Cellular Respiration

1. Cellular Respiration

2. Cellular Respiration: The Big Picture • We are energy beings – cellular respiration is the process by which we gain energy. • We normally run aerobic cellular respiration in which we harvest energy from organic compounds using oxygen (O2). • The molecule of choice for fuel is glucose. C6H12O6 + 6O2 6CO2 + 6H2O • Glucose has an abundance of energy in its bonds. We must release it in a series of small REDOX reactions so the energy that is released does not increase cell temperature too much or the proteins may freak out!

3. Cellular Respiration: The Big Picture • There are a variety of ways to carry out cellular respiration and not all of them require oxygen to assist in the breakdown of glucose. • Obligate Aerobes – They require oxygen to oxidize organic molecules to make energy. • Obligate Anaerobes – They oxidize inorganic molecules without oxygen to gain energy. (O2 kills!) • Facultative Anaerobes – They oxidize inorganic molecules with or without oxygen. • Note the type of molecule being oxidized – organics give big energy boosts while inorganics do not yield much energy.

4. Cellular Respiration: The Details AKA: The Hard Part!

5. Cellular Respiration: The Details • Aerobic cellular respiration is as follows… C6H12O6 + 6O2 6CO2 + 6H2O • From this, we can gather that… • cellular respiration involves breaking the bonds in glucose to make six carbon dioxide molecules. • the hydrogens get torn off of glucose to make water. • the free energy released in the breakdown of glucose is harnessed to make ATP. • So how do we do these jobs?…

6. The Reactions We’ll See • There are several types of reactions that we will encounter along the way. • REDOX – Electrons being taken from one and added to another. • Phosphorylation/Dephosphorylation – The adding/removal of a phosphate group (PO4). • Carboxylation/Decarboxylation – The adding/removal of a carbon. • Hydration/Dehydration - The adding/removal of a water molecule (H2O). • Isomerization – Making a molecule into its isomer – same parts, different arrangement.

7. Order of Operations • Here is what we have to do…in order… • Glycolysis – Cytosol – Glucose splitting. • Pyruvate Oxidation – Matrix – Connect to Kreb’s a la pyruvate  Acetyl-CoA • Kreb’s Cycle – Matrix – Energy given off mainly as NADH and FADH2. • Electron Transport Chain (ETC) – Mitochondrial inner membrane – NADH & FADH2 give their energy to the ETC to create a proton problem. • Chemiosmosis – Mitochondrial inner membrane – We solve the proton problem and get a big bunch of ATP while we’re at it.

8. Glycolysis • Glycolysis means “sugar splitting”. It occurs in the cytoplasm. • Glucose goes through a series reactions that see it eventually turning into two pyruvate molecules. These will go on to the next stage. • We get a net gain of 2 ATP and 2 NADH. The ATP are ready to use and the NADH goes in our back pocket for later. • Overall… Glucose  2 Pyruvate (2 ATP & 2 NADH)

10. 2. Pyruvate Oxidation • The pyruvate goes into the mitochondrion and makes it way to the matrix. • Once in the matrix, the pyruvate is oxidized and turned into Acetyl-CoA (which will start the next stage). • Along the way, a NAD becomes an NADH which we will put in our back pocket for later. • Glucose gave us 2 pyruvate so we will end up with 2 Acetyl-CoA and 2 NADH’s. • Overall… 2 Pyruvate  2 Acetyl-CoA (2 NADH)

11. Pyruvate Oxidation

12. 3. Kreb’s Cycle • The two Acetyl-CoA molecules made by the previous stage now enters a cyclical series of reactions called the Kreb’s cycle. • For each glucose, the Kreb’s cycle turns twice and we will get… • 2 ATP • 6 NADH • 2 FADH2 • The ATP are used immediately and the NADH and FADH2 molecules will go in our back pocket for later.

13. The Kreb’s Cycle

14. 4. The Electron Transport Chain • The ETC is basically a conga line of REDOX reactions – pass the electrons to the right everybody! It all takes place on the mitochondrial inner membrane. • Electrons from NADH and FADH2 are passed into the chain and are handed down the line – hitting proton pumps along the way. • The proton pumps take protons (H+) from the matrix and pump them across the membrane into the intermembrane space of the mitochondrion. • This is a problem as an electrostatic & pH gradient is set up which is no good for the mitochondrion. • NADH operates 3 proton pumps while FADH2 operates just 2 proton pumps.

15. 5. Chemiosmosis • Most texts put this step and the ETC together as one for good reason. • The proton problem created by the ETC is relieved by an enzyme, found embedded in the mitochondrial inner membrane, called ATP Synthase. • ATP Synthase allows the protons (H+) to come back into the mitochondrion – we’re saved! • But wait!…It gets better…ATP synthase fixes the problem and in doing so, it makes ATP! • Its like a carpenter saying, “Yeah, I can fix your roof but you have to let me pay you for it!”.

16. The ETC & ATP Synthase

17. The ATP Balance Sheet • Here’s how we get the 36 ATP from one molecule of glucose. • 1 ATP = 1 ATP (ATP is ATP already!) • 1 NADH = 3 ATP (goes through 3 H+ pumps) • 1 FADH2 = 2 ATP (goes through 2 H+ pumps) • This gives us 38 ATP! What the…?!?!? • The trick is the 2 NADH’s made in glycolysis – in the cytosol. They have to get into the mitochondrion first and when they enter it, they are converted into FADH2’s. • So what is the bottom line?

18. The Bottom Line!

19. FIN (You worked hard – nice job!)