Senin, 23 September 2013

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Krebs Cycle or Citric Acid Cycle


Krebs Cycle

Before the Krebs cycle starts, oxidative decarboxylation. of pynrvic acid occurs in mitochondria in which the pymvic acid (3 carbon molecules) is converted into acetyl CoA (2 carbon molecules) by producing 1 NADH molecule and 1 carbon dioxide molecule (CO2).

The Krebs cycle begins when acetyl group binds with oxalacetate acid (4 carbon molecules) to form citric acid (6 carbon molecules). Meanwhile coenzyme A is released and ready to join the other pyruvic acid. That is the reason why Krebs cycle is also known as citric acid cycle. The cycle is named after the scientist who discovered the cycle in 1990s, Hans Krebs.

Iook at Figure In the conversion of isocitrate (6 carbon molecules) into α-ketoglutarate acid (5 carbonmolecules), CO2 is released and NAD. is converted into NADH. In the conversion of α-ketoglutarate into succinyl-CoA (4 carbon molecules), CO, is released again and NAD+ is reduced into NADH. Then, in the conversion of succinyl-CoA into succinate acid, ATP is formed from ADP.

Besides the NAD+, electron source is also obtained from FAD. FAD (Flavin Adenin Dinucleotide) is reduced through the additional of 2 hydrogen ions (H.) to form MDH,. The example is succinate acid conversion into fumarate acid.

In the last phase, malate acid changes into oxaloacetate acid In this phase, NAD+ changes into NADH. NADH and FADH, are electron carriers that are necessary in the next phase, the electron transport.

Therefore, from each glucose molecule in Krebs cycle it is produced 2 ATP, 2FADH2, 6NADH, and 4 CO' Look at Table

The Input And Output In Krebs Cycle

source: Biology, The unity and diversity of life, 2004.

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