Aerobic Resp. , Krebs & Coenzymes

Where does Krebs take place?

Mitochondrial matrix

How many times does the Krebs Cycle occur?

2

• Happens once for every pyruvate molecules, so twice per molecule of glucose

Krebs Cycle process

1. Acetyl group (2C) combines w. oxaloacetate (4C) to form citrate (6C)

2. Citrate undergoes decarboxylation & dehydrogenation, producing a red. NAD and CO2

3. Citrate (5C) undergoes further decarboxylation & dehydrogenation, (4C) producing 2 red. NAD and 1 red. FAD

4. Substrate level phosphorylation occurs - ADP + Pi = ATP

   1. Inorganic phosphate from matrix

5. Oxaloacetate is regenerated (from step 3.)

Net products from Krebs Cycle

• 6x reduced NAD

• 2x red. FAD

• 2x ATP

• 4x CO2

NOTE: Is produced per glucose molecule (each glucose molecule splits to form 2 pyruvates)

Link reaction image

Why are coenzymes needed in respiration?

Required to transfer protons, electrons, & functional groups between the many enzyme-catalysed reactions

• Without the coenzymes, electrons & protons can’t be transferred for the redox reactions

NAD

• Takes part in all stages of cellular resp.

• Accepts 1 H+ to become red. NAD

• Red. NAD oxidised at start of ETC, releasing protons & electrons

• Red. NAD results in synthesis of 3 ATP molecules (actually varies)

FAD

• Only accepts H+ in Krebs Cycle, used in oxidative phosphorylation

• FAD accepts 2 H+

• red. FAD is reduced further along ETC

• red. FAD results in synthesis of 2 ATP molecules (actually varies)