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Creating a markscheme.

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Creating a markscheme.

Postby Draco » Mon Nov 26, 2007 10:20 am

I've been set the task of creating a marksheme for a question however two parts of that question are troubling me.
They are:

Explain why carbon dioxide is produced when mitochondria are incubated with pyruvate but not when incubated with glucose.

and

Explain why, in the presence of cyanide, lactate production does occur, but not carbon dioxide production.

Both of these are three mark questions however I have to find all the marking points. If anyone spots any simple ones I've overlooked then please tell me, for the others information an websites will be helpful.
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Postby woolleyy » Mon Nov 26, 2007 10:42 am

glycolysis? Tricarboxylic acid (TCA) cycle?
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Postby Navin » Mon Nov 26, 2007 2:04 pm

I can help with the first question:

These might be possible answers
1. Pyruvate is the substrate that enters mitochondria and participates in link reaction
2. Glucose can only participate in glycolysis - a process in which the enzymes are present only in the cytoplasm (NOT the mitochondria)
3. Hence, glucose not metabolised, but pyruvate participates in oxidative decarboxylation in Link Rxn and Kreb's Cycle in mito - releasing CO2.
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Postby Navin » Mon Nov 26, 2007 2:12 pm

Oh i think i can help with the 2nd qn too:

Possible Answers

1. Cyanide is an inhibitor of the Electron Transport Chain (specifically the enzyme cytochrome c)
2. Hence, ETC cannot proceed, so no oxidative phosphorylation, no regeneration of Hydrogen carriers, no Link Rxn nor Kreb's cycle --> and ultimately no aerobic respiration so no CO2 released.
3. Anaerobic repiration occurs instead, so pyruvate is reduced to lactate.
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Postby MrMistery » Tue Nov 27, 2007 7:51 pm

cytochrome c is not an enzyme, it is simply a small protein used as an electron carrier. Cytochrome c oxidase for example, is an enzyme
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