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cell ultrastructure

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BIL 116

Cell Ultrastructure  Magnification → increases the size of an object  Resolution/resolving power → ability to distinguish between adjacent points Table 1-10-2: Microscopes (1) Optical microscope Electron microscope Feature Radiation Light Electrons Magnification 400x (max1500) ≈500 000x Resolution 2µm 1nm / 0,001µm Electrons have a small wavelength \ Higher resolution Vacuum in microscope Absent Present Specimen is - Alive or dead - Dead (vacuum!) - Stained Transmission microscope: Electrons pass through internal structure of specimen Scanning microscope: Beams of electrons are reflected off specimens surface. Allows a three dimensional view Cell wall (plant cells only)  Made up of cellulose fibres which provide strength  Cell does not burst if surrounding solutions become dilute Nucleus (5µm)  Contains chromosomes (genes made of DNA which control cell activities)  Separated from the cytoplasm by a nuclear envelope  The envelope is made of a double membrane containing small holes  These small holes are called nuclear pores (100nm)  Nuclear pores allow the transport of proteins into the nucleus Rough Endoplasmic Reticulum (rough ER)  Have ribosomes attached to the cytosolic side of their membrane  Found in cells that are making proteins for export (enzymes, hormones, structural proteins, antibodies)  Thus, involved in protein synthesis  Modifies proteins by the addition of carbohydrates, removal of signal sequences  Phospholipid synthesis and assembly of polypeptides Smooth Endoplasmic Reticulum (smooth ER)  Have no ribosomes attached and often appear more tubular than the rough ER  Necessary for steroid synthesis, metabolism and detoxification, lipid synthesis  Numerous in the liver Ribosomes (20-30nm)  Small organelles often attached to the ER but also found in the cytoplasm  Large (protein) and small (rRNA) subunits form the functional ribosome o Subunits bind with mRNA in the cytoplasm o This starts translation o
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