A View of the Cell

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Chapter 7

• A View of the Cell

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Cell Theory

• CD-ROM
• Before microscopes, people thought diseases were
  caused by curses and supernatural spirits
• They had no idea microorganisms, such as bacteria
  and viruses existed
• When the microscope was invented, scientists
  discovered cells exist
• Cells are the basic units of living organisms

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Cell Theory

• Anton van Leeuwenhoek (Dutch) used the first
  simple light microscope in the 1600s
• It had one lens (page 1064)
• Gradually, lenses got better
• Compound light microscopes use a series of lenses
  to magnify objects in steps
• Can magnify up to 1500 times
• The microscopes we use in the lab

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Cell Theory

• Robert Hooke (1600s, English) used a compound
  light microscope to study cork, the dead cells of
  oak bark
• He saw small, geometric shapes that reminded him
  of the small rooms monks lived in called cells
• Cells are the basic units of all living things

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Cell Theory

• Matthias Schleiden (1830s, German) discovered
  that all plants are made of cells
• Theodor Schwann (German) discovered that all
  animals are made of cells
• Rudolf Virchow discovered that all cells come
  from existing cells
• All these scientists (plus others) contributed
  ideas that are now summed up in what we call the
  cell theory

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Cell Theory

• All organisms are composed of one or more cells.
• The cell is the basic unit of structure and
  organization of organisms.
• All cells come from preexisting cells.

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Electron Microscopes

• Electron Microscopes let us see a much greater
  magnification than light microscopes
• They use beams of electrons to produce images
• Scanning Electron Microscope
• Used for scanning 3-D surfaces

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Electron Microscopes

• Transmission Electron Microscope
• Used for scanning interior structures of cell

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Types of Cells

• Organelles are small, specialized structures
  within cells
• Many, but not all are surrounded by membranes
• Prokaryotes are organisms that do not have
  membrane-bound organelles (biology.arizona.edu)
• Kingdom Monera ( now split into Eubacteria
  Archaebacteria)
• Eukaryotes are organisms that do have
  membrane-bound organelles
• Kingdoms Animalae, Plantae, Fungi, Protista

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Types of Cells

• Robert Brown (Scottish) observed that eukaryotic
  cells have a prominent structure, the nucleus
• the nucleus manages cellular functions
• Rudolf Virchow concluded that this prominent
  structure was responsible for cell division

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Section 1 Review

• How has the history of microscopes influence the
  study of cells?
• What are the three parts of the cell theory?
• What is the difference between a light microscope
  and an electron microscope?
• What is the difference between a prokaryote and a
  eukaryote?

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The Plasma Membrane

• Cells must maintain proper conditions within
  itself to function
• The plasma membrane is a flexible boundary
  between the cell and its environment
• It allows a steady supply of nutrients into and
  out of the cell at the appropriate levels
• The plasma membrane is selectively permeable
• This means that it allows some molecules to pass
  through while keeping others out.
• Like a screen in a window

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The Plasma Membrane

• Phospholipids
• The head is polar, or slightly charged
• It is hydrophilic (likes water)
• The tail is nonpolar, or not charged
• It is hydrophobic (repels water)
• The phospholipids arrange themselves form a
  bi-layer with the fatty acid
  tails forming the interior
  and the heads facing the
  watery environments
  outside and inside the cell

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Plasma Membrane

• The plasma membrane is called a phospholipid
  bilayer
• Arranged in this manner, a barrier is created
  that is water-soluble at its outer surfaces and
  water-insoluble in the middle
• Keeps out both
  water soluble
  and water
  
  insoluble
  molecules

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Plasma Membrane

• The current model of the plasma membrane is
  called the fluid mosaic model.
• The phospholipids actually move around like a
  fluid.
• The other components of the membrane (proteins,
  carbohydrates, cholesterol, etc.) move around as
  well

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Plasma Membrane

• Cholesterol helps to stabilize the phospholipids
  by preventing their fatty acid tails from
  sticking together
• Transport proteins move span the membrane and
  move needed substances or waste materials through
  the plasma membrane
• Other proteins and carbohydrates that stick out
  help cells to identify surface signals and other
  cells
• These proteins play an important part in
  protecting cells from infection

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Section 2 Review

• What is a phospholipid?
• Why is the cell membrane a bilayer?
• What does polar and nonpolar mean?
• What are the specialized parts of the cell
  membrane?
• Why is the cell membrane referred to as fluid
  mosaic?

