Retta - L9

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Questions and Answers

What direction do dyneins primarily move along microtubules?

Toward the center of the cell

Toward the plus-end

In random directions

Toward the minus-end (correct)

What is the role of ATP in the movement of kinesins and dyneins?

It provides a binding site for the cargo

It inhibits movement along the microtubule

It destabilizes the microtubule structure

It causes a conformational change in the protein (correct)

Which of the following statements about kinesins is accurate?

Kinesins share similar head domains but vary in cargo specificity (correct)

Kinesins move cargo toward the minus-end of microtubules

Kinesins can only interact with a single type of cargo

All kinesins have their head domains at the C-terminus

What distinguishes kinesin-14 from other kinesins?

It has head domains at the C-terminus Signup and view all the answers

How do dyneins typically interact with their cargo?

Through an adaptor protein Signup and view all the answers

What is the main mechanism by which kinesins and dyneins achieve movement along microtubules?

Hydrolysis of ATP causing head movement Signup and view all the answers

What role does kinesin-13 specifically perform regarding microtubules?

Regulates the dynamic instability of microtubules. Signup and view all the answers

What is a key difference in attachment duration between kinesin and myosin motor proteins?

Kinesin's head domain is attached for 50% of the time, compared to 5% for myosin. Signup and view all the answers

What distinguishes dyneins from kinesins in terms of motor domain arrangement?

Dyneins can have two or three heavy chains, while kinesins consist of two identical motor heads. Signup and view all the answers

Which statement accurately describes the movement of kinesins along microtubules?

Kinesins perform a hand-over-hand walking movement powered by ATP hydrolysis. Signup and view all the answers

What is the rate at which the fastest kinesin family proteins can move?

They can achieve speeds of 2-3 µm/sec. Signup and view all the answers

How do dyneins typically interact with their cargo during movement?

Mediating interaction through multiple accessory proteins. Signup and view all the answers

Which element is essential for the kinesin motor's movement cycle and its conformational changes?

ATP binding and hydrolysis. Signup and view all the answers

What role do dyneins play in the pigmentation changes of fish?

They move pigments granules along microtubules. Signup and view all the answers

Which statement is true regarding the movement of cargo along microtubules in nerve cells?

Kinesins transport cargo to the plus-end while dyneins transport to the minus-end. Signup and view all the answers

How do motor proteins like kinesins return to their starting point after reaching one pole of the microtubule?

They detach and diffuse within the cell to reattach at the opposite end. Signup and view all the answers

What is the primary function of the endoplasmic reticulum as mediated by kinesins?

To distribute it toward the plasma membrane along microtubules. Signup and view all the answers

What structural feature allows kinesins to move predominantly toward the plus-end of microtubules?

The location of their binding sites. Signup and view all the answers

Which organelle is primarily moved towards the centrosome by dyneins?

Golgi apparatus Signup and view all the answers

What characterizes the dynamic behavior of microtubules?

They undergo dynamic instability with constant extension and retraction. Signup and view all the answers

What happens to kinesin motors when they reach the plus-end of microtubules?

They detach, diffuse, and reattach at another site. Signup and view all the answers

What is the primary role of motor proteins in intracellular dynamics?

To facilitate the movement and distribution of organelles and vesicles. Signup and view all the answers

What is the structural characteristic of intermediate filaments that differentiates them from actin filaments and microtubules?

Intermediate filaments are composed of a helical array of tetramers. Signup and view all the answers

What mechanical property do intermediate filaments exhibit due to their structure?

They are resistant to stretching and can be deformed. Signup and view all the answers

Which of the following cell types primarily relies on intermediate filaments for mechanical strength?

Epithelial cells of the skin. Signup and view all the answers

What is the consequence of alterations in keratins within intermediate filaments in epithelial cells?

Sensitivity to blistering due to mechanical stress. Signup and view all the answers

How do intermediate filaments interact with other cell structures?

