Carbohydrate Metabolism.pdf

Biochemistry

1. 1
Carbohydrate Metabolism
6 CO
2+ 6 H
2O + light energy → C
6H
12O
6+ 6 O
2

2. 2

3. 3
Digestionisthebiochemicalprocess
bywhichfoodmolecules,through
hydrolysis,arebrokendowninto
simplerchemicalunitsthatcanbe
usedbycellsfortheirmetabolic
needs.
DIGESTION AND ABSORPTION OF CARBOHYDRATES

4. 4
DIGESTION AND ABSORPTION OF CARBOHYDRATES
Thedigestionofcarbohydratesbegins
inthemouth,wheretheenzyme
salivarya-amylasecatalyzesthe
hydrolysisofa-glycosidiclinkagesin
starchfromplantsandglycogenfrom
meatstoproducesmaller
polysaccharidesandthedisaccharide
maltose.

5. 5
DIGESTION AND ABSORPTION OF CARBOHYDRATES
Theprimarysiteforcarbohydrate
digestioniswithinthesmallintestine,
wherea-amylase,thistimesecretedby
thepancreas,againbeginstofunction.The
pancreatica-amylasebreaksdown
polysaccharidechainsintoshorterand
shortersegmentsuntilthedisaccharide
maltose(twoglucoseunits;andglucose
itselfarethedominantspecies.

6. 6
DIGESTION AND ABSORPTION OF CARBOHYDRATES
Thefinalstepincarbohydratedigestionoccurs
ontheoutermembranesofintestinalmucosal
cells,wheretheenzymesthatconvert
disaccharidestomonosaccharidesarelocated.
Theimportantdisaccharidaseenzymesare
maltase,sucrase,andlactase.Theseenzymes
convert,respectively,maltosetotwoglucose
units,sucrosetooneglucoseandonefructose
unit,andlactosetooneglucoseandone
galactoseunit.

7. 7
DIGESTION AND ABSORPTION OF CARBOHYDRATES
Thethreemajorbreakdownproducts
fromcarbohydratedigestionarethus
glucose,galactose,andfructose.
Thesemonosaccharidesareabsorbed
intothebloodstreamthroughthe
intestinalwall.

8. 8
DIGESTION AND ABSORPTION OF CARBOHYDRATES

9. 9
DIGESTION AND ABSORPTION OF CARBOHYDRATES
Aftertheirabsorptionintothe
bloodstream,monosaccharidesare
transportedtotheliver,wherefructose
andgalactosearerapidlyconvertedinto
compoundsthataremetabolizedbythe
samepathwayasglucose.

10. 10
Glycolysis
Glycolysisisthemetabolicpathwayby
whichglucose(aC6molecule)isconverted
intotwomoleculesofpyruvate(aC3
molecule),chemicalenergyintheformof
ATPisproduced,andNADH-reduced
coenzymesareproduced.

11. 11
Glycolysis
Theconversionofglucosetopyruvateisan
oxidationprocessinwhichnomolecularoxygen
isutilized.Theoxidizingagentisthecoenzyme
NAD.Metabolicpathwaysinwhichmolecular
oxygenisnotaparticipantarecalledanaerobic
pathways.Pathwaysthatrequiremolecular
oxygenarecalledaerobicpathways.Glycolysisis
ananaerobicpathway.

12. 12
Six-Carbon Stage of Glycolysis (Steps 1–3)
Step1:Phosphorylation:Formationof
Glucose6-Phosphate.

13. 13
Six-Carbon Stage of Glycolysis (Steps 1–3)
Step2:Isomerization:Formationof
Fructose6-Phosphate.

14. 14
Six-Carbon Stage of Glycolysis (Steps 1–3)
Step3:Phosphorylation:Formationof
Fructose1,6-Bisphosphate.

15. 15
Three-Carbon Stage of Glycolysis (Steps 4–10)

16. 16
Three-Carbon Stage of Glycolysis (Steps 4–10)
Step4:Cleavage:FormationofTwoTriose
Phosphates.

17. 17
Three-Carbon Stage of Glycolysis (Steps 4–10)
Step5:Isomerization:Formationof
Glyceraldehyde3-Phosphate.

18. 18
Three-Carbon Stage of Glycolysis (Steps 4–10)
Step6:OxidationandPhosphorylation:
Formationof1,3-Bisphosphoglycerate.

19. 19
Three-Carbon Stage of Glycolysis (Steps 4–10)
Step7:PhosphorylationofADP:Formationof
3-Phosphoglycerate.

20. 20
Three-Carbon Stage of Glycolysis (Steps 4–10)
Step8:Isomerization:Formationof2-
Phosphoglycerate.

