Respiration: The Krebs Cycle in a Snap! Unlock the full A-level Biology course at bit.ly/2W46XWD created by Adam Tildesley, Biology expert at SnapRevise and graduate of Cambridge University.
The key points covered of this video include:
1. Introduction to the Krebs Cycle
2. Stages of the Krebs Cycle
Introduction to the Krebs Cycle
The Krebs Cycle is the third stage of aerobic respiration and it takes place in the mitochondrial matrix. In the Krebs cycle a series of enzyme catalysed reactions occur to oxidise the acetylcoA produced in the links reaction. In the Krebs cycle, ATP molecules and reduced coenzymes, such as reduced NAD and FAD, are produced and carbon dioxide is released. For every molecule of glucose there are two turns of the Krebs cycle.
The Stages of the Krebs Cycle
In the first stage of the Krebs cycle the acetyl group is released from acetyl CoA. The carbon acetyl group then combines with the 4 carbon compound oxaloacetate to form the 6 carbon compound called citrate. Citrate is then decarboxylated and dehydrogenated. This reaction results in the production of one molecule of carbon dioxide, one molecule of reduced NAD and a 5 carbon compound. This 5 carbon compound is then decarboxylated and dehydrogenated. This reaction also produces one molecule of carbon dioxide, one molecule of reduced NAD and a 4 carbon compound. This 4 carbon compound then temporarily combines with coenzyme A and at this stage ATP is also produced from ADP and Pi. This production of ATP in the Krebs cycle is called substrate level phosphorylation. The 4 carbon compound is then dehydrogenated. This reaction produces a different 4 carbon compound and also reduces a coenzyme called FAD. The new 4 carbon compound is then also dehyrdrogenated. This reaction is catalysed by the enzyme called isomerase to produce oxaloacetate and a reduced NAD. The cycle can then continue again - altogether each Krebs cycle results in the production of 3 redNAD, 2 carbon dioxide molecules, one ATP and one redFAD.
Summary
The Krebs cycle is the third part of aerobic respiration and occurs in the mitochondrial matrix
In the Krebs cycle, the acetyl group dissociates from coenzymeA
It then undergoes a series of decarboxylation and dehydrogeanation reactions
Substrate level phosphorylation also takes place
Altogether per Krebs cycle results in the production of 3 redNAD, 2 carbon dioxide molecules, one ATP and one redFAD