Through desmosomes connecting intermediate filaments of adjacent cells. Signup and view all the answers

Which characteristic of intermediate filaments allows them to span the length of epithelial cells?

High tensile strength due to lateral connections. Signup and view all the answers

What distinguishes nuclear intermediate filaments from cytoplasmic intermediate filaments?

Nuclear intermediate filaments form the nuclear lamina. Signup and view all the answers

What proteins are commonly associated with cytoplasmic intermediate filaments?

Keratins, vimentin, and neurofilaments. Signup and view all the answers

What is the main structural characteristic that differentiates cilia from flagella?

Cilia use a power stroke and recovery stroke for movement. Signup and view all the answers

What is the primary function of intermediate filaments in cells?

Providing physical strength to resist mechanical stress. Signup and view all the answers

Which proteins are known to mediate the interactions between microtubules within cilia and flagella?

Dyneins. Signup and view all the answers

What type of structural arrangement do cilia and flagella follow?

9+2 arrangement of microtubules. Signup and view all the answers

Which statement about the movement of flagella is accurate?

Flagella produce a wave-like motion to propel cells through fluid. Signup and view all the answers

Which type of intermediate filament is primarily found in epithelial cells?

Keratins. Signup and view all the answers

What characteristic do all eukaryotic cells share regarding cytoskeletal components?

The presence of actin and tubulin. Signup and view all the answers

How do the basic units of intermediate filaments differ from those of actin filaments and microtubules?

They are formed by coiled-coil dimers. Signup and view all the answers

Which types of proteins are included in the composition of intermediate filaments found in muscle cells?

Desmin. Signup and view all the answers

What happens during the repetitive bending movement of cilia and flagella due to dynein activity?

Bending occurs due to linking proteins preventing sliding. Signup and view all the answers

Study Notes

Motor Proteins and Intermediate Filaments

Motor proteins include kinesins and dyneins, which interact with and move along microtubules.
Kinesins generally transport cargo toward the plus end, whereas dyneins move toward the minus end of microtubules.
Both kinesins and dyneins utilize ATP binding and hydrolysis for movement, with at least one head always in contact with the microtubule.

Structure and Function of Kinesins

Kinesins consist of two identical motor heads, with a coiled-coil region that promotes dimerization.
The C-terminal domain binds to specific cargo, while motor activity is associated with the N-terminal head domain.
Kinesins like kinesin-13 function as catastrophins that destabilize microtubules at the plus end rather than transporting cargo.

Kinesin Movement Mechanism

Kinesins exhibit a "hand-over-hand" walking motion along microtubules, moving about 80 nanometers per step.
ATP hydrolysis leads to a conformational change that propels the kinesin forward, allowing it to progressively transport cargo.

Comparison with Myosin

Kinesins retain attachment to the microtubule for 50% of the cycle time, unlike myosin, which only remains attached for 5% of the time.
Kinesins are more persistent in their interactions with microtubules compared to the transient interactions of myosin with actin filaments.

Dyneins: Structure and Action

Dyneins are larger motor proteins with two or three heavy chains and are categorized into cytoplasmic dyneins and axonemal dyneins.
Dyneins are specialized for minus-end movement and are the fastest known molecular motors, moving at 14 µm/sec.

Interaction with Cargo

Dyneins usually interact with their cargo through adaptor proteins, moving vesicles or organelles toward the minus end of microtubules.
Dynein is crucial for processes such as the redistribution of pigment granules in certain organisms in response to stimuli.

Microtubule Dynamics

Motor proteins like kinesins and dyneins facilitate the movement of organelles and vesicles, contributing to cellular organization.
The endoplasmic reticulum is distributed along microtubules by kinesins, while dyneins transport the Golgi apparatus inward.

Cellular Directionality

Kinesins and dyneins enable bidirectional transport within nerve axons, with kinesins moving toward the plus end (nerve terminal) and dyneins moving toward the minus end (cell body).
Motor proteins must detach from microtubules to return, as they cannot reverse direction; they diffuse and reattach at the opposite end.

