The work is a major step toward understanding how some biological structures convert sunlight into chemical energy, a biological innovation that is essential to life. The team originally was led by University of Illinois physics professor Klaus Schulten and continued the work after Schulten's death in The study fulfills, in part, Schulten's decades-long dream of discovering the mechanisms by which atomic-level interactions build and animate living systems.
Schulten decided very early in his career to study photosynthetic systems, said study co-author Melih Sener, a research scientist at the U. Schulten and Sener modeled the chromatophore, a primitive photosynthetic organelle that produces chemical energy in the form of a molecule known as ATP. That work involved a long-term collaboration with Neil Hunter from the University of Sheffield, who provided much of the experimental data. And the only way to do that was with supercomputers.
Over the years, Schulten recruited and supported collaborators at Illinois and elsewhere to help him tackle the challenge. The team constructed a million-atom model of the chromatophore, an effort that required a colossal amount of supercomputer power over a period of four years.
Schulten and his colleagues had already conducted molecular simulations of many of the individual protein and lipid components of the chromatophore, which produces the ATP needed to power a living cell.
The antenna harvests light, the battery directs that energy to the motor and the motor cranks out ATP, he said. Singharoy worked with Schulten at Illinois before accepting a professorship at Arizona State University, Tempe in Figuring out how the system worked required putting all the parts together, said Illinois physics professor Aleksei Aksimentiev, who guided the project to completion after Schulten's death.
This meant dissecting the chromatophore with every tool available to science, from laboratory experiments to electron microscopy, to programming innovations that broke down the computing challenge into manageable steps, Aksimentiev said. Once they had a working model of the chromatophore, the researchers watched simulations that revealed how the organelle functioned under different scenarios.
They changed the concentration of salt in its environment, for example, to see how it coped with stress. At times of high activity, thylakoids stack up one on top of another to create structures called grana. Embedded in the membranes of the grana are photosynthetic pigments which begin the energy trapping process by harvesting light. In a complex series of energy transfer reactions, light energy is converted to electron energy, and as the electron is passed from one type of pigment to another, this energy is used to pump hydrogen ions across the grana membrane.
As the hydrogen ions return across the membrane ATP is formed. This form of short term energy storage is only the beginning. Cells convert glucose to ATP in a process called cellular respiration. Mitochondria are complex organelles that convert energy from food into a form that the cell can use.
They have their own genetic material, separate from the DNA in the nucleus, and can make copies of themselves. Chemical energy produced by the mitochondria is stored in a small molecule called adenosine triphosphate ATP. The cytoskeleton is a structure that helps cells maintain their shape and internal organization, and it also provides mechanical support that enables cells to carry out essential functions like division and movement. The cell membrane or plasma membrane is the structure that keeps cytoplasm from spilling out of a cell.
This membrane is composed of phospholipids, which form a lipid bilayer that separates the contents of a cell from the extracellular fluid. The cytoplasm is a thick, usually colorless solution that fills each cell and is enclosed by the cell membrane. Cytoplasm presses against the cell membrane, filling out the cell and giving it its shape.
Sometimes cytoplasm acts like a watery solution and sometimes it takes on a more gel-like consistency. The cytoplasm consists of a clear liquid called cytosol, a supportive cytoskeleton and networks of membranes and organelles.
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