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Chapter 5: A Tour of the Cell AP Biology http://vimeo.com/37107992 Overview of Cells AP Biology elements p+, no, e- Cell structure & function Cell structure correlates to cell function AP Biology Structure-function: red blood cells need to be able to squeeze through one-cell wide capillaries…you would want them to be squishy and balloon like, not wirey like neurons or long and spindly like muscle cells etc… These are neurons, shaped like wires to carry electrical information between cells. They act like wires. AP Biology These striped (striated) cells are skeletal muscle cells (the ones you voluntarily control to move your bones, etc…). I outlined part of one in black below. They are multi-nucleated (each cell has many nuclei) because they form from the fusion (joining together) of many individual cells. The stripes are the actin and myosin proteins, which contract (shorten) the cells. nuclei AP Biology Brief History of the Microscope Leeuwenhoek made major advances in microscopy and was the first to observe free living protists and bacteria (both known as microorganisms of Mos), which combined he called animalcules … Antonie Philips van Leeuwenhoek (1632 – 1723) AP Biology http://inventors.about.com/od/mstartinventions/a/microscope.htm Dutch Scientist, The Father of Microscopy/Microbiology Brief History of the Microscope Robert Hooke (1665) Communicated with and confirmed Leeuwenhoek’s findings, improved on the microscope and coined the term “cell”. Drawing of the structure of cork as appeared in Hooke’s book Micrographia in 1665 AP Biology Robert Hooke (1635 – 1703) English Scientist The “English” Father of Microscopy How do we describe the strength of a microscope? 1. Magnification - Simply how much larger the object appears to be relative to its actual size. 2. Resolution - Measure of the clarity of the image - The distance two points can be separated and still be distinguished as two points AP Biology 10 m Human height Different Microscopes Light Microscope Length of some nerve and muscle cells 0.1 m 1 cm Frog egg 1 mm 100 µm Image is a called a micrograph Most plant and Animal cells 10 µ m Nucleus Most bacteria Mitochondrion 1µm Smallest bacteria 100 nm Viruses 10 nm Ribosomes Proteins 1 nm Lipids Small molecules AP Biology http://learn.genetics.utah.edu/content/cells/scale 0.1 nm Atoms Electron microscope Visible light passing through a specimen Light Microscope Chicken egg Unaided Eye 1m Light Microscope sperm Ovum AP Biology Cells are for the most part colorless like the sea urchin egg (ovum) and sperm shown here. If they are colored, they have either been stained by the scientist or they are naturally colored like red blood cells by some type of molecule that gives off colored light. Light Microscope Bamboo Vascular (transport) Cells Here you are looking at cells from a bamboo plant. These cells have been stained to make them more visible. AP Biology Light Microscope Plants cells The small green structures inside the rectangular plant cells are their chloroplasts. AP Biology Very important, these cell are ALIVE!! You can view living cells as they exist in nature with a light microscope… (just an aside: if you stain them they die) Methods for viewing cellular structures TECHNIQUE Differential-interference-contrast (Nomarski). Uses optical modifications to exaggerate differences in density, making the image appear almost 3D. Brightfield (unstained specimen). Human cheek epithelial cell Brightfield (stained specimen). Staining with various dyes enhances contrast. Phase-contrast. Enhances contrast in unstained cells by amplifying variations in density within specimen AP Biology 50 µm Fluorescence. Tags specific molecules with dyes 50 µm Confocal.. A sharp image results, as seen in stained nervous tissue (top), where nerve cells are green, support cells are red, and regions of overlap are yellow. A standard fluorescence micrograph (bottom) of this relatively thick tissue is blurry. Electron Microscopes Focus a beam of Cross section of cilium electrons through a specimen TEM – transmission Detailed study of internal structure SEM- surface Detailed study of the surface of specimen AP Biology Cilia 1 µm Red Blood Cells Compare the SEM micrograph to the Light Micrograph in the bottom right AP Biology Viruses This is a colored SEM micrograph of a number of viruse particles (herpes virus – virus that causes herpes). Each viral particle is around 50nm which is about 100x smaller than bacteria. AP Biology Bacteria being eaten by a The bacteria WBC are in green and the WBC is tan. Bacteria (prokaryotes) are around 100X smaller than eukaryotes. AP Biology A mosquito. AP Biology TEM showing internal structure of a plant cell (outlined in blue)… AP Biology Yet even higher Magnification of the EUKARYOTIC CELL Mitochondri a AP Biology Cell Fractionation Takes cells apart and separates major organelles from one another The centrifuge Is used to fractionate cells into their component parts AP Biology Cell Fractionation APPLICATION Cell fractionation is used to isolate (fractionate) cell components, based on size and density. Homogenization Tissue cells TECHNIQUE 1000 g Homogenate (1000 times the force of gravity) Differential centrifugation 10 min First, cells are homogenized in a blender to break them up. The resulting mixture (cell homogenate) is then centrifuged at various speeds and durations to fractionate the cell components, forming a series of pellets. Supernatant poured into next tube 20,000 g 20 min RESULTS In the original experiments, the researchers used microscopy to identify the organelles in each pellet, establishing a baseline for further experiments. In the next series of experiments, researchers used biochemical methods to determine the metabolic functions associated with each type of organelle. Researchers currently use cell fractionation to isolate particular organelles in order to study further details of their function. AP Biology Pellet rich in nuclei and cellular debris 80,000 g 60 min 150,000 g 3 hr Pellet rich in mitochondria (and chloroplasts if cells are from a Pellet rich in plant) “microsomes” (pieces of plasma membranes and Pellet rich in cells’ internal ribosomes membranes)
