Finish Membranes, Start Organelles

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Stephen Fish, Ph.D. Marshall University J. C. E.
School of Medicine Fish_at_Marshall.edu
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Note to instructors I use these PowerPoint
slides in cell biology lectures that I give to
first year medical students. Copy the slides, or
just the illustrations into your own teaching
media. We all know that teaching science often
requires compromises and simplification for
specific student populations, or the requirements
of a specific course. Please feel free to offer
suggestions for improvements, corrections, or
additional illustrations. I would be pleased to
hear from anyone who finds my work useful, and am
always willing to make it better. Also, the
images have been compressed to screen resolution
to keep PowerPoint file size down, and I can
provide them at any resolution. Stephen E.
Fish, Ph.D.
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General traffic diagram
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(No Transcript)
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Organelles Molecular Traffic Cytosol
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Size packing of cytosolic molecules
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Polyribosome or polysome
Note progressive folding of protein as it emerges
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Protein folding (2D model)

• Unfolded protein has
• Nonpolar (hydrophobic) side chains
• Polar (hydrophilic) side chains
• When folded
• Polar side chains are on the outside in contact
  with water
• Nonpolar ones hidden in center
• Folding mostly maintained by hydrogen bonds the
  hydrophobic effect

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When proteins dont fold correctly
Native protein
Correct
Incorrect
Clumping of incorrectly folded proteins
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Hsp 70 ATPase chaperones bind proteins during
translation

• Hsp 70 helps proteins to fold
• Bind to covers hydrophobic patches
• Protect from misfolding or clumping
• Bend protein a little release

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Hsp 60 finishes protein folding
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Hsp 60
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Ubiquitin tags misfolded proteins for destruction
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Ubiquitin tags misfolded proteins for destruction
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Proteosomes digest ubiquitin tagged proteins

• They are large multisubunit hollow proteins
• They bind ubiquitin transport protein inside
  (ATP)
• They are lined with multiple proteolytic enzymes
• Misfolded proteins are reduced to useable
  components

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Correct protein shape matching provides for
strong binding
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Some types of binding you have already seen in
the membrane lectures
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Binding can change the conformation of a protein
to perform a function
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Sequential binding organizes some cellular
processes
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Correct folding of individual proteins is
required for correct assembly function of large
multisubunit protein machines
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Sherman says