Grizzly bears love eating fish. Since the rivers are frozen in winter, they have to build up body fa — Analytical Chemistry Chemistry Question
Fatty Acid Degradation
Grizzly bears love eating fish. Since the rivers are frozen in winter, they have to build up body fat in autumn which they burn during hibernation. [VISUAL]
The reaction cascade specific to fatty acid degradation is called “β–oxidation”. It takes place in the mitochondria of the bear’s cells. In each cycle of β–oxidation an acetyl group is split off the fatty acid and two different reaction partners A, B are reduced.
The acetyl group is further oxidized in a second reaction cycle, which takes place in the matrix of the mitochondrion.
The reduced products A and B are reoxidized to build up adenosine triphosphate (ATP) in a third cascade of reactions, called the respiratory chain, at the inner mitochondrial membrane.
Draw a typical triglyceride and name its building blocks. Mark centres of chirality.
Model Answer
Glycerol (chirality centre marked by *), saturated or unsaturated fatty acids, e.g., stearic acid (C18, position 1), linoleic acid (C18, position 2), palmitic acid (C16, position 3).
[VISUAL]
Write down the complete names and the commonly used abbreviations of the molecules A and B. Draw the line bond structures of the reactive moieties of these molecules in the oxidized and reduced forms.
Model Answer
NADH: nicotinamide adenine dinucleotide
[VISUAL]
FADH2: flavin adenine dinucleotide
[VISUAL]
What is the name of this reaction cycle? Which oxidation product is released from the cycle? What are the reduced products?
Model Answer
Krebs–cycle; alternative names are: citric acid cycle or tricarboxylic acid cycle. The oxidation product is CO2. The reduced products are NADH and FADH2.
What is the oxidation product of the respiratory chain? How is the free energy stored at the inner mitochondrial membrane independently of chemical bonds, and how is it used for the synthesis of ATP?
Model Answer
The oxidation product is H2O. The free energy is stored at the inner mitochondrial membrane as a proton concentration gradient across the membrane. The re–entry of protons into the mitochondria causes ATP synthesis, catalysed by the enzyme ATP–synthase involving a unique rotary mechanism.
Write down the molecular formula of the overall oxidation reaction of a fatty acid in these three reaction cascades. What roles do A and B play in these reaction cascades?
Model Answer
For example for palmitic acid: C16H32O2 + 23 O2 → 16 CO2 + 16 H2O
NADH and FADH2 are electron carriers – they carry redox equivalents from the β–oxidation and the Krebs cycle to the respiratory chain.