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Respiration Question Help

Hi all,

Just working through some questions on the metabollic pathways to respiration.

Come accross this one that has me a little unstuck for some reason. Understand the concepts, just don't know if I'm on the right tracks here

In an investigation of aerobic respiration, isolated mitochondria were added to a prepared medium containing succinate and inorganic phosphate. Succinate is a 4 carbon compounds, which occurs in the Krebs cycle, and can be used as a respiratory substrate. The medium was saturated with Oxygen. Equal amounts of ADP were added at one-minute intervals. The graph shows the results

There then follows a downward, stepwise moving line graph. Each step is marked X, Y then Z. The first two steps move down equally, the last one falls less.

1. Why was inorganic phosphate added to the medium?

My Answer: To generate ATP.

2. Explain why the concentration of Oxygen in the medium decreased after adding ADP at X.

My thoughts:

Presumably we are starting from the Krebs cycle. However, I'm struggling with this as we haven't got any Acetyl Co-enzyme A.
I think it could be to do with the NAD passing on to the electron-transport chain and water being generated in the process, hence the fall in Oxygen. This requires energy so ADP is used to create ATP hence why the drop occurs when ADP is added.

2. Explain why the drop in Oxygen is the same at X and Y.

Same number of Co-enzymes? So same fall in O2?

3. Explain why the drop is less at Z than Y.

Less O2 available?

This one does have me stumped. Only been doing this a week! Grr!

Any help would be much appreciated as I feel I'm on the wrong train of thought.

Many thanks,
Luke.

Reply 1

Corpsetaker

Will give this a try:

1) You should probably mention ATP is being regenerated, as it is a continual process. At least, in Scotland, you've to mention regeneration because 'generation' implies a finite supply of ATP reagents.

edit: In fact, you should probably mention that it's being used to regenerate ADP in the Cytochrome System, just to ensure you can't be marked down.

2) I'm not to sure, but perhaps that question implies Succinate is being used to free up Hydrogen in lieu of Acetyl-CoA? In Higher Biology (roughly around AS level, I suspect) we just called those "Intermediate Acids" or something.

I agree with your thoughts though. The NAD would be quickly reduced to NADH (one of these is toxic, either NAD itself or free-floating H protons, I can't recall) in the Cytochrome System using the Hydrogen liberated through the various steps of Krebs Cycle, and hence require more oxygen to produce water.

3/4) I don't really understand these without a graph to interpret.

I'm presuming the axis on your graph are Oxygen content against time, right?

Dublin

Reply 2

gunther13 69lol

sounds good to me :0Tony