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Download Unit A Notes #1 Cell Intro - Mr. Lesiuk
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Transcript
CELL STRUCTURE : PART ONE Cell Theory: - The study of cells had its birth with the invention of the microscope. Advances in Cytology (study of cell) took place in the 1900’s with the invention of better scanning microscopes. - In the late 1830’s two German biologists, Schleiden (a botanist) and Schwann, (a zoologists) made similar claims. They found that all organisms they had studied were composed of cells. Their discoveries were generalized in the following statement: 1. “ The cell is the basic building block of all organisms.” 2. "All organisms consist of one or more cells" - A few years later, Rudolph Virchow added the following observation: 3. “ All cells come from pre-existing cells.” Virchow: - These three statements comprise what is now known as the “CELL THEORY”. Cell Types: A) Prokaryotic Cells – (Pro = First, Karyo = Nucleus) Primitive (simple) cells. - Do not contain a nucleus or any membrane bound organelles. - Lack internal membranes. - Only Kingdom Monera (bacteria) have Prokaryotic cells. - In Prokaryotic cells, the reactions occur all over the cytoplasm, and reactions are less efficient. B) Eukaryotic Cells – (Eu =True, Karyo = Nucleus) Complex cells - Have a nucleus and many membrane bound organelles. - Contains internal membranes. - Each organelle carries out a certain function. - Eukaryotic cells make up Plants, Animals, Protists, and Fungi. Cellular Organelles and Other Cellular Components: Nucleus - Largest organelle. - Surrounded by a double-layered membrane (the nuclear envelope). - Membrane has pores through which larger molecules pass. (Nuclear Pores) - Control centre for the cell’s functions. (The brain). - Contains a fluid called the nucleoplasm. - Contains chromatin (DNA strands which form chromosomes during cell division). Nucleolus - Dark region in the Nucleoplasm. - One or more found in the nucleus. - Site where ribosomal RNA (rRNA) is produced or stored and ribosomes are made. - Involved in interactions between the nucleus and the cytoplasm. Chromatin: - The hereditary material of the cell. - Condenses to form chromosomes during cell division. - Composed of Protein (Histones) and DNA PROTEIN HISTONE Chromosomes - Rod-shaped bodies in the nucleus, only visible during cell division. - Contains the hereditary information. (genes) - Condensed (bunched up) chromatin. 23 pairs of chromosomes in a healthy human = 46 Cytoplasm = (Cytosol and cytoplasmic organelles) - A colloidal substance, which can change from a solid (gel) to a liquid (solution) state with the addition of heat or change in metabolic activity. - It contains and supports all the cells organelles. Cell Membrane or Plasma Membrane - Composed of proteins and phospholipids (fats containing a phosphate group). - Acts as skin around the cells contents. - Acts as a selectively permeable membrane to allow movement of materials in and out of the cell. - Located around the outside of the cell. - Single- layered membranes are located around the vacuoles, lysosomes, E.R., Golgi Apparatus. - Double-layered membrane around the nucleus and mitochondria. - Hydrophilic (water-loving) polar phosphate heads sticking out, with Hydrophobic (water fearing) fatty acid tails sticking in. Smooth Endoplasmic Reticulum - System of interconnected flattened tubes, sacs, or canals. - Begins at the nuclear envelope and branches throughout the cytoplasm to the cell membrane. - Moves molecules from one area to another. - It is the site of phospholipid (and steroid) manufacturing. - Cells that produce steroid hormones, have an abundant amount of smooth ER. - Section of both types of ER can break free “blebbing” to produce small membrane bound sacs of either proteins or lipids called vesicles. - Often these vesicles contain enzymes that synthesize lipids and related products such as steroids. - Some contain enzymes that detoxify drugs. - Amount of E.R. in a cell increases or decreases depending on the cell’s activity. Rough ER Rough Endoplasmic Reticulum - Like Smooth E.R., but with attached ribosomes. - Abundant in cells that produce large amounts of protein for export from the cell. The combination of phospholipid-membranous structures including the Nuclear Envelope, Endoplasmic Reticulums, Cell Membrane and Golgi Apparatus; collectively work together to form what is known as the Endomembrane System.