Structures of the Cell

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Structures of the Cell
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Cell Theory

• 1. All living things are composed of cells.
• 2. Cells are the basic unit of structure and
  function in living things.
• 3. All cells come from preexisting cells.

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Cell Size

• Microscopic to the size of an ostrich egg yolk

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Microscopes

• Light Microscope - visible light passes through a
  specimen and then through glass lenses, which
  magnify the image

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SEM

• Scanning electron microscopes (SEMs) focus a beam
  of electrons onto the surface of a specimen,
  providing images that look 3-D

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TEM

• Transmission electron microscopes (TEMs) focus a
  beam of electrons through a specimen
• TEMs are used mainly to study the internal
  structure of cells

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Cell fractionation

• Cell fractionation takes cells apart and
  separates the major organelles from one another

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Fig. 6-5b
TECHNIQUE (cont.)
1,000 g (1,000 times the force of gravity) 10 min
Supernatant poured into next tube
20,000 g 20 min
80,000 g 60 min
Pellet rich in nuclei and cellular debris
150,000 g 3 hr
Pellet rich in mitochondria (and chloro-plasts if
cells are from a plant)
Pellet rich in microsomes (pieces of
plasma membranes and cells internal membranes)
Pellet rich in ribosomes
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Cell Types- Eukaryotes

• Eukaryotes (animals, plants, protists, fungi)
• -have a nucleus bound by an envelope
• -have membrane bound organelles
• -large cells

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Cell Types- Prokaryotes

• Prokaryotes- (bacteria)
• No nucleus, they have a nucleoid - an unbound
  region where their DNA is found
• No membrane bound organelles.
• Small cells

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Cell Parts
(a)

• Organelles cell structures with specialized
  functions
• Cell Membrane- organelle that regulates what
  comes in and out of the cell, provides
  protection, and support.
• phospholipid Bilayer- structure of the cell
  membrane
• Hydrophilic
• head
• Hydrophobic
• Tail

Carbohydrate side chain
Hydrophilic region
Hydrophobic region
Hydrophilic region
Phospholipid
Proteins
(b) Structure of the plasma membrane
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Cell Wall

• Cell wall- surrounds cell membrane only in plants
• Made out of cellulose (starch)
• Adds extra support

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Nucleus (center of the cell)

• Nucleus- center of the cell, contains nucleic
  acid (DNA)
• Enclosed by a nuclear envelope lipid bilayer. It
  has pores.
• Nucleolus inside the nucleus. Makes ribosomal
  RNA that form ribosomes.

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Cytoplasm

• Cytoplasm- in between cell membrane and nucleus.
  Made of a fiber matrix and a liquid called
  cytosol.
• Holds organelles in place
• Kind of like Jello
• With fruit in it

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Mitochondria

• Mitochondria- release energy stored in glucose in
  the form of ATP through cell respiration.
• Double membrane (inner and outer) , the inner has
  folds called cristae and that form the
  mitochondrial matrix and the inner membrane
  space.

0.1 µm
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Plastids

• Store materials in plants (chloro- plasts-

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Chloroplasts

• Chloroplasts- make glucose from sunlight (only in
  plants) through photosynthesis.
• Contains the pigment chlorophyll that makes
  plants green
• Thylakoid discs containing chlorophyll stacked
  in granum
• Stroma fluid in the space outside the granum.

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Ribosomes

• Make proteins

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Endoplasmic Reticulum (ER)

• ER makes and transports materials through the
  cell in vesicles
• -Smooth ER makes and transports lipids and
  carbohydrates
• -Rough ER contains, ribosomes to make and
  transport proteins (gives it its rough look)

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Golgi Apparatus

• Labels, packages, sorts and sends molecules from
  the ER out of cells in vesicles.

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Lysosome

• Lysosomes membrane sacs filled with enzymes
  that break down materials (food or old
  organelles)
• Lysosomes will merge with food vacuoles break
  down food or engulf (phagocytosis) an old
  organelle to digest and recycle it.
• Peroxisomes - are like mini lysosmes that contain
  an enzyme called catalase that converts peroxide
  in to water and oxygen.

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Vacuoles

• Store materials (food, water, etc)
• Plants have a large central vacuole, animals have
  may small scattered vacuoles

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Endomembrane system

• All connected by membrane or vesicles
• Nuclear envelope
• Rough ER
• Smooth ER
• Golgi
• Lysosomes
• Vacuoles

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Cytoskeleton frame work

• Made of 3 types of fibers

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Microtubules

• Three main types of fibers make up the
  cytoskeleton
• Microtubules are the thickest of the three
  components of the cytoskeleton, help separate
  cells during cell division, make up flagellum,
  and guide moving vesicles like a train track
• Ex. 9 microtubules make up a centriole.

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Intermediate Filaments

• Intermediate filaments are fibers with diameters
  in a middle range. They, anchor organelles and
  maintain cell shape

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Microfilaments

• Microfilaments, also called actin filaments, are
  the thinnest components and are found in muslces
  for contracting.
• In muscle cells, thousands of actin filaments are
  arranged parallel to one another
• Thicker filaments composed of myosin interact
  with the thinner actin fibers

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Cell Junctions

• Plasmodesmata pores in the
• cell walls between plant cells
• Gap Junctions pores in the
• membranes between animal cells
• Desmosomes anchores that
• hold cells together
• Tight Junctions tightly pressed
• cells to seal fluid out

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Animal vs. Plant
Animal Cells Plant Cells
No cell wall Cell Wall
No chloroplasts Chloroplasts
Lysosomes Lysosomes (rarely)
Scattered Vacuoles Large Central Vacuole