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Metabolism Regulation
Sry Suryani W
Biochemistry Department
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• Metabolic pathways fall into three categories:
– Anabolic pathways : involved in the synthesis ofcompounds such as protein.hey are endergonic.
–
!atabolic pathways : involved in the brea"down oflarger molecules# commonly involving o$idativereactions # they are e$ergonic# producing reducinge%uivalents and mainly via the respiratorychain#A&.
– Amphibolic pathways : occur at the ' crossroads 'of metabolism# acting as lin"s between theanabolic and catabolic pathways# eg the citric acidcycle.
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• (ndergonic reaction )also called anunfavorable reaction or anonspontaneous reaction* is achemical reaction in which thestandard change in free energy ispositive# and energy is absorbed.
http://en.wikipedia.org/wiki/Thermodynamic_free_energyhttp://en.wikipedia.org/wiki/Thermodynamic_free_energy
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• ($ergonic reactions are ones thatrelease energy+ these reactions willusually occur spontaneously since they
do not re%uire energy to occur.• ,n the other hand# endergonic
reactions absorb energy to form bonds#
so they do not occur spontaneously.-nstead# they occur only if energy isavailable to be used in the reaction.
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. ormal metabolism includes :adaptation to periods of starvation#e$ercise# pregnancy# and lactation.
• Abnormal metabolism may resultfrom nutritional de/ciency# en0ymede/ciency# abnormal secretion of
hormones# or the actions of drugsand to$ins# e$p : diabetes mellitus.
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&athways that process thema1or products of digestion
• All the products of digestion aremetaboli0ed to a common product :acetyl !o2A# which is then o$idi0ed by
the citric acid cycle.• !arbohydrate metabolism is centered on
the provision 3 fate of glucose
• 4ipid metabolism is concerned mainly
with fatty acids and cholesterol.• Amino acid metabolism involves
transamination.
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Metabolism carbohydrate
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4ipid Metabolism
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Metabolism Amino Acid
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• Metabolic pathways :
– at tissue and organ level.
–
At subcellular level.• At tissue and organ level:
– 4iver:
• 5lucose : glycogenesis
• 6at : lipogenesis
• Between meal : glycogenolysis
• With "idney : gluconeogenesis ) converting noncarbohydrate metabolites such as lactate#glycerol
and amino acids to glucose.• Synthesi0es ma1or plasma proteins ) albumin*
and deaminates amino acids# forming urea#whichis transported to "idney.
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• At Subcellular level:
– 5lycolysis occurs in cytosol and citricacid cycle in mitochondria.
– &entoses phosphate pathway
– 6atty acid synthesis.
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Starve2feed cycle
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-n the well2fed state# diet supplies theenergy re%uirements.
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-n the early fasting state hepaticglycogenolysis is an important source
of blood glucose.
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6asting state re%uires gluconeogenesisfrom amino acids and glycerol
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-n early refed state# fat is metaboli0ednormally and normal glucose metabolism is
slowly reestablished
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5lucose 7omeostasis
• &hase - : well fed state# in which glucoseis provided by dietary carbohydrate.
• &hase -- : once the supply is e$hausted#
hepatic glycogenolysis is used tomaintain blood glucose.
• ,nce the supply of glucose starts to
decreased#hepatic gluconeogenesisfrom lactate#glycerol and alanin ta"esplace.
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• &hase --- : gluconeogenesis is the ma1orsource of blood glucose. ) these changeshappen within 89 hours of fasting*
• &hase - : Dependence ongluconeogenesis decrease. ;etonebodies high enough concentration to
enter the brain and meet some of itsenergy needs.
• Renal gluconeogenesis ta"es place.
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• &hase : energy needs of almostevery tissue were supply by eitherfatty acids or "eton body o$idation.
) after long starvation of e$tremlyobese patient*
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4iver metabolism in the well2fed and starvedstates
• -n a well2fed liver process engaged is :glycogenic# glycolytic and lipogenic.
• he fasting liver :
glycogenolytic#gluconeogenic#"etogenicand proteolytic.
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• Metabolic interrelationships of tissues invarious nutritional and hormonal states :
– Staying in the well2fed state results : obesity
and insulin resistance. – ype 8 Diabetes Mellitus
– ype < Diabetes Mellitus.
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Glucose
Blood glucose is important
–
Normal [glucose]: 70-110 mg/dl –High [glucose] (>140 mg/dl
–o! [glucose] ("#0 mg/dl$
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54=!,S=R-A
• he e$cess passes into the urine to
produce 5lucosuria• ormal individual : glucosuria occurs when
the venous blood glucose concentration :
> ?#@
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