Understanding How Cells Work

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Understanding How Cells Work
Standard Set 1 Cell Biology 1c, 1e, 1a
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Two Major Groups of CellsProkaryotic Cells Pro
(before) karyotic (nucleus)

• No nucleus
• No membrane-bound organelles
• Most 1-10 microns in size
• Evolved 3.5 billion years ago
• Only bacteria

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Two Major Groups of Cells Eukaryotic Cells Eu
(true) karyotic (nucleus)

• Nucleus
• Many organelles
• From 100-1,000 microns in size
• Evolved 1.5 billion years ago
• All other cells

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An Internal Membrane System Processes Proteins

• Proteins are made by ribosomes on the rough ER.
• Vesicles carry proteins from the rough ER to the
  Golgi apparatus.
• Proteins are modified in the Golgi apparatus and
  enter new vesicles.

• Some vesicles release their proteins from the
  cell.
• Other vesicles remain in the cell and become
  lysosomes.

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Understanding the Processing of Proteins

• In the library (ER) students (ribosomes) produce
  homework (proteins).
• Backpacks (vesicles) carry the homework
  (proteins) from the library (ER) to the teacher
  (Golgi apparatus).
• The teacher (Golgi apparatus) grades (modifies)
  the homework (proteins), which enters folders
  (new vesicles).
• Some folders (vesicles) release their homework
  (proteins) from the school (cell).

• Other folders (vesicles) remain in the school
  (cell).

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Cell Membranes Provide a Barrier that separates
the inside of a cell from the outside of a cell.

• Cell membranes are not rigid, instead, they are
  fluid like a soap bubble.
• Lipids create the fluid foundation of membranes
  by forming a lipid bilayer.
• Cell membranes are selectively permeable,
  allowing only certain substances to leave and
  enter the cell.

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Plasma Membranes are made of Phospholipids

• Phospholipids are fat molecules shaped like a
  head with two tails.
• phospholipids have a polar (water loving) region
  and a nonpolar (water hating) region.
• phospholipids automatically form a bilayer when
  in water.

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Cell Surface Proteins in the lipid bilayer

• Channel proteins act as gates in and out of a
  cell, transporting food and other molecules in
  and wastes out.
• Marker proteins name tags of the cell for
  identification.
• Receptor proteins gather information about the
  cells surroundings and triggers reactions.

• Many types of proteins are found embedded in the
  lipid bilayer.

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Types of Cellular Transport

• Passive Transport does not require energy
  to move across the cell membrane
• Active Transport requires energy to move
  across the membrane

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Diffusion

• The movement of molecules from a region of higher
  concentration to a region of lower concentration
  through a selectively permeable membrane until an
  equilibrium is reached.

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Facilitated Diffusion

• The movement of specific molecules from higher to
  lower concentration through a membrane by using a
  channel protein.

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Osmosis is simply the diffusion of water

• Water molecules are attracted and stick to
  solute molecules.
• This reduces the number of water molecules that
  can move freely on that side.
• Water moves by osmosis from a greater to lesser
  concentration.

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Osmosis creates three different osmotic
conditions

• Hypotonic The solute concentration in the
  environment is lower than in the cell.
• Hypertonic The solute concentration in the
  environment is higher than in the cell.
• Isotonic The solute concentration in the
  environment is equal to that in the cell.

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Examples of Osmosis in Nature ...

• Animal cells burst (lysis) due to pressure on the
  plasma membrane when placed in a hypotonic
  solution.
• Animals cells shrivel (crenation) when water
  leaves the cell while in a hypertonic solution.

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Examples of Osmosis in Nature ...

• Plant cells are supported by turgor pressure
  within the vacuole when placed in a hypotonic
  solution.
• Plant cells wilt when water leaves the vacuole
  due to plasmolysis when placed in a hypertonic
  solution.

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Active Transport

• Protein Pumps Protein pumps require energy
  (ATP) and channel proteins to move ions (/-
  charged particles) and large molecules (glucose)
  through a membrane against a concentration
  gradient. Example Sodium-Potassium Pump

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Membrane Assisted Transport

• Materials are placed inside of a membrane bubble
  called a vesicle
• Exocytosis (exit) the dumping of waste materials
  outside of the cell by discharging them from
  waste vesicles.
• Endocytosis (taking in) the engulfing of
  material by cells