cytology2 RIBOSOMES& CYTOSKELETON gehan_organized (1).pdf

STRUCTURE OF THE CELL CELL Nucleus Cytoplasm Nuclear envelope Chromatin Organelles Cytoskeleton Nucleolus Nuclear sap Inclusions Cytosol 3 B- Non-membranous organelles Free ribosomes. Microtubules. Centriole, cilia, flagella. Filaments. Free ribosomes non-membranous organelles, present in all cells...

STRUCTURE OF THE CELL CELL Nucleus Cytoplasm Nuclear envelope Chromatin Organelles Cytoskeleton Nucleolus Nuclear sap Inclusions Cytosol 3 B- Non-membranous organelles Free ribosomes. Microtubules. Centriole, cilia, flagella. Filaments. Free ribosomes non-membranous organelles, present in all cells except mature RBCs. Formation: Free ribosomes are formed in the nucleolus from rRNA and proteins, released into the cytoplasm to perform their function. May appear in groups (polysomes). L/M: not seen * free ribosomes cause cytoplasmic basophilia due to their contents of rRNA. E/M: *Low magnification: small electron dense granules. *High magnification: two subunits (large and small). Function: free ribosomes synthesize proteins needed by the cell itself. Attached ribosomes (RER) synthesize proteins which are extruded outside the cells. Microtubules * Non membranous organelle. LM: too small to be seen (can not be seen). EM: straight, hollow cylinders. In cross section, they appear as tiny circles. Their walls are more denser than central parts (hollow). Formation: Formed in the cytoplasm from a protein called tubulin. Each microtubule contains 13 protofilaments. Functions: 1- Formation of internal skeleton of cells. 2- Transport of substances within the cytoplasm. 3- Formation of mitotic spindle during cell division. 4- Enter in structure of centrioles, cilia and flagella. Filaments thread-like structures that may be called fibres, fibrils or filaments. Types of filaments: 1-Actin (microfilaments): - smallest in size (5-7 nm in diameter). - consist of protein actin. -Sites: -a) mainly in striated muscles. - b) in terminal web. - c) blood platelets. 2-Myosin filaments: - They are thick filaments (15 nm in diameter). - consist of protein myosin. -Sites: as actin filament. 3-Intermediate filaments: - intermediate in size (10-12 nm in diameter). -Sites: Present in many cells e.g. in epithelial cells (tonofilaments) and in nerve cells (neurofilaments). Functions: 1-Formation of the skeleton of cells (cytoskeleton). 2-Actin and myosin have a role in contraction of muscles.