from one another more easily Signup and view all the answers

What structure forms during cytokinesis to separate the two daughter cells?

Contractile ring Signup and view all the answers

What triggers the movement of neutrophils toward bacteria?

Chemotactic signals Signup and view all the answers

Which component is not part of the cytoskeleton?

Focal adhesions Signup and view all the answers

What is a notable feature of epidermolysis bullosa related to intermediate filaments?

Mutations in keratin genes Signup and view all the answers

How do microtubules contribute during mitosis?

They pull apart the chromosomes Signup and view all the answers

Which proteins are responsible for anchoring one cell to another in epithelial tissues?

Keratins Signup and view all the answers

What occurs at the leading edge of a migratory cell?

Extension of filaments pushing the plasma membrane Signup and view all the answers

What role does the nuclear lamina play in mitosis?

It must disassemble to allow the process of mitosis to occur. Signup and view all the answers

Where are microtubules primarily organized in eukaryotic cells?

From the microtubule organizing center. Signup and view all the answers

Which motor proteins are responsible for transporting cargo towards the periphery of the cell?

Kinesins Signup and view all the answers

What is the primary function of actin filaments in the context of cell migration?

To push the plasma membrane and form protrusions. Signup and view all the answers

Identify the structure that separates the front edge of a polarized migrating cell from the rear edge.

Focal adhesion Signup and view all the answers

What distinguishes cilia from microvilli?

Cilia have a motile function, while microvilli increase surface area. Signup and view all the answers

Which of the following structures is primarily responsible for cell shape and movement?

Actin filaments Signup and view all the answers

During cellular processes, how do motor proteins facilitate movement within the cell?

By moving along cytoskeletal structures. Signup and view all the answers

In a polarized cell, which would be considered the 'leading edge'?

The edge that guides migration forward. Signup and view all the answers

What would happen if the nuclear lamina does not disassemble during mitosis?

The nuclear structure would remain intact. Signup and view all the answers

Study Notes

Microfilaments and Microtubules

Actin filaments, known as microfilaments, have a diameter of 7 nm, making them the thinnest cytoskeletal components.
Microtubules are larger, with a diameter of 25 nm, and are composed of tubulin proteins.
Intermediate filaments are so named because their diameter is between that of microfilaments and microtubules.
Microfilaments are made of globular actin subunits that twist to form protofilaments, which further twist to create the filament structure.
Microtubules are composed of dimers formed by alpha and beta tubulin subunits arranged in a hollow cylindrical structure.
Both microfilaments and microtubules can dynamically elongate or shorten based on the addition or removal of monomeric subunits.

Cytoskeletal Filaments and Cell Morphology

Actin filaments contribute to the structural integrity of the cell, supporting processes like the formation of microvilli.
The distribution and dynamics of actin filaments influence cellular shape and morphology, especially during cell migration.
Cell attachment to the extracellular matrix is mediated by focal adhesions linked to actin filaments, crucial for tissue stability.
Actin filaments are essential in muscle contraction, forming the sarcomere structure, which is key in muscular function.

Microtubule Organization and Functions

Microtubules originate from the Microtubule Organization Centre (MTOC) near the nucleus, extending in star-like patterns throughout the cell.
They provide a structural framework for the intracellular transport of various cargo, including vesicles and organelles, in both directions using motor proteins.
Kinesin moves cargo toward the cell periphery, while dyneins move it toward the cell center, reflecting the dynamic nature of microtubule function.

Intermediate Filaments

Intermediate filaments are composed of various proteins, including lamins (forming the nuclear lamina), keratins (found in epithelial cells), and vimentin (in connective tissues).
They provide mechanical stability through cytoskeletal integrity, helping to resist cellular stress and maintain tissue structure.
Diseases such as epidermolysis bullosa arise from mutations in intermediate filament proteins, leading to fragile skin.

Dynamic Behavior During Cell Division

During cell division, microtubules form the mitotic spindle that separates chromosomes, while actin filaments create a contractile ring for cytokinesis, dividing the cytoplasm of the daughter cells.
The coordinated action of actin filaments and microtubules enables effective cell division, which includes both mitosis and the cytokinetic phase of division.

Cellular Organization and Migration

The cytoskeleton plays a significant role in determining cellular organization and polarity, enabling cells to respond to external signals for movement.
Migratory cells exhibit distinct leading and trailing edges; the leading edge has extensive protrusions for movement, while the rear edge contracts and detaches from the substrate.### Cytoskeleton Overview
The cytoskeleton consists of different filament types, providing structural support and organization in epithelial cells.
Key components include actin filaments, microtubules, and intermediate filaments; each performing unique functions.

Cellular Polarity and Attachment

Actin filaments and microtubules exhibit polarity with distinct plus and minus ends, aiding in directionality of cellular functions.
Intermediate filaments lack polarity, presenting a uniform structure.
Epithelial cells utilize the cytoskeleton for anchoring to the extracellular matrix, facilitating adhesion between cells.

Dynamics of Cytoskeleton

Migratory cells exhibit rapid assembly and disassembly of cytoskeletal components, especially actin, enabling swift responses to environmental changes.
Actin filaments undergo processes of elongation and shortening, driven by the reassembly of globular actin subunits.

Microtubule Structure and Function

Microtubules are composed of dimeric subunits of alpha and beta tubulin, forming protofilaments that combine into a hollow, cylindrical structure.
Microtubules can grow or shrink quickly, responding to cellular needs by adding or removing subunits.

Intermediate Filament Characteristics

Intermediate filaments are unique, forming from elongated proteins in a staggered manner, resulting in a rope-like structure that provides mechanical strength.
These filaments associate both longitudinally and laterally for increased stability.

Accessory Proteins and Regulation

Accessory proteins play a critical role in regulating the dynamics of cytoskeletal components, influencing polymerization and depolymerization.
Microtubule organizing centers initiate the assembly of microtubules through a nucleation process.

Types of Accessory Proteins

Nucleating proteins help form initial filaments, encouraging growth from nucleated structures.
Monomer sequestering proteins prevent premature assembly by binding to monomers.
Lateral cross-linking proteins stabilize bundles of filaments, enhancing structural integrity.
Motor proteins, such as myosin, facilitate movement by enabling reciprocal sliding of filaments, contributing to cell contractility.
Capping proteins regulate filament stability and growth at both ends of the filaments.
Severing proteins enhance disassembly by cutting filaments into shorter segments, speeding up the process compared to gradual subunit removal.

Significance of Cytoskeletal Dynamics

The cytoskeleton's adaptability allows cells to sense and respond to environmental signals, including chemotactic cues.
Changes in cytoskeletal dynamics can result in cellular movements, attachment stability, and division in response to stimuli.

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Description

Explore the two types of cytoskeletal components: actin filaments and microtubules. This quiz covers their diameters, structural differences, and functions in the cytoskeleton. Test your knowledge on these fundamental cellular structures!