1.) The_________________________structure of proteins include the alpha helix an
ID: 33121 • Letter: 1
Question
1.) The_________________________structure of proteins include the alpha helix and beta sheet
2.)A red blood cell placed in a ____________-tonic solution will shrivel, but a red blood cell placed in a ________-tonic will burst
3.) of the three mian kinds of cytoskeletal filaments,_____________________are the strongest and are used for mor epermanent structures such as the stron nuclear envelope.
4.)_____________ is the process in which nutrients and other foreign material are actively taken into the cell.
5.) list three types of things you can view with a light microscope, such as a human hair. List three types of things you can view with an electron microscope, such as a virus.
Explanation / Answer
1)secondary
2)hypotonic ,hypotonic solution
3)The eukaryotic cytoskeleton
Actin cytoskeleton of mouse embryo fibroblasts, stained with phalloidin.Eukaryotic cells contain three main kinds of cytoskeletal filaments, which are microfilaments, intermediate filaments, and microtubules. The cytoskeleton provides the cell with structure and shape, and by excluding macromolecules from sobitchesme of the cytosol it adds to the level of macromolecular crowding in this compartment Cytoskeletal elements interact extensively and intimately with cellular membranes.
Actin filaments / Microfilaments
Main article: Microfilament
Around 6 nm in diameter, this filament type is composed of two intertwined chains. Microfilaments are most concentrated just beneath the cell membrane, and are responsible for resisting tension and maintaining cellular shape, forming cytoplasmatic protuberances (like pseudopodia and microvilli- although these by different mechanisms), and participation in some cell-to-cell or cell-to-matrix junctions. In association with these latter roles, microfilaments are essential to transduction. They are also important for cytokinesis (specifically, formation of the cleavage furrow) and, along with myosin, muscular contraction. Actin/Myosin interactions also help produce cytoplasmic streaming in most cells.
Further information: Actin
Intermediate filaments
Microscopy of keratin filaments inside cells.Main article: intermediate filament
These filaments, around 10 nanometers in diameter, are more stable (strongly bound) than actin filaments, and heterogeneous constituents of the cytoskeleton. Although little work has been done on intermediate filaments in plants, there is some evidence that cytosolic intermediate filaments might be present, and plant nuclear filaments have been detected. Like actin filaments, they function in the maintenance of cell-shape by bearing tension (microtubules, by contrast, resist compression. It may be useful to think of micro- and intermediate filaments as cables, and of microtubules as cellular support beams). Intermediate filaments organize the internal tridimensional structure of the cell, anchoring organelles and serving as structural components of the nuclear lamina and sarcomeres. They also participate in some cell-cell and cell-matrix junctions.
Different intermediate filaments are:
made of vimentins, being the common structural support of many cells.
made of keratin, found in skin cells, hair and nails.
neurofilaments of neural cells.
made of lamin, giving structural support to the nuclear envelope.
Microtubules
Microtubules in a gel fixated cell.Main article: microtubule
Microtubules are hollow cylinders about 23 nm in diameter (lumen = approximately 15nm in diameter), most commonly comprising 13 protofilaments which, in turn, are polymers of alpha and beta tubulin. They have a very dynamic behaviour, binding GTP for polymerization. They are commonly organized by the centrosome.
In nine triplet sets (star-shaped), they form the centrioles, and in nine doublets oriented about two additional microtubules (wheel-shaped) they form cilia and flagella. The latter formation is commonly referred to as a "9+2" arrangement, wherein each doublet is connected to another by the protein dynein. As both flagella and cilia are structural components of the cell, and are maintained by microtubules, they can be considered part of the cytoskeleton.
They play key roles in:
intracellular transport (associated with dyneins and kinesins, they transport organelles like mitochondria or vesicles).
the axoneme of cilia and flagella.
the mitotic spindle.
synthesis of the cell wall in plants.
4)Phagocytosis
5)The Compound Light Microscope
The Stereo Microscope
The Digital Microscope
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