Transcript Document 7799808

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 WBC’s 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.
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• Ann. Review of Biophysics and Biomolecular Structure 4
Vol. 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 cytoskeleton
FUSINITA VAN DEN ENT, LINDA A. AMOS & JAN
LÖWE
Nature 413, 39-44 (6 September 2001)
Illustrations: entry into cells
Only eukaryotes.
Both prokaryotes and
eukaryotes.
http://bio.winona.msus.edu/bates/genbio/images/endocytosis.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/Membranes/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/06memb3.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
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• 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/media
lib/media_portfolio/text_images/FG0
9_32.JPG
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+)
– Doesn’t require energy
DIRECTLY, but making the
electrical gradient DOES
require energy.
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Antiport and Symport
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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.