The Production of Secretory Proteins

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The Production of Secretory Proteins

• How a secretory protein is produced, refined,
  packaged and finally transported out of the cell

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Proteins produced at the free floating ribosomes
and those produced at the ribosomes on the RER
have different functions

• Proteins produced at ribosomes on the rough ER
  and Golgi

• Proteins produced at free floating ribosomes

• Translated on the ribosomes, modified on the
  rough ER and Golgi
• Secretory proteins (messenger molecules,
  antibodies)
• Lysosomal enzymes
• Membrane proteins (channel proteins, enzymes,
  receptors)

• Translated on free floating ribosomes, modified
  by enzymes in the cytosol
• RNA polymerase
• DNA polymerase
• Transcription factors
• Proteins in microtubules and microfilaments

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• Label your diagram as we go through this!
• Label the diagrams with the number, and write the
  descriptions on a sheet of paper.
• (easier for you to study)

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Some background info

• The number of golgi sacs in a cell varies with
  how active a cell is in secreting proteins. More
  active more golgi sacs
• Golgi receives transport vesicles produced by the
  ER. Then it chemically modifies them marks and
  sorts the protein molecules into different
  batches for different destinations (this is why
  it has the nickname the post office!)

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Production, Refinement, Packaging and Transport
of Proteins

• Transcription of mRNA in the nucleus. Ribosomes
  produced in nucleolus, migrate to RER (ribosome
  receptor proteins on membrane of RER)
• 2. Translation of polypeptide at the ribosome on
  the RER

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• 3. Polypeptide moves into lumen of RER. Enzymes
  in the lumen of the RER modify/ refine the
  polypeptide
• Some aa removed (methionine)
• Sometimes sugar added to make glycoprotein
• Tertiary or quaternary structure established
• key terms for RER refinement, transport
• 4. Modified polypeptide transported through the
  lumen of ER

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• ER membrane pinches or buds off into a transport
  vesicle. A transport vesicle is just a part of
  the ER membrane surrounding the protein. The
  vesicle is now carried by the cytoskeleton
  through the cytoplasm to the Golgi complex.
• 6. The vesicle fuses with the membrane of the
  Golgi stack.

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• Enzymes in the Golgi modify the proteins further.
  Final refinement occurs here. Some sugars are
  removed, proteins are further modified, sorted
  into different batches depending on their
  destinations, and packaged into vesicles
• key terms for Golgi modify, sort, package
• 8. Proteins move in vesicles from 1 stack to the
  next for more modification

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• Final sorting and packaging of proteins into
  vesicles so they can move to their final
  destinations (proteins are sorted and batched
  together for their correct destination)
• 10. Vesicle buds off the Golgi and travels to the
  cell membrane

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1. The vesicle fuses to the cell membrane and
   releases the protein into the intercellular fluid
   (exocytosis!)
2. Protein travels through the bloodstream to other
   body cells where they are needed.

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• So, what kind of proteins are produced in this
  way?
• Secretory, lysosomal enzymes, membrane proteins
• Why? These are usually used in cells other than
  those in which they are produced.
• The proteins produced at free floating ribosomes
  are modified in the cytoplasm and are primarily
  used right in the cell in which they are produced.