Integrated SequencePhysics Chemistry Organic Biology

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Special points of emphasis

Work, Energy, and Power

Electricity

Atomic Theory

Periodic Properties

The Chemical Bond

Intermolecular Forces

The Eukaryotic Cell

Oxidation-Reduction

Bioenergetics and Cellular Respiration

Mitochondria are the central organelles for the creation of ATP in oxidative metabolism. A mitochondrion can be as small as a few hundred nanometers long, although they are usually more than ten times larger. A few hundred nanometers is a few thousand angstroms. So the mitochondrion would be a few thousand to a few tens of thousands of chemical bonds long. In a few weeks, we are going to be studying oxidative metabolism, and it will really help if you can visualize a mitochondrion in a concrete way down to the molecular level. Picture the plasma membranes of its outer and inner membranes. Picture he cytochrome system on the inner membrane. Picture the contents of the matrix (water, ATP, NADH, the intermediates of the citric acid cycle). Picture the proton gradient between the inner and outer compartment. Strive for a picture of the biological molecules within the aqueous solution environment as a very complex system of electric charges with chemical structure. Imagine step by step, pulling the atoms apart of the molecules of glycolysis or the citric acid cycle and letting them fall together into the next forms in the pathways. What is happening to energy? Imagine chemiosmosis across the inner membrane as if you were watching water fall through the hydroelectric power station, but instead of gravitational potential energy doing the work of pumping protons, in the mitochondrion, the potential energy decrease is electrostatic. The key to chemiosmosis is oxygen down at the end of the electron transport chain, electron greedy, with its thin electron cloud barely shielding its powerful nucleus, pulling the electrons towards itself, driving the proton pumps.

We are getting close to oxidative metabolism in this course! Not long now.




Proteins

Nucleic Acids

The Eukaryotic Cell

Although all of the RNA of mitochondria are derived from mitochondrial DNA, only a few of the proteins of mitochondria are. Mitochondrial proteins are synthesized in the cytosol by free ribosomes. These proteins possess highly specific mitochondrial entry sequences on their amino termini specifying final destination, the outer membrane, the inner membrane, the intermembrane space and the matrix.

This is another episode in the important theme of protein targetting, or protein sorting. Some crucial points to remember for the MCAT is that the mechanisms of protein targeting are based on information contained in the proteins themselves. Furthermore, sorting targets can be the exterior of the cell by secretion, or it can be a location in the cell. A common fallacy among students is to think that the posession of a signal peptide must necessitate translation on the rough ER or that it is a definitive test of a secretory protein. Signal peptides target many other destinations besides secretion including mitochondria or into the nucleus.




The Eukaryotic Cell

Evolution

Mitochondria are most likely descendents of symbiotic prokaryotes that invaded proto-eukaryotic ancestors over a billion years ago. Mitochondria are only formed by the division of other mitochondria. They have their own ribosomes and DNA. Mitochondrial ribosomes are of a bacterial type. Mitochondrial DNA is often, though not always, circular.







The WikiPremed MCAT Course is a free comprehensive course in the undergraduate level general sciences. Undergraduate level physics, chemistry, organic chemistry and biology are presented by this course as a unified whole within a spiraling curriculum.

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