An atomic-resolution mechanism of 3-hydroxy-3-methylglutaryl-CoA synthase

The citric acid cycle, also known as the Krebs cycle or TCA cycle, consists of several energy-generating reactions that yield one ATP molecule, three NADH molecules, one FADH2 molecule, and two CO2 molecules.

In animals, the mitochondrial F1F0 ATP synthase is the key protein that synthesizes ATP molecules through a complex catalytic mechanism. While the nuclear genome encodes the majority of ATP synthase subunits, the mitochondrial genome encodes some of the enzyme's most critical components. The formation of this multi-subunit enzyme is a complex multi-step process regulated at the level of transcription, translation, and assembly. Defects in one or more of these steps can result in decreased ATP...

After glycolysis, the charged pyruvate molecules enter the mitochondria via active transport and undergo three enzymatic reactions. These reactions ensure that pyruvate can enter the next metabolic pathway so that energy stored in the pyruvate molecules can be harnessed by the cells.
First, the enzyme pyruvate dehydrogenase removes the carboxyl group from pyruvate and releases it as carbon dioxide. The stripped molecule is then oxidized and releases electrons, which are then picked up by NAD+...

Lipids also are sources of energy that power cellular processes. Like carbohydrates, lipids are composed of carbon, hydrogen, and oxygen, but these atoms are arranged differently. Most lipids are nonpolar and hydrophobic. Major types include fats and oils, waxes, phospholipids, and steroids.
Fatty acids are catabolized in a process called beta-oxidation, which takes place in the matrix of the mitochondria and converts their fatty acid chains into two-carbon units of acetyl groups. The acetyl...

In aerobic organisms, the citric acid cycle is the second stage of cellular respiration wherein molecules derived from the breakdown of carbohydrates, proteins, and fats are oxidized into carbon dioxide and energy. This process is also known as the tricarboxylic acid (TCA) cycle as the first product of the cycle, citric acid, contains three carboxyl groups in its structure. Alternatively, this cycle is also referred to as the Krebs cycle, in honor of its discoverer Sir Hans Krebs.
The citric...

Carboxylic acids, upon heating, undergo a decarboxylation reaction by releasing carbon dioxide gas. Monocarboxylic acids do not undergo decarboxylation easily. However, a silver salt of carboxylic acid reacts with bromine or iodine under high temperature to release carbon dioxide gas and forms halide with one less carbon. This reaction is called the Hunsdiecker reaction.