Cytoskeleton, ECM, and Cell Motility: Microtubules, Actin, and Motor Proteins

What are the three major components of the cytoskeleton?

Microtubules, microfilaments, and intermediate filaments.

What is the primary function of microtubules?

Motility and structural support of the cell.

What is the role of actin filaments in the cytoskeleton?

They provide motility and structural support, and help form the cleavage furrow during cell division.

What is the function of intermediate filaments?

They are helpful in cell junctions and connecting cells.

What is the dynamic instability of microtubules?

It refers to the ability of alpha and beta subunits to depolymerize, allowing microtubules to be easily built up or broken down.

What are Microtubule-Organizing Centers (MTOCs)?

Specialized structures that organize the nucleation of microtubules.

What is the role of centrosomes in animal cells?

They initiate microtubule formation and are made up of microtubules.

What is the significance of gamma tubulin in microtubule construction?

Gamma tubulin is required for the initiation of microtubule construction from the MTOC.

How do cilia and flagella differ in structure and function?

Cilia are short and numerous, moving in a synchronized wave-like pattern, while flagella are long and few, moving in a whip-like motion.

What motor protein drives the movement of cilia and flagella?

Axonemal dynein.

Describe the sliding microtubule mechanism in cilia and flagella movement.

Dynein heads bind to adjacent microtubules, hydrolyze ATP for energy, and cause microtubules to slide relative to each other, resulting in bending.

What is the function of linking proteins like nexin in the axoneme?

They connect microtubule doublets and convert sliding motion into localized bending.

What are kinesin and dynein in the context of motor proteins?

Kinesin moves vesicles toward the plus end of microtubules, while dynein moves them toward the minus end.

What is the structural composition of kinesin?

A tetramer consisting of two heavy chains and two light chains.

What is the role of ATP in the function of motor proteins?

ATP hydrolysis provides the energy needed for motor proteins to move along microtubules.

What is the significance of the plus and minus ends of microtubules?

The plus end is where subunits are added, while the minus end is where they are anchored at the MTOC.

What is the role of dynein in flagellum movement?

Dynein facilitates the bending motion of the flagellum by sliding microtubules against each other.

What is the function of the cleavage furrow during cell division?

It helps to divide the cell by constricting the cell membrane.

What type of cells have cilia and flagella?

Cilia are found in eukaryotes, while flagella are found in both eukaryotes and prokaryotes.

What happens to beta tubulin during microtubule assembly?

Beta tubulin binds to GTP, which is hydrolyzed to GDP after incorporation into the filament.

What is the role of motor proteins in intracellular movements?

They transport vesicles along the cytoskeletal filaments, facilitating movement within the cell.

What is the quaternary structure of microtubules?

Microtubules are composed of multiple globular proteins arranged in longitudinal rows called protofilaments.

What is the relationship between actin filaments and the cytoskeleton?

Actin filaments are polymers of actin proteins that contribute to the structural integrity and motility of the cell.

What are the roles of microtubule motor proteins?

They facilitate the movement of vesicles along microtubules, with kinesin moving from minus to plus and dynein moving from plus to minus.

What is the function of dynein in the nervous system?

Dynein is involved in the transmission of neurotransmitters from one neuron to the next, moving vesicles toward the axon terminus.

What are intermediate filaments and their primary role?

Intermediate filaments provide cytoskeletal support and help cells resist mechanical stress, with keratin being a well-known example.

What is the main role of actin microfilaments?

Actin microfilaments help the cell extend its cytoskeleton forward for movement and are involved in cell motility.

How do actin filaments exhibit dynamic behavior?

Actin filaments can be readily constructed and deconstructed, with subunit assembly influenced by ATP levels.

What is the structure of myosin II?

Myosin II consists of two heavy chains and four light chains, with heavy chains having two globular heads and a structural tail.

How does myosin II convert to a filament?

Myosin II monomers undergo phosphorylation, unfolding and aligning side by side to form bipolar thick filaments.

Describe the process of muscle contraction involving actin and myosin.

Calcium ions bind to troponin, moving tropomyosin off actin's binding sites, allowing myosin heads to bind and slide actin filaments, shortening the sarcomere.

What is the extracellular matrix (ECM) and its significance?

The ECM is a scaffold of proteins between tissue layers that provides structural support and facilitates cell organization.

What are the main proteins found in the extracellular matrix?

Fibronectin and collagen are two key proteins in the ECM, with collagen being the most abundant protein in the body.

What is the structure and function of collagen?

Collagen is a fibrous protein with a trimeric helix structure, providing scaffolding for tissues and ligaments.

How does vitamin C relate to collagen synthesis?

Vitamin C is essential for the enzyme proline hydroxylase, which is necessary for building collagen.

What is a proteoglycan?

A proteoglycan is a protein-polysaccharide complex that attracts water and forms a gel-like structure, crucial for connective tissues like cartilage.

What is the role of fibronectin in the ECM?

Fibronectin is important for cell attachment and migration through the ECM.

What is the RGD loop in fibronectin?

The RGD loop is a cell-binding domain made of arginine, glycine, and aspartic acid, allowing cells to recognize and bind to fibronectin.

What is laminin and its role in the basement membrane?

Laminin is a key component of the basement membrane, influencing cell migration and growth.

How do germ cells interact with the basement membrane?

Germ cells attach to basement membrane proteins like laminin and collagen to migrate to developing gonads.

What is the glycocalyx?

The glycocalyx is a carbohydrate coat around the cell membrane that mediates cell-cell and cell-substratum interactions.

What happens during muscle relaxation after contraction?

Calcium ions are removed, blocking actin's binding sites, and ATP hydrolysis detaches myosin from actin.

What is the significance of the basement membrane in tissue organization?

The basement membrane provides structural support, signals cell survival, maintains polarity, and acts as a barrier.