Cell Theory and Microscopy PDF

# **Cell theory** 1. All living things are composed of one or more cells 2. Cells are the smallest units of living organisms 3. New cells come only from pre-existing cells by cell division # **Microscopy** Most cells are so small that they cannot be seen with the naked eye. The microscope is a...

# **Cell theory** 1. All living things are composed of one or more cells 2. Cells are the smallest units of living organisms 3. New cells come only from pre-existing cells by cell division # **Microscopy** Most cells are so small that they cannot be seen with the naked eye. The microscope is a magnification tool that enables researchers to structure and function of cells. Magnification, resolution, and contrast are the three important parameters in microscopy. ## **Magnification** Ratio between the size of an image produced by a microscope and its actual size. ## **Resolution** Ability to observe two adjacent objects as distinct from one another. ## **Contrast** Ability to visualize a particular cell structure may depend on how different it looks from an adjacent structure. The contrast can be enhanced using dyes. # **Microscopy** There are two types of Microscopes: ## **Light Microscope** * Uses light for illumination * Resolution 0.2μm ## **Electron Microscope** * Uses an electron beam * Resolution 2 nm **Below is a diagram illustrating the range of magnifications for the different types of microscopes** * **Electron microscope:** atoms, lipids, ribosomes, smallest bacteria, most bacteria * **Light microscope:** most plant and animal cells, fish egg * **Unaided human eye:** human height # **Prokaryotic cells** Prokaryotes: [grk. Pro, before, and karyon, nucleus] * Simple cell structure * Lack a membrane-enclosed nucleus * Much smaller than eukaryotic cells * Present in great numbers in the air, in bodies of water, in the soil, and even in the human organs. * Two categories: **bacteria** and **archaea** * Both small * Bacteria are abundant, most not harmful * Archaea are less common, often found in extreme environments # **Typical bacterial cell** Below is a diagram of a typical rod-shaped bacterium. * **Cell envelope:** includes plasma membrane, cell wall, and glycocalyx (layer of polysaccharides outside cell wall) * **Plasma membrane:** * A phospholipids' bilayer much like the plasma membrane of eukaryotic cells. * Has an important role in regulating the entrance and the exit of substances into the cytoplasm. * **Cell wall:** * Composed of a complex molecule peptidoglycan (amino disaccharides and peptide fragments). * The cell wall maintains the overall shape of a bacterial cell (coccus, bacillus, and spiral). * Mycoplasma are bacteria that have no cell wall and therefore have no definite shape. * **Glycocalyx:** * Layer of polysaccharide lying outside the cell wall. Glycocalyx aids against drying out by traping water and help bacteria to resist a host's immune system. * It allows the bacterium to attach itself to inert surfaces (like teeth or rocks), eukaryotes (e.g. streptococcus pneumoniae attaches itself to lung cells), or other bacteria (their glycocalyxes can fuse to envelop the colony). * **Capsule:** * Well organized layer of polysaccharide. * Protects the bacterial cell and is often associated with pathogenic bacteria because it serves as a barrier against phagocytosis by white blood cells. * **Cytoplasm** * **Appendages** # **Structure of a Prokaryotic Cell: Cytoplasm** * Cytoplasm is semi-fluid solution encapsulated by the plasma membrane. * Contains all sort of enzymes required for bacterial metabolism. * Single chromosome located in gel-like region called nucleoid. * Thousands of ribosomes involved in protein synthesis. * Inclusion Bodies which are Storage granules of various substances. Some are nutrients that can be broken down when needed # **Structure of a Prokaryotic Cell: Appendages** Bacteria may have the following appendages: * **Flagella:** * Responsible for most types of bacterial motility. * Flagella are long appendages which rotate by means of a "motor" located just under the plasma membrane. * Bacteria may have one, a few, or many flagella in different positions on the cell. * **Fimbriae:** * Small fibers that sprout from the cell surface. * Not involved in the motility. * Help bacteria to attach to a surface. * **Sex Pili:** * Rigid tubular structure used by bacteria to pass DNA from a cell to cell. * Bacteria reproduce asexually by binary fission, but they can exchange DNA through the sex pili..