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provides an internal protein framework that gives the cytoplasm strength and flexibility

The _________ of all cells includes microfilaments, intermediate filaments, and microtubules


Muscle cells contain ________ __________ in the cytoskeleton in addition to the 3 types of filaments contained in all cells

thick filaments

The ___________ plays a key role in the metabolic organization of the cell by determining where in the cytoplasm key enzymatic reactions occur and where specific proteins are synthesized



the smallest of the cytoskeletal elements; typically less than 6 nm in diameter

typical microfilaments are composed of the protein ________


3 major functions of microfilaments

1. Anchor the cytoskeleton to integral proteins of the cell membrane; provides the cell additional strength and attach the cell membrane to the enclosed cytoplasm
2. Determine the consistency of the cytoplasm. Where microfilaments form a dense, flexible network, the cytoplasm has a gelatinous consistency; where they are widely dispersed, the cytoplasm is more fluid.
3. Actin (a microfilament) can interact with the protein myosin to produce active movement of a portion of a cell or to change the shape of the entire cell.

intermediate filaments

protein composition varies among cell types; range from 7 to 11 nm in diameter

3 major functions of intermediate filaments

1. Strengthen the cell and help maintain its shape
2. Stabilize the positions of the organelles
3. Stabilize the position of the cell with respect to surrounding cells through specialized attachment to the cell membrane

__________ filaments, which are insoluble, are the most durable of the cytoskeletal elements



hollow tubes built from the globular protein tubulin; the largest components of the cytoskeleton, with a diameter of about 25 nm

5 major functions of microtubules

1. Form the primary components of the cytoskeleton, giving the cell strength and rigidity and anchoring the position of major organelles
2. The dis-assembly of microtubules provides a mechanism for changing the shape of the cell
3. Can move vesicles or other organelles within the cell, using proteins called molecular motors.
4. During cell division, microtubules form the spindle apparatus, which distributes duplicated chromosomes to opposite ends of the dividing cell.
5. Form structural components of organelles, such as centrioles and cilia.

thick filaments

are relatively massive bundles of subunits composed of the protein myosin; about 15 nm in diameter, and appear only in muscle cells


small, finger-shaped projections of the cell membrane on their exposed surfaces; greatly increase the surface area exposed to the extracellular environment


cylindrical structures composed of short microtubules (9 groups of 3). During cell division, the centrioles form the spindle apparatus associated with the movement of DNA strands

__________ are found in all animal cells capable of undergoing cell division


Name 4 types of cells that have no centrioles and are incapable of dividing

mature red blood cells
skeletal muscle cells
cardiac muscle cells
typical neurons


the cytoplasm surrounding the centrioles


relatively long, slender extensions of the cell membrane

Name two places cilia are found

on cells lining the respiratory tract
on cells lining the reproductive tract

__________ can beat rhythmically to move fluids or secretions across the cell surface



the organelles responsible for protein synthesis

composition of a ribosome

roughly 60 percent ribosomal RNA
40 percent protein

_________ are made up of two subunits


before protein synthesis can begin, a small and large ribosomal subunit must join together with a strand of _________

messenger RNA

free ribosomes

are scattered throughout the cytoplasm; the proteins they manufacture enter the cytosol

fixed ribosomes

are attached to the endoplasmic reticulum; the proteins they manufacture enter the ER, where they are modified and packaged for secretion


are organelles that contain an assortment of protein-digesting enzymes, or proteases; are responsible for removing and recycling damaged or denatured proteins, and for breaking down abnormal proteins

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