Cellular Respiration Essential knowledge 2.A.1 (c) and 2.A.2

 The function of cellular respiration is the take the glucose made during photosynthesis and use the energy found in that molecule to make ATP, which provides energy for cells to do work. (ATP is the main “currency” we need for energy)  Glucose is a more stable form of energy storage than ATP, so we need to take that glucose and break it up when we’re ready to use it  It’s an exergonic reaction, using catabolic pathways  The equation for respiration is the opposite of photosynthesis.  WRITE THE EQUATION!

Because respiration takes place (mostly) in the mitochondria, you will need to be familiar with its parts The mitochondria is made of compartments that carry out specialized functions The compartments include: the outer membrane, the intermembrane space, the inner membrane, and the cristae (which are little internal compartments formed by the inner memrane) and matrix (a viscous space with the DNA and ribosomes)

1. Glycolysis (breaks down glucose into 2 molecules of pyruvate) 2. Kreb Cycle (completes the breakdown of pyruvate) 3. Electron Transport Chain (this is where most of the ATP is generated) These steps are happening all at the same time *you do not need to memorize the steps in glycolysis and the Krebs cycle, or the structures of the molecules and names of the enzymes involved ; you also don’t need the names of specific electron carries in the ETC (just understand what is happening in each step)

Takes place right outside of the mitochondria (in the cytoplasm) You take glucose (a 6 carbon molecule) and break it down into 2 molecules of pyruvate (a 3 carbon molecule) It generates 2 ATP and a chemical called NADH (we transferred high energy electrons to it) *you now have 2 ATP’s and 2 molecules of NADH

The pyruvate diffuses into the matrix of the mitochondria and it enters the pyruvate dehydrogenase complex This takes the 3 carbon molecule of pyruvate and transforms it into acetyl CoA (coenzyme A) which is a 2 carbon molecule (you have gone from a 3-carbon molecule to a 2-carbon molecule) – this is the bridge between glycolysis and the citric acid/Krebs cycle This gives off Carbon in the form of CO2 – so every time you exhale, 1/3 of that CO2 has come from the pyruvate dehyrogenase complex It now enters the Kreb Cycle (also called the Citric Acid Cycle)

Takes place in the mitochondrial matrix The Kreb Cycle breaks down the 2- Carbon acetyl CoA and releases more CO2, 2 ATP, and adds more energy to NADH and FADH (which have high energy electrons) At this point, all of the energy that we started with in glucose has been essentially transferred to NADH and FADH You have now released 2 more ATP (4 total) and created a lot of NADH AND FADH (6 NADH, and 2 FADH2) The high energy electrons found in NADH and it’s friend FADH are then carried to the electron transport chain (ETC)

Takes place in the cristae The electrons from NADH and FADH are moved through the ETC (which is basically a series of protein pumps) This is done with electrons transporting hydrogen molecules through the membrane and into the inner membrane space. By doing this there is a gradient created with a high concentration of hydrogen on the outside and a low concentration inside. Naturally, the hydrogen molecules will want to diffuse to create equilibrium. But the only way that they can get back in is through a protein pump called the ATP synthase.

As every proton moves through it, ATP is generated (every time a proton goes through, it attaches a phosphate onto ADP to make ATP) – about ATP are generated in this process The electrons are then added to the protons and the oxygen that we breathe in to form our waste/bi- product – H2O (oxygen is the terminal receptor for the electrons, so it is reduced)

What happens if there is no O2 or mitochondria present? Fermentation occurs Glycolysis can produce ATP with or without O 2 (in aerobic or anaerobic conditions) – but the Krebs cycle and ETC are aerobic (need oxygen) In the absence of O 2, glycolysis couples with fermentation to produce ATP (2 types of fermentation: alcohol and lactic acid) You can take glucose during glycolysis and break it into 2 pyruvates, but when you add the electrons to NAD and transfer them to NADH, the NAD runs out and glycolysis shuts down

Pyruvate Glucose CYTOSOL No O 2 present Fermentation Ethanol or lactate Acetyl CoA MITOCHONDRION O 2 present Cellular respiration Citric acid cycle

Lactic acid fermentation – takes place in your muscles (like when you’ve been sprinting really fast or holding your breath for a long time) In lactic acid fermentation, pyruvate is reduced to NADH, forming lactate as an end product, with no release of CO 2 Your cells can take the pyruvate and break it down into lactate (or lactic acid) which will accept the electrons from NADH to form more NAD+ (so you’re just recycling) and the process can occur over and over again to create 2 ATP each time If you’ve ever sprinting, you do both aerobic and anarobic respiration; this builds up lactate (lactic acid) in your muscles. Lactate is like a toxin that needs oxygen to break it down (that’s why you’re really out of breath when you run – you’re trying to take in a lot of O2)

Alcohol fermentation In alcohol fermentation, pyruvate is converted to ethanol in two steps, with the first releasing CO 2 Alcohol fermentation by yeast is used in brewing, winemaking, and baking Again, pyruvate is broken down only this time instead of lactate, it becomes ethyl alcohol The same thing occurs, with electrons being donated to form NAD+, except with 1 difference Lactate was a 3 carbon molecule, but this time you make CO2 (that’s why yeast forms bubbles)

Oxidation – when electrons are lost Reduction – when electrons are gained (called reduction because you lose a positive charge) They occur together, which is why they are called RedOx reactions (in respiration, glucose is oxidized and the electrons and hydrogen atoms are added to oxygen, which is reduced) Think of Oil Rig: Oil – oxidation is a loss Rig – reduction is a gain

Draw and label a diagram of the process of cellular respiration (no specific names of enzymes or proteins are needed, but you will need to label all reactants and products for each step)