History of Cell Theory. Organization of Life

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1 History of Cell Theory Robert Hooke first observed cells while examining cork under the microscope (mid s) Anton van Leeuwenhoek first observed microscopic organisms in pond water, as well as blood and sperm cells. Henry Dutrochet proposed that all living things are composed of cells. Robert Brown first observed the nucleus in plant cells, Matthias Schleiden theorized that all plants are made of cells. Theodor Schwann proposed that all animals are made of cells. Rudolph Virchow proposed that all new cells arise from existing cells. All of these people contributed research that led to the development of the Cell Theory: 1) All organisms are made up of one or more cells and the products of those cells. 2) All cells carry on their own life activities 3) New cells can only arise from other living cells by the process of cell division or reproduction. Organization of Life Organisms -> Organ Systems -> Organs -> Tissues -> Cells -> Organelles Organelles - The parts of a cell which work together to perform necessary metabolic functions. Cells - The smallest living unit (study of = cytology). Tissues - A group of cells that specialize in the same activity,may be same type or a mixed type (study of = histology). Organs - A group of tissues that work together to perform a function. Organ Systems - A group of organs which work together to accomplish one or more of life s processes. Organism - A living individual. Organelles show compartmentalization, and cells and tissues demonstrate division of labor. Advantageous for multicellular organisms to gain greater independence from the environment.

2 The Cell Cell = the basic unit of life Organism composed of cells with true nuclei. Eukaryote e.g. Animals, Plants, Fungi and Protoctists (Protists) The following structures are found in Animal and Plant Cells: Plasma Membrane (a.k.a. Cell Membrane) - A phospholipid bilayer with embedded protein channels- it is semi-permeable. Cytoplasm - watery substance containing biological molecules needed for metabolism, esp. proteins. Nucleus: Structure in the cell containing DNA Nuclear Envelope - multiple layered membrane barrier that separates the nucleus from the cytoplasm. Nuclear Pore - openings in the nuclear membrane that allow the passage of materials in and out of the nucleus. Nucleolus - Composed of DNA, RNA and protein. Site of ribosome production. Chromatin - long thin threads of DNA (not coiled into chromosomes) floating in the neucleoplasm. Must be relaxed to allow for DNA replication, and protein transcription. Ribosome - complex made of protein subunits- site of protein synthesis. Rough Endoplasmic Reticulum (Rough ER) - extensive system of membranes running through the cytoplasm with ribosomes attached. Secretory proteins produced on ribosomes enter the lumen (interior) of the ER, folding into their native conformation as they enter, and travel through the ER toward the Golgi, where the proteins are placed in transport vesicles for travel through the cytoplasm to the Golgi. Also site of membrane formation. Smooth Endoplasmic Reticulum (Smooth ER) - extensive system of membranes running through the cytoplasm with NO ribosomes attached. Production site of enzymes important to the synthesis of lipids and enzymes that detoxify drugs and poisons. Also site of calcium ion storage. Golgi Apparatus (a.k.a. Golgi Body or Golgi Complex) - multiple cysternae (flattened sacs) which receive proteins from the ER, tag the proteins with a marker which designates the proteins destinations, and sends the proteins out to their destination. Golgi Vesicle - structures that carry the proteins to their destination Mitochondria: the organelle where cellular (aerobic) respiration occurs and ATP is produced.

