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--CELLULAR RESPIRATION STEP VIDS--
Glycolysis: (in production)
Krebs (Citric Acid) Cycle: (in production)
Electron Transport Chain: (in production)

--RECOMMENDED STUDY GUIDES--
Genetics: https://amzn.to/2BzK1S2
Biology I: https://amzn.to/2SasaIl
Biology II: https://amzn.to/2EKKGEv
Biology terminology: https://amzn.to/2BBHuXo

--VIDEOS AND PLAYLISTS--
Test tips and tricks: https://bit.ly/2VAnjTb
Eukaryotic vs Prokaryotic Cells: https://bit.ly/2QDqkOY
Plant cell vs Animal cell: https://bit.ly/2M10y6j
Smooth ER: https://bit.ly/2FpvYD4

Images adapted from Wikipedia and OpenStax Biology

--TRANSCRIPT--
Thanks for stopping by, this is 2 Minute Classroom and today we are doing an overview of cellular respiration. This will be a good introduction to the topic or a good refresher before a test or homework assignment.

Cellular respiration is the process by which your cells break down macromolecules (like glucose) to produce ATP, the energy currency of the cell.

There are three main steps in cellular respiration. Glycolysis, the Krebs (or citric acid) Cycle, and the electron transport chain (also known as oxidative phosphorylation)

We’ll cover each of these steps briefly in this video and focus on the total ATP produced from a single glucose molecule going through each step. You can find links to a more detailed video of each step in the description below once they are produced.

The first step, Glycolysis, is a series of reactions that take place in the cytosol.

Glucose is a high energy molecule and glycolysis starts the process of extracting that energy from the glucose molecule.

Glycolysis requires the input of a glucose and two ATP molecules and puts out four ATP, two NADH molecules and two pyruvate molecules.

So the net ATP production of glycolysis is two ATP.

The two NADH will come into play later.

The two pyruvates then undergo oxidation to produce two acetyl-COA molecules, also producing two more NADH.

These two acetyl-COAs go into the next step, the Krebs Cycle. The pyruvate oxidation and Krebs cycle both take place in the mitochondria.

Each Acetyl-COA goes through the Krebs cycle separately and produces three NADH, one FADH2, and one ATP (or GTP).

Since this happens twice our total production in the Krebs Cycle is six NADH, two FADH2, and two ATP.

As stated earlier, the NADH and FADH2 will be used in the final step of cellular respiration.

This brings us to our final step, oxidative phosphorylation and the electron transport chain or ETC, which also takes place in the mitochondria.

Without getting too complex, this step utilizes the NADH and FADH2 to create a concentration of hydrogen ions (an electrochemical gradient) on one side of a membrane. This sounds complicated but just think of it like a dam holding a high concentration of water on one side.

Our hydrogen ions are like the water.

Just as the water pressure of a dam can push a turbine to create energy, the high concentration of hydrogen ions powers a “pump” to create ATP. The pump in this case is a very efficient enzyme called ATP synthase.

For each NADH that goes into the ETC we get approximately 2.5 ATP out and for each FADH2 we get 1.5 ATP out.

Looking at our totals from a single glucose molecule we have:

10 NADH (2 from glycolysis, 2 from pyruvate oxidation and 6 from the kreb’s cycle)
Which yields approximately 25 ATP in the final step of oxidative phosphorylation.

We also have the 2 FADH2 from the krebs cycle which will produce 3 more ATP.

And finally we have 4 ATP molecules, two ATP from glycolysis and two ATP from the krebs cycle for a grand total of 32 ATP from a single glucose molecule.

It is very important to note that there is a theoretical yield of 38 ATP, but conditions in the cell put the actual yield between 30-32 ATP.

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