Cell Biology L ec. 3 Dr: Buthaina Al- Sabawi Date: 14/12/2009 Cell Biology L ec. 3 Dr: Buthaina Al- Sabawi Date: 14/12/2009

The cytoskeleton is a network of fibers throughout the cell's cytoplasm that helps the cell maintain its shape and gives support to the cell and enables cellular motion (using structures such as cilia and flagella plays important roles in both intracellular transport, )the movement of vesicles and organelles, for example) and cellular division. and providing mechanical strength. The cytoskeleton is a network of fibers throughout the cell's cytoplasm that helps the cell maintain its shape and gives support to the cell and enables cellular motion (using structures such as cilia and flagella plays important roles in both intracellular transport, )the movement of vesicles and organelles, for example) and cellular division. and providing mechanical strength.cellular divisioncellular division

The cytoskeleton is made up of three kinds of protein filaments: 1- Actin filaments (also called microfilaments) 2- Intermediate filaments 3- Microtubules

Microfilaments Microfilaments are rigid hollow rods approximately 7 nm in diameter. Made of a protein known as actin. Actin appears in a globular form (G-actin). Microfilaments are rigid hollow rods approximately 7 nm in diameter. Made of a protein known as actin. Actin appears in a globular form (G-actin). Microfilaments are long polymerized chains of the molecules are intertwined in a helix, creating a filamentous form of protein (F- actin). Microfilaments are long polymerized chains of the molecules are intertwined in a helix, creating a filamentous form of protein (F- actin).

Microfilaments considered part of the cell cortex, which regulates the shape and movement of the cell’s surface. Functions of microfilaments: 1- Provides mechanical strength to the cell 2- Link transmembrane proteins (e.g., cell surface receptor) to cytoplasmic proteins. 3-Anchors the centrosomes at opposite poles of the cell during motosis. 4-Pinches dividing animal cells apart during cytokinesis. 5-Generate cytoplasmic streaming in some cell.

7-Interact with myosin (“ thick”) filaments in skeletal muscle fibers to provide the force of muscular contraction. 8- They function in the maintenance of cell- shape. 9- These filaments are associated with membrane activities such as endocytosis and exocytosis.

Microtubules Microtubules are hollow cylinders of about 25 nm in diameter (lumen = approximately 15nm in diameter), most commonly comprised of 13 protofilaments which, in turn, are polymers of alpha and beta tubulin. They have a very dynamic behavior, binding GTP for polymerization. Microtubules are hollow cylinders of about 25 nm in diameter (lumen = approximately 15nm in diameter), most commonly comprised of 13 protofilaments which, in turn, are polymers of alpha and beta tubulin. They have a very dynamic behavior, binding GTP for polymerization.

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. 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. They play key roles in: Determine cell shape and in a variety of cell movements, including some form of cell locomotion, the intercellular transport of organelles, and the separation of chromosomes during mitosis. The axoneme of cilia and flagella. The axoneme of cilia and flagella. The mitotic spindle. The mitotic spindle. Synthesis of the cell wall in plants Synthesis of the cell wall in plants

Intermediate Filaments Intermediate filaments have a diameter of about 10nm, which is intermediate between the diameter of two other principle elements of the cytoskeleton, actin filaments and microtubules. Like actin filaments, they function in the maintenance of cell-shape. Intermediate filaments have a diameter of about 10nm, which is intermediate between the diameter of two other principle elements of the cytoskeleton, actin filaments and microtubules. Like actin filaments, they function in the maintenance of cell-shape. Filaments serving as structural components of the nuclear lamina and sarcomeres. They also participate in some cell-cell and cell-matrix junctions. Filaments 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. Type I and type II: acidic keratin and basic keratin, respectively.Produced by different types of epithelial cells ( bladder, skin,etc) Neurofilaments of neural cells. Type I and type II: acidic keratin and basic keratin, respectively.Produced by different types of epithelial cells ( bladder, skin,etc) Neurofilaments of neural cells. Made of lamin inside the inner nuclear envelope.. Lamins are vital to the re-formation of the nuclear envelope after cell division. Desmin, found in muscle cells.

In cell biology, the centrosome is an organelle that serves as the main microtubules organizing center In cell biology, the centrosome is an organelle that serves as the main microtubules organizing center ( MTOC) of the animal cell as well as a regulator of cell-cycle progression.Centerioles found only in animal cells, these paired organelles are located together near the nucleus. Each centerioles is made of nine bundles of microtubules (three per bundle) arranged in a ring. ( MTOC) of the animal cell as well as a regulator of cell-cycle progression.Centerioles found only in animal cells, these paired organelles are located together near the nucleus. Each centerioles is made of nine bundles of microtubules (three per bundle) arranged in a ring.

