TITLE:

BOUNDARY CONDITIONS FOR THE CATALYSIS OF MEMBRANE FISSION OF ENDOCYTOSIS.

DATE:

Friday, Feb 24th, 2012

TIME:

3:30 PM

LOCATION:

GMCS 214

SPEAKER:

Joshua Zimmerberg.
National Institutes of Health.

ABSTRACT:

Life is complicated, because of ~4 billion years of auto-optimization. The organizational element
of the cell can be represented by a spheroid whose diameter can be found anywhere between
one micron and one millimeter, although most cells in the human body range from 5 to 50
microns in diameter. The cell membrane is a thin hydrophobic film surrounding the cell that
forms the main barrier to aqueous material transfer in and out of cells, so that cells can maintain
gradients of materials that distinguish the inside of the cell from the outside, and concentrate
the incredibly high organization of intracellular space needed for biological processes. To further
regulate the transfer of materials through the cell membrane, a number of specific mechanisms
have evolved for feeding, excretion, secretion, communication, etc. I will discuss one of these
mechanisms, membrane remodeling. Essentially, topological transformations occur to bud off
parts of the cell membrane and bring these parts (termed vesicles) inside the cell (phagocytosis,
endocytosis, pinocytosis). As these vesicles become speroids in their own right, new topologies
are created. Since the diameter of these vesicles vary roughly between 50 and 300 nm they
capture some extracellular aqueous volume. This extracellular volume communicates within
a network of such membrane sacs, sometimes connected with tubes, and can be returned to
the outside when a vesicle fuses to the cell membrane. The mechanism of these remodeling
steps involves proteins that work at a distance, suggesting that the physical conditions of the
membrane set by proteins forming a ring-like boundary on a tubule are the essential ingredients
to catalysis by stressing membrane components elastically.

HOST:

Dr. Jose Castillo.

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