Q) Using named examples, explain the advantages of metabolic pathways in cells
Main points | |
Key idea: | What is a metabolic pathway |
· Ref to series of rx where product of one rx becomes substrate for next rx | |
Key idea: | Adv 1 : Allows a crucial molecule to be made from different sources |
· Named example: Acetyl-CoA (of aerobic resp) · Acetyl-CoA as product of link rx which becomes substrate for Krebs cycle · Ref to its synthesis fr breakdown of glucose, fatty acids or aa throu other pathways; hence diff entry points to Krebs cycle | |
Key idea: | Adv 2 : End product inhibition + channel intermediate products to other pathways to make another product |
· Named example: Glycolysis · Glucose mol oxidized throu a series of rxs (each rx catalyzed by an enz), form pyruvate, ATP & NADH · When ATP is sufficient, it acts as an allosteric inhibitor · Ref to it binding to an allosteric site on enz (phosphofructokinase) at initial part of glycolytic pathway, inhibits the enz · Result: Not only prevents formation of excess ATP but allows glucose-6-phosphate to be diverted to another pathway that makes glycogen | |
Key idea: | Adv 3 : Cell responds appropriately to its environmental conditions |
· Named example: (fate of) Pyruvate when O2 absent · Will not enter mitochondrion (to combine w co-enzyme A to form acetyl-CoA) · Pyruvate reduced to lactate (in animals) or ethanol (in plants) in cytosol instead · Result: anaerobic respiration still proceed to yield 2 ATP/glucose | |
Key idea: | Adv 4 : A cyclical metabolic pathway allows its 1st substrate to be regenerated |
· Named example: Krebs cycle & Calvin cycle · Result: (i) Krebs cycle (aerobic resp) - regenerate oxaloacetate, hence NADH produced continuously for ATP syn during oxidative phosphorylation (ii) Calvin cycle (light independent rx, photosyn) - regenerate RuBP for continuation of CO2 fixation · Ref to some phosphates made during reduction of glycerate-3-phosphates channeled to another pathway that synthesizes starch | |
Key idea: | Adv 5 : Crucial in cell signalling |
· Named example: Insulin & glucagon signalling · Ref to binding of a signal mol (e.g. hormone) to its specific receptor, result: activation of signal transduction pathways + eventual cellular responses · Details: (i) Insulin binds to receptor tyrosine kinase, activation of several relay mol, in turn activate diff pathways · Ref to diff cellular responses due to binding of hormone to one target cell · Details: (ii) Glucagon binds to G-protein linked receptor, activation of many G proteins, in turn activate adenylyl cyclases · Ref to enz yield enormous amt of second messager cAMP · Each cAMP activates a protein kinase, in turn activates many other protein kinases · Result: phosphorylation cascade + ‘weak’ signal carried by a hormone greatly amplified (i.e. strong cellular response) | |
Comments: (i) Visualize the answer with the aid of a labelled diagram. (ii) Verbalize the answer + write down the main points w/o referring to the answer (use abbreviations) (iii) Read again within the next 24h & once more within 72h (do not spend more than 10min) (iv) A rather challenging question as it requires a deeper understanding of the various concepts from different topics (e.g. respiration, photosynthesis and cell signaling). (v) The answer provided is more than sufficient to gain full credit for this question | |
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