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Introduction to the Cell Introduction • Every living thing-from the tiniest bacterium to the largest whale-are made of one or more cells. • Before the seventeenth century, no one knew that cells existed. • Most cells are too small to be seen with the unaided eye. • Cells were not discovered until after the invention of the microscope in the early seventeenth century. The Microscope • One of the first microscopes was made by the Dutch drapery store owner Anton von Leewenhoek (16321723). • With his hand-held microscope, Leewenhoek became the first person to observe and describe microscopic organisms and living cells. • Leeuwenhoek is known to have made over 500 "microscopes," of which fewer than ten have survived to the present day. In basic design, probably all of Leeuwenhoek's instruments -- certainly all the ones that are known -were simply powerful magnifying glasses, not compound microscopes of the type used today. • In 1665, the English Scientist Robert Hooke (1635-1703) used a microscope to examine a thin slice of cork and described it as consisting of "a great many little boxes". It was after his observation that Hook called what he saw "Cells". They looked like "little boxes" and reminded him of the small rooms in which monks lived, so he called the "Cells". • The invention of the microscope lead to several important statements: • In 1838, German Botanist Matthias Schleiden studied a variety of PLANTS and concluded that all PLANTS "ARE COMPOSED OF CELLS". • The next year, German Zoologist Theodor Schwann reported that ANIMALS are also made of CELLS and proposed a cellular basis for all life. • In 1855- 1858, German Physician Rudolf Virchow induced that "THE ANIMAL ARISES ONLY FROM AN ANIMAL AND THE PLANT ONLY FROM A PLANT" OR " THAT CELLS ONLY COME FROM OTHER CELLS". Fundamental Ideas of Cell Theory 1. All living matter is composed of cells. 2. All cells arise from cells. 3. The cell is the basic unit of structure and function. (Smallest unit of life.) The Cell Theory A. Major Contributors. 1. Robert Hooke- 1600’s 2. Anton von Leewenhoek 3. Mattias Schleiden 1838 German botanist 4. Theodor Schwann 1839 German Zoologist 5. Rudolf Virchow 1858 How Cells are Studied - Microscopy 1. Light Compound Microscope How the light microscope works: • Most microscopes are called light microscopes because they accomplish their task by using lenses to bend light rays. Observing and Drawing Objects • Because the light rays from an object cross before reaching your eye, the image you see through our light microscopes will be inverted and upside down. Important terms with the microscope: • Magnification: the increase of an object's apparent size. • Field of view: the area visible through the microscope lenses. Field of view decreases as magnificaiton increases. • Resolution: the power to show details clearly. Resolution allows the viewer to see two objects that are very close together as two objects rather than as one. How Cells are Studied con’t… 2. Scanning Electron Microscope (SEM) 3. Transmission Electron (TEM) Micrograph – a photograph of the view through a microscope Light microscope SEM TEM How Does an Electron Microscope Work? • Electrons are very tiny negatively-charged particles. Because they are negatively-charged, they are attracted to anything that is positively-charged. • By applying voltage to a metal plate, we are able to make the plate positively-charged so that it attracts the electrons. • Some of the electrons flow through a small hole that is in the plate, creating a beam of electrons that we aim at our sample with the help of magnetic lenses. • When the electrons hit our sample, the interaction is detected and transformed into an image. Microscopy and Amoeba proteus Microscopy and Cheek Cells How Cells are Studied (even more!) 4. Cell Fractionation and Differential Centrifugation Cell Fractionation and Differential Centrifugation • Cell fractionation is the breaking apart of cellular components • Differential centrifugation: – Allows separation of cell parts – Separated out by size & density • Works like spin cycle of washer • The faster the machine spins, the smaller the parts that settled out Cell Structure and Size • Structure is related to function! • Cells take the shape that best allows them to perform their job. – Ex. Nerve cells – Ex. Skin cells • The ratio of cell surface to cell volume limits cell size. Cell Size • Most much smaller than one millimeter (mm) • Some as small as one micrometer (mm) • Size restricted by Surface/Volume (S/V) ratio – Surface is membrane, across which cell acquires nutrients and expels wastes – Volume is living cytoplasm, which demands nutrients and produces wastes – As cell grows, volume increases faster than surface – Cells specialized in absorption modified to greatly increase surface area per unit volume Surface to Volume Ratio TotalSurfaceArea (HeightWidthNumberOfSidesNumberOfCubes) 96 cm2 192 cm2 384 cm2 TotalVolume (HeightWidthLengthXNumberOfCubes) 64 cm3 64 cm3 64 cm3 SurfaceAreaPerCube/VolumePerCube (SurfaceArea/Volume) 1.5/1 3/1 6/1 Structure and Function The Prokaryotic Cell • Two domains: Bacteria and Archaea • Lacks a nucleus and most other organelles • DNA concentrated in nucleoid region • Contains ribosomes, cell wall, and in some cases a capsule, pili, and flagella. • 1-10 micrometers •Appear earliest in earth’s fossil record Figure 7.4x1 Bacillus polymyxa Figure 7.4x2 E. coli Prokaryotes PROKARYOTES were the only life form for 2 BY! Prokaryotic Cells: Visual Summary Prokaryotic Cells: The Envelope • Cell Envelopes – Glycocalyx • Layer of polysaccharides outside cell wall • May be slimy and easily removed, or • Well organized and resistant to removal (capsule) – Cell wall – Plasma membrane • Like in eukaryotes • Form internal pouches (mesosomes) Prokaryotic Cells: Cytoplasm & Appendages • Cytoplasm – Semifluid solution • Bounded by plasma membrane • Contains inclusion bodies – Stored granules of various substances • Appendages – Flagella – Provide motility – Fimbriae – small, bristle-like fibers that sprout from the cell surface – Sex pili – rigid tubular structures used to pass DNA from cell to cell The Eukaryotic Cell A. True nucleus B. Membrane-bounded organelles C. Size: 10-100 microns (much bigger!) D. Members of Kingdom Animalia, Plantae, Fungi and Protista Eukaryotic cell • Nucleus surrounded by its membrane • Internal organelles bounded by membranes • 10 – 100 micrometers • Domain Eukarya • Kingdoms: Protists, Fungi, Plants, Animals Membranes Allow for More Efficient Cellular Metabolism • Membranes separate areas to maintain specific chemical conditions. (Think about your stomach and intestines!) – This way different chemical processes can take place simultaneously. • Membranes increase the surface area needed for many chemical reactions. • In other words, the cell can increase in size and combine together to form tissues! • There is no such thing as a multicellular prokaryotic organism! • More on the eukaryotic cell in the next power point… • Wait… how did membranes and organelles evolve? Hypothesized Origin of Eukaryotic Cells Theory of Endosymbiosis Prokaryotes vs. Eukaryotes • – – – – Prokaryotes NO nuclear membrane No membrane bound organelles • contain ribosomes 1-10 microns Found in the kindgoms: Eubacteria, Archaebacteria • Eukaryotes – nuclear membrane – membrane bound organelles (Golgi bodies, lysososome, mitochondria, vacuoles, etc.) – 10-100 microns – Found in the kindgoms: Plantae, Animalia, Fungi, Protista Sizes of Living Things The size range of cells