A Tour of the Cell

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• A Tour of the Cell
• Chapter 6

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Central Dogma of Biology

• DNA
• RNA
• Amino acids
• Proteins
• Cell parts
• Cell
• Tissue group of cells functioning together.
• Organ group of tissues functioning together.
• Organ System group of organs functioning
  together.
• Organism group of organ systems functioning
  together.

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The History of the Cell

• The Cell
• The basic unit of an organism
• Discovery made possible by the invention of the
  microscope

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Microscopes and Cells

• Robert Hooke used the first compound microscope
  to view thinly sliced cork cells.

• Compound scopes use a series of lenses to magnify
  in steps.
• Hooke was the first to use the term cell.

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Microscopes and Cells

• 1600s.
• Anton van Leeuwenhoek first described living
  cells as seen through a simple microscope.

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Microscopes and Cells

• 1830s.
• Mathias Schleiden identified the first plant
  cells and concluded that all plants
• made of cells.

- Thomas Schwann made the same conclusion about
animal cells.
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Cell Theory (3parts)

• All organisms are made up of one or more cells.
• The cell is the basic unit of organization of all
  organisms.
• All cells come from other cells all ready in
  existence.

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• The discovery and early study of cells progressed
  with the invention and improvement of microscopes
  in the 17th century.
• In a light microscope (LMs), visible light passes
  through the specimen and then through glass
  lenses.
• The lenses refract light such that the image is
  magnified into the eye or a video screen.

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• Light microscopes can magnify effectively to
  about 1,000 times the size of the actual
  specimen.
• At higher magnifications, the image blurs.

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• Techniques developed in the 20th century have
  enhanced contrast and enabled particular cell
  components to be labeled so that they stand out.

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• While a light microscope can resolve individual
  cells, it cannot resolve much of the internal
  anatomy, especially the organelles.
• To resolve smaller structures we use an electron
  microscope (EM), which focuses a beam of
  electrons through the specimen or onto its
  surface.

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• Transmission electron microscopes (TEM) are used
  mainly to study the internal ultrastructure of
  cells.
• A TEM aims an electron beam through a thin
  section of the specimen.
• To enhance contrast, the thin sections are
  stained with atoms of heavy metals.

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• Scanning electron microscopes (SEM) are useful
  for studying surface structures.
• The sample surface is covered with a thin film of
  gold.
• The beam excites electrons on the surface.
• These secondary electrons are collected and
  focused on a screen.
• The SEM has great depth of field, resulting in
  an image that seems three-dimensional.

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Microscope Summary

• Electron microscopes reveal organelles, but they
  can only be used on dead cells and they may
  introduce some artifacts.
• Light microscopes do not have as high a
  resolution, but they can be used to study live
  cells.
• Microscopes are a major tool in cytology, the
  study of cell structures.

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An Overview of Animal and Plant Cells

• All cells are surrounded by a plasma membrane
• The semi-fluid substance within the membrane is
  the cytoplasm, containing the organelles
• Organelles parts in a cell with a specific
  job/function
• All cells contain chromosomes which have genes in
  the form of DNA
• All cells also have ribosomes, tiny organelles
  that make proteins using the instructions
  contained in genes

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Two Basic Cell Types

• Prokaryote
• Lacks internal compartments
• No true nucleus
• Most are single-celled (unicellular) organisms
• Ex bacteria

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The prokaryotic cell is much simpler in
structure, lacking a nucleus and the other
membrane-enclosed organelles of the eukaryotic
cell.
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• A major difference between prokaryotic and
  eukaryotic cells is the location of chromosomes.
• In a prokaryotic cell, the DNA is concentrated in
  the nucleoid without a membrane separating it
  from the rest of the cell.

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Two Basic Cell Types

• Eukaryote
• Has several internal structures (organelles)
• True nucleus, which is enclosed in a membrane
• Either unicellular or multicellular
• unicellular ex yeast
• multicellular ex
• plants and animals

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• Eukaryotic cells are generally much bigger than
  prokaryotic cells
• Surface Area to Volume Ratio
• The logistics of carrying out metabolism set
  limits on cell size
• At the lower limit, the smallest bacteria are
  between 0.1 to 1.0 micron
• Most bacteria are 1-10 microns in diameter
• Eukaryotic cells are typically 10-100 microns in
  diameter

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The Parts of The Eukaryotic Cell

• Plasma Membrane
• Serves as a boundary between the cell and its
  external environment
• Allows materials to pass in and out of the cell
• What is it made of?

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• Phospholipids
• Composition the plasma membrane is made of
  millions of phospholipids

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• The plasma membrane functions as a selective
  barrier that allows passage of oxygen, nutrients,
  and wastes for the whole volume of the cell.

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• The general structure of a biological membrane is
  a double layer of phospholipids with other lipids
  and diverse proteins.
• Each type of membrane has a unique combination of
  lipids and proteins for its specific functions.
• For example, those in the membranes of
  mitochondria function in cellular respiration.

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• Figure 6-8A cell's plasma membrane contains a
  diversity of proteins that drift about in the
  phospholipid bilayer. Even the phospholipid
  molecules themselves can move along the plane of
  the fluid-like membrane. Some membrane proteins
  and lipids have carbohydrate chains attached to
  their outer surfaces.

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Functions of Membrane Proteins
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Boundaries

• B) Cell Wall
• -- Surrounds the plasma membrane of the cells of
  plants, bacteria, and fungi.
• -- Plant cell walls contain cellulose while
  fungi cell walls contain chitin.

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Diffusion the movement of a substance from a
high concentration to a low.

• Figure 6-11Dye molecules diffuse across a
  membrane. At equilibrium, the concentration of
  dye is the same throughout the container.

