Non-Membranous Organelles Lecture Notes PDF

Professor of histology  Membranous organelles Mitochondria Endoplasmic reticulum Golgi Apparatus Lysosome peroxisome Non-Membranous organelles Ribosomes Proteasomes Cytoskeleton Microtubules Filaments ...

Professor of histology  Membranous organelles Mitochondria Endoplasmic reticulum Golgi Apparatus Lysosome peroxisome Non-Membranous organelles Ribosomes Proteasomes Cytoskeleton Microtubules Filaments  Learning objectives Defin Describ e Describe Underline Define Underline e Describe the Describe the structures Underline the Define structures and Underline correlated to the medical application Microtubules, correlated the medical Define the functions of MTOC & functions of application ribosomes. related to the ribosome. Centrioles microtubules related to the ribosome. microtubules and centrioles. Define Describe Underline Define Describe Describe the Underline the Describe the structures and medical Define cilia, Define and structure and correlated application filaments and classify cell correlated functions related to the proteasomes inclusions functions of cell filaments and filaments and inclusions proteasomes proteasomes  Ribosomes Non-membranous rounded or oval bodies [12 X 25 nm] Formed of strands of rRNA + associated proteins Formed in the nucleolus, then pass to cytoplasm through nuclear pores Found in large numbers in protein synthesizing cells Ribosomes  Ribosomes L.M Basophilic polysomes stained cytoplasm by H&E E.M Small electron-dense granules Formed of 2 subunits (Large & Small) Forms: 1-Free: -Single or in groups connected by mRNA Free strand → forming spiral chains (polysomes) Fixed 2-Attached (fixed): -To the outer surface of rER by the large subunit at receptors (Ribophorins) polysomes Formed in the nucleolus, then pass to cytoplasm through nuclear pores Fixed ribosome Free ribosome protein Structural Functional protein protein Secretory protein  PROTEASOMES Proteasomes are small, non-membranous barrel-shaped (cylindrical) organelles that functioning in degradation of mis- folded or unwanted proteins Considered as a quality control unit to ensure quality of exported proteins They are functioning to destroy damaged or unwanted proteins that have Been labeled for destruction with ubiquitin (a regulatory protein involve in elimination of damaged proteins). They differ from lysosomes, Proteasomes deal with free proteins as individual molecules, whereas lysosomes digest organelles or membranes by autophagy.  PROTEASOMES, Clinical application: In Parkinson’s disease, accumulations of misfolded proteins kill cells in the brain that regulate muscle function, because the proteasome system is not functioning properly. Function: 1. They function to degrade and digest damaged or unneeded proteins (The denatured or nonfunctional polypeptides are tagged with the polypeptide ubiquitin to be targeted for destruction). 2. They ensure quality of exported proteins. 3. They restrict the activity of a specific protein to a certain time. Cytoskeleton diameter 25 nm 5-7nm 8-10nm 20nm  protofilament tubulin Microtubules  Microtrabecular Lattice Lattice = network Microtrabecular Lattice Microtubules + Filaments + Proteins linking them together and to the cell membrane form a framework called [Microtrabecular Lattice]  Microtubules Non branching & rigid hollow fine tubes Formed of tubulin protein. L.M: Not seen, Needs IHC for antitubulin Iron hematoxylin E.M: Fine tubules -Diameter: 20-25nm -Length: Changed by adding or removal of tubulin molecules at their end  centrioles centrosome microtubuleorganizing center (MTOC) microtubuleorganizing center (MTOC)  microtubuleorganizing center (MTOC) -VE +VE  microtubuleorganizing microtubuleorganizing center (MTOC) center centrioles +ve -ve  Microtubules Forms of microtubules 1-Dynamic: Continuous assembly & disassembly → Rapid reshaping of the cell 2-Stable: Solid microtubules forming the wall of centrioles & flagella Microtubules Function of microtubules 1.Maintain cell shape e.g. platelets 2.Intracellular vesicular transport 3.Formation of mitotic spindle during cell division 4.Formation of centrioles, cilia & flagella. mitotic spindle vesicle