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2015-06-28 22:00:55
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  1. Four glucose transporters
    GLUT 1 through 4

    GLUT 2: low-affinity in hepatocytes and pancreatic  cells (high Km) ; fx only when glucose concentrations are high

    GLUT 4: adipose and mscle; rate of glucose transport increased by insulin; Km is lower; responds when glucose just a tad above normal
  2. Muscle stores excess glucose as __, and adipose tissue requires glucose to form __, which is converted to glycerol phosphate to store incoming fatty acids as __


  3. In the liver, glycolysis is part of the process by which __
    excess glucose is converted to fatty acids for storage
  4. hexokinase and glucokinase
    phosphorylate glucose to trap it in the cell
  5. hexokinase
    low Km

    inhibited by glucose-6-phosphate
  6. glucokiase
    high Km

    located in hepatocytes and pancreatic beta-islet cells

    induced by insulin
  7. Phosphofructokinase-1
    • rate-limiting enzyme
    • fructose-6-phosphate is phosphorylated to fructose 1,6-bisphosphate

    • inhibited by: ATP and citrate; glucagon
    • activated by: cAMP; insulin
  8. Insulin activates __, which converts a tiny amount of __ to __, which activates __.
    • PFK-2
    • fructose-6-phosphate
    • fructose-2,6-bisphosphate
    • PFK-1
  9. Glucagon inhibits __, lowering __ and thereby inhibiting __.
    • PFK-2
    • F2,6-BP
    • PFK-1
  10. By activating __, it allows these cells to override the inhibition caused by ATP so that glycolysis can continue, even when the cell is energetically satisfied.
  11. Gylceraldehyde-3-phosphate dehydrogenase
    catalyzes an oxidation and addition of inorganic phosphate to its substrate, glyceraldehyde 3-phosphate, which results in production of a high energy intermediate 1,3-bisphosphoglycerate and reduction of NAD+ to NADH
  12. 3-phosphoglycerate kinase
    transfers phosphate from 1,3-bisphosphoglycerate to ADP, forming ATP and 3-phosphoglycerate
  13. Pyruvate kinase
    catalyzes the substrate-level phosphorylation of ADP using the high-energy substrate PEP

    activated by fructose 1, 6-bisphosphate from PFK-1 reaction
  14. Key fermentation enzyme in mammals
    lactate dehydrogenase (oxidizes NADH to NAD+)
  15. DHAP
    used in hepatic and adipose for triacylglycerol synthesis

    can be isomerized to glycerol 3-phosphate
  16. 1,3-bisphosphoglycerate and phosphoenolpyruvate
    high-energy intermediates used to generate ATP by substrate-level phosphorylation
  17. Irreversible enzymes
    • Glucokinase
    • hexokinase
    • PFK1
    • pyruvate kinase
  18. Red blood cell glycolysis
    uses bisphosphoglycerate mutase, which produces 2,3-bisphosphoglycerate (2,3-BPG) from 1,3-BPG
  19. adapatations to high altitudes (low pO2)
    • increased respiration
    • increased oxygen affinity for hemoglobin
    • increased rate of glycolysis
    • increased [2,3-BPG] in RBC (over a 12-24 hour period)
    • normalized oxygen affinity for hemoglobin restored by increased level of 2,3-BPG
    • increased hemoglobin (over days to weeks)
  20. How can galactose enter the pathway?
    Phosphorylated to galactokinase, trapping it in cell. 

    The resulting galactose 1-phosphate is converted to glucose 1-phosphate by galactose-1-phosphate uridyltransferase and an epimerase
  21. How does fructose enter the pathway?
    fructose converted to frucose 1-phosphate by fructokinase. Then, glyceraldehyde and DHAP convert it to aldolase B.
  22. PDH complex

    cannot convert acetyl-CoA to pyruvate or to glucose

    activated by insulin (liver)
  23. Three fates of pyruvate
    • 1) conversion to acetyl-CoA by PDH
    • 2) coversion to lactate by lactate dehydrogenase
    • 3) Conversion to oxaloacetate by pyruvate carboxylase
  24. Explain glycogen granules.
    central protein core with polyglucose chains radiating outward to form a sphere

    composed entirely of linear chains and have the highest density of glucose near the core

    branched chains are more dense at periphery, allowing more rapid release of glucose on demand
  25. Glycogenesis
    synthesis of glycogen granules

    begins with core protein glycogenin and glucose addition begines with glucose 6-phosphate, which is converted to glucose 1-phosphate

    uridine diphosphate permits integration into glycogen chain by glycogen synthase
  26. glycogen synthase
    rate limiting enzyme of glycogen synthesis and forms alpha-1,4 glycosidic bond found in linear glucose chains of the granule
  27. glycogen synthase is stimulated and inhibited by __
    stimulated by glucose 6-phosphate and insulin

    inhibited by epinephrine and glucagon
  28. Branching enzyme
    introduces alpha-1,6-linked branches into the ranule

