Bilder summary notes - Lecture 1 Cell Organization Cell...

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Lecture 1: Cell Organization (1/20/16) Cell evolution As far as we know so far, all life is cellular. The three domains are: bacteria, archaea, and eukaryotes. Cell size Observing cells and subcellular organization: microscopy Microscopy is based on three main concepts: magnification, resolution, and contrast. The basic point of microscopy is magnification, or an increase in size. However, this would be useless without resolution, or the minimum distance at which two closely spaced objects can be distinguished. The smaller r is, the better (higher) the resolution is. Finally, contrast is the difference between the object being observed and its surroundings. The higher the contrast, the more signal to noise problems there are. Light microscopy uses transmitted light to magnify and resolve images. Its maximum resolution is about 200 nm. Phase contrast is a subcategory of light microscopy which allows visualization of internal cellular structure via differences in refractive index. Electron microscopy uses electrons, which have higher energy (smaller wavelength) than photons. Its maximum resolution is about 2 nm. However, unlike in light microscopy, in EM we need to kill the cells
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and fix them. TEM (transmission EM) is a subcategory of EM in which we section the cell using a diamond cutter, then use heavy metal staining to scatter electrons, creating contrast. An improvement on light microscopy, EM allowed us to differentiate between types of cells based on internal organization. For examples, we became able to differentiate between prokaryotes, which do not have organelles, and eukaryotes which do. It is important to note that even simple prokaryotic cells have a high degree of internal organization, i.e. compartments and cytoskeleton. Moving forward, we began to identify specific molecules within the cell. This began with fluorescence microscopy, another subset of light microscopy. In fluorescence microscopy, excitation light (e.g. UV source or laser) hits a fluorescent tag attached to the target molecular and results in emission light at a lower wavelength, which can then be detected by the microscopy via special filters. The discovery of GFP in particular made this method extremely useful . GFP’s gene and protein can be expressed in most organisms, it is non-toxic, and it glows autonomously in the living cell. A big advantage to this is that it allows us to visualize the cells without killing them. A molecular census in cells Cells are extremely crowded, meaning that there are constant random collisions and interactions. Essentially, life is driven by shifts in chemical equilibrium, i.e. concentrations, diffusion rates, etc. Membranes: assembly and organization Here are some advantages of compartmentalization and organization: - Provide a distinct microenvironment - Sequester harmful molecules - Concentrate specific molecules - Enable regulation Here are some functions of membranes: - Container for cellular biochemistry - Gives structure to the cell/organelle - Fluidity within the plane - Allow regulated permeability o Small hydrophobic molecules (e.g. gases) pass easily
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