Microscopy1590 microscope was inventedRefined in the 1600sCell walls first seen by Robert Hooke in 1665Looked at dead cells from an oak treeAntoni can LeeuwenhoekCrafted lenses able to visualize living cellsTypes of MicroscopesLight MicroscopeVisible light is passed through the specimen and then through a glass lens.The lenses refract (bend) the light in such a way that the image of a specimen is magnified as it is projected into the eye or a camera.Magnify effectively to about 1,000 times the actual sizeHigher than that details cannot be seen clearlyResolution of 0.2 micrometers to 200 nanometers, regardless of magnificationContrast-staining to labeling cell components to enhance contrastTHREE IMPORTANT PARAMETERS IN MICROSCOPYMagnificationRatio of an objects image size to its real sizeResolutionmeasure of the clarity of the image.The minimum distance two points can be separated and still be distinguished as two pointsContrastAccentuates differences in parts of the samplesElectron Microscope (EM)-1950Focuses a beam of electrons through the specimen or onto its surfaceResolution is related to the wave length of the radiation a microscope uses for imaging.Electron beams have much shorter wavelengths than visible light.Modern electron microscopes have a resolution of 0.002nm.Cannot resolve structures smaller than 2nm acrossScanning electron microscope (SEM)Useful for detailed study of the topography of a specimenElectron beam scans the surface of them sample.Usually coated with a thin film of goldThe beam excited electrons on the surface, these secondary electrons are detected by a device that translates the pattern of electrons into an electronic signal to a video screen.The result is an image of the specimens surface that appear 3D.Transmission Electron Microscope (TEM)Used to study internal structure of cellsTransmits electrons through a very thin section of the specimen, specimen has been stained with atoms of heavy metals, with attach to certain cellular structures, thus enhancing the electron density of some parts of the cell more than others.Electrons passing through the specimen are scattered more in denser regions, so fewer are transmitted.Uses electromagnets as lenses to bend the paths of the electrons, ultimately focusing the image onto a monitor for viewing.Light Microscopes allow the viewing of living cells.Electron microscopy-method to prepare the specimen kills the cells.Microscopes are the most important tool in cytology (the study of cell structure)Cell FractionationTakes apart and separates major organelles and other subcellular structures from one another.The instrument used is the centrifuge.Spins test tubes holding mixtures of disrupted cells at a series of increasing speeds.At each speed the resulting force causes a fraction of the cell components to settle to the bottom of the tube, forming a pellet.Lower speeds-pellet consists of larger componentsHigher speeds-pellet with smaller components.Enables researchers to prepare specific cell components in bulk and identify their functions, a task not usually possible with intact cells.Two types of cellsEukaryoticProtists, fungi, animals, plantsInternal membranes that compartmentalize their functionsProkaryoticDomains Bacteria and ArchaeaComparing Prokaryotic and Eukaryotic CellsAll bounded by a selective barrierCalled plasma membraneInside all cells is a semifluid, jelly like substance called cytosolSubcellular components are suspended in cytosolInterior of both cells is called the cytoplasm*In eukaryotic cells cytoplasm ONLY refers to the region between the nucleus and the plasma membraneWithin the cytoplasm, suspended in cytosol, are a variety of organelles of specialized form and function.These membrane bound structures are absent in prokaryotic cellsAll cells contain chromosomesCarry genes in the form of DNAAll cells have ribosomesTiny complexes that make proteins according to instructions from the genesDifferences in the NucleusEukaryotic cell (means “true nucleus, Greek ue=true, and karyon=kernel, referring to the nucleus)Most of the DNA is in the nucleus which is bounded by a double membrane.Prokaryotic cell (means before nucleus, Greek pro=before, reflecting that prokaryotic cells evolved before eukaryotic cells)DNA is concentrated in a region that is not membrane enclosedCalled the nucleoidEukaryotic cells are generally much larger than prokaryotic cellsSize is a general feature of cell structure that relates to functionLogistics of carrying out cellular metabolism sets limits on cell sizeThe plasma membrane functions as a selective barrier that allows passage of enough oxygen, nutrient, and wastes to service the entire cell.For each square micrometer of membrane, only a limited amount of a particular substance can cross per second.The ratio of surface area to volume is criticalAs a cell increases in size, its volume grows proportionately more than its surface area.Area is proportional to a linear dimension squaredVolume is proportional to the linear dimension cubedNeed for a surface area sufficiently large to accommodate the volume.Explains the microscopic size of most cellsThe narrow elongated shapes of others.Nerve cellsSufficiently high ratio of surface area to volume is especially important in cells that exchange a lot of material with their surroundings.Intestinal cellsCells may have long, thin projections from their surface called microvilliThese increase surface are without increasing volume.Larger organisms do not generally have larger cells that smaller organisms, they have more cells.A panoramic view of the Eukaryotic CellHas internal membranes (in addition to plasma membrane) that divide cells into compartments (organelles)These membranes participate directly in the cell’s metabolism because many enzymes are built right into the membranesBasic fabric of most biological membranes is a double layer of phospholipids and other lipids.Embedded in this lipid bilayer or attached to its surface are diverse proteinsCell’s genetic instructions are housed in the nucleus and carried out by the ribosomes.The nucleus: Information CentralThe nucleus contains most of the genes in the eukaryotic cell.Some genes are located in the mitochondria and chloroplastsNucleus is the most conspicuous organelle in a eukaryotic cellNuclear envelope encloses the nucleus, separating its contents from the cytoplasm.Nuclear envelope is a double membrane.Each membrane is a Lipid bilayers with associated proteins.20-40