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Cell Wall

• Fairly rigid structure located outside the plasma
  membrane of some cells that provides additional
  support and protection
• Plants, fungus, most bacteria
• The cell wall is very porous, made of a
  tough mesh of fibers
• Like framing of a house

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Nucleus

• Membrane-bound (called nuclear envelope)
  organelle that contains the directions to make
  proteins
• Nuclear pores allow passage through the nuclear
  envelope
• Chromatin - uncondensed strands of DNA
• When cell is dividing, DNA condenses into
  chromosomes
• Nucleolus - organelle within the nucleus that
  make ribosomes

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Organelles

• Ribosomes are the sites where the cell produces
  proteins according to the directions of DNA
• One organelle without a membrane
• Cytoplasm is the clear, gelatinous fluid inside
  the cell
• Acts as a medium for things to move around in the
  cell
• Organelles cant fly

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Organelles

• The endoplasmic reticulum (ER) is arranged in a
  series of highly folded membranes suspended in
  the cytoplasm
• In general, ER is involved in the movement of
  materials throughout the cell
• Rough ER has ribosomes, which is where protein
  synthesis takes place
• Smooth ER has no ribosomes and is involved in
  numberous biochemical activities, including the
  production and storage of lipids

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Organelles

• The Golgi apparatus is a flattened stack of
  tubular membranes that modifies the proteins
• The Golgi sorts proteins into packages and packs
  them into membrane-bound structures called
  vescicles for later transport (like UPS)

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Organelles

• Vacuoles are membrane-bound compartments for
  temporary storage of materials
• Store food, enzymes, water, waste
• Plant cells have one very large vacuole

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Organelles

• Lysosomes are organelles that contain digestive
  enzymes
• Digest old organelles, food, viruses, bacteria,
  etc.
• Can fuse with a vacuole to dump waste or give
  enzymes
• Lysosomes digest a tadpoles tail

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Organelles

• Plastids are a group of organelles used for
  storage
• Named for the color or pigment they contain
• Chloroplasts are organelles that capture light
  energy and convert it to chemical energy
  (photosynthesis occurs here)
• Plastid containing chlorophyll, which actually
  traps the light and gives plants green color

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Organelles

• Mitochondria are membrane-bound organelles in
  plant and animal cells that transform stored
  chemical energy into a usable form for the cell
  (ATP)
• Has an outer and inner highly folded membrane
• ATP produced on inner folds

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Organelles

• The cytoskeleton forms a framework for the cell
• A network of tiny rods and filaments
• Cytoskeleton is constantly changing its shape
• Microtubules are thin, hollow cylinders made of
  protein
• Microfilaments are smaller, solid protein fibers
  
• Give support for cell
• Provide highway system for organelles to move
  throughout cell

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Organelles

• Centrioles are organelles made up of microtubules
  that play a part in cell division
• In animals and most protists
• Cilia are short, numberous projections that look
  like hairs
• Made of microtubules and help organelles move and
  feed
• Flagella are longer projections that move in a
  whip-like motion
• Made of microtublules - help with movement
• Cells usually only have 1 or 2

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Animal Cell
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Plant Cell
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Section 3 Review

• How are highly-folded membranes an advantage for
  the functions of cellular parts?
• Name an organelle that has highly-folded
  membranes.
• If a cell synthesizes large quantities of protein
  molecules, which organelles might be numerous in
  that cell?
• A cells digestive enzymes are enclosed in a
  membrane-bound organelle. How can these
  molecules function in the cell?
• Compare and contrast the functions of a cell wall
  to the functions of a plasma membrane.
• What are the functions of the cytoskeleton?
• Why are mitochondria and chloroplasts referred to
  as energy transporters?