Review of eukaryotic cells

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Review of eukaryotic cells
www.steve.gb.com/ science/cell_biology.html
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Eukaryotic cell reminders

• Eukaryotic cells have a variety of compartments
• Membrane-bound organelles, carry out functions
• DNA in nucleus. NO NUCLEUS in Prokaryotes!
• Mitochondrion is an enslaved bacterium
• Inner and outer membrane like a Gram bacterium
• Mitochondrion has its own DNA and ribosomes
• It is the same size as a bacterium.
• Lysozome is an organelle
• Contains various digestive enzymes
• Important part of WBCs defenses against bacteria

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How things get in (and out) of cells

• Eukaryotic cells
• Have transport proteins in membrane
• Have a cytoskeleton made of microtubules
• Allows for receptor mediated endocytosis,
  phagotcytosis, etc.
• Cell membrane pinches in, creates vesicle
• Prokaryotic cells
• Have a stiff cell wall
• Can NOT carry out endocytosis
• Entry of materials into cell by diffusion or
  transport processes ONLY.

4

• Ann. Review of Biophysics and Biomolecular
  StructureVol. 33 177-198 January 7, 2004
• MOLECULES OF THE BACTERIAL CYTOSKELETON
• Jan Löwe, Fusinita van den Ent, and Linda A. Amos
  
• The structural elucidation of clear but distant
  homologs of actin and tubulin in bacteria and GFP
  labeling of these proteins promises to
  reinvigorate the field of prokaryotic cell
  biology.

Prokaryotic origin of the actin
cytoskeletonFUSINITA VAN DEN ENT, LINDA A. AMOS
JAN LÖWENature 413, 39-44 (6 September 2001)
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Illustrations entry into cells
Both prokaryotes and eukaryotes.
Only eukaryotes.
http//bio.winona.msus.edu/bates/genbio/images/end
ocytosis.gif http//www.gla.ac.uk/jmb17n/Teaching
/JHteaching/Endocytosis/figures/howdo.jpg
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Type of molecule affects transport

• Small molecules can pass through a lipid bilayer
• Water otherwise, no osmosis
• Gases such as O2 and CO2
• Lipid molecules can
• Dissolve in lipid bilayer, pass through membrane
• Many antibiotics, drugs are lipid soluble
• Larger, hydrophilic molecules cannot
• Ions, sugars, amino acids cannot pass through
  lipids
• Transport proteins required

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Transport through membranes

• Simple diffusion
• Molecules travel down concentration gradient
• Membrane is not a barrier to their passage
• Facilitated diffusion
• Molecules travel down concentration gradient
• Cannot pass through lipid bilayer their passage
  is facilitated by protein transporters
• Active transport
• Molecules travel against concentration gradient
• Requires input of metabolic energy (ATP),
  transporter

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How molecules get through the membrane
http//www.rpi.edu/dept/chem-eng/Biotech-Environ/M
embranes/bauerp/diff.gif
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ABC transport systems

• Include a periplasmic binding protein, a
  transmembrane channel, and an ATP-hydrolyzing
  enzyme.
• High affinity binding system.
• Family of related proteins.
• Example of Active Transport
• Requires transport protein
• Requires metabolic energy

http//www.ugr.es/eianez/Microbiologia/images/06m
emb3.jpg
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Group translocation

• As molecule passes through the membrane, it is
  chemically changed.
• Requires energy in the form of PEP.
• Requires series of proteins
• Prevents substrate from backing out of cell
• Use energy that would have been spent anyway
  prepares substrate for use.

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Permeases

• Transport proteins are often called permeases
  (-ase enzyme) because they have the same
  properties
• Instead of changing a chemical, they change its
  location
• Permeases have an active site
• Permeases are specific
• Permeases are saturable

http//cwx.prenhall.com/horton/medialib/media_port
folio/text_images/FG09_32.JPG
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ATP is not always used directly in active
transport

• An electrochemical gradient exists across the
  cell membrane
• Positive just outside the membrane, negative
  within
• Gradient in the form of H ions
• Maintained by the hydrolysis of ATP or by the
  same metabolic reactions that make ATP
• Powers uniports, symports and antiports

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Uniport

• Transport of a single substance
• Example transport of K into the cell
• Against its chemical gradient, but down its
  electrical gradient.
• (red ball K)
• Doesnt require energy DIRECTLY, but making
  theelectrical gradient DOESrequire energy.

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Antiport and Symport
www.cat.cc.md.us/.../ prostruct/u1fig6e1.html
Molecules (red balls) transported against a
gradient. Coupling to flow of H into the cell
powers this.