KREB and DUMPLIN

TCA CYCLE

Today, we learn about the TCA cycle as known as the famous Krebs cycle for all our scientist out there and is sometimes called the Citric Acid cycle. TCA stands for tricarboxylic acid. So what is the purpose or the end product of the TCA cycle? Well the easy answer would be energy but as a tertiary level student, more information would be needed to express the level of knowledge and understanding that I should be at. The TCA cycle can be defined as a continuation of different chemical reactions to produce energy in the form of ATP (Adenosine Triphosphate) via the oxidation of acetate. The TCA cycle can be considered as the step following glycolysis in the breakdown of sugar towards producing energy. Be sure to remember that the cycle takes place in ALL aerobic organisms and must take place under aerobic condition to generate ATP via oxidative phosphorylation.

So if glycolysis takes place in the cytosol, where does the TCA cycle take place? The answer to that would be in the mitochondria. Remember those little things? In eukaryotic cells? I’m sure you do. Yes, so the cycle takes place on the inner cristae within the mitochondria.

We need to link glycolysis to the TCA cycle via a reaction. This reaction will be:

Pyruvate + CoA+ NAD+      →     acetylCoA + CO2 + NADH

The primary substrate in the TCA cycle is Pyruvate(3C) but it is immediately turned into acetylCoA(2C) which is the main product of the reaction above. The above reaction is catalysed by three enzymes and collectively, they are called the pyruvate dehydrogenase complex. Once this is produced, our eight chemical reactions can begin. For our level, we must know these 8 enzymes used in the reactions. So let’s list them.

ü  Citric synthase- Synthesises Citrate(6C) from Oxaloacetate(4C) + acetyl CoA(2C)

ü  Aconitase- produces cis-aconitate(6C) and isocitrate(6C)

ü  Iso-citrate dehydrogenase- produces α-ketoglutarate (5C)

ü  α ketoglutarate dehydrogenase- produces succinyl CoA(4C)

ü  Succinyl-Coenzyme A synthetase- produces succinate(4C)

ü  Succinate dehydrogenase- produces fumerate(4C)

ü  Fumerase- produces malate(4C)

ü  Malate dehydrogenase- produces olaloacetate(4C)

 1335px-Citric_acid_cycle_with_aconitate_2.svg

TIPS

  • An easy way to remember these reactions is by abbreviating but I’m sure everyone will have their own special way to remember.
  • Always pay close attention to the carbon balance when learning and doing the Krebs cycle
  • The TCA cycle is not an easy topic so be sure to go it over in much more detail.

 REFERENCES

Wikipedia. “Citric acid cycle with aconitate 2.svg.” 2014. http://en.wikipedia.org/wiki/File:Citric_acid_cycle_with_aconitate_2.svg (accessed 23 Mar 2014).

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