Ch 6 Summary Biologists use microscopes and the tools of biochemistry to study cells 1950 invention of microscopes cell walls first seen by Robert Hooke 1665 dead oak tree cells Light Microscope visible light is passed though the specimen and then through glass lenses o the lenses retract or bend the light in such a way that the image of the specimen is magnified and then projected into the eye or into a camera Magnification ratio of an object s size to its real size Resolution clarity of the image Contrast accentuates differences in parts of the sample Organelles the membrane enclosed structures within Eukaryotic cells Electron Microscope Scanning Electron Microscope Focuses a beam of electrons through the specimen or onto its surface Good for detailed study of the topography of a specimen The electron beam scans the surface of the sample usually coated with a thin film of gold The beam excites electrons on the surface and these secondary electrons are detected by a device that translates the pattern of electrons into an electronic signal to a video screen Transmission Electron Microscope Used to study the internal structure of cells Aims an electron beam through a very thin section of the specimen the specimen has been stained with atoms of heavy metals which attach to certain cellular structures enhancing the electron density of the cell o Disadvantage methods used to prepare specimen kill the cells Cell Fractionation takes cells apart and separates major organelles other subcellular structures from one another Allows scientists to prepare specific cell components in bulk and identify their functions How do stains used for light microscopy compare with those used for electron microscopy Stains used for light microscopy are colored molecules that bind to cell components affecting the light passing through while stains for electron microscopy involve heavy metals that affect the beams of electrons passing through Which type of microscope would you use to a Study changes in the shape of a living white blood cell a Light microscope b Study details of surface texture of a hair a Scanning electron microscope Eukaryotic cells have internal membranes that compartmentalize their functions Eukaryotic Cells Protists fungi animals plants Most of the DNA is inside nucleus True nucleus Cytoplasm refers only to the region between the nucleus and plasma membrane within the cytoplasm suspended in the cytosol are a variety of organelles Much larger Prokaryotic Cells Organisms from domains Bacteria and Archaea DNA concentrated to area that is not enclosed in the nucleoid Before Nucleus No membrane bound structures suspended in the cytosol Much smaller All cells have a plasma membrane with cytosol inside chromosomes and ribosomes Cytoplasm the name for the interior of either type of cell Plasma Membrane Functions as a selectively permeable barrier that allows passage of enough oxygen nutrients and wastes to service the entire cell A smaller object has a greater ratio of surface area to volume Larger organisms aren t made up of larger cells they just have more cells Microvilli Increase surface area without an appreciable increase in volume Animal Cells Lysosomes Centrosomes with Centrioles Flagella but present in some plant sperm Plant Cells Chloroplasts Central vacuole Cell wall Plasmodesmata The Eukaryotic Cell s genetic instructions are housed in the Nucleus and carried out by the ribosomes Nucleus contains most of the genes in the Eukaryotic cell Nuclear envelope encloses the nucleus separating its contents from the cytoplasm Nuclear envelope has double membrane two membranes each a lipid bilayer o Pore Complex lines each pore and regulates the entry and exit of proteins and RNA s and large complexes of macromolecules Nuclear Lamina may help to organize the genetic material so that it functions efficiently a net like array of protein filaments that maintains the shape of the nucleus by mechanically supporting the nuclear envelope o Nuclear matrix framework of protein fibers extending throughout the nuclear interior Chromosomes carry genetic information reside in the nucleus Each chromosome contains one long DNA molecule associated with many proteins Chromatin is the complex of DNA and proteins making up the chromosomes As a cell prepares to divide the chromosomes coil becoming thick enough to be distinguished as separate structures Nucleolus where rRNA is synthesized from instructions in the DNA Proteins imported from the cytoplasm are also assembled with rRNA into large and small subunits of ribosomes o These subunits then exit the nucleus through the nuclear pores to the cytoplasm where a large and small subunit can assemble into a ribosome The nucleus directs protein synthesis by synthesizing messenger RNA according to instructions provided by the DNA mRNA is then transported to the cytoplasm via the nuclear pores once in the cytoplasm the ribosomes translate the mRNA s genetic message into the primary structure of a polypeptide Ribosomes complexes made of ribosomal RNA protein and carry out protein synthesis free ribosomes cytosol o most protein made on free ribosomes functions within the bound ribosomes attached to the outside of the endoplasmic reticulum or nuclear envelope o generally make proteins that are destined for insertion into membranes for packing within certain organelles Cells that specialize in protein secretion pancreas frequently have high proportions of bound membranes What role do ribosomes play in carrying out genetic instruction Ribosomes in the cytoplasm translate the genetic message carried from DNA in the nucleus by MRNA into a polypeptide chain Describe the molecular composition of the nucleoli and explain their function Nucleoli consist of DNA and rRNA made according to its instructions as well as protein from the cytoplasm Together the rRNA and proteins are assembled into large and small ribosomal subunits As the cell begins the process of dividing its chromatin becomes more and more condensed Does the number of chromosomes change during this process Explain No Each chromosome is present whether its chromatin is relatively diffuse or condensed The Endomembrane system regulates protein traffic and performs metabolic functions in the cell Endomembrane system includes nuclear envelope endoplasmic reticulum golgi apparatus lysosomes various kinds of vesicles vacuoles and the plasma membrane o This system carries out synthesis of proteins o Transport of proteins o
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