(7) Cellular Respiration (E) Regulation of pathways through feedback inhibition (A) Role of ATP & Phosphorylation (B) The metabolic pathway of respiration: Glycolysis and the citric acid cycle (C) The metabolic pathway of respiration: electron transport chain & ATP synthesis (D) Substrates for Respiration

Cellular Respiration (b) Describe the process of the Citric Acid Cycle Using the terms coenzyme, regeneration, oxaloacetate, FAD

Stage 2

Citric Acid Cycle (occurs only if oxygen is present) Pyruvate NAD NADH CO2 Acetyl group Coenzyme A Acetyl Coenzyme A Notice the 2 is present on the FAD but not the NAD citrate 2 CO2 oxaloacetate 3FAD 3FADH2 ADP ATP Many enzyme controlled reactions 3NAD 3NADH

A similar step also occurs, but the coenzyme is FAD. Pyruvate is broken down to an acetyl group that combines with coenzyme A to be transferred to the citric acid cycle as acetyl coenzyme A. Acetyl (coenzyme A) combines with oxaloacetate to form citrate followed by the enzyme mediated steps of the cycle. This cycle results in the generation of ATP in one of the steps, the release of carbon dioxide in 2 of the steps and the regeneration of oxaloacetate in the matrix of the mitochondria. In three steps in the cycle, the dehydrogenase enzyme removes H+ ions along with high energy electrons. Both become bound to NAD to form NADH. A similar step also occurs, but the coenzyme is FAD. 1 2 3 4 5 6 7 This is a handout 8 9 10 10

Checklist Name of stage Location Starting molecule(s) Intermediate molecule(s) Final molecule(s) ATP Carbon dioxide Hydrogen Oxygen Any other points?

Extra info that will help you understand (but you will not be examined on this) Number of carbons in each molecule: GLUCOSE 6 (gets broken down) PYRUVATE 3 (gets broken down more!) ACETYL CO A 2 OXALOACETATE 4 CITRATE 6 (2+4=6)

Investigating the activity of dehydrogenase enzyme in yeast Yeast is a fungus and a living organism. All living organisms can respire. Like us, it also contains the enzyme dehydrogenase which controls the release of hydrogen during respiration. To show the release of hydrogen during respiration a blue dye called resazurin is used. The dye changes colour upon becoming reduced (gaining hydrogen). Blue Pink Colourless (Not reduced) (partially reduced) (reduced)

Colour change of resazurin dye Aim: To investigate… Method: Results: Test tube Colour change of resazurin dye A B C

Conclusion: What test tube changed colour the fastest? Describe the process which occurred in tube A: ______ enzymes present in the _____ have acted on the substrate _____ and oxidised it. This rapid release of _____has reduced the resazurin dye and caused it to change colour. Explain why the reaction in test tube B was slower than test tube A. Test tube was slower than A because no glucose was added. The dehydrogenase enzymes could act upon the little respiratory substrate already present in the yeast. Explain why test tube C remained unchanged. Test tube C remained unchanged since boiled yeast was added. Boiling the yeast destroys the cells and denatures the dehydrogenase enzymes.

Cellular Respiration (b) Describe the process of the Citric Acid Cycle Using the terms coenzyme, regeneration, oxaloacetate, FAD