Cilia and Flagella

Cilia and flagella are built from microtubules and dyneins, arranged in a "9+2" structure to facilitate movement.
Cilia perform a power stroke followed by a recovery stroke, while flagella exhibit wave-like motion, aiding in the propulsion of cells.

Intermediate Filaments

Intermediate filaments provide mechanical strength to cells and vary in composition depending on the tissue type.
Common types include keratins in epithelial cells, vimentin in mesenchymal cells, and desmin in muscle cells.
Neurons contain neurofilaments and glial fibrillary acidic protein (GFAP), serving structural roles.

Structure of Intermediate Filaments

Intermediate filaments share a conserved alpha-helical rod domain but differ at their amino and carboxyl termini.
Coiled-coil dimers form through lateral bundling and twisting, enhancing stability in response to mechanical stress.### Intermediate Filaments Structure and Function
Intermediate filaments form from two dimers interacting antiparallelly, creating staggered tetramers.
Intermediate filaments are 10 nm in diameter, larger than actin filaments (7 nm) and microtubules (25 nm).
Polarity is absent in intermediate filaments, unlike actin filaments and microtubules which have distinct plus and minus ends.
Tetramers organize into twisted filaments, contributing to their strong resistance to tensile stretching.
Intermediate filaments can bend easily but are extremely tough to break, fulfilling a crucial mechanical role in cells.

Distribution and Importance in Epithelial Cells

Present in vertebrates and certain soft-bodied animals, intermediate filaments provide structural integrity to animal cells.
Found prominently in epithelial cells, especially in the skin, where they connect via desmosomes.
They span cell lengths, critical for resisting external stresses and preventing tissue rupture.

Composition and Hierarchy

Intermediate filaments are made of eight strands twisted together, with two monomers forming a dimer, forming tetramers aligned in staggered arrays.
Cytoplasmic intermediate filaments include keratins (in epithelia), vimentin (in connective tissues), and neurofilaments (in nerve cells).
Nuclear intermediate filaments, known as lamins, provide support for the nuclear envelope and anchor chromosomes.

Mechanical Properties and Stability

Intermediate filaments enhance the stability of animal cells due to extensive lateral interactions and their unique structure.
They resist deformation more effectively compared to actin filaments and microtubules.
Disruption of intermediate filaments can lead to diseases such as epidermolysis bullosa simplex, characterized by skin blistering from mechanical stress.

Connection and Disease Implications

Plectin is a protein that cross-links intermediate filaments with other cytoskeletal elements, critical for maintaining tissue integrity.
Genetic mutations in intermediate filament proteins can lead to severe conditions like muscular dystrophy and neurodegeneration.
Filaggrin contributes to keratin filament stability; mutations can result in atopic dermatitis.

Role in Cell Migration and Morphology

Cell movement relies heavily on intermediate filaments in conjunction with microtubules and actin filaments.
The Rho GTPase family regulates cell polarization and movement through their action on actin dynamics.
- Rac induces lamellipodia formation, while Rho promotes stress fiber development.
- Cdc42 facilitates filopodia formation.
The leading edge of migratory cells extends via lamellipodia, while contraction occurs at the rear edge, promoting forward motion.

Cell Mechanics and Dynamics

The cytoskeletal dynamics allow cells to exert traction forces during migration, involving interactions with the extracellular matrix.
Actin polymerization and associated proteins like formin and the Arp2/3 complex play vital roles in protrusions like lamellipodia and filopodia.
Mechanical and molecular coordination during migration elucidates the dynamic interplay among various cytoskeletal components.

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Description

Explore the fascinating roles of motor proteins like kinesins and dyneins in cellular movement! This quiz will focus on how these proteins interact with microtubules. Test your understanding of their mechanisms and functions within the cell.