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Questions and Answers

What is the cytoskeleton?

A network of protein filaments extending throughout the cytoplasm of eukaryotic cells.

What are the three main types of protein filaments that make up the cytoskeleton?

Actin filaments, Microtubules, Collagen filaments
Actin filaments, Microtubules, Intermediate filaments (correct)
Actin filaments, Myosin filaments, Intermediate filaments

The cytoskeleton is rigid and does not change shape.

False (B)

What is the primary role of actin filaments in the cytoskeleton?

To provide structural support and to be involved in various types of cellular movement. Signup and view all the answers

What is the diameter of actin filaments?

7 nanometers Signup and view all the answers

What are the two main types of actin-binding proteins?

Actin-bundling proteins and proteins that organize actin networks. Signup and view all the answers

What are the two main types of actin bundles?

Parallel bundles and contractile bundles. Signup and view all the answers

Why are red blood cells useful for studying the cortical cytoskeleton?

They lack a nucleus and organelles, making it easier to isolate the plasma membrane and associated proteins. Signup and view all the answers

What is the function of spectrin in the red blood cell cytoskeleton?

It forms a network with actin filaments that helps maintain the biconcave shape of red blood cells. Signup and view all the answers

What is the function of ankyrin in the red blood cell cytoskeleton?

It links the spectrin-actin network to the plasma membrane by binding to spectrin and a transmembrane protein called band 3. Signup and view all the answers

What is the function of protein 4.1 in the red blood cell cytoskeleton?

It links spectrin-actin junctions to the transmembrane protein glycophorin. Signup and view all the answers

What is the function of dystrophin in muscle cells?

It links actin filaments to transmembrane proteins in the plasma membrane, which in turn link to the extracellular matrix. Signup and view all the answers

Patients with muscular dystrophy have an increase in dystrophin levels.

False (B) Signup and view all the answers

What are stress fibers?

Large actin bundles that are contractile bundles, cross-linked by alpha-actinin and stabilized by tropomyosin. Signup and view all the answers

What are focal adhesions?

Sites of attachment for stress fibers to the extracellular matrix, mediated by transmembrane proteins called integrins. Signup and view all the answers

What are adherens junctions?

Cell-cell contacts that form a continuous adhesion belt around each cell, mediated by transmembrane proteins called cadherins. Signup and view all the answers

What are microvilli?

Fingerlike extensions of the plasma membrane that are abundant on cells involved in absorption. Signup and view all the answers

What is the brush border?

A layer of microvilli on the apical surface of epithelial cells lining the intestine. Signup and view all the answers

What is the function of myosin I in microvilli?

It helps attach actin bundles to the plasma membrane in association with the calcium-binding protein calmodulin. Signup and view all the answers

What are pseudopodia?

Extensions of moderate width that are responsible for phagocytosis and movement of amoebas. Signup and view all the answers

What are lamellipodia?

Broad, sheetlike extensions at the leading edge of fibroblasts. Signup and view all the answers

What are filopodia?

Thin projections of the plasma membrane supported by actin bundles. Signup and view all the answers

What are the three stages of cell movement across a surface?

Extension of the leading edge, attachment of the leading edge to the substratum, and retraction of the rear of the cell into the cell body. Signup and view all the answers

What is the role of Rho proteins in cell movement?

They regulate the formation of cell surface protrusions in response to extracellular stimuli. Signup and view all the answers

How do Rho proteins activate the formation of branched actin filaments?

They activate WASP proteins, which then stimulate the Arp2/3 complex. Signup and view all the answers

What is the role of microtubules in the cytoskeleton?

To provide structural support and to be involved in various types of cellular movement, including organelle transport and cell division. Signup and view all the answers

What are the subunits of microtubules?

Tubulin dimers, which consist of alpha-tubulin and beta-tubulin. Signup and view all the answers

Microtubules are non-polar structures.

False (B) Signup and view all the answers

What is the function of gamma-tubulin in microtubule assembly?

It helps initiate microtubule assembly at the centrosome. Signup and view all the answers

What is dynamic instability?

The alternating cycles of growth and shrinkage that microtubules undergo in response to GTP hydrolysis and the binding of new tubulin subunits. Signup and view all the answers

The plus end of a microtubule is the end that is typically stabilized.