vesicular transport centrioles  dynein COP II COP I Kinesin  Basal body/centriole  Cilia Basal body Centriole  Cilia 9 peripheral doublet and 2 central singlet Basal body & centriole 9 peripheral triplets  Centrioles Non-membranous organelle Formed of microtubules Responsible for cell division Absent in non-dividing cells [RBCs & nerve cells] Present near the nucleus [Centrosome] L.M: Stained with iron hematoxylin Appears as paired small dark bodies in a pale area [Centrosome] E.M: 2 Short hollow cylinders (0.5x0.2um) Perpendicular to each others Wall is formed of 9 bundles Each bundle consists of 3 microtubules (triplet) [i.e.: 9 X 3 = 27 Microtubules  Centrioles Functions: 1-Formation of mitotic spindle during cell division During cell division, The centrosomes divide in two, move to the opposite poles of the cell, become organizing centres for microtubules of mitotic spindle [Microtubule Organizing Centre or MTOC] 2-Formation of cilia & flagella Medical application: Anti-mitotic drugs such as colchicines can stop mitosis as they prevent the development of the mitotic spindle, which bind to tubulin and prevent its addition at the plus end. Therefore, the colchicines are used in karyotyping and in treatment of cancer.  filaments Def: Minute threads that maintains cell shape. L.M: -Only seen when present in bundles -Stained by special stain (Ag). Thin Microfilaments [Actin] Cortical actin  microvilli [Actin] pseudopodia Actin ring terminal web actin myosin Thin Microfilaments [Actin] G actin 5-7nm in diameter, Formed of actin protein helical, rod- or thread-like protein fibers Sites & Functions: A-In Cytoplasm: Forms dense mesh under cell membrane 1-Provide strength to cells 2-Link integral proteins to cytoplasmic proteins 3-Initiate motility & change cell shape [Amoeboid movement] B-In muscle: Interact with myosin for contraction C-In terminal web and microvilli: Forming the core Cell junction Contractile ring (cortical actin) during cell division Actin network Cell junction Actin ring  Terminal web and microvilli microvilli Terminal web Actin filament Intermediate Filaments (They are the most stable cytoskeletal component, strong mechanical stability to cells). 8-10 nm diameter Many types [about 50 in human] formed of several protein The main function is to provide structural support & stabilize junctions between cells Intermediate Filaments Types: a-Cytokeratin [Tonofilaments]: in epithelial cells & form hairs and nails b-Vimentin: in connective tissue & muscle c-Desmin: in muscle. d-Neurofilaments: in nerve cells e-Glial filaments: in glial cells e-Glia filaments in glia cells f- Lamins: support inner aspect of the inner nuclear memebrane Intermediate Filaments Function: a) It is one component of the cytoskeleton which supports the cell, and serves to maintain its shape. b) Helps to ensure equal distribution of the tensile forces throughout the cells (in smooth muscles and keratinocytes of skin). c) Involved in muscle contraction. d) Plays a role in cell division Thick Filaments (Myosin) More than 20 nm thickness Formed of myosin protein, arranged in bundles Present in muscle cells → Interact with actin for muscle contraction Functions 1. Maintenance of cell shape (tension myosin bearing elements). 2. Anchorage of nucleus and other organelles. Cell organelles 3. Connect cytoskeleton to plasma membrane membrane nucleus Carbohydrates [Glycogen] Site: in liver & Muscles E.M: -Electron-dense granules -Either single L.M: -Not seen by H&E [water soluble] [α Granules] or in rosette-shaped groups [β -Stained by Best's Carmine (red Granules] -Mostly concentrated in granules) or PAS (purple). cytoplasm in areas rich in sER  LIPID Liver: Small droplets Fat cells: Stored as large  L.M: In H&E appear as empty vacuoles [Xylol dissolves fat] Special stains: -Sudan III → Orange -Sudan black → black  Summary Non-Membranous organelles Ribosomes Proteasomes Cytoskeleton Microtubules Filaments Cytoplasmic Inclusions Stored Food granules Pigments  Peptidyl transferase (is the main enzyme used in Translation) Peptidyl transferase is released by ……….. a b What is the structure ? What is the function ? What is the structure ? What is the function ?