BIOL 225 Lecture 17.pdf - Lecture 17 Glycolysis and...

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Unformatted text preview: 2/27/17 Lecture 17 Glycolysis and Fermentation BIOL 225 Prof. Liz Allison February 27, 2017 MasteringBiology Homework • Chapters 7 & 15 • Due Thursday, March 2 at 11:59 pm • 2.5 points each Cellular respiration occurs in three stages Glycolysis – the lysis (splitting) of glucose Lecture 18 • The first step in glucose Today’s lecture Citr ic Acid Cycle oxidation • A series of 10 chemical reactions • Each reaction is catalyzed by a specific enzyme The complete oxidation of one molecule of glucose gives a net yield of about 29 ATP ATP is produced in each of these cycles. However, these sets of chemical reactions occur in seperate compartments. The enzyme name reflects what reaction is catalyzed by the enzyme Each of these 10 reactions is catalyzed by an enzyme. The enzymes are nicely named, they correspond to the name of the chemical reaction. The two pyruvates are the products of this glycolysis. 1 2/27/17 All 1 0 re a c tions of gly c oly s is occ ur in the c y tos ol All 10 reactions of glycolysis occur in the cytosol Di hydr oxyacet one Wha t goe s in: Glucose Enz y m e Gluc os e 6 -phos pha te Fruc tos e 6 -phos pha te Gly c oly s is begins with an e ne rgy -inv es tm ent phas e: 2 ATP→ 2 ADP Wha t c om e s out: phosphat e Fruc tos e 1 ,6 -bis phos pha te NO! G l ycer al dehyde- 3- phosphat e The “ 2 ” indic ate s tha t fructos e -1,6 bis phos pha te ha s be en s pli t into two 3 -c a rbon s uga rs (only one is shown) Why so many steps? • Slow Should you memorize all of this slide …? release of energy • Some steps reorganize the molecule into a favorable configuration for the next reaction These reactions are taking placing within the cytosol. The number of steps allow a slow release of energy, meaning the energy is not lost as heat or light. This means as much energy as possible is stored. 1 ,3 -Bis phos phogly ce ra te 3 -Phos phogly c e ra te 2 -Phos phogly c e ra te Phos phoe nolpy ruv a te Pyr uvate During the e ne rgy -pa yoffphas e, 4 ATP a re produce d fora ne tgain of 2 ATP There's no reason to memorize each of these enzymes. BUT JOKE'S ON HER I HAVE ALREADY. Step 1 What you should know… Enzyme that catalyzes phosphorylation Steps 1 and 3: • Energy input is required 2ATP → 2ADP + phosphate + energy Activated high energy sugar • Transfer of a phosphate group from ATP to the sugar (one at each step) Step 2: Reorganization fructose-6-phosphate Step 3: Addition of another phosphate fructose-1,6-bisphosphate Energy input is required: ATP must go in. Out comes ADP, phosphate, and heat, some of which is not captured. The phosphate has been attached to carbon 6 here. This is glucose 6-phosphate. The addition of the phosphate makes this an activated high energy sugar. 2 2/27/17 • What happens to phosphofructokinase when ATP binds here? • What type of regulation is this an example of? An important step: Regulation of glycolysis by feedback inhibition ATP at regulatory site Fructose-6phosphate at active site ATP at active site To make this fructose, the 1st carbon is ejected from the ring. Step 4: Steps 7 and 10 The 6-carbon sugar splits into two 3-carbon molecules Energy harvest: Substrate-level phosphorylation Step 6: 2ADP→ 2ATP at each step Oxidation of glyceraldehyde phosphate Example: Steps 9-10 Reduction of NAD+ 2 +H + End product of glycolysis NAD+ is a cofactor (see Chapter 8) Energy storage The reduction of NAD + makes NADH which is an electron carrier. ATP receives the phosphate group from the sugar 3 2/27/17 What happens next? 1) Aerobic pathway: Respiration – Lecture 18 Net energy yield from glycolysis 2) Anaerobic pathway • Alcohol fermentation: ethanol + CO2 • Lactate (lactic acid) fermentation Glucose → → → 2 pyruvate + 2ATP + 2NADH 4 molecules of ATP are produced but 2 are used during steps 1 & 3 Don't forget the NADH because it can go on to carry electrons for future reactions. The gross creation of ATP is 4, but the net production is 2, because 2 are used in glycolysis. If fina l e le c tron a c c e ptor in ETC is pre s e nt PYRUVATE PROCESSING CITRIC ACID CYCLE ELECTRON TRANSPORT AND OXIDATIVE PHOSPHORYLATION GLYCOLYSIS If fina l e le c tron a c c e ptor in ETC is NOT pre s e nt FERMENTATION If a final electron acceptor (in most cases, oxygen) in ETC is present, respiration can occur. But if not, Fermentation can occur. Only 2 ATP molecules per glucose molecule are formed but …. and in some microorganisms … and bacteria and some plants Is pyruvate oxidized or reduced to form lactate? What can NAD+ be used for? Pyruvate is accepting the hydrogen, thus accepting electrons, gaining electrons. Fermentation allows glycolysis to continue. A by-product of fermentation is carbon dioxide which allows bread to rise. The goal is to regenerate NAD+ to allow glycolysis to continue. 4 2/27/17 Recommended readings from the textbook Chapter 9: p. 189-196, 206-208 5 ...
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