Non-Membranous Organoids (Cytoskeletons & Proteosomes) Lecture 5 PDF

 lecture 5 2023-2024 Non-Membranous Organoids (Cytoskeletons & Proteosomes) By Dr. Dr Doaa Khaled Lecturer of HISTOLOGY & CYTOLOGY, Faculty of Medicine , Helwan University  Objectives 1- Classify types of cytoskeletons 2- Describe the his...

 lecture 5 2023-2024 Non-Membranous Organoids (Cytoskeletons & Proteosomes) By Dr. Dr Doaa Khaled Lecturer of HISTOLOGY & CYTOLOGY, Faculty of Medicine , Helwan University  Objectives 1- Classify types of cytoskeletons 2- Describe the histological structure of each type. 3- Describe histological structure of proteosomes. 3- Correlate the functions of these organelles to their structure.  B) Non-Membranous Cell Organoids 1- Ribosomes and polyribosomes (Discussed before)- 2- Microtubules (Centroiles, cilia and flagella). 3- Filaments. Cytoskeleton 4-Proteosomes  Cytoskeleton (Microtubules ,Microfilaments & intermediate filaments)  Cytoskeleton The cytoplasmic cytoskeleton is a network complex of 1- Microtubules and 2- Microfilament (actin) and 3- Intermediate filaments. General function of cytoskeleton ? A) Structural-------------- b) Movement.------------------- 1- Microtubule Defintion : Microtubules are very small hollow Tubes (25nm diameter & 5 nm thick), only seen by E.M.  EM of microtubules  It is characterized by rigidity (semiflexible). Vary in length & have spiral organization Each microtubule consists of 13-rod shaped structure called Protofilaments arranged parallel to the long axis of the microtubule. The formation of microtubules: A-Sites of formation. B-Mode of formation. C-Drugs affecting formation. Sites of formation: - MTOCs act as nucleating sites for further polymerization & formation of microtubule. - The length of microtubule is dynamic. - (MTOC) or centrosome is an area of cytoplasm full of tubulin subunits & other ptns and - Organized around 2 cylindrical centrioles. B)- Mode of formation: 1- Subunite : α and β Tubulin (dimers) 2- Longitudinally aligned α and β (dimers) subunits make up(protofilaments). 3. Each 13 protofilaments arranged to form the wall of a microtubule. tubulin Dimers→protofilament→13 protofilaments → M.T  Microtubules show dynamic instability (Continous tubulin polymerization (adding tubulin subunite) & depolymerization (lost tubulin) C-Drugs affecting formation: -The formation of MT is inhibited by Vinblastin &vincristine (chemotherapies)…….cell division will be affected. Types of cellular microtubules: 1) Unstable form : (mitotic spindle). 2) Stable form, (centrioles, cilia & flagella)  A) The Centrosome & the Centriole Definition: 1- The centrosome is the microtubule-organizing center (MTOC) consists of 2 cylindrical centrioles 2- The TEM reveals that the two centrioles exist at right angles to one another Each centriole(highly organized) consists of 9 triplets of microtubules. - Each triplet is composed of 3 microtubules Function of centriole: At the onset of mitosis, what is happened? (This part will be discussed later in cell division lecture).  Function of Microtubules (MT( 1- intracellular transport of organelles and vesicles. Examples include: a- Axoplasmic transport in neurons. b- Melanin transport in pigment cells, c- Chromosome movements by the mitotic spindle d- Transport along microtubules is under control of special motor proteins (kinesin & dynein) which use ATP to move molecules and vesicles along microtubule. - Kinesins carry organelles or vesicles away from the centre of the cell toward cell membrane ; cytoplasmic dynein carry vesicles in the opposite direction Motor proteins associated with microtubules 2- Microfilaments (Actin )  Actin filaments a- (5–7 nm diameter) , more flexible than microtubule. b- Microfilaments composed of globular subunits (G actin) organized into a double-stranded helix (F actin) Actin filament Site of actin filaments: - Concentrated in 1) Cell extensions (core of microvilli). 2) Pseudopodia: Induce amoeboid movement of the cell  Function of actin filaments Interaction between actin & myosins MOTORS form the basis of cell movements: 1- Cytoplasmic streaming. 2- Contractile ring (actin +myosine II)---to produce TWO cells by cytokinesis during mitosis. 3- Interacrion of actin filaments with thicker(16 nm) myosin filaments are responsible for contractile movements of muscles 3- Intermediate filaments Definition : a class of filaments intermediate in size (8-10 nm) between the microtubule & microfilaments. - In comparison with microtubules and actin filaments, intermediate filaments are much more stable(not dynamic) provide mechanical stability to the cell). - Have various protein components in different cell types. Structure : All are essentially rod-like rather than globular proteins that form coiled tetramers What are types of intermediate filaments? 1-keratin (cytokeratin) filaments… Bundles of keratin filaments called (tonofibrilis). Site : in epithelial cells –hair- nail 2-Neurofilaments: Site: in neurons to support their long processes 3-Desmin: in muscle cells to connect myofibrils together. - Vimentin: (most common type) connective tissues -muscle cells – 4- Lamins: in nuclear envelop..  Medical application Identification of intermediate filaments ptns by immunocytochemical methods This means that we can recognize the origin of tumors So it is imp for diagnosis & treatment of tumors ….  Proteasomes They are non membranous cell organelles, They are protein complexes including proteases that digest proteins. The protein targeted for destruction is marked by its attachment to ubiquitin which is a cytosolic protein found in all cells Proteasomes deal primarily with free proteins as individual molecules.  Function of proteasomes: Protein degradation which is essential to remove: ✓ Misfolded and denatured proteins. ✓ Excess enzymes and other proteins that become unnecessary after performing their normal functions as cyclins that regulate cell cycle.  Clinical application Failure of proteasomes allow accumulation of malformed proteins which interfere with cell functions e.g: Alzheimer disease 46  Test yourself Which of the following is true? a) Actin filament is measured 25 nm. b) Desmin is an intermediate filament present in nerve cell. c) Centrioles are formed of microfilaments d) Intermediate filament is non dynamic structure Which of the following is FALSE concerning proteosome? A- It is non membranous organelles B- It has enzymes for digestion of secretory proteins C- It has enzymes for digestion of misfolded proteins D- It deals with bulk organelles ( like lysosomes)  Home activity Compare between 3 types of cytoskeleton ( microtubule, microfilament & intermediate filament Reference Chapter 2, The Cytoplasm Junqueira's Basic Histology Text and Atlas, 16e 50