Download Lab 1 Organelles

Cells and their
Organelles
Cell Theory
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Scientific theories have two components:
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Pattern and process
All organisms are made of cells (pattern).
All cells arise from pre-existing cells
(process).
Relative Sizes
Cellular Sizes
Prokaryotes
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Bacteria
Lack a distinct nucleus
 No cytoskeleton and essentially no organelles
 Often have a cell wall
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Two Domains or Groups of Prokaryotes:
Eubacteria - found commonly
 Archaea - found in harsh environments;
discovered by Dr. Carl Woese
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Eukaryotes
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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
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Most visible of all organelles
Usually centrally located
Houses DNA
Contains the nucleolus
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Site of ribosomal RNA processing and
ribosomal subunit organization
Has a unique membrane called the nuclear
envelope - know the features of this!
Endoplasmic Reticulum
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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
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Evolution of Membranes
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There is speculation that the nuclear and ER membranes
resulted from an invagination of the plasma membrane.
Golgi Apparatus
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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
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Lysosomes
Site of intracellular digestion
 Rarely found in plant cells
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Peroxisomes
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Site where hydrogen peroxide is generated
and degraded
Secretory vesicles
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Move secretions such as hormones from the
Golgi to the plasma membrane
Vesicle Transport
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Endocytosis - import
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A portion of the cell
membrane invaginates
and pinches off to
deliver extracellular
contents to the inside
Exocytosis - export
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A vesicle fuses with
the cell membrane and
expels its contents into
the extracellular space
Mitochondria
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The “power plants” of the cell
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About the size of bacteria
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Why might this be?
Two membranes
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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
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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
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Capture sunlight energy via
photosynthesis
Contain their own DNA, divide in two
Mitochondrial Origin
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It is thought that mitochondria arose as a result
of a eukaryote engulfing a prokaryote.
Cytosol
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Internal pool of the cell excluding
membrane-bound organelles
Contained by plasma membrane
Loaded with proteins responsible for:
Metabolism
 Division
 Translation
 Signaling
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Cytoskeleton
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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
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Largest cytoskeletal
component
Primarily responsible
for separating
duplicated
chromosomes during
cell division
Very small, hollow
tubes
Intermediate Filaments
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Intermediate
cytoskeletal
component
Provide mechanical
strength
Actin Filaments
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Smallest cytoskeletal
component
Also called
microfilaments
Primarily responsible
for contraction
Predominant in
muscle cells
Centrosome
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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
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Amphipathic lipid bilayer enclosing the
cell
Hydrophilic heads at membrane surfaces
 Hydrophobic tails intermingle in interior
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Creates and maintains unique
environment within
Controls entrance and exit of materials
Strongly associated with proteins
Vacuole
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Generally small in animal cells
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Responsible for intracellular digestion and
removal of cellular waste
Much larger in plant cells
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Responsible for maintaining turgor pressure
 Rigidity and upright support
Cell Wall
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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
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In order to visualize cells and their
components we must employ microscopy
Types:
Light
 Fluorescent
 Confocal
 TEM
 SEM
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Light Microscopy
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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
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Types: brightfield, phase-contrast,
interference-contrast
Fluorescent Microscopy
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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
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Used to selectively visualize molecules in
the cell
Confocal Microscopy
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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
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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
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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
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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
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Each organelle can have myriad defects that
lead to a host of disorders and diseases
Lysosome Malfunctions
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As you can imagine, lysosome
malfunction can have dire consequences
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Asbestosis - asbestos fibers lodge in
lysosomes and cause them to leak
 Results in severe coughing and shortness of breath
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Rheumatoid arthritis - lysosomal enzymes
leak into joint fluid
 Results in painful joints due to inflammation
Lysosomal Storage Diseases
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Inclusion-cell disease
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Lysosomal enzymes are missing
 Results in skeletal and facial deformities and
mental retardation
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Tay-Sachs disease
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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
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Parkinson’s disease
Alzheimer’s disease
Huntington’s disease
Multiple sclerosis
Stroke
Amyotrophic lateral sclerosis (ALS)
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All appear to be associated with damage to
the electron transport chain
Other Associations
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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
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The cell is a magnificent entity.
It is minute.
 It is complex.
 It is efficient.
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We have a variety of microscopic tools to
reveal various degrees of detail.
Dire consequences can result when any
part are the machinery malfunctions.