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 (O 2 ). The molecule of choice for fuel is glucose. C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O 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!
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. (O 2 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.
Cellular Respiration: The Details AKA: The Hard Part!
Cellular Respiration: The Details Aerobic cellular respiration is as follows C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O 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?
The Reactions Well See There are several types of reactions that we will encounter along the way. 1. REDOX Electrons being taken from one and added to another. 2. Phosphorylation/Dephosphorylation The adding/removal of a phosphate group (PO 4 ). 3. Carboxylation/Decarboxylation The adding/removal of a carbon. 4. Hydration/Dehydration - The adding/removal of a water molecule (H 2 O). 5. Isomerization Making a molecule into its isomer same parts, different arrangement.
Order of Operations Here is what we have to doin order 1.Glycolysis Cytosol Glucose splitting. 2.Pyruvate Oxidation Matrix Connect to Krebs a la pyruvate Acetyl-CoA 3.Krebs Cycle Matrix Energy given off mainly as NADH and FADH 2. 4.Electron Transport Chain (ETC) Mitochondrial inner membrane NADH & FADH2 give their energy to the ETC to create a proton problem. 5.Chemiosmosis Mitochondrial inner membrane We solve the proton problem and get a big bunch of ATP while were at it.
1.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)
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 NADHs. Overall 2 Pyruvate 2 Acetyl-CoA (2 NADH)
3. Krebs Cycle The two Acetyl-CoA molecules made by the previous stage now enters a cyclical series of reactions called the Krebs cycle. For each glucose, the Krebs cycle turns twice and we will get 2 ATP 6 NADH 2 FADH 2 The ATP are used immediately and the NADH and FADH 2 molecules will go in our back pocket for later.
The Krebs Cycle
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 FADH 2 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 FADH 2 operates just 2 proton pumps.
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 were saved! But wait!It gets betterATP 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!.
The ETC & ATP Synthase
The ATP Balance Sheet Heres 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 NADHs made in glycolysis in the cytosol. They have to get into the mitochondrion first and when they enter it, they are converted into FADH 2 s. So what is the bottom line?
The Bottom Line! Stage of Cellular Respiration MoleculeProduced # of ATP Produced Glycolysis 2 ATP 2 NADH 2 FADH 2 4 ATP Pyruvate Oxidation 2 NADH 6 ATP Krebs Cycle 2 ATP 6 NADH 18 ATP 2 FADH 2 4 ATP THE GRAND TOTAL 36 ATP