The Geographic

  Mitochondria are organelles found in eukaryotic cells that play an important role in the production of ATP, the universal energy currency used in all cells. Most mitochondrial proteins are transported from the cytosol into mitochondria through specialized protein translocator complexes. Interactions between these complexes bring the outer and inner mitochondrial membranes into proximity. The successful targeting of many proteins that reside in the intermembrane space requires translocator complexes that cross both the outer and inner membranes. After entering the inner membrane translocator, many of these proteins do not completely cross the membrane, but instead are released into the membrane and diffuse laterally. They then remain embedded in the inner membrane or are cleaved, releasing a portion into the intermembrane space. Very few resident proteins are simply transported across the outer membrane translocator complex. Matrix proteins do not transit through the intermembrane spa

 By: S Raza Ali Shah | We know by now that glycolysis takes place in the cytoplasm, and leads to the formation of two molecules of pyruvate per molecule of glucose. These pyruvate molecules are converted into acetyl coenzyme A, also known as acetyl-CoA, and this happens inside the mitochondrial matrix. Therefore, acetyl-CoA is the key metabolic intermediate that links glycolysis and the citric acid cycle. For clarity, we will not show the coenzyme portion of acetyl-CoA, and instead are simply representing it as the two-carbon molecule acetate. So how does the pyruvate get into the mitochondrial matrix? This depends on a carrier protein that transports pyruvate into the mitochondrial matrix, where there it is oxidized to form acetyl-CoA by the enzyme pyruvate dehydrogenase. In this reaction, a molecule of carbon dioxide is generated as pyruvate is oxidized to acetyl-CoA, and a molecule of NAD+ is reduced to NADH. This last reaction is not shown for clarity. The citric acid cycle consi

    By: S.Raza Ali | First steps towards understanding the electrical properties of individual neurons. We learned how electrical forces and diffusion give rise to membrane potentials, and we learned how cells can generate and propagate signals called action potentials, or 'spikes', along the membrane. Understanding the properties of the neuronal membrane is essential, but understanding just these properties isn't sufficient to give us insight into the collective behavior of the billions of connected neurons in our brains. Luckily for us, we can approach neuroscience at many different scales and levels of analysis, and we don't have to confront the full complexity of everything all at once. That's what we'll be exploring throughout the rest of this course as we slowly go from our understanding of single molecules such as ion channels'..to the electrical behavior of neurons...to their collective behavior in small circuits...and finally onto how they bec