False (B) Signup and view all the answers

What is the function of colchicine and colcemid?

They inhibit microtubule assembly and are used as experimental tools and in cancer treatments. Signup and view all the answers

What is the function of vincristine and vinblastine?

They inhibit microtubule polymerization and are used in cancer chemotherapy. Signup and view all the answers

What is the function of taxol in microtubule dynamics?

It stabilizes microtubules, which also blocks cell division. Signup and view all the answers

What are microtubule-associated proteins (MAPs)?

Proteins that regulate the dynamic behavior of microtubules. Signup and view all the answers

What is the function of polymerase MAPs?

They accelerate microtubule growth by increasing the incorporation of GTP-bound tubulin. Signup and view all the answers

What is the function of depolymerase MAPs?

They dissociate GTP-bound tubulin from the plus end of microtubules, leading to microtubule shrinkage or catastrophe. Signup and view all the answers

What is the function of CLASP proteins?

They rescue microtubules from catastrophe by stopping disassembly and restarting growth. Signup and view all the answers

What is the centrosome?

A microtubule-organizing center in animal cells, from which most microtubules extend outward. Signup and view all the answers

What is the mitotic spindle?

A structure formed by microtubules extending outward from duplicated centrosomes during mitosis, which controls chromosome separation and distribution to daughter cells. Signup and view all the answers

How do plant cells differ from animal cells in terms of microtubule organization?

Plant cells lack centrosomes, and microtubules instead form an array underlying the plasma membrane, which is involved in plant cell wall synthesis. Signup and view all the answers

What is the function of the gamma-tubulin ring complex?

It is a ring-shaped structure in the centrosome that helps initiate microtubule growth, bypassing the rate-limiting nucleation step. Signup and view all the answers

What are centrioles?

Cylindrical structures found in most animal cell centrosomes, containing nine triplets of microtubules. Signup and view all the answers

What are the two families of motor proteins responsible for microtubule-based movements?

Kinesins and dyneins. Signup and view all the answers

What is the direction of movement for kinesins along microtubules?

Towards the plus end. Signup and view all the answers

What is the direction of movement for dyneins along microtubules?

Towards the minus end. Signup and view all the answers

Axonemal dynein was the first identified microtubule motor protein due to its abundance in cilia.

True (A) Signup and view all the answers

What is the function of cytoplasmic dynein?

It moves along microtubules towards the minus end, responsible for transporting cargo towards the minus end of microtubules. Signup and view all the answers

What is the main function of microtubules in the cell?

To transport macromolecules, vesicles, and organelles through the cytoplasm. Signup and view all the answers

Kinesins and dyneins always transport cargo in the same direction.

False (B) Signup and view all the answers

Microtubules can help position organelles within the cell.

True (A) Signup and view all the answers

What is the role of cytoplasmic dynein in relation to the Golgi apparatus?

It helps position the Golgi apparatus near the centrosome. Signup and view all the answers

What are cilia and flagella?

Microtubule-based projections of the plasma membrane that are responsible for movement in many eukaryotic cells. Signup and view all the answers

Both cilia and flagella have the same structure, referred to as the axoneme.

True (A) Signup and view all the answers

What is the function of nexin in the axoneme?

It links the A and B tubules of each doublet, helping keep the microtubules in proper arrangement. Signup and view all the answers

Dynein arms in the axoneme are attached to the B tubule of each doublet.

False (B) Signup and view all the answers

What is the function of the basal body?

It anchors the minus end of microtubules in cilia and flagella, similar in structure to a centriole. Signup and view all the answers

The movement of cilia and flagella is powered by the sliding of outer microtubule doublets relative to one another.

True (A) Signup and view all the answers

How does the mitotic spindle form?

The centrosome replicates, and the resulting centrosomes migrate to opposite poles of the cell, creating the two poles of the spindle. Signup and view all the answers

What are the different types of microtubules that make up the mitotic spindle?

Kinetochore microtubules, chromosomal microtubules, polar microtubules, and astral microtubules. Signup and view all the answers

What is the function of kinetochore microtubules in mitosis?

They attach to condensed chromosomes at the centromeres, stabilizing them. Signup and view all the answers

What is the function of chromosomal microtubules in mitosis?

