The link reaction occurs between glycolysis and the Krebs cycle. The two pyruvates that are created in glycolysis eventually turn into acetyl CoA. This process begins in the cytoplasm and membrane proteins move the pyruvates into the mitochondria and eventually into the mitochondrial matrix. In the matrix enzymes break down pyruvate, taking off H and CO2 (decarboxylated)(Campbell 167). The H+ is then accepted by NAD+ which turns it into NADH+H+ and the CO2 is a waste product (Campbell 167). The remaining product is an acetyl group which is accepted by CoA and forms acetyl CoA.
The acetyl CoA that has been produced directly plays a role in the Krebs cycle. In the Krebs cycle the acetyl CoA is combined with oxaloacetate (4-carbon) which forms citrate (6-carbon) (Campbell 169). The next step is turning it into isocitrate. From there one CO2 molecule is lost and the compound is oxidized, giving its electrons in the form of H+ to NAD+ forming NADH+H+. Another water molecule is then lost and also another H+ to NAD+ forming Succinyl CoA (Campbell 169). Next it goes to Succinate and also produces one ATP from GDP. Then the compound is further oxidized forming FADH2 from FAD+. An addition of a water molecule then rearranges the structure which then allows for it to be oxidized yet again forming NADH+H+(Campbell 169). The resulting substance is oxaloacetate which allows the cycle to begin again and doing the same processes.
In the Electron transport chain (ETC) most of the ATPs are produced by H+ ions. The ETC occurs on the bilayer between the mitochondrial matrix and the intermembrane space. The way is which it works is specific membrane proteins use the electrons from the NADH+H+ and the FADH2 to transport H+ against its gradient and into the intermembrane space. Once an NADH+H+ gives up electrons the electrons cause the pump to move an H+ and then they move to the next protein which uses the energy again from the electrons to pump more H+ and once more the electrons are used in a third protein to pump yet another H+ (Campbell 172). From there the electrons travel to the ATP synthase where the last of their energy is used to combine one hydrogen with O2 (oxygen) which then produces water (Campbell 172). The way that this works is the concentration of H+ flow down through the ATP synthase protein structure which uses the energy of the H+ to combine a phosphate group to ADP forming ATP (Campbell 171). This process occurs with every NADH+H+ and FADH2. This series of redox reactions is what allows for this process to occur.
C.3.5 Explain oxidative phosphorylation in terms of chemiosmosis.
As the H+ molecules are transported against their gradient through the protein pump in the ETC as described above they begin to create a high concentration on one side of the membrane. Eventually, once a high enough concentration has been built, the H+ flow down the concentration gradient through a protein complex called ATP synthase. This complex uses the gradient and the energy from the H+ ions to attach a phosphate to ADP, thus forming ATP (Hrycyna 1). This process of using the concentration gradient to drive cellular processes is call chemiosmosis (Campbell 171).
C.3.6 Explain the relationship between the structure of the mitochondrion and its function.
The mitochondria is specifically shaped so its parts can work together to carry out a function. The Cristae, or multiply foldings of the inner membrane allow for more surface area which therefore allows more of the electron transport chain which means more ATP producing enzymes. The small space between the inner and outer membranes is specifically for the accumulation, or buildup of H+ ions which allows a concentration gradient to be formed. The specific mitochondrial matrix contains all of the enzymes necessary to carry out the Krebs cycle which produces the H+ for the ETC.
Works Cited
Asato, Robert. "Introduction: Oxydation/ Reduction." Internet Chemistry. Kapiolani Community College. 6 Nov. 2008 <http://library.kcc.hawaii.edu/external/chemistry/introduction.html>.
Campbell, Neil A., Jane B. Reece, and Lisa A. Urry. Biology. 7th ed. Boston: Benjamin-Cummings Company, 2004. 166-73.
Hrycyna, Christine. "Oxidative Phosphorilation." CHM333. Purdue University. 6 Nov. 2008 <http://www.chem.purdue.edu/courses/chm333/oxidative_phosphorylation.swf>.
Nave, Rod. "Oxidation and Reduction." Geohia State University. 6 Nov. 2008 <http://hyperphysics.phy-astr.gsu.edu/hbase/chemical/oxred.html>.
