Biology 107 Cell II

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Biology 107Cell II

• September 26, 2003

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Cell II

• Student Objectives As a result of this lecture
  and the assigned reading, you should understand
  the following
• Ribosomes are non-membranous organelles that are
  the sites of synthesis of proteins in the cell.
  Ribosomes consist of two subunits, the large and
  the small, comprised of proteins and specific
  RNAs, called rRNAs (ribosomal RNAs). The mRNA
  and the amino acids with their carriers (tRNAs or
  transfer RNAs) bind to ribosomes, and polypeptide
  chains are formed by dehydration synthesis.
• Ribosomes may be attached to membrane or "free"
  (non-membrane attached) in the cytoplasm.

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Cell II

• Endoplasmic reticulum is a membranous organelle
  that may be subdivided into two different types
  with different functions.
• a. Rough endoplasmic reticulum (RER) is so named
  because it is studded with ribosomes. RER
  functions to make proteins for secretion by the
  cell or for incorporation into cellular
  membranes. The RER also begins the
  compartmentalization and processing of some
  proteins so they can be shipped out of the
  cells or distributed to specific
  subcompartments.
• b. Smooth endoplasmic reticulum (SER) is a
  series of interconnected membrane tubules that
  lack ribosomes. SER and RER are continuous.
  One of the functions of ER lacking ribosomes is
  the synthesis of lipids, including
  phospholipids, fats and steroids. SER also
  contains enzymes that are involved in
  detoxification, and in some cells SER is
  involved in calcium storage and release.

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Cell II

• The Golgi apparatus is a stack of flattened
  membrane sacs, but they are not interconnected
  like ER stacks. Golgi receives, modifies and
  segregates different proteins.
• a. Some of the proteins modified and sorted by
  the Golgi are parts of membranes (such as
  channel proteins or receptor molecules), some of
  the proteins are secreted, and some of the
  proteins are routed to other organelles (e.g.,
  lysosomes).
• b. Within the Golgi are enzymes to add sugar
  molecules, sulphate groups and phosphate groups
  to proteins.
• c. Specific chemical modifications help tag and
  sort molecules through the Golgi into different
  destination streams.

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Cell II

• Vesicles are relatively small membrane sacs that
  function to shuttle materials around the cells
  and between the cell surface and the membranous
  organelles. For those membranous organelles that
  do not have direct membranous continuity,
  vesicles provide indirect, functional continuity
  through pitching off, movement to a new site,
  fusion and transfer of materials. This shuttling
  system has directionality and provides points of
  control of passage. When vesicles fuse with a
  new membrane system they are adding not only
  contents but also membrane.
• 6. The lysosomes are membrane-bounded sacs
  (vesicles) that contain hydrolytic (digestive)
  enzymes necessary for the normal turnover of cell
  components. The membrane enclosure of the
  hydrolytic enzymes keeps these enzymes from
  destroying the cell.

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Ribosomes Consist of Large and Small Subunits
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Ribosomes May be Free or Bound to ER Membrane
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RER Contains Bound Ribosomes
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RER Synthesizes Integral Membrane Proteins,
Lysosomal Proteins, and Proteins for Secretion
from the Cell
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Endoplasmic Reticulum (ER)
Rough endoplasmic reticulum (RER) is involved in
protein synthesis Smooth endoplasmic reticulum
(SER) is involved in lipid synthesis, breakdown
of certain toxins, and calcium sequestration
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Golgi Apparatus
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Golgi Apparatus Processes and Sorts Materials it
Receives from the RER
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Lysosmes Contain Hydrolytic Enzymes
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Example of Pathway for Proteins Synthesized in
RER and Processed/Sorted in the Golgi
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Synthesis and Processing of Lysosomal Proteins
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