3 Mitochondial Envelope - multiple layered membrane barrier that separates the mitochondrion from the cytoplasm. Cristae - the inner membrane folds that project into the interior matrix Matrix - the fluid-filled interior of the mitochondrion Small Vacuoles: - container-type organelles floating in the cytoplasm. Several kinds: Lysosome - small sac-like structures that contain digestive (hydrolytic) enzymes. Enzymes digest food, break down worn-out cell parts, aid lymphocytes in digesting bacteria and are involved in digestion and re-adsorption of tadpole tails. Food Vacuole - small sac-like structure that stores food and nutrients in the cell Peroxisomes - contains enzymes that transfer hydrogen from various substances to oxygen, producing hydrogen peroxide (H 2 O 2 ). Peroxisomes use oxygen to break down fatty acids into smaller molecules that can be used in the mitochondria as fuel for respiration. In the liver, peroxisomes detoxify alcohol and other toxic substances. H 2 O 2 is toxic to the cell, so the enzyme to convert H 2 O 2 to water is also present in the same organelle! Some peroxisomes in plant seed mobilize sugar for emerging seedlings until they can begin photosynthesis. Peroxisomes are NOT made from the ER, rather they are produced from proteins in the cytoplasm Contractile Vacuole - small sac-like structures that contain water and extrude the water from the cell to maintain osmotic balance. Cytoskeleton: intercellular fibers which maintain cell shape as well as other functions Microtubules - Composed of the protein tubulin, Also important in cell motility (cilia and flagella), chromosomal separation (centrioles) and organelle movement. Microfilaments - Composed of actin - responsible for cytoplasmic streaming, changes in cell shape, muscle contraction, cell motility (e.g. pseudopodia), and formation of cleavage furrow in cell division. Intermediate Filaments - Composed of keratin - also anchors organelles and makes up the nuclear lamina (maintains the nuclear shape via added support) Centrosome - The area of cytoplasm where the aster of microtubules originates and organizes into the spindle. Contains centrioles in animals, but not in plants. It will still function, even if centrioles are destroyed via laser beam in lab. The following are only seen in Animal Cells: Centriole - small structures composed of microtubules found near the nucleus which separate the chromosomes during mitosis and meiosis Cilia - small hair-like projections that may be used for locomotion in unicellular organisms and for sensory perception in unicellular and multicellular organisms.

4 Flagella - small whip-like filament that is used for locomotion in unicellular organisms, sperm cells, and bacteria. The following are only found in Plants / Plant Cells: Cell Wall - Composed of cellulose- it protects and gives structural support to the cell, preventing the cell from bursting with the addition of water. It is fully permeable. Middle Lamella - sticky substance made of pectin and lignin, glues cells together. Plasmodesmata - fine strands of cytoplasm that link plant cells to allow for intracellular transport and chemical communication Large Vacuole - fluid filled vacuole containing cell sap (a solution of mineral salts, sugars, O 2, and CO 2 ) that helps to regulate the osmotic properties of the cell. Tonoplast - membrane around vacuole that controls exchange of fluid between the vacuole and the cytoplasm Plastids: (membrane enclosed organelles found in almost all plants) Chloroplast: plastid containing chlorophyll (green pigment in plants); the site of photosynthesis. Chloroplast Envelope - multiple layered membrane barrier that separates the chloroplast from the cytoplasm. Grana -stacks of Thylakoid Membranes- the membranes contain the chlorophyll and are the membranes where photosynthetic reactions occur. Stroma - the fluid-filled interior of the chloroplast Starch grains - accumulations of starch in the chloroplast formed from the glucose produced by photosynthesis Leucoplasts (a.k.a. Amyloplasts) - colorless plastids in which glucose is converted to starch, place where starch and other nutrients are stored Chromoplasts - contain pigments that give bright colors to fruits, flowers and leaves.

5 Organism composed of cells without true nuclei. Prokaryote e.g. Bacteria Structures always present in Prokaryotes: Cell Wall See previous notes Cell Membrane (a.k.a. Plasma Membrane) See previous notes Cytoplasm See previous notes Circular DNA - DNA in a ring shape that floats around in the cytoplasm Ribosome See previous notes Structures sometimes present in Prokaryotes: Flagellum See previous notes Capsule - additional outer protection, made of protein. Infolding of Plasma Membrane - may form a photosynthetic membrane or carry out nitrogen fixation Mesosome - branched infolding of the plasma membrane associated with DNA during cell division and helps with the formation of new cell walls. Plasmid - small circle of DNA, may be several present Pili - think fibers used for attachment to other cells or surfaces, involved in sexual reproduction Cell structure is related to cell function!