Centrioles play an important role in cell division. During interphase of an animal cell, the centrioles are duplicated. As mitosis initiates, the original centrosome divides and the pairs are split up so that one set of centrioles is located in each of the new microtubule-organizing centers. These new centers radiate microtubules in star-shaped clusters known as asters. Centrioles play an important role in cell division. During interphase of an animal cell, the centrioles are duplicated. As mitosis initiates, the original centrosome divides and the pairs are split up so that one set of centrioles is located in each of the new microtubule-organizing centers. These new centers radiate microtubules in star-shaped clusters known as asters.

As the asters move to opposing poles of the cells, the microtubules, with the help of the centrioles, become organized into a spindle- shaped formation that spans the cell. As the asters move to opposing poles of the cells, the microtubules, with the help of the centrioles, become organized into a spindle- shaped formation that spans the cell. These spindle fibers act as indicator for the alignment of the chromosomes as they separate later during the process of cell division. These spindle fibers act as indicator for the alignment of the chromosomes as they separate later during the process of cell division.

Cilia & flagella are motile cellular appendages found in most microorganisms and animals, cilia function to move a cell or to help transport fluid or materials past them. The respiratory tract in humans is lined with cilia that keep inhaled dust, and harmful microorganisms from entering the lungs. Cilia are usually shorter and occur together in much greater numbers than flagella. Cilia & flagella are motile cellular appendages found in most microorganisms and animals, cilia function to move a cell or to help transport fluid or materials past them. The respiratory tract in humans is lined with cilia that keep inhaled dust, and harmful microorganisms from entering the lungs. Cilia are usually shorter and occur together in much greater numbers than flagella.

In eukaryotic cells, cilia and flagella contain the motor protein (dynein) and (microtubles), the core of each of the structures is termed the (axoneme) and contains two central microtubules that are surrounded by an outer ring of nine doublet microtubules. Dynein molecules are located around the axoneme. A plasma membrane surrounds the entire axoneme complex, which is attached to the cell at a structure termed the basal body. In eukaryotic cells, cilia and flagella contain the motor protein (dynein) and (microtubles), the core of each of the structures is termed the (axoneme) and contains two central microtubules that are surrounded by an outer ring of nine doublet microtubules. Dynein molecules are located around the axoneme. A plasma membrane surrounds the entire axoneme complex, which is attached to the cell at a structure termed the basal body.

Basal body (also known as a kinetosome). Basal bodies maintain the basic outer ring structure of the axoneme of the cilia and The basal body is structurally identical to the centrioles. Basal body (also known as a kinetosome). Basal bodies maintain the basic outer ring structure of the axoneme of the cilia and The basal body is structurally identical to the centrioles.

Inclusions: are considered to be nonliving components of the cell that neither possess metabolic activity nor are bounded by membranes. The most common inclusions are glycogen, lipid droplet, pigments, and crystals. Inclusions: are considered to be nonliving components of the cell that neither possess metabolic activity nor are bounded by membranes. The most common inclusions are glycogen, lipid droplet, pigments, and crystals. 1- Glycogen: Glycogen is the most common storage form of glucose in animals and is especially abundant in cells of muscle and liver. 1- Glycogen: Glycogen is the most common storage form of glucose in animals and is especially abundant in cells of muscle and liver.

2- lipids: is a storage forms of triglycerides, are stored in specialized cells, adipocytes, also located as individual droplets in various cell types. Especially those of the liver, lipids are sourse of energy. 3- Pigments: there are deposits of colored substances include: A- Melanin: the most common pigment in the body, its dark brown pigment present in the skin, hair, retina, and some parts of the central nervous system (C.N.S)

B- Lipofuscin: its yellow to brown pigment found in long lived cells, like neurons of the C.N.S and cardiac muscles. Lipofuscin pigments aremembrane-bound and represent the indigestible remnants of lysosomal activity. C- Hemosiderin: it’s a cold-yellow pigment. It’s the end product of Hb degradation of old red blood cells. They are present in the liver, spleen and bone marrow. D- Crystals: crystals are structures of crystalline forms of certain proteins. They are not commonly found in cells, with the exception of steroid cells, and interstitial cells of testes, and occasionally in macrophages.