They connect to chromosome ends via chromokinesin. Signup and view all the answers

What is the function of polar microtubules in mitosis?

They are not attached to chromosomes but are stabilized by overlapping with each other in the center of the cell. Signup and view all the answers

What is the function of astral microtubules in mitosis?

They extend outward from the centrosomes with the plus ends anchored in the cell cortex. Signup and view all the answers

What is the function of chromokinesin?

It connects chromosomal microtubules to chromosome ends, ensuring proper alignment at the metaphase plate. Signup and view all the answers

What are the two steps of chromosome movement in anaphase?

Anaphase A, where chromosomes move towards the poles along kinetochore microtubules, and Anaphase B, where spindle poles separate. Signup and view all the answers

What is the function of kinesins in Anaphase A?

They depolymerize and shorten kinetochore microtubules, pulling chromosomes towards the poles of the cell. Signup and view all the answers

What is the function of plus-end-directed kinesins in Anaphase B?

They cross-link overlapping interpolar microtubules and move them towards the plus end, pushing spindle poles apart. Signup and view all the answers

What is the function of cytoplasmic dynein in Anaphase B?

It is anchored to the cell cortex and moves along astral microtubules towards the minus end, pulling spindle poles apart. Signup and view all the answers

What are intermediate filaments?

Filaments that have diameters intermediate between actin filaments and microtubules. Signup and view all the answers

Intermediate filaments are directly involved in cell movement.

False (B) Signup and view all the answers

What are the main types of intermediate filaments?

Keratins, vimentin, desmin, neurofilament proteins, and nuclear lamins. Signup and view all the answers

What is the function of keratins?

They provide structural support in epithelial cells. Signup and view all the answers

What is the function of vimentin?

It forms a network that extends from the nucleus towards the cell periphery, providing structural support in various cell types. Signup and view all the answers

What is the function of desmin?

It connects the Z discs of individual contractile elements in muscle cells. Signup and view all the answers

What is the function of neurofilament proteins?

They provide structural support for long axons in neurons. Signup and view all the answers

What is the function of nuclear lamins?

They form a meshwork that underlies the nuclear membrane, providing structural integrity and regulating nuclear shape. Signup and view all the answers

Intermediate filaments have distinct ends, similar to actin filaments and microtubules.

False (B) Signup and view all the answers

Intermediate filaments are more stable than actin filaments and microtubules.

True (A) Signup and view all the answers

What is the function of the central rod domain in intermediate filament assembly?

It plays a central role in filament assembly by forming a coiled coil with another polypeptide. Signup and view all the answers

What is the function of the head and tail domains in intermediate filaments?

They determine the specific functions of the intermediate filament protein. Signup and view all the answers

Intermediate filaments can associate with other cytoskeleton elements.

True (A) Signup and view all the answers

What are desmosomes?

Junctions between adjacent cells that involve the attachment of keratin filaments to dense protein plaques. Signup and view all the answers

What is the function of desmoplakin?

It mediates the attachment of keratin filaments to dense protein plaques in desmosomes. Signup and view all the answers

What are hemidesmosomes?

Junctions that connect epithelial cells to underlying connective tissue, involving the attachment of keratin filaments to integrins via plakins. Signup and view all the answers

What is the function of plectin?

It binds actin filaments and microtubules, forming bridges between them and between intermediate filaments, increasing the mechanical stability of the cell. Signup and view all the answers

Experimental evidence for the function of intermediate filaments is highly established and has been available for many years.

False (B) Signup and view all the answers

What is Epidermolysis bullosa simplex (EBS)?

A genetic disorder that causes skin blistering from cell lysis after minor trauma, caused by mutations in keratin genes that interfere with the assembly of keratin filaments. Signup and view all the answers

Flashcards

Actin Filaments

Flexible protein fibers (microfilaments) in the cytoskeleton, 7 nm diameter, involved in cell movement and structure

Actin Polymerization

The process of actin monomers joining together to form actin filaments, a crucial step in cell structure and movement.

Actin-Binding Proteins

Proteins that regulate actin filament assembly, disassembly, and interactions with other cell components. They control filament organization and shape.

Actin Filament Polarity

Actin filaments have distinct ends (barbed and pointed ends) that grow at different rates, influencing the direction of associated molecules.