Oxidation–Reduction Reactions Electrons in the outer energy orbit have more energy than any other electrons in the atom. These valence electrons are called high energy electrons.(Those electrons closer to the nucleus have lower energy) During chemical reactions, when the electrons in the outer orbit are striped away, some energy is released. The atom that has lost an electron has been OXIDIZED(lost a negative charge) The atom that gains the electron is REDUCED(Gained a negative charge)
These reactions are called oxidation reduction reactions. The electrons that are lost or gained are high energy electrons. Example: if one atom is oxidized or loses an electron, that atom becomes partially charged(an ion) Atom X(oxidized)----------- Ion X+ +e_ The electron is picked up by another positive ion and becomes an atom Ion Y + + e_ -------------Atom Y
Oxidation –reduction reactions occur in the cell during cellular respiration. High energy electrons move from one compound to another. In the cell, these electrons can’t move on their own- they need a carrier. A proton(+) can join with one electron and become a hydrogen atom. So we write the movement of these high energy electrons as H atoms. A high energy electron is contained in an H atom
Other Energy Storing Compounds NADH- nicotine adenine dinucleotide FADH- flavin adenine dinucleotide Both of these high energy storing compounds pick up energy electrons that have been lost from atoms that have been oxidized.
NADH and FADH are called H acceptors because during a chemical reaction, like cellular respiration they pick up H atoms that contain high energy electrons Molecules of this compound when written with an H, contain a high energy electron and are considered high energy storing compounds similar to ATP. Cell can use these compounds as a source of energy. When written as ADP+ or NAD+- they have lost their H or high energy electron.
Cellular Respiration Occurs in the mitochondria Break down glucose to make ATP-enough energy is produced to change ADP back to ATP. 3 stages 1.Glycolysis 2.Citric Acid Cycle (Krebs) 3.Electron Transport Chain
Glycolysis-glucose breaking • Does not require oxygen(anaerobic) • Takes place in cytoplasm of cell • Glucose 2 PGAL 2 Pyruvic Acid (6C) phosphoglyceraldehyde 2 (3C’s) PGAL is oxidized and NAD+ is reduced to NADH Need 2 ATP to start reaction Make 4 ATP during glycolysis Net ATP Production- 2 ATP
Citric Acid Cycle(Krebs) No oxygen needed but will only continue if oxygen is present. Produces 2ATP and 2CO2 Takes place in mitochondria-in matrix Total ATP so far- 4 ATP ( -2+4+2)
Pyruvic acid cannot enter the cycle Must be broken down into acetic acid with the help of an enzyme: Coenzyme A (CoA) CoA is actually the vitamin niacin Acetic acid enters CAC as acetyl CoA Acetyl Co A changed to citric acid Citric Acid becomes oxidized and produces : NADH,FADH,CO2, and 2ATPs FADH and NADH are the H acceptors. They are important in the next step.
Electron transport chain Occurs in the cristae (folds) of the inner mitochondrial membrane There are many enzymes located in that membrane. Requires oxygen Oxygen is “final electron acceptor” Produces 32 ATP +H2O Final ATP Count make 38-2needed to start Glycolysis 36 ATP TOTAL
The high energy compounds FADH2 and NADH pass their electrons from enzyme to enzyme along the chain. Energy is lost as the electrons travel down the chain. This energy is used to bond phosphate groups to ADP.
ETC Steps 1. As FADH2 and NADH arrive at the beginning of the transport chain, these molecules drop off their high energy electrons (remember they’re H atoms. 2. The H atom splits apart into a proton and an electron. 3. The electron begins its journey down the enzyme chain.
4. The H+ ion (proton) passes through the membrane to the other side. Once it passes through the membrane it cannot come back through. This causes protons to build up a concentration of positive charges on the backside of the membrane. The front side of the membrane where the electrons are traveling, has a negative charge. This difference in charge on the membrane is called a charge differential and is a source of potential energy. The H+ flows back through at ATP Synthase due to diffusion. This fuels the production of ATP. 5. As electrons go from enzyme to enzyme, energy is lost. This energy along with the potential energy from the charge differential is used to bond 32 phosphate groups to 32 ADP molecules to regenerate 32 ATP molecules at ATP synthase Enzyme
6. At the end of the transport chain the electrons are reunited with the H+ ions to reform a hydrogen atom. Two H atoms then meet up with oxygen - the final electron acceptor – and form water. Oxygen is absolutely necessary for this to work. We breathe oxygen for this reason. From l molecule of glucose the following molecules of ATP are produced: glycolysis = 2 ATP(-2+4) CAC/Kreb’s = 2 ATP ETC = 32 ATP Grand Total = 36 molecules of ATP
What happens if no oxygen FERMENTATION-anaerobic respiration The first part of fermentation, glycolysis, is just like cellular respiration,because it’s anaerobic. But the second part of fermentation is different since no oxygen is available. Pyruvic acid does not go into the Kreb’s Cycle or the ETC and no ATP is not produced. Instead, pyruvic acid produces other products depending on the type of cell in which the fermentation occurs.
ANIMAL CELLS Lactic acid fermentation occurs when oxygen is not available. This happens during vigorous exercise when the lungs cannot bring enough oxygen to body cells. Glycolysis takes place in muscle cells but pyruvic acid is oxidized to form lactic acid rather than going on to the CAC and the ETC to form ATP. The build up of lactic acid causes muscle cramping. When oxygen does become available, for example when the exercising stops, the cells switch back to aerobic respiration. The lactic acid that was produced is transported to the liver where it’s converted back to glucose.
Other Cells In unicellular cells such as yeasts, the same process occurs but instead of lactic acid being produced from the oxidation of pyruvic acid, alcohol and carbon dioxide are formed. This production of ethyl alcohol is used in beer brewing and the making of wine. When more carbon dioxide is produced the yeasts are used in the baking industry.