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Transcript
Cells and their Organelles Cell Theory Scientific theories have two components: Pattern and process All organisms are made of cells (pattern). All cells arise from pre-existing cells (process). Relative Sizes Cellular Sizes Prokaryotes Bacteria Lack a distinct nucleus No cytoskeleton and essentially no organelles Often have a cell wall Two Domains or Groups of Prokaryotes: Eubacteria - found commonly Archaea - found in harsh environments; discovered by Dr. Carl Woese Eukaryotes Protozoa, Fungi, Plants and Animals Have a distinct nucleus Great subcellular complexity represented by cytoplasm and the variety of organelles Significantly larger than prokaryotes Can be single-celled organisms or complex multicellular organisms The Nucleus Most visible of all organelles Usually centrally located Houses DNA Contains the nucleolus Site of ribosomal RNA processing and ribosomal subunit organization Has a unique membrane called the nuclear envelope - know the features of this! Endoplasmic Reticulum Begins as an extension of the nuclear membrane Site of synthesis for cell membrane components and export molecules Two varieties: Smooth : lipids, cell membrane components Rough : exported proteins Evolution of Membranes There is speculation that the nuclear and ER membranes resulted from an invagination of the plasma membrane. Golgi Apparatus Consists of a stack of membrane bound sacs Receives, modifies, sorts and packages molecules from the ER Small portions of the Golgi pinch off to create vesicles for transport and delivery Vesicles Lysosomes Site of intracellular digestion Rarely found in plant cells Peroxisomes Site where hydrogen peroxide is generated and degraded Secretory vesicles Move secretions such as hormones from the Golgi to the plasma membrane Vesicle Transport Endocytosis - import A portion of the cell membrane invaginates and pinches off to deliver extracellular contents to the inside Exocytosis - export A vesicle fuses with the cell membrane and expels its contents into the extracellular space Mitochondria The “power plants” of the cell About the size of bacteria Why might this be? Two membranes Produce almost all of the energy necessary for cellular processes in the form of ATP Cellular respiration - uses O2 and produces CO2 Outer is smooth Inner is highly convoluted - Why? Contain their own DNA, divide in two Chloroplasts Large green organelles in higher plants and algae; absent in animals and fungi More complex than mitochondria Two surrounding membranes An internal stack of membranes containing chlorophyll Capture sunlight energy via photosynthesis Contain their own DNA, divide in two Mitochondrial Origin It is thought that mitochondria arose as a result of a eukaryote engulfing a prokaryote. Cytosol Internal pool of the cell excluding membrane-bound organelles Contained by plasma membrane Loaded with proteins responsible for: Metabolism Division Translation Signaling Cytoskeleton System of filaments transversing the cytoplasm Anchored to the cell membrane or a point adjacent to the nucleus Provides direction for organelles moving within the cell Provides shape and mechanical strength Responsible for cell mobility Microtubules Largest cytoskeletal component Primarily responsible for separating duplicated chromosomes during cell division Very small, hollow tubes Intermediate Filaments Intermediate cytoskeletal component Provide mechanical strength Actin Filaments Smallest cytoskeletal component Also called microfilaments Primarily responsible for contraction Predominant in muscle cells Centrosome Centrally located Site of microtubule production and organization Short cylinders that contain an array of microtubules in nine groups Replicate themselves during division and move to opposite poles of the nucleus, then of the cell Lacking in plant cells Cell Membrane Amphipathic lipid bilayer enclosing the cell Hydrophilic heads at membrane surfaces Hydrophobic tails intermingle in interior Creates and maintains unique environment within Controls entrance and exit of materials Strongly associated with proteins Vacuole Generally small in animal cells Responsible for intracellular digestion and removal of cellular waste Much larger in plant cells Responsible for maintaining turgor pressure Rigidity and upright support Cell Wall Found in plants and prokaryotes Rigid structure surrounding cell membrane Comprised of the polysaccharide cellulose Provides structural support and shape Acts as a barrier Cellular Organelles Microscopy In order to visualize cells and their components we must employ microscopy Types: Light Fluorescent Confocal TEM SEM Light Microscopy Allows magnification of up to one thousand times Resolution to 0.2 µM: cells and nucleus Requires: Bright light focused on specimen Specimen prepared to allow passage of light Set of lenses must focus an image Types: brightfield, phase-contrast, interference-contrast Fluorescent Microscopy Similar to light microscope Requires fluorescent dye for cell staining Specimen illumination differs by two filters: Filter 1 (before specimen) only allows passage of wavelengths that excite the particular dye Filter 2 (after specimen) only allows passage of wavelengths emitted when dye fluoresces Used to selectively visualize molecules in the cell Confocal Microscopy Fluorescent scope with specimen illumination coming from a laser Provides optical sectioning as it specifically focuses on one plane, or one particular depth in the specimen, at a time Transmission Electron Microscopy Allows magnification of up to one million times Resolution of 2 nm: organelle details Uses a beam of electrons instead of a beam of light for illumination Specimen must be extremely thin and in a vacuum Contrast supplied by heavy metal dyes Scanning Electron Microscopy Resolution from 3 nm to 20 nm Specimen is coated with a very thin film of heavy metal Uses a beam of electrons instead of light Generates a detailed 3-D surface image of organelle structure Organelles and Disease Organelles provide efficiency and an excellent division of labor for the cell However, as with any system, the greater number of parts involved, the greater the chances of something going wrong Each organelle can have myriad defects that lead to a host of disorders and diseases Lysosome Malfunctions As you can imagine, lysosome malfunction can have dire consequences Asbestosis - asbestos fibers lodge in lysosomes and cause them to leak Results in severe coughing and shortness of breath Rheumatoid arthritis - lysosomal enzymes leak into joint fluid Results in painful joints due to inflammation Lysosomal Storage Diseases Inclusion-cell disease Lysosomal enzymes are missing Results in skeletal and facial deformities and mental retardation Tay-Sachs disease Absence of a single lysosomal enzyme Results glycolipid accumulation in the brain, leading to rapid mental deterioration, paralysis and death Diseases associated with Mitochondrial Disorders Parkinson’s disease Alzheimer’s disease Huntington’s disease Multiple sclerosis Stroke Amyotrophic lateral sclerosis (ALS) All appear to be associated with damage to the electron transport chain Other Associations Alzheimer’s disease and ALS are also thought to be associated with defects of the Golgi. Stroke is associated with ER defects. Hemolytic anemias are associated with defects of the red blood cell membrane. Synthesis The cell is a magnificent entity. It is minute. It is complex. It is efficient. We have a variety of microscopic tools to reveal various degrees of detail. Dire consequences can result when any part are the machinery malfunctions.