Biology meets geometry

PUBLIC RELEASE DATE:

30-Oct-2014

Contact: Julie Cohen 805-893-7220 University of California - Santa Barbara @ucsantabarbara

(Santa Barbara, Calif.) Architecture imitates life, at least when it comes to those spiral ramps in multistory parking garages. Stacked and connecting parallel levels, the ramps are replications of helical structures found in a ubiquitous membrane structure in the cells of the body.

Dubbed Terasaki ramps after their discoverer, they reside in an organelle called the endoplasmic reticulum (ER), a network of membranes found throughout the cell and connected to and surrounding the cell nucleus. Now, a trio of scientists, including UC Santa Barbara biological physicist Greg Huber, describe ER geometry using the language of theoretical physics. Their findings appear in print and online in the Oct. 31 issue of Physical Review Letters.

"Our work hypothesizes how the particular shape of this organelle forms, based on the interactions between Terasaki ramps," said Huber, who is deputy director of UCSB's Kavli Institute for Theoretical Physics. "A physicist would like to say there's a reason for the membrane's shape, that it's not just an accident. So by understanding better the physics responsible for the shape, one can start to think about other unsolved questions, including how its form relates to its function and, in the case of disease, to its dysfunction."

The rough ER consists of a number of more or less regular stacks of evenly spaced connected sheets, a structure that reflects its function as the shop floor of protein synthesis within a cell. Until recently, scientists assumed that the connections between adjacent sheets were like wormholes that is, simple tubes.

Last year, however, it was discovered that these connections are formed by spiral ramps running up through the stack of sheets. According to lead author Jemal Guven of the Universidad Nacional Autnoma de Mxico, this came as a surprise because spiral geometries had never previously been observed in biological membranes.

Attached to the membrane, ribosomes, which serve as the primary site for protein synthesis, dot the ER like cars populating a densely packed parking structure. "The ribosomes have to be a certain distance apart because otherwise they can't synthesize proteins," Huber explained.

"So how do you get as many ribosomes per unit volume as possible but not have them bump up against each other?" Huber asked. "The cell seems to have solved that problem by folding surfaces into layers that are nearly parallel to each other and allow a high density of ribosomes."

Originally posted here:
Biology meets geometry