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Passive Transport movement of substances
without energy expended

• Figure 6-12Both diffusion and facilitated
  diffusion are forms of passive transport, as
  neither process requires the cell to expend
  energy. In facilitated diffusion, solute
  particles pass through a channel in a transport
  protein.

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Osmosis water transport across a membrane

• Hypertonic- solution with more substance than
  water concentration
• Isotonic equal concentration of substance on
  both sides of the membrane
• Hypotonic solution with less substance than
  water concentration

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• The same cell is a hypertonic environment will
  loose water, shrivel, and probably die.
• A cell in a hypotonic solution will gain water,
  swell, and burst.

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• For a cell living in an isotonic environment (for
  example, many marine invertebrates) osmosis is
  not a problem.
• Similarly, the cells of most land animals are
  bathed in an extracellular fluid that is isotonic
  to the cells.
• Organisms without rigid walls have osmotic
  problems in either a hypertonic or hypotonic
  environment and must have adaptations for
  osmoregulation to maintain their internal
  environment.

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• The cells of plants, prokaryotes, fungi, and some
  protists have walls that contribute to the cells
  water balance.
• An animal cell in a hypotonic solution will swell
  until the elastic wall opposes further uptake.
• At this point the cell is turgid, a healthy
  state for most plant cells.

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• Turgid cells contribute to the mechanical support
  of the plant.
• If a cell and its surroundings are isotonic,
  there is no movement of water into the cell and
  the cell is flaccid and the plant may wilt.

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• In a hypertonic solution, a cell wall has no
  advantages.
• As the plant cell looses water, its volume
  shrinks.
• Eventually, the plasma membrane pulls away from
  the wall.
• This plasmolysis is usually lethal.

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Active Transport requires energy to move
molecules across a membrane

• Figure 6-16Like an enzyme, a transport protein
  recognizes a specific solute, molecule or ion.
  During active transport, the protein uses energy,
  usually moving the solute in a direction from
  lesser concentration to greater concentration.

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Transport of Large Molecules

• Vesicles
• Exocytosis
• Endocytosis

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The Parts of The Eukaryotic CellControls

• A) Nucleus
• Regulates cell function.
• Surrounded by a double-layered membrane (nuclear
  enveloped) with large pores that allow materials
  to pass in and out of the nucleus.
• Contains chromatin long tangles of DNA.

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Controls

• B) Nucleolus
• Found in the nucleus and responsible for ribosome
  production. Ribosomes are the sites of protein
  production.

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The Parts of The Eukaryotic CellAssemblyRibosom
es protein assembly lines that make cell parts

• Figure 6-19A ribosome is either suspended in the
  cytoplasm or temporarily attached to the rough
  endoplasmic reticulum (ER). Though different in
  structure and function, the two types of ER form
  a continuous maze of membranes throughout a cell.
  The ER is also connected to the nuclear envelope.

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The Parts of The Eukaryotic CellTransport

• Endoplasmic reticulum
• -located near the nucleus
• Folded membrane that acts as the cells delivery
  system.
• Smooth E.R. contains enzymes for lipid synthesis.
• Rough E.R. is studded with ribosomes for protein
  synthesis.

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Transport

• B) Golgi apparatus (or Golgi body)
• A series of flattened sacs where newly made
  lipids and proteins from the E.R. are repackaged
  and shipped to the plasma membrane.

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The Parts of The Eukaryotic Cell Storage

• A) Vacuoles - a sac of fluid surrounded by a
  membrane used to store food, fluid, or waste
  products.

Food vacuoles, from phagocytosis, fuse with
lysosomes. Contractile vacuoles, found in
freshwater protists, pump excess water out of the
cell. Central vacuoles are found in many mature
plant cells.
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• Lysosomes can fuse with food vacuoles, formed
  when a food item is brought into the cell by
  phagocytosis.
• As the polymers are digested, their monomers pass
  out to the cytosol to become nutrients of the
  cell.
• Lysosomes can also fuse with another organelle
  or part of the cytoplasm.
• This recycling,this process of autophagyrenews
  the cell.

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Storage

• B) Lysosomes
• Contain a digestive enzyme.
• Can fuse with vacuoles to digest food, or can
  digest worn cell parts.
• Also known as suicide sacs because they can
  also destroy the whole cell.

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• The lysosomal enzymes and membrane are
  synthesized by rough ER and then transferred to
  the Golgi.
• At least some lysosomes bud from the trans
  face of the Golgi.

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The Parts of The Eukaryotic Cell Energy
Transformers

• Mitochondria
• Produce the energy for the cell.
• Also known as the powerhouse of the cell.
• Has a highly folded inner membrane (cristae).

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Energy Transformers

• Chloroplasts
• -- Found in plant cells and some protists.
• -- Transforms light energy into chemical energy
  which is stored in food molecules.
• -- Contain chlorophyll a green pigment that
  traps light energy and gives plants their green
  color.

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The Parts of The Eukaryotic Cell Support

• Cytoskeleton
• A network of thin, fibrous materials that act as
  a scaffold and support the organelles.
• Microtubules hollow filaments of protein.
• Microfilaments solid filaments of protein.

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The Parts of The Eukaryotic Cell Locomotion

• A) Cilia
• Short, numerous, hair-like projections from the
  plasma membrane.
• Move with a coordinated beating action.

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Locomotion

• B) Flagella
• Longer, less numerous projections from the plasma
  membrane.
• Move with a whiplike action.

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The Parts of The Eukaryotic Cell Cell Division

• Centrioles
• made of protein.
• play a role in the splitting of the cell into two
  cells.
• found in animal and fungi cells.

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Composite Animal Cell
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Flagella
nucleolus
Nucleus
Chromosomes
Ribosomes
Endoplasic reticulum
Microtuble
Mitochondrion
Golgi apparatus
Centrioles
Cillia
Composite Animal Cell