A Tour of the Cell

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A Tour of the Cell
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Basics of Cells

• Plasma Membrane
• Forms external border
• Distinguishes cell from surroundings
• Cytoplasm
• Everything between plasma membrane and nucleus
• Typically known as fluid
• Organelles
• Play specific key roles in the lifecycle of cells

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Basics of Microscopes

• Light Microscope (LM) passes light through a
  specimen
• Typically is compound (two lenses) or simple (one
  lens)
• Electron Microscopes (EM) replaces the beam of
  light with one of electrons
• Specimen must be dead
• Held within a veritable vacuum
• Much more detailed- can see within cells, and
  under certain conditions individual atoms

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Types of Electron Microsopes

• Scanning (SEM) studies cell surfaces by passing
  electrons over the surface of a cell that has
  been coated with metal
• 3D images
• Transmission (TEM) studies the internal
  structures of cells by aiming electrons through a
  section of the cell

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Different Types of Microscopes Are Necessary
for Different Sized Cells
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How they work

• Magnification increase in the apparent size of
  an object
• Ocular is typically 10x
• Objectives are typically 4x, 10x, 40x, and 100x
• Total Magnification is ocular x objective
• Resolution the measure of the clarity of an
  image
• Increases with the sophistication of the
  microscope

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Cell Theory

• ALL living things are composed of cells
• Schleiden and Schwann
• ALL cells come from other cells
• Biogenesis
• Virchow
• Cells are the most basic unit of life
• ??????????????????

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Cell Size versus function

• Smallest are mycoplasmas (.1 to 1.0 micrometers)
• Muscle and nerve cells are longest (almost 1
  meter in length!)
• Many fall somewhere between
• The Ratio of cell surface to cell volume that
  imposes upper limits on cell size

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Cell Size Regulation
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Prokaryotic Cells

• Bacteria and Archaea
• Cannot be seen with a low power microscope
• Lacks a nucleus ? instead compacts DNA into a
  nucleoid region
• Ribosomes in the cytoplasm detect messages from
  the DNA and assemble amino acids into
  polypeptides accordingly

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Surrounding those bacteria!

• Plasma Membrane encloses the cytoplasm
• Outside of the plasma membrane is a bacterial
  cell wall
• Protects
• Maintains shape
• Very Complex!
• Some have a capsule that surrounds the cell wall
• Help with attachment to surfaces/substrates
• Pili assist with attachment and sharing of
  genetic information
• Flagella assist with movement
• Not the same as eukaryotic flagella!

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Eukaryotic Cells are Compartmentalized!

• Endomembrane System
• Nucleus, Endoplasmic reticulum (ER), Golgi
  Apparatus (GA), Lysosomes, Peroxisomes, Vacuoles
• Work in the synthesis, storage, and export of
  important molecules
• Energy Converting Organelles
• Chloroplasts, Mitochondria
• Cytoskeleton
• Cilia, flagella

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Nucleus

• Genetic Control Center
• DNA fibers form into fibers of chromatin
• Each fiber contains a chromosome
• Surrounded by a nuclear envelope, perforated by
  nuclear pores
• Nucleolus in the center is responsible for
  producing ribosomes

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ER network within the cell

• ROUGH (RER) is dotted with ribosomes
• Produces membrane for use within the cell
• Produces proteins for export out of the cell
• Antibodies are a good example
• Releases these secretory proteins via transport
  vesicles for protection

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ER network within the cell

• SMOOTH (SER) is continuous with the RER, but
  lacks ribosomes
• Activity is a result of enzymes that are embedded
  within the membrane
• Synthesizes lipids, phospholipids and steroids in
  specific cells
• In the liver, SER assists with the breakdown of
  harmful substances and the regulation of blood
  sugar
• Can also store calcium ions- necessary for
  musculature

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ROUGH
SMOOTH
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GA (The UPS of the Cell)

• Non-interconnected
• sacs of pancakes
• A varied resume
• Molecular warehouse/finishing factory
• Receives and modifies products from the ER
• Ships out the secretory proteins from there
• Incorporates products that are made within the
  cell into the membranes and organelles that they
  are destined to become a part of

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Lysosomes and Peroxisomes

• Lysosomes contain digestive enzymes (produced in
  ER and GA)
• Protect cell by being enclosed in a membrane
• Engulf nutrients into food vacuoles- then fuse
  and digest them
• Destroy bacteria or other invaders
• Recycling center for damaged organelles
• Embryonic development why we dont have webbing
• Peroxisomes produce hydrogen peroxide and break
  it down into water and oxygen also assist in the
  breakdown of various products

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Peroxisomes are SImilar
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Lysosomal Storage Diseases

• Missing a hydrolytic enzyme that is normally
  found in the lysosome
• Pompes disease too much glycogen accumulates
  in the liver cells
• Tay-Sachs lack a lipid digesting enzyme which
  allows the nervous system to be damaged due to an
  accumulation of lipids on the cells
• Deadly, though carriers can be detected

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Vacuoles

• Membranous sacs
• Central Vacuole in plants can contain a large
  lysosome, or help the cell to grow by absorbing
  water
• Typically store food, water and waste for the cell

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The Endomembrane System
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Chloroplasts

• Only found in photosynthetic organisms
• Plants and some protists
• Contain an inner and outer membrane
• Intermembrane space in between
• Fluid within the inner membrane is known as
  stroma
• Contain stacks of thylakoid disks, known as grana
• These are the actual sites where the chlorophyll
  traps solar energy

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Mitochondria

• Convert energy from one chemical form into
  another
• Carry out cellular respiration
• Food/Sugar ? ATP, the cells energy currency
• Also has an outer and an inner membrane
• Interior is a fluid area known as the
  mitochondrial matrix
• Where the chemical reactions of cellular
  respiration occur
• Heavily folded (folds cristae)

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Folds increase surface area for C.R.
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Endosymbiosis

• Mitochondria and Chloroplasts resemble their own
  cells
• Double membranes
• Contain their own DNA
• Implication is that they were cannibalized by
  other cells

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Cytoskeleton

• Supportive network of fibers
• Microfilaments mainly composed of actin
• Often assist with muscle contraction
• Microtubules composed of tubulins
• Elongate(stretch)
• Provide anchorage for organelles
• A network of railroad tracks?

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Cilia and Flagella

• Cilia short, numerous appendages
• Paramecium
• Flagella longer, less numerous
• Euglena
• Both assist with movement
• Similar in physical structure to centrioles
• Involved with cellular division

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Comparing the 2
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Cell Surfaces and Junctions

• Mostly for Support
• Cell junctions allow them to connect to each
  other
• Plasmodesmata form channels between cells so that
  they can interact appropriately as tissue
• Extracellular matrix holds the tissue together
• Tight junctions make a leak-proof surface
  ltthink stomach acid..gt
• Anchoring Junctions hold cells loosely together
  so that substance scan still flow between them
• Communicating Junctions allow for cells to share
  necessary substances

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Connections
Forming channels
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Thus, there are four main functional categories

• Manufacture
• Breakdown
• Energy Processing
• Support, Movement, and Communication

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Thus, there are four main functional categories

• Manufacture
• Nucleus, Ribosomes, RER, SER, GA
• Breakdown
• Lysosomes, Peroxisomes, Vacuoles
• Energy Processing
• Chloroplasts, Mitochondria
• Support, Movement, and Communication
• Cytoskeleton, Cell Walls, Extracellular Matrix,
  Cell Junctions

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