by JIGAR S. MEHTA Asst. Professor ( BIOCHEMISTRY ) M.Sc. B.Ed. M.B.A. ADVANCE STUDIES IN CELL BIOLOGY -------------the cytoskeleton--------------- by JIGAR S. MEHTA Asst. Professor ( BIOCHEMISTRY ) M.Sc. B.Ed. M.B.A.

OVERVIEW OF THE UNIT 5.1 CYTOSKELETON 5.2 Cell movements & locomotion 5.3 CELL CELL INTERACTION 5.4 OVERVIEW OF STEM CELLS (SC) 5.5 Cancer Biology -Microfilaments - signal Cancer -Microtubules Amoeboid -Intermediate Filaments - types of signal -Potency Types Cyclosis -Types of stem cells: Tumors & their types Flagellated - pathway Ciliated - mechanism BSC Causes MSC Molecular transport - receptor Molecular basis - types of receptor OSC TSC Prevention & 3 Therapies i) Intracellular PSC ii) Cell surface receptor USC ESC a) G protein linked ASC -Stem Cells b) Enzyme linked Therapy c) Ion channel linked

5.1 CYTO-SKELETON Definition: The cytoskeleton also known as(aka)CSK is a cellular framework or skeleton contained within a cell’s cytoplasm and is made up of proteins .  It was thought to be unique in eukaryotes , but recent research has identified it in prokaryotes also.  Eukaryotes contain 3 main types of CSK: Microfilaments (MFs) or Actin Filaments Microtubules (MTs) Intermediate Filaments (IFs)

5.1.1 MICRO-FILAMENTS LOCATION/DISTRIBUTION: Cortical region just beneath plasma membrane Microvilli of the brush border of intestinal epithelium Cells which perform amoeboid movement & cyclosis Myofibrils ( muscle cells )

FEATURES & CHEMICAL COMPOSTION of MFs: Thin solid filaments of actin proteins 5-7 nm in diameter Concentration of actin in non-muscle cells is 10% of all protein content.( total cell protein) G-actin & F actin transition is the basis of the clasical sol-gel transition in the cytoplasm of moving cells. This actins are of three types : Alpha actin (in fully mature muscle cells) Beta & Gamma actin in non muscle cells

ACTIN DYNAMICS

FUNCTIONS OF ACTIN FILAMENTS: Involved in the movement associated with formation of “furrow/cleavage” duringh cell division. Cytoplasmic streaming ( cyclosis) in plant cells.eg: Nitella & Chara Cell migration during embryonic development. Amoeboid movement of cells like WBCs. Muscle Contraction & Relaxation. Maintanaince of cell structure & shape. Function inhibitors: Cytochalasin B ( A plant extract/ alkaloid)

MICROTUBULES(MTs) First observed by : Robertis & Franchi (1953) They called it as “ Neurotubules”. Mts of plant cells were first described by Ledbetter& Porter (1963) Occurrence : Found in all eukaryotic cells either free in cytoplasm or forming part of centrioles (axoneme). See figure on next slide Its high density exist in axons & dendrites of nerve cells.

Structure of MTs: Consist of long unbranched , hollow tubules of 25 nm in diameter. Each MT is made of sub unit- protofilaments , each consist of 13 tubulin proteins. ( alpha & beta tubulins). The wall of MT is 6nm thick. MTs are polar structures having a plus end/ fast growing end & minus end / slow growing end. Minus end are bound with MTOCs that helps in its polymerization. Plus end are protected from disassembly by capping proteins. The MT also contains MAPs (microtubule associated proteins) egs: HMW & tau proteins .

Functions: Intracellular transport (associated with dyenins & kinesins, they transport organelles like Mitochondria or vesicles forming a bridge. It forms the axoneme of cilia & flagella . Forms mitotic spindle during cell division. Synthesizes cell wall in plants . Function Inhibitors: Calcium ions,. calmodulin, colchicine, vinblastin , vincristine & Taxol.

INTERMEDIATE FILAMENTS Intermediate filaments are tough and durable protein fibers in the cytoplasm of most eukaryotic cells . Constructed like woven ropes 8-10nm in diameter. First described in muscle cells In animal cells they form the basket around the nucleus.

IFs are found mostly where cells are subjected to mechanical stress such as epithelia, smooth muscle cells etc. IFs in epidermal cells are called Tono-filaments. IFs in nerve cells are called Neuro-filaments. IFs in glial cells and astrocytes are called GFAP(Glial fibrillary acidic protein)

THE CYTOSKELETN END OF TOPIC 5.1

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