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2010-10-14 02:00:43
metabolism catabolism anabolism enzyme

Introduction to Metabolism
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  1. differences between anabolism and catabolism
    anabolism is energy-requiring while catabolism releases energy; anabolism is diverging while catabolism is converging; anabolism results in complex molecules while catabolism results in simple molecules
  2. types of chemical reactions in metabolism
    oxidation-reduction (involves electron transfer); ligation requiring ATP cleavage (results in formation of C-C bonds); isomerization (results in rearrangement of atoms); group transfer (results in transfer from one functional group to another); hydrolytic (involves cleavage by water); addition or removal of functional groups (involves breaking or creation of double bonds)
  3. common themes underlying metabolic pathways
    irreversible under physiological conditions; have a committed step - must continue down pathway (usually = rate-limiting step); regulated (especially at rate-limiting step & branch points); compartmentalized
  4. mechanisms for regulating enzymes
    isoforms; substrate concentrations; product inhibition; allosteric regulation; covalent modification; changes in enzyme protein concentration (induction & repression & sequestration & degradation)
  5. energy charge
    varies between 0 (only AMP) and 1 (only ATP); equal to ([ATP]+ 0.5[ADP])/([ATP]+[ADP]+[AMP]); high energy charge -> increase in anabolic reactions and decrease in catabolic reactions
  6. importance of enzymes in medicine
    determination of level of metabolites in blood (esp. glucose & cholesterol & triglycerides); release of enzymes into bloodstream following tissue necrosis in disease state; ELISA (link immunology with enzymology - Ab coupled to enzyme -> colorimetric assay); enzymes can be targeted by poisons
  7. enzyme vs. coenzyme vs. apoenzyme
    enzymes are usually protein and catalyze reactions without being used up; coenzymes are small molecules or metals that combine with apoenzymes (proteins) to form a functional enzyme; coenzymes and apoenzymes cannot function as enzymes on their own
  8. Michaelis-Menton equation
    hyperbolic curve representing rate of rxn vs. substrate concentration; Vo = Vmax[S]/(Km + S); [S] = substrate concentration; Vmax represents rate of catalysis and enzyme concentration (large Vmax -> high reaction speed); Km reflects enzyme affinity for substrate (large Km -> low affinity)
  9. description of kinetic constants
    Vmax = reaction rate (depends on amount of enzyme [Et]); Kcat = turnover number = number of units of substrate molecule each enzyme molecule converts to product per unit time = Vmax/[Et]; unit of enzyme activity = micromoles of product formed/minute; specific activity = units/mg protein = enzyme activity per mg of total protein = measure of enzyme processivity at a certain level of substrate
  10. classification of enzyme-catalyzed reactions
    oxidoreductases; transferases; hydrolases; lyases; isomerases; mutases; ligases
  11. oxidoreductases
    catalyze oxidation-reduction reactions - include dehydrogenases (remove hydrogen); oxidases (oxidation-reduction involving oxygen as the electron acceptor); reductases (catalyze reductions); peroxidases (reduce hydrogen peroxide & other peroxides); catalase (catalyze decomposition of hydrogen peroxide to hydrogen and water); oxygenases (catalyzes the incorporation of an oxygen into a substrate); hydroxylases (catalyzes the addition of -OH groups)
  12. transferases
    transfer functional groups between donors and acceptors; examples: kinases (transfer phospho groups); phosphomutases (transfer phosphate esters from one OH group on a substrate molecule to another OH group on the same molecule)
  13. hydrolases
    catalyze cleavage of bonds through the addition of water; include proteases (hydrolyze amide bonds in proteins); lipases (hydrolyze ester bonds in lipids); phosphatases (hydrolyze phosphoester bonds)
  14. lyases
    add or remove elements such as water/ammonia/carbon dioxide to/from a substrate molecule; include decarboxylases and dehydratases such as fumerate and malate
  15. isomerases
    "heterogeneous; catalyze inversions at asymmetric carbons (ie
  16. mutases
    heterogeneous; catalyze intramolecular transfer of groups such as phosphates from one site to another site within the molecule
  17. ligases
    catalyze the joining of two molecules using energy derived from ATP; also called synthetases
  18. enzymes that indicate presence of myocardial infarction
    creatine phosphokinase (peaks around 24h after MI); lactate dehydrogenase (peaks around 36040h after MI); aspartate aminotransferase; gamma glutamyl transferase
  19. enzymes targeted by toxins/poisons
    acetylcholinesterase inhibited by organophosphates (pesticides/nerve gases); cyclooxygenase 1 & 2 modified by aspirin

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