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BIO1011: Textbook Summary - A tour of the cell

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Microscopes o In a light microscope, visible light is passed through the object under the microscope and then through glass lenses. o The lenses bend the light so that the image of the object is magnified. o Important parameters in microscopy: - Magnification - Resolution (resolving power) - Contrast o Magnification is the ratio of an object’s image size to its real size. o Resolution is a measure how clear the image is. o Contrast emphasises differences in parts of the sample. o Electron microscope focuses a beam of electrons through the object or onto its surface. o The scanning electron microscope is used for detailed study of the surface of a specimen. The electron beam scans the surface of the sample, which is coated with a thin film of gold. o Transmission electron microscope is used to study the ultrastructure of cells. It aims an electron beam through a very thin section of the specimen. Cell Fractionation o Cell fractionation takes cells apart and separates the major organelles and other subcellular structures from one another. o It enables researchers to prepare specific cell components in bulk and identify their functions. Comparing eukaryotic and prokaryotic cells o All cells have a selective barrier – plasma membrane o The cytosol surrounds the membrane and it is where all the organelles and other components are found. o All cells contain chromosomes, which carry genes in the form of DNA. o All cells have ribosomes, which makes proteins according to instructions from the genes. o The difference between eukaryotic and prokaryotic cells is the location of their DNA. o Eukaryotic cell’s DNA is found in the nucleus which is bounded by a double membrane. o Prokaryotic cell’s DNA is concentrated in a region that is not membrane-enclosed – nucleoid. o Eukaryotic cells are much larger than prokaryotic cells. o The plasma membrane acts as a selective barrier that allows sufficient passage of oxygen, nutrients and wastes to the entire cell. BACTERIA AND ARCHAEA Cell-surface structures o Prokaryotic cells have a cell wall which maintains cell shape, provides physical protection and prevents the cell from bursting in a hypotonic environment. o Peptidoglycan is present in bacterial cell wall which is a network of modified-sugar polymers cross-linked by short polypeptides. o Gram
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