LEC 6 Biology PDF

Cytoskeleton of a cell disteducation.mashreq.edu.sd/ Cytoskeleton of a cell :  Consists of a network of tiny protein filaments and tubules, that extend through out the cytoplasm.  It form the framework of the cell’s structural. The cytoskeleton: 3 types (a) microtubules (b) microfilament...

Cytoskeleton of a cell disteducation.mashreq.edu.sd/ Cytoskeleton of a cell :  Consists of a network of tiny protein filaments and tubules, that extend through out the cytoplasm.  It form the framework of the cell’s structural. The cytoskeleton: 3 types (a) microtubules (b) microfilaments (c) intermediate filaments Microtubules Microtubules ▶ Largest filaments in cytoskeleton. ▶ Found in almost all cell types except red blood cells. ▶ Are hollow, un branched structures composed of the two- protein subunit of tubulin.  determine the cell shape  movement of organelles and secretory granules in intracellular ▶ Form from centrosome ▶ Most visible in cilia and flagella Microfilaments - Thinnest structures of the cytoskeleton. -They are composed of the protein actin(shape the cells). -Distributed through out cell and used as anchors at cell junctions. Form pulp of microvilli and cilia. In muscle tissues(Skeletal and cardiac muscles) , the actin filaments fill the cells and are linked with myosin proteins to make muscle contractions.  Responsible for cell movements e.g.: bending of microvilli, contraction of pseudopodia, formation of cell division Cardiac muscle Skeletal muscle Intermediate filaments:  Are thicker than microfilaments  The most permanent, like guy wires Comprise a variety of other filaments found in the cell, e.g: Myosin filaments of sarcomere Tono filaments of desmosomes Neuro filaments found in neurons keratin filaments Components at apical end of epithelial cells Lamin filaments found in nuclear membrane  Cell Junctions Tight junctions – So close that are sometimes impermeable Adherens junctions –Transmembrane linker proteins Desmosomes – Anchoring junctions – Filaments anchor to the opposite side Gap junctions – Allow small molecules to move between cells Cell Junctions 1. Zonula occludens 2. Zonula adherens 3. Desmosome structures a. macula adherens – desmosome b. hemidesmosome c. septate desmosome 4. Gap junction 5. Interdigitating membrane  Apical surface (cell surface) Microvilli  Fingerlike extensions of the plasma membrane of apical epithelial cells.how can makes that?? The cytoplasmic projections from the free surface of some cells. In EM : Why the epithelial cells are make Microvilli?? For increasing its surface area The function of Microvilli : ▶ Absorb nutrients (small intestine). ▶ Transport ions (kidneys). Cilia –Whip like, motile extensions of the apical surface membranes Flagellum –Long isolated cilium –Only found as sperm in human The structure : ▶ The wall of the cilia consist of (9) tubules, each tubules consist of pairs of microtubules surrounding (2) central microtubules. Cillia Respiratory Mucosa Euglena (Flagellum) Paramicum (cilia) The functions of cilia: ▶ 1-They get and moves foreign particles away (respiratory system). ▶ 2-They push the ova in the fallopian tube. The functions of Flagella:- ▶ Use for movement or swimming. Pseudopodia (false feet):  Are amoeboid movement.  In human: Are present in phagocytic cells (white blood cells).  In protozoa: Are present in amoeba ▶ ▶ Amoeba