21. 21
Three-Carbon Stage of Glycolysis (Steps 4–10)
Step8:Isomerization:Formationof2-
Phosphoglycerate.

22. 22
Three-Carbon Stage of Glycolysis (Steps 4–10)
Step9:Dehydration:Formationof
Phosphoenolpyruvate

23. 23
Glycolysis

24. 24
Glycolysis

25. 25
Glycolysis

26. 26
Entrypointsforfructoseandgalactoseintothe
glycolysispathway.

27. 27
Entrypointsforfructoseandgalactoseintothe
glycolysispathway.

28. 28
RegulationofGlycolysis
Glycolysis,likeallmetabolic
pathways,musthavecontrol
mechanismsassociatedwithit.In
glycolysis,thecontrolpointsare
Steps1,3,and10

29. 29
FATESOFPYRUVATE
Threecommonfatesfor
pyruvateareofprime
importance:conversioninto
acetylCoA,intolactate,and
intoethanol

30. 30
FATESOFPYRUVATE

31. 31
FATESOFPYRUVATE
Akeyconceptinconsideringthese
fatesofpyruvateistheneedfora
continuoussupplyofNADfor
glycolysis.Asglucoseisoxidizedto
pyruvateinglycolysis,NADisreduced
toNADH.

32. 32
FATESOFPYRUVATE

33. 33
FATESOFPYRUVATE
OxidationtoAcetylCoA

34. 34
FATESOFPYRUVATE
FermentationProcesses
Fermentationprocessessolvethis
problem.Fermentationisa
biochemicalprocessbywhichNADHis
oxidizedtoNADwithouttheneedfor
oxygen.

35. 35
FATESOFPYRUVATE
LactateFermentation
Lactatefermentationistheenzymatic
anaerobicreductionofpyruvateto
lactate.Thesolepurposeofthisprocessis
theconversionofNADHtoNAD.The
lactatesoformedisconvertedbackto
pyruvatewhenaerobicconditionsare
againestablishedinacell

36. 36
FATESOFPYRUVATE
LactateFermentation

37. 37
FATESOFPYRUVATE
LactateFermentation
overall reaction for the conversion of
glucose to lactate

38. 38
FATESOFPYRUVATE
EthanolFermentation
Ethanolfermentationistheenzymaticanaerobic
conversionofpyruvatetoethanolandcarbon
dioxide.Ethanolfermentationinvolvingyeast
causesbreadandrelatedproductstoriseasa
resultofCO2bubblesbeingreleasedduring
baking.Beer,wine,andotheralcoholicdrinksare
producedbyethanolfermentationofthesugars
ingrainandfruitproducts.

39. 39
FATESOFPYRUVATE
EthanolFermentation

40. 40
FATESOFPYRUVATE
EthanolFermentation

41. 41
FATESOFPYRUVATE
EthanolFermentation

42. 42
ATP PRODUCTION FOR THE COMPLETE
OXIDATION OF GLUCOSE

43. 43
ATP PRODUCTION FOR THE COMPLETE
OXIDATION OF GLUCOSE

44. 44
GLYCOGEN SYNTHESIS AND DEGRADATION
Glycogen,abranchedpolymericformof
glucose,isthestorageformof
carbohydratesinhumansandanimals.Itis
foundprimarilyinmuscleandlivertissue.
Inmusclesitisthesourceofglucose
neededforglycolysis.Intheliver,itisthe
sourceofglucoseneededtomaintain
normalglucoselevelsintheblood.

45. 45
GLYCOGEN SYNTHESIS AND DEGRADATION
Glycogenesis
Glycogenesisisthemetabolic
pathwaybywhichglycogenis
synthesizedfromglucose6-phosphate.
Glycogenesisinvolvesthreereactions
(steps).

46. 46
GLYCOGEN SYNTHESIS AND DEGRADATION
Step 1: Formation of Glucose 1-phosphate.

47. 47
GLYCOGEN SYNTHESIS AND DEGRADATION
Step 2: Formation of UDP-glucose.

48. 48
GLYCOGEN SYNTHESIS AND DEGRADATION
Step 2: Formation of UDP-glucose.

49. 49
GLYCOGEN SYNTHESIS AND DEGRADATION
Step 3: Glucose Transfer to a Glycogen Chain.

50. 50
GLYCOGEN SYNTHESIS AND DEGRADATION
Glycogenolysis
Glycogenolysisisthemetabolicpathway
bywhichglucose6-phosphateisproduced
fromglycogen.Thisprocessisnotsimply
thereverseofglycogensynthesis
(glycogenesis),becauseitdoesnotrequire
UTPorUDPmolecules.Glycogenolysisisa
two-stepprocessratherthanathree-step
process.

