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Lecture 7

Lecture 7- Notes.docx

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Biology 1002B
Tom Haffie

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Biology 1002B Lecture 7 Energy Transformation 2 - Photosynthesis is endergonic and anabolic. - Cellular respiration is exergonic and catabolic. - Cellular respiration is converting free energy in CH bonds into ATP. - Potential energy in food has lots of CH bonds, is conserve energy by changing to a form that cells can use (ATP). Cellular Respiration (what we should know for exam): - Where is it found in cell? - What glycolysis does it do? - How does free energy change in relative amounts? - Does it require oxygen? - Where is the carbon? Starting with glucose we have 6 carbons. - Compare with photosynthesis (photosynthetic electron transport). Glycolysis: - Splitting of glucose, beginning of cellular respiration. - Almost every living organism has - Cytosolic pathway, don’t need specialized membrane, just need enzymes floating around in cytosol. - Nothing particularly eukaryotic about cellular respiration. - Only the location is different in eukaryotes as opposed to in bacteria for example. - Two molecules of pyruvate is the product of glycolysis, extract energy from glucose to reduce NAD to NADH (oxidation). - What has more free energy, a molecule of glucose or two molecules of pyruvate? A molecule of glucose. - Initial consumption of ATP (energy investment stage) and then get two ATP out and two NADH from one glucose molecule. - Energy coupling: first reaction, glucose and hexokinase come together with phosphate, gives positive delta G, endergonic. Couple this endergonic reaction with exergonic reaction. Exergonic reaction powers overall reaction. - Hydrolysis of ATP is the exergonic reaction in energy coupling. Water removes phosphate. - Energy coupling happens all over metabolic pathways. - Kinetically it’s not a very fast reaction although it’s very spontaneous. - Hexokinase can bind glucose or ATP; water cannot get into active site. Not really hydrolysis of ATP, more break down of ATP. - Energy in terminal phosphate is conserved and transferred immediately to glucose. - Want phosphorylate glucose because: makes the glucose more reactive, more readily wanting to break down, more free energy. Also, it stops it from leaving the cell (phosphate is negative, glucose is positive). - Substrate-level phosphorylation: second reaction in glycolysis. Enzyme used is pyruvate kinase, catalyzes removal of phosphate from PEP, generates ATP. Phosphoryl transfer potential, when they can generate ATP through substrate level phospholrylation. Mitochondria: Where rest of cellular respiration occurs - Chloroplasts have 3 membranes, mitochondria only have 2. - Pyruvate in cytosol, if charged you have to transport it, won’t just leak through membrane. - Mitochondrial matrix is where it wants to go. - Lots of CH bonds in pyruvate. - Decarboxylation occurs and it takes carbon dioxide from pyruvate. No free energy in this part of molecule so get rid of it. - Dehydrogenase: group of enzymes which catalyze the oxidation and reduction of NAD NADP, etc. - Gives 2 NADH, want to make acetyl group more reactive, coenzyme A helps with this. Acetyl CoA is the result of this reaction. - Pyruvate dehydrogenase complex is where these enzymes for this part of cellular respiration are located. - Citric Acid cycle pulls remaining electrons from CH bonds to get ATP, this occurs still in the matrix. - 1 glucose gives two acetyl CoA, watch how many carbons in cycle. - Oxaloacetate is substrate of citris acid cycles, 4 carbon compound. - 2 carbon from actetyl CoA giving 6 carbon molecule citrate in first step of cycle. - All carbon gets lost in this cycle. Remaining two carbon lost here. - Free energy trapped in citrate. Then oxidizing citrate to reduce NAD, we get NADH, ADP and FADH2. - Oxidative phosphorylation (in matrix): goal is to get energy in electron carriers and convert to ATP. Electron carriers are the FADH, NADH and ADP generated in citric acid cycle. - Complex 1 drives oxidation of NADH, mobile carri
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