Lec. 7 Eukaryotic Cytoskeleton, Centrosome, Inclusion Bodies PDF

College of Medicine, University of Mosul/ Department of Anatomy Subject: Medical Biology Stage: 1 st Lec. 7 Title: Eukaryotic Cytoskeleton, Centrosome, Inclusion Bodies Cytoskeleton: Structure and Function: The cyto...

College of Medicine, University of Mosul/ Department of Anatomy Subject: Medical Biology Stage: 1 st Lec. 7 Title: Eukaryotic Cytoskeleton, Centrosome, Inclusion Bodies Cytoskeleton: Structure and Function: The cytoskeleton is a complex network of protein filaments and tubules found in eukaryotic cells. It plays a crucial role in providing structural support, maintaining cell shape, facilitating intracellular transport, and enabling various cellular processes. The cytoskeleton consists of three main types of protein filaments: three-eukaryotic-cells-cytoskeletal-filaments-microfilaments-microtubules-intermediate-198630308 Microfilaments (Actin Filaments): Microfilaments are the thinnest and most flexible component of the cytoskeleton. They are composed of actin protein subunits arranged in a helical structure. Functions of microfilaments include: -Providing mechanical support to the cell's plasma membrane. -Facilitating cell motility, such as muscle contraction. -Participating in cell division. -Enabling cell shape changes and cytoplasmic streaming. -Anchoring and organizing membrane proteins. 1 Intermediate Filaments: They are made up of various types of fibrous proteins, including keratins, vimentins, and lamins, depending on the cell type. Functions of intermediate filaments include: -Maintaining cell shape and resistance to mechanical stress. -Anchoring cell organelles. -Serving as structural components of various tissues, such as hair, skin, and nails. -Providing support to the nuclear envelope. Microtubules: Microtubules are the largest of the cytoskeletal components and are composed of tubulin protein subunits of (α and β- Tubulin forming dimer). Functions of microtubules include: -Forming the mitotic spindle during cell division, and separating chromosomes. -Serving as tracks for intracellular transport of organelles and vesicles. -Anchoring and organizing the centrosome. -Providing structural support to cilia and flagella. -Playing a role in the maintenance of cell shape and axonal transport in nerve cells. 2 Centrosome: The centrosome consists of a pair of centrioles surrounded by pericentriolar material. Centrioles: Centrioles are small, cylindrical organelles found in animal cells, as well as in some lower plants and protists. Centrioles are typically found in pairs near the nucleus of animal cells. Each centriole is composed of nine triplets of microtubules arranged in a cylindrical structure organized in a 9+0 pattern, meaning that each triplet is composed of three microtubules and there is no central microtubule in the structure. The two centrioles in a pair are oriented at right angles to each other. Cilia & Flagella Cilia and flagella are slender, hair-like cellular structures found on the surface of many types of cells in various organisms. Structure: Cilia and flagella are composed of a microtubule-based core, known as the axoneme, surrounded by a plasma membrane. The axoneme consists of nine microtubule doublets arranged in a 9+2 pattern (two central microtubules surrounded by nine outer pairs). Cilia are short, hair-like structures that extend from the cell surface. They are typically present in large numbers on a single cell. Function: -Movement: Cilia help move mucus and trapped particles out of the lungs. -Sensory Functions: Retina has non-motile cilia with sensory functions, helping to detect light or other stimuli. -Feeding: In some protists, cilia are used to capture food particles. 3 Flagella: Flagella are long, whip-like structures that extend from the cell surface. Function: -Cell Locomotion: Flagella are used for cell movement. e.g. sperm cells. -Sensory Functions: Non-motile flagella are detecting environmental cues. Inclusions bodies (non-organelle) Abnormal, structures or aggregates of proteins or other substances that can be found within cells. Types of Inclusion Bodies: 1. Protein Aggregates: Some inclusion bodies consist of misfolded or aggregated proteins. These can form as a result of protein misfolding (α-Synuclein) accumulation, or improper protein degradation. Examples include Lewy bodies in Parkinson's disease. 2. Viral Inclusions: These inclusions can be sites of viral replication or assembly. Examples include Negri bodies in rabies and Cowdry bodies in herpes infections. 3. Storage Granules :Glycogen granules are inclusion bodies where excess glucose is stored within liver cells. 4. Pigment Inclusions: In some cases, cells may accumulate pigmented inclusion bodies. e.g. lipofuscin, a pigment associated with cellular aging, and melanin granules in melanocytes. 4 5. Hyaline Inclusions: These are amorphous, glassy inclusions found in certain cells and can contain a variety of substances. They are often associated with various diseases, such kidney diseases. Functions and Significance:  The presence of inclusion bodies can be indicative of underlying cellular stress, disease, or genetic mutations.  Inclusion bodies are associated with the accumulation of toxic proteins and can contribute to cell damage and disease progression.  Viral inclusion bodies can be diagnostic markers for specific infections and may indicate the presence of an active viral replication process. Detection and Analysis:  Inclusion bodies are often observed through microscopy, and their presence can be an important diagnostic tool in the study of diseases and infections.  Various staining techniques, such as immunohistochemistry and electron microscopy, can be used to visualize and analyze inclusion bodies.  Modern molecular and cellular biology techniques of proteomics, can be employed to study the protein composition and structure of inclusion bodies.  5