Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Lecture 5: The Cell Microtubules and microfilaments The Cytoskeleton اهليكل اخللوى A network of fibres شبكة من االليافthat provide structural support تدعيم to the cell. The cytoskeleton also functions in cell motility تحرك الخليةand regulation The Cytoskeleton اهليكل اخللوى The cytoskeleton is a network of fibers extending throughout تمتد عبرthe cytoplasm. The cytoskeleton organizes يرتب structures the cell. the and activities of Cytoskeleton Microtubules أنيبيبات دقيقة Thick سميكة Responsible for cell motility, and separation of chromosome during cell division. (Tubulin protein) Microfilaments ألياف دقيقة Intermediate filaments ألياف متوسطة Thin Middle رفيعة متوسطة Support cell motility and transport materials within the cell. Reinforcing the cell shape and fixing position of organelles. (Actin protein) (Fibrous protein) Cilia and Flagella Microtubules are the central structural supports both cilia األهداب and flagella األسواط. Both can move unicellular and small multicellular organisms by propelling water outside the organism. • Cilia usually occur in large numbers on the cell surface. • Flagella usually occur in just one or a few per cell. • Cilia move more like oars مجادبفwith alternating power and recovery strokes. • Flagella have an undulatory movement حركة تموجية. • So, They differ in their beating pattern أسلوب الحركة. cilia flagellum Cilia and flagella are formed of arms of a motor protein (dynein )بروتين الداينين. Dynein arms alternately grab, move, and release the outer microtubules. Protein cross-links limit sliding and the force is expressed as bending إلتواء. Thus, many prokaryotes are motile متحركة About half of all prokaryotes are capable of directional movement الحركة الموجهة by the following:1- By the flagella األســواط, scattered مبعثرة over the entire surface, is the most common شائعةmethod of movement. 2- By two or more filaments ألياف. 3- By threads خيوطthat anchors تربطthe cells to the substratum السطح الذى تعيش عليه. 4- By cilia أهدابthat differ from flagella in beating pattern 7- Cell membrane • The plasma membrane functions as a selective barrier حاجز إختيارىthat allows passage of oxygen, nutrients, and wastes for the whole volume of the cell. Cell membrane Composed of lipids (phospholipids) and proteins Lipid layer contains hydrophilic and hydrophobic regions Carbohydrate chains Hydrophilic ُمحب للماء Phospholipid Hydrophobic كاره للماء Proteins Comparison between Prokaryotes and Eukaryotes Term Prokaryotes Eukaryotes Size 1-10 µm in diameter 10-100 µm in diameter Cell wall Existed In plant cell (not animal cell) nucleus No nuclear envelope but Nucleoid True nucleus exists with nuclear envelope DNA As fibre in the nucleoid As Chromatin (DNA and region (plasmids in some cases) protein) Specialized Most of them are absent Organells All are existed Cell division Meiotic and/or Mitotic By Binary Fission