Quiz 2/Exam 2 Cytoskeletal Proteins

kinesis

another kind motor protein (which moves along the exposed side of the microtubules). kinesin, occurs in microtubules during the mitosis stage of cell division, as spindle fibers lead chromosomes during migration from the equatorial plate to the opposite poles. Kinesin also plays a role in the movement of organelles across the cytosol.

How microtublues disassemble?

dynamic instability: The opposite process, called depolymerization, involves the detachment of αβ dimers from a microtubule. When microtubules disassemble, the detached tubulin units polymerize in another location within the cell, where their presence assists in the completion of a particular cellular activity. The opposite process, called depolymerization, involves the detachment of αβ dimers from a microtubule (attatchemnt and detachment beta/ (+) end).

actin

microfilaments are made of the globular protein actin (red fibers). microfilaments contain the protein actin, which form two chains that twist against each other.

spindle fibers

structures that seperate chromosomes for cell division.

Intermediate filmants located

1) The nuclear lamina, located next to the interior lining of the nuclear envelope, consists of intermediate filaments that maintain nuclear shape and assist the nucleus in performing its function in the cell. 2) In the nervous system, intermediate filaments provide strength to the long axons of neurons (nerve cells), thereby assisting in the transmission of signals from neurons to recipient cells.

Why are cross-linking proteins and anchorage in the cell important for flagellar motion?

Without cross-linking proteins and an anchorage site, the walking motion of dynein proteins would simply push one microtubule doublet past the other. Cross-linking proteins between microtubules cause the flagella to bend.

dynein

a motor protein (which moves along the exposed side of the microtubules). It assists in the bending motions typical of cilia and flagella, mainly by interconnecting doublets and allowing these to slide against each other.

tubulin

a protein that appears to be hollow rods. Makes up the microtubules.

microfilaments and cell division

when a cleavage furrow develops across the area where the metaphase plate earlier appeared. The CONTRACTION of the ring of microfilaments surrounding this area results in the PINCHING of the cytoplasm to generate two separate daughter cells. The cleavage furrow later serves as the boundary between daughter cells.

cell motility and microfilaments

Actin filaments function in cell motility. In muscle cells, actin filaments arrange in a parallel fashion with myosin, the motor protein localized between filaments. Myosin slides along the actin filaments, resulting in muscle contraction. The amoeba (a single celled freshwater protist eukaryote) utilizes the same actin-myosin strategy for producing pseudopodia for movement. The pseudopodium attaches to a surface using the extensions containing actin filaments, undergoing cycles of contraction and extension for each movement.

cytoskeleton function

All three cytoskeletal structures mechanically support and preserve the shape of a cell. This network also provides anchorage sites for the enzymes and organelles of the cell. The cytoskeleton functions in the motility of the entire cell as well as the movement of components inside cells. For example, cilia and flagella bend due to the interactions of microtubules. In plant cells, the cytoskeleton allows cytoplasmic streaming, ensuring delivery of nutrients to the entire cell.

How are the functions of intermediate filaments and microfilaments similar and different?

Both function in providing cell shape and structure. However, intermediate filaments have more to do with anchorage and holding organelles in place, while microfilaments have a greater role in motion, such as cytoplasmic streaming, cell motility, and muscle contraction.

cleavage furrow

During cytokinesis in animals, the contractible ring of microfilaments around the equator of the cell.

Discuss the functions of cytoskeletal proteins.

Cytoskeletal proteins, which make up the different components of the cytoskeleton, have several functions including support and strength, movement of the organism, muscle contraction, cytoplasmic streaming, and roles in cell division.

During dynamic instability, what processes occur at the (+) end of a microtubule?