    • hydrolyzes one alpha-1,4-bonds to release oligoglucose
    • form an alpha-1,6-bond to create a branch
  29. Glycogenolysis
    breakdown of glycogen granules
  30. Enzymes involved in glycogenolysis
    glycogen phosphorylase: breaks alpha-1,4-glycosidic bonds, releasing glucose 1-phosphate 

    cannot break alpha-1,6 bonds
  31. Debranching enzyme
    breaks alpha-1,4 bond adjacent to the branch point and moves the small oligoglucose chain that is released to teh exposed end of the other chain

    form a new alpha-1,4-bond

    hydrolyzes the alpha-1,6-bond, releasing the single residue at the branch point as free glucose
  32. Gluconeogenesis
    the production of glucose from other biomolecules; carried out by the liver and kidney
  33. The liver maintains glucose levels in blood during fasting through either __ or __.
    • glycogenolysis
    • gluconeogenesis
  34. Gluconeogenesis or glycogenolysis stimulated or inhibited by...?
    stimulated by glucagon and epinephrine

    inhibited by insulin
  35. During fasting, what happens?
    glycogen reserves drop dramatically in the first 12 hours, during which time gluconeogenesis increases. After 24 hours, it represents the sole source of glucose
  36. Important substrates for gluconeogenesis are
    • glycerol 3-phosphate
    • lactate
    • glucogeneic amino acids
  37. glucogenic amino acids
    can be converted into intermediates that feed into gluconeogenesis
  38. ketogenic amino acids
    converted into ketone bodies, which can be converted into alternative fuel, particularly during periods of prolonged starvation
  39. True or False:

    It is possible to convert acetyl-CoA back to glucose
    False: it is not
  40. Lactate is converted to pyruvate by __. Alanine is converted to pyruvate by __. Glycerol 3-phosphate is converted to DHAP by __
    lactate dehydrogenase

    alanine aminotransferase

    glycerol 3-phosphate dehydrogenase
  41. Important enzymes of gluconeogenesis
    • pyruvate carboxylase
    • PEPCK
    • fructose-1,6-bisphophatase
    • glucose-6-phosphatase
  42. pyruvate carboxylase
    mitochondrial enzyme activated by acetyl CoA and produces OAA
  43. PEPCK
    induced by glucagon and cortisol

    • acts to raise blood sugar levels
    • converts OAA to PEP in a reaction that requires GTP
  44. Fructose 1,6 bisphosphatase
    key control point of gluconeogenesis and represents rate limiting step of the process

    reverse the action of PFK-1, the RLS of glycolysis, by hydrolyzing phosphate from fructose 1,6-bisphosphate to produce fructose 6-phosphate

    • activated by ATP
    • inhibted by AMP
  45. Glucose-6-phosphatase
    converts glucose-6-phosphate into glucose
  46. Alanine is the major __, but almost all amino acids are also __
    • glucogenic amino acid
    • glucogenic
  47. Gluconeogenesis requires expenditure of ATP that is provided by __.
    Beta-oxidation of fatty acids

    hepatic gluconeogenesis always dependent on Beta-oxidation of fatty acids in the liver
  48. Extended periods of low blood sugar are usually accompanied by __
    high levels of ketones in the blood
  49. Pentose phosphate pathway (hexose monophosphate (HMP) shunt)
    two functions: 

    • production of NADPH
    • serving as a source of ribose 5-phosphate for nucleotide synthesis
  50. Parts of the PPP pathway
    begins with glucose 6-phosphate, ends with ribulose 5-phosphate, and is irreversible

    produces NADPH and involves the important rate limiting enzyme glucose-6-phosphate dehydrogenase
  51. Glucose-6-phosphate dehydrogenase (G6PD)
    G6PD is induced by insulin because the abundance of sugar entering the cell under insulin stimulation will be shunted into both fuel utilization pathways (glycolysis and aerobic respiration) as well as fuel storage pathways

    The shunt is also inhibted by its product, NADPH, and is activated by one of its reactants, NADP+
  52. Second part of the pathway
    represents series of reversible reactions that produce an equilibrated pool of sugars for biosynthesis, inclduign ribose 5-phosphate for nucleotide synthesis
  53. NADPH acts as an __
    electron donor in a number of biochemical reactions; ptent reducing agent
  54. Cells require NADPH for:
    • biosnthesis
    • assisting in celular bleach production in certain white blood cells
    • maintenance of a supply of reduced glutathione to protect against reactive oxygen species