glycolysis review

glycolysis review - METABOLISM We covered the following in...

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METABOLISM We covered the following in our review session during the week of September 13 th , 2010. 1. Brief explanation on the types of energy a. Negative-Positive-Balanced 2. Catabolism vs. Anabolism 3. Become comfortable with the 5 Principles of Metabolism a. Irreversible steps b. Different paths taken for anabolic and catabolic reactions c. Committed steps d. Regulation e. Localization 4. Free Energy and its Impact on Directionality 5. Glycolysis a. Transport b. Reaction Steps and Regulation c. Energetics 6. Dietary Carbohydrates 7. Pentose Phosphate Pathway (PPP)
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WHAT IS THE DIFFERENCE BETWEEN AN IRREVERSIBLE STEP AND A COMMITTED STEP? - Irreversible steps confer directionality to a reaction - They are exergonic (release heat/work), i.e. when the deltaG<0 the reaction is pushed forward - An alternative pathway (read enzyme) is required for the reverse reaction to occur. There are 3 irreversible reaction in Glycolysis: Glucose ------> G6P by HK (or GK in the liver) F6P ---- FBP by PFK-1 PEP ---- Pyruvate by PK However, there can be only 1 committed step, where the products of this step can only be used for one thing. In glycolysis, the committed step is: F6P ---- FBP by PFK-1 FBP only gives rise to glycolytic intermediates - G6P can be shunted towards glycogen synthesis or it can enter the PPP - Pyruvate enters the CAC and it can be converted back into other carbohydrates via gluconeogenesis (a process we’ll be learning about shortly).
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- Depending on the tissue, we have developed 2 types of ways to transport glucose into our cells: Passive and Active Transport. 1. PASSIVE DIFFUSION a. Occurs in most tissues b. Allows for the movement of glucose in an energy independent manner c. We must differentiate between [BLOOD GLUCOSE] and [GLUCOSE INSIDE THE CELL] d. Glucose will diffuse DOWN its concentration gradient because [BG] > [GLUCOSEcell]
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2. ACTIVE TRANSPORT a. Occurs in the intestine, (think digestion) b. Requires transport proteins i. Symporter: transports 2 substrates in the SAME direction (SGLUT1 in the intestine) ii. Anti-porter: transports 2 substrates in the OPPOSITE direction, with the use of ATP. (Na/K ATPase in the intestine) WHAT DOES THE TRANSPORT OF GLUCOSE LOOK LIKE IN THE INTESTINE?
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- This prevents free glucose from diffusing out (remember that Passive Diffusion occurs in most cells) - Promotes influx of glucose from the blood
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Low BG: GKRP binds GK and inhibits it High BG: GKRP is released from GK, and GK is active
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Depending on the tissue and the signal, PFK-1 will be affected differently
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Note: Drawing schematics like this will help you visualize what is going on.
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SUBSTRATE CYCLING - IN THE MUSCLE - Results in a 100x boost in glycolysis - The math was shown as one perspective, but it’s important to understand the concept. The numbers used were based on experimental values So here goes. ..
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glycolysis review - METABOLISM We covered the following in...

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