During dynamic instability, both disassembly and assembly of microtubules occur at the same time. This process involves the binding of a GDP molecule to a β-tubulin unit, preventing hydrolysis and attachment of new tubulin subunits on the growing microtubule.

dynamic instability

Dynamic instability describes the ease of microtubules to disassemble and then reorganize at different sites within the cell. During dynamic instability, both disassembly and assembly of microtubules occur at the same time. Dynamic instability, entails the presence of β-tubulin subunit bound to a GDP molecule instead of a GTP molecule. The presence of the GDP molecules prevents further hydrolysis (kinda like microfilaments with ATP) ( hydrolysis is a reaction that triggers the ATTACHMENT of an α-tubulin for further polymerization) Scientists have named the end of the microtubule with the exposed α subunit the (-) end, and the end with the exposed β subunit is referred to as the (+) end. Microfilaments are elongated at the (+) end through the addition of new tubulin subunits. The (+) end is also where subunits are removed as part of the disassembly process. This results in the (+) end showing higher rates of accumulation and release of tubulin dimers than the (-) end.

what allows flagella and cilia to bend

Flagella and cilia bend when ATP powers the movement of the dynein arms. Cross-linking proteins connect outer doublets of flagella and motile cilia. Every outer doublet carries two chains of the motor protein dynein, protruding at even-spaced intervals along the flagella or cilia. Dyneins allow flagella and cilia to bend, through ATP-fueled structural changes that allow the protein to act as a motor on the fiber. The mechanism of dynein-based bending "resembles" the action of walking, wherein (looks like) two "feet" move along the microtubule. Dynein is a motor protein that undergoes a change in tertiary structure when phosphorylated by ATP. In this case, to make the flagellum bend to the right, the dynein pushes the left microtubule doublet up. Because the doublets are connected to each other by nexin proteins, instead of moving up, the doublet bends to the right. Because they are attached, the bending of the left doublet eventually causes the right doublet to bend as well.

Explain how cells use the cytoskeleton for the intracellular trafficking of both organelles and other materials.

In ANIMAL cells, the cytoskeleton governs intracellular transport of organelles. They do this via centrioles, which serve as microtubule-organizing centers that generate microtubules. These microtubule-organizing centers function in cell division and movement of organelles throughout the cell.

Intermediate filament structure

Intermediate filaments are made up of several elements belonging to a large family of proteins. For example, certain intermediate filaments contain keratin, while others contain vimentin or lamins. Intermediate filaments are NOT as dynamic as microfilaments or microtubules, but they can form PERMANENT STRUCTURES in certain cells. Some of these permanent structures remain within cells even after death. Intermediate filaments support and ANCHOR structures that need to maintain their shapes or positions. The filaments maintain the positions of organelles within a cell, including the common position of the nucleus.

Microtubule organizing centers (MTOC)

Microtubule organizing centers (MTOC) are sites within the cell where microtubules originate. Animal cells possess two microtubule organizing centers: one that generates cilia and flagella for motility, and the centrosome, which produces spindle fibers (structures that separate chromosomes) for cell division. In plant cells, which do not have centrioles (assist in mitosis), the nuclear envelope acts as a microtubule organizing center.

microtubule function?

Microtubules interact with motor proteins, such as dynein and kinesin, in order to create movement within the cell. Microtubules aggregate into groups of two, or doublets, on which motor proteins move along the exposed side of each microtubule. One type of motor protein, dynein, assists in the bending motions typical of cilia and flagella, mainly by interconnecting doublets and allowing these to slide against each other. Another motor protein, kinesin, occurs in microtubules during the mitosis stage of cell division, as spindle fibers lead chromosomes during migration from the equatorial plate to the opposite poles. Kinesin also plays a role in the movement of organelles across the cytosol. Microtubules are like the railroad tracks of the cell. vesicles and etc are guided by microtubules and moved by motor proteins.

structure of microtubules?

Microtubules, which are generally present in eukaryotic cells, are made up of hollow rods of the protein tubulin. Each tubulin unit comes as a dimer, or two subunits of slightly different proteins, namely α-tubulin and β-tubulin.

actin filament elongation process

The attachment of other proteins to actin filaments typically utilizes energy through the hydrolysis of ATP to ADP. This mechanism repeats for the entire time that the cell needs the structural support of actin microfilaments. Once the actin filaments reach the length desired by the cell, the elongation process ends, with the terminal actin subunit containing an ADP molecule. The presence of the hydrolyzed form of ATP (ADP) triggers the depolymerization or disassembly of the actin filament. The instantaneous occurrence of disassembly and assembly on the same site is an example of dynamic instability.

