WEEK 6: Cellular Respiration and the ADP-ATP CycleLEARNING OUTCOMESBy the end of these lessons, you should be able

to: Explain the series of reactions that result in the

transfer of chemical energy to ATP. Describe ATP and explain how it is used by cells. Describe aerobic respiration. Describe anaerobic respiration.

What’s it all about? Takes place in the inner membrane of

mitochondria. Breaking down (catalysing) glucose to release

energy. Exergonic reactions. Redox reactions relocating electrons. This energy is then used to synthesise ATP (a

process called phosphorylation). Three steps:

1. Glycolysis2. Krebs cycle3. Electron transport

Stage 1: Glycolysis Occurs in the cell cytosol. A 10-step process catalysed by enzymes. Begins the process of breaking glucose down:

one molecule of glucose is broken down into two molecules of pyruvate (a 3-C sugar).

A small amount of energy is released. Two molecules of ATP and two of NADH are

released. NADH is an acceptor molecule carrying two

hydrogen ions and two electrons. No CO2 is released in this stage.

C C CC CC 1 glucoseCYTOSOL

C C CC C C 2 pyruvate

2 ADP + Pi

2 ATP2 NAD+

2 NADH

Stage 2: The Krebs cycle Occurs in the mitochondrial matrix. Many enzymes are involved in this 8-step

cycle. Completes the job of breaking pyruvate

down into carbon dioxide. Each pyruvate molecule yields: 3 carbon dioxide molecules Four loaded NADH molecules (carrying H+ and

electrons) One loaded FADH2 molecule (another acceptor

molecule carrying H+ and electrons) One ATP molecule.

Krebs cycle summary

INPUTS: (per half glucose) 1 pyruvate 4 NAD+

1 FAD 1 ADP + Pi

OUTPUTS: 3 CO2 4 NADH 1 FADH2 1 ATP(Most of the energy is shuttled as electrons to the next stage.)

Stage 3: Electron transport chain Takes place on the inner membranes of the

mitochondria. Electrons from the NADH and FADH2 are

passed along a chain of components called cytochromes; mainly proteins through the membrane.

The last component of the chain passes its electrons to oxygen, which also picks up a pair of hydrogen ions from solution. This forms water.

The chain eases the fall of electrons from food to oxygen to release energy is smaller amounts.

Not there yet?! Where is the ATP? An enzyme at the end of the process called

ATP synthase (what do you think it does...?) is used.

It puts the ADP + Pi together to form ATP.

FADH2 comes in here

Linking photosynthesis and cellular respiration