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Chapter 7 Blog: Cellular Respiration, Fermentation, and Secondary Metabolism (Pankhuri)

Page history last edited by Pankhuri Garg 13 years, 6 months ago

A.  Daily Blog


10/20/2010 (submitted 10/20/2010)


Well today I missed the first 10 minutes of lecture thanks to a deer who decided he wanted to run into my car on Route 78 and destroy the car bonnet. So now the car is not working and I had to wait for my dad to get back with the rental to get me to class. So Dr.Weber, sorry bout that :)! Anyhow, ATP can be produced in two ways, Substrate-level phosphorylation and Chemiosmosis. In substrate-level phosphorylation, enzymes directly transfer phosphates from one molecule to another, giving a net yield of 4 ATP molecules. Chemiosmosis on the other hand uses gradients and steps to produce a net yield of 28-32 ATP molecules. In a normal exergonic reaction, 686 kcal/mol energy is released, which then just becomes heat and unusable and harmful to us. Chemiosmosis releases energy in intervals, and that energy is stored and derived from bonds. Chemiosmosis consists of 3 phases consisting of 20 total steps: Glycolysis, Formation of CoA, and the Citric Acid Cycle. Our focus today was Glycolysis. 


Glycolysis, a 10 step process is also split into 3 phases: Energy Investment (Steps 1-3), Cleavage (Steps 4-5), and Energy Liberation (Steps 6-10). In step 1, a phosphate is added to the 6th carbon of glucose (glucose-6-phosphate) by hexokinase enzyme. In step 2, G6P is changed into its isomer, fructose-6-phosphate (F6P) by isomerase enzyme. In step 3, another phosphate is added to the 1st carbon of fructose (fructose-1,6-bisphosphate) by PFK (phosphofructokinase) enzyme. All this energy investment makes glucose unstable, and it stats to cleave. Fructose-1,6-bisphosphate splits into two molecules of glyceraldehyde-3-phosphate (G3P). In step 6, G3P is oxidized when NAD+ gains two electrons and a H atom (becomes NADH) by dehydrogenase enzyme. G3P is now 1,3-BPG because two phosphates are added to the 1st and 3rd carbon to conserve energy. Chemiosmosis, altogether a exergonic reaction, consists of energy intermediates, which are molecules that act as temporary electron carriers and create temporary short endergonic reactions to conserve energy when atoms need to be transferred. The main intermediates of glycolysis are ATP and NAD+. 



10/22/2010 (submitted 10/25/2010)


Today we continued with the process of Chemiosmosis. The Energy Liberation phase of Glycolysis ends with the production of ATP by the kinase enzyme. The net gain of Glycolysis is 2 ATPs (2 invested, 4 produced; 4-2 = 2) and 2 NADHs. The two molecules produced by Glycolysis are called pyruvates. When oxygen is present, the pyruvates proceed to the mitochondria for the citric acid cycle. When oxygen is not present, the pyruvates either ferment in the cytoplasm or proceed to anaerobic respiration in the mitochondria. Dr.Weber's explanation continued with the presence of oxygen (ha!). The citric acid cycle happens in the mitochondrial matrix. Each pyruvate breaks down into a acetyl group, and for each pyruvate, one NADH is formed. Through out the process, the acetyl groups are further modified and a total of 3 NADHs are produced for each acetyl group. Also, one FADH is released. Removal of carboxyl gorups releases CO2. In the entire reaction, from Glycolysis to the Citric Acid cycle, the net products include 6 CO2, 10 NADHs, 4 ATPs, and 2 FADH.



10/27/2010 (submitted 10/29/2010)


We first went over what Glycolysis and the citric acid cycle were. We then proceeded to talk about the electron transport chain where oxidative-phosphorylation occurs. The electron transport chain is the last and final stage of chemiosmosis. A main part of this stage is oxygen, which is the final electron acceptor. This process produces the bulk of ATP in Glycolysis, about 28-34. This ATP production is started merely by the reduction of NADH to NAD+. NADH donates two electrons and one proton to the proteins involved. The proton moves into the intra-membrane space of the mitochondrial membranes, when the electrons travel through the inner membrane from one protein to another. At the electrons flow through, proton are attracted and moved through the protein creating a highly unstable electromagnetic gradient. The last protein in the sequence, ATP synthase, brings these protons down there concentration gradient, and the energy released by the movement of these protons, makes ATP. The protons are added to O2 molecules and water is produced. It there was no oxygen, NADH would never oxidized and it would never reduce. No ATP would be formed because of lack of electron acceptor.



10/29/2010 (submitted 10/29/2010)


After a moderately successful attempt at scaring Dr.Weber on 'Halloween' we finished discussion about the the effects of low or no oxygen. When oxygen is limited, NADH accumulates and NAD+ decreases. This is not favorable for cells because they require a NAD+ to be a electron carrier and as an oxidizing agent in the citric acid cycle. This leads to the decrease in the citric acid cycle, in pyruvate oxidation, and glycolysis. This cause glucose to build up in cells and no ATP is produced. The NADH undergoes fermentation. It donates its electrons to pyruvate and becomes NAD+. From here, of the two pyruvates, one breaks down into lactic acid in the muscle cells, while the other breaks down into ethanol and CO2. Any respiration without the presence of oxygen is called anaerobic respiration and DOES NOT PRODUCE ATP





We reviewed for Exam 2 on Chapters 6 and 7. I am still a bit iffy on Chapter 7, but I will go home and look into this! :)


B.  Useful Materials


1. Targeting Mitochondrial Metabolism and Machinery as a Means to Enhance Photosynthesis - Photosynthesis and Respiration are interrelated. One's products acts as the substrate for another, while the others products acts as a substrate for the first. The combination of photosynthesis  and respiration can produce a greater amount of energy and enhance photosynthesis. Although each function is precisely defined, when together, they create a greater effect and more positively affect the cell.  


2. Electron Transport Change - This is a great lecture that explains every aspect of the electron transport change, the proteins involved, and how its works. This video really helped me learn a lot because everything is really clear and the professor uses many colors to differentiate processes.



3. Citric Acid Cycle - Here is another awesome lecture about the citric acid cycle. This video was easier to understand simply because it talked mainly about the products that are formed through each step. Its also explains how a molecule gets to this process and the net gains at each step. 



Comments (1)

Derek Weber said

at 2:54 am on Oct 26, 2010

Thanks for the update. I am glad you are OK.

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