Compare and contrast the structure of microtubules, microfilaments, and intermediate filaments.

The cytoskeleton is made up of three major structures: microtubules, microfilaments, and intermediate filaments. Microtubules are hollow rods of the protein tubulin that interact with motor proteins to create movement within the cell. Microfilaments are the thinnest cytoskeletal structures. They support the shape of the eukaryotic cell and strengthen the outermost layer of the cytoplasm, or cortex, distinguishing it from the fluid cytoplasm. Intermediate filaments are midrange in size and have varied molecular composition. They are not as dynamic as microfilaments or microtubules but can form permanent structures within cells.

microfilament structure

The filaments exist as two chains of actin twisting against each other. actin is a globular protein. These chains form networks of microfilaments within a cell. Certain proteins attach to these actin filaments to form branching networks. Microfilaments withstand tension, especially from forces pulling against the cells.

centrioles

centrioles, cylinder-shaped organelles that assist in mitosis, during cell division. A cellular organelle formed by nine microtubules; forms spindle fibers at the poles of eukaryotic cells during prophase; in pairs, forms the MTOC; does not exist in most plant cells.

cyclosis

cytoplasmic streaming or cyclosis, a process that involves the cytosol flowing around the cell in a circular motion. This intracellular movement results from the assembly and disassembly of MICROFILAMENTS, which drags organelles around in a stream-like fashion. IMPORTANCE: Cytoplasmic streaming ensures the distribution of nutrients and other materials to all regions of the cell. This intracellular action becomes a critical activity in large cells, due to the greater volume needing nourishment.

The cytoskeleton and mitosis

cytoskeleton also plays a major role in cell division in both plants and animals. Long before researchers knew the role of microtubules, DNA-staining techniques revealed chromosomes lining up along the equator of the cell during metaphase and moving apart during anaphase. The movement of the chromatin material suggest that microtubules assist in cell division.

How microtublues elongate?

dynamic instability: The elongation of a microtubule occurs through the attachment of tubulin dimers to one end of the tubule. Polymerization is critical to the process of microtubule assembly, mainly involving the association of αβ dimers in a lateral fashion. (attatchemnt and detachment beta/ (+) end).

Microstructure of a eukaryotic flagellum (cilia and flagella)

eukaryotic cilia and flagella have the same structural features. Both eukaryotic cilia and flagella carry a bundle of microtubules wrapped by a membrane extension of the cell. Microtubules occur as two units, called doublets, in nine sets arranged as a ring. In addition, two single microtubules occupy the center of the ring. This "9 + 2" pattern occurs in most flagella and cilia of eukaryotes. In contrast, a "9 + 0" pattern exists in non-motile cilia, lacking the central pair of single microtubules in the center of the ring. The microtubules anchor to the basal body of a cell, an organelle similar in function to the centriole.

Intermediate Filaments

intermediate filaments are "in the middle," or between microfilaments and the microtubules.intermediate filaments are larger than microfilaments but smaller than microtubules.

cytoskeleton

known as the cytoskeleton, the fibrous network organizes the cellular components and activities. It is based on three major cytoskeletal structures, namely the microtubules, the microfilaments, and the intermediate filaments. These structures differ in size, structure, composition and function. All three cytoskeletal structures mechanically support and preserve the shape of a cell. Both prokaryotic and eukaryotic cells benefit from the cytoskeleton. Among eukaryotes, animal cells benefit more than plant cells, since they lack the additional support of a cell wall.

microfilaments

microfilaments, the thinnest cytoskeletal structures, scientists observe the area within the cell that is closest to the plasma membrane. Also known as cortical microfilaments, the filaments in that area support the shape of the eukaryotic cell and strengthen the outermost layer of the cytoplasm, or cortex, distinguishing it from the fluid cytoplasm.

myosin

myosin, the motor protein localized between filaments. Myosin slides along the actin filaments (example: results in muscles contraction). The core protein within the "thick" filament; motor protein that binds actin and initiates muscle contraction.