51. 51
GLYCOGEN SYNTHESIS AND DEGRADATION
Step 1: Phosphorylation of a Glucose
Residue.

52. 52
GLYCOGEN SYNTHESIS AND DEGRADATION
Step 2: Glucose 1-phosphate
Isomerization.

53. 53
GLYCOGEN SYNTHESIS AND DEGRADATION

54. 54
GLYCOGEN SYNTHESIS AND DEGRADATION

55. 55
GLUCONEOGENESIS
Gluconeogenesisisthemetabolic
pathwaybywhichglucoseis
synthesizedfromnoncarbohydrate
materials.Glycogenstoresinmuscle
andlivertissuearedepletedwithin
12–18hoursfromfastingorineven
lesstimefromheavyworkor
strenuousexercise.

56. 56
GLUCONEOGENESIS
Theprocessesofgluconeogenesis
(pyruvatetoglucose)andglycolysis
(glucosetopyruvate)arenotexact
opposites.Themostobvious
differencebetweenthesetwo
processesisthat12compoundsare
involvedingluconeogenesisandonly
11inglycolysis.

57. 57
GLUCONEOGENESIS

58. 58
GLUCONEOGENESIS

59. 59
GLUCONEOGENESIS

60. 60

61. 61
The CORI CYCLE
TheCoricycleisacyclicbiochemical
processinwhichglucoseisconverted
tolactateinmuscletissue,thelactate
isreconvertedtoglucoseintheliver,
andtheglucoseisreturnedtothe
muscletissue.

62. 62
The CORI CYCLE

63. 63
The CORI CYCLE

64. 64
GLUCOSE METABOLIC PATHWAYS

65. 65
THE PENTOSE PHOSPHATE PATHWAY
Thepentosephosphatepathway
isthemetabolicpathwaybywhich
glucoseisusedtoproduceNADPH,
ribose5-phosphate(apentose
phosphate),andnumerousother
sugarphosphates.

66. 66
THE PENTOSE PHOSPHATE PATHWAY

67. 67
THE PENTOSE PHOSPHATE PATHWAY

68. 68
THE PENTOSE PHOSPHATE PATHWAY

69. 69
THE PENTOSE PHOSPHATE PATHWAY

70. 70
HORMONAL CONTROL OF CARBOHYDRATE METABOLISM
Asecondmajormethodforregulating
carbohydratemetabolism,besides
enzymeinhibitionbymetabolites,is
hormonalcontrol.Amongothers,
threehormones—insulin,glucagon,
andepinephrine—affectcarbohydrate
metabolism.

71. 71
HORMONAL CONTROL OF CARBOHYDRATE METABOLISM
Insulin
Insulin,a51-amino-acidprotein,isa
hormoneproducedbythebetacellsof
thepancreas.Insulinpromotesthe
uptakeandutilizationofglucoseby
cells.Thusitsfunctionistolower
bloodglucoselevels.Itisalsoinvolved
inlipidmetabolism.

72. 72
HORMONAL CONTROL OF CARBOHYDRATE METABOLISM
Thereleaseofinsulinistriggeredbyhigh
blood-glucoselevels.Themechanismfor
insulinactioninvolvesinsulinbindingto
proteinreceptorsontheoutersurfacesof
cells,whichfacilitatesentryofglucoseinto
thecells.Insulinalsoproducesanincrease
intheratesofglycogensynthesis,
glycolysis,andfattyacidsynthesis.

73. 73
HORMONAL CONTROL OF CARBOHYDRATE METABOLISM
Glucagon
Glucagonisapolypeptidehormone(29amino
acids)producedinthepancreasbyalphacells.It
isreleasedwhenblood-glucoselevelsarelow.Its
principalfunctionistoincreaseblood-glucose
concentrationsbyspeedinguptheconversionof
glycogentoglucose(glycogenolysis)and
gluconeogenesisintheliver.Thusglucagon’s
effectsareoppositetothoseofinsulin.

74. 74
HORMONAL CONTROL OF CARBOHYDRATE METABOLISM
Epinephrine
Epinephrine,alsocalledadrenaline,is
releasedbytheadrenalglandsinresponse
toanger,fear,orexcitement.Itsfunctionis
similartothatofglucagon—stimulationof
glycogenolysis,thereleaseofglucosefrom
glycogen.Itsprimarytargetismusclecells,
whereenergyisneededforquickaction.It
alsofunctionsinlipidmetabolism.

75. 75
HORMONAL CONTROL OF CARBOHYDRATE METABOLISM

76. 76

77. 77
Carbohydrate Metabolism
6 CO
2+ 6 H
2O + light energy → C
6H
12O
6+ 6 O
2