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7/24/2019 Metabolism Glucidic - Curs 1
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METABOLISMUL:
ASPECTE GENERALE
Dr. Elena Petrescu
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Tipuri de ci metabolice
Degradarea oxidativ a combustibililor metabolici din diet i din depoziteletisulare (glucoz, acizi grai, aminoacizi)
Stocarea combustibililor metabolici (n perioadele post-prandiale), respectiv
mobilizarea rezervelor (n perioadele inter-prandiale)
Biosinteza de molecule biologice avnd diverse roluri structurale ifuncionale
Degradarea biomoleculelor cu rol structural sau funcional formare deprodui reziduali eliminai ca atare sau dup detoxifiere
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Catabolism vs.anabolism
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Etapele catabolismului
combustibililor biologici
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Rolurile diferite ale NADH / FADH2i NADPH formate n cursul catabolismului
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Reglarea cilor metabolice
Enzima cheie (reglatorie)catalizeaz etapa limitant de vitez:
este reacia cea mai lent din ntreaga cale metabolic viteza sa determin vitezaglobal a cii
are un caracter ireversibil (fiind puternic exergonic)
este situat n prima parte a cii metabolice
Mecanismele de control:
- modificarea activitii sau a cantitii enzimelor cheie ajustarea vitezei reaciei pe
care o catalizeaz => modificarea vitezei globale a cii metabolice
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Reglarea independent icoordonat a cilor catabolice i anabolice
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Mecanisme de reglare enzimatic
I. Reglarea activitii moleculelor individuale de enzim
Reglarea alosteric
- metabolii din celul
- NADH/NAD+sau ATP/ADP/AMP
Reglarea covalent - influenat hormonal
II. Reglarea cantitii enzimelor n celule
Inducia i represia - aciuni hormonale (frecvent), uneori metabolii
Tipuri particulare de reglare:
Inhibiia feed-back
Activarea feed-forward
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Reglarea covalent a activitii enzimatice
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METABOLISMUL GLUCIDIC
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Structura glucidelor - aldoze
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Structura glucidelor - cetoze
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Ciclizarea glucozei
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Ciclizarea fructozei
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Tipuri de izomerie la monozaharide
Izomeri D i L (enantiomeri)Epimeri
Anomeri i
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Dizaharide
2 monozaharide unite prin legtur O-glicozidic
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Polizaharideamidonul
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Polizaharideglicogenul
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Cile de metabolizare ale glucozei
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GLICOLIZA
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Glicolizatrsturi generale
Scop: eliberarea parial a energiei coninute n molecula glucozei sintez de ATP
Se desfoar n toateesuturile Localizat n citosol
Poate funciona att n condiii aerobe, ct i anaerobe
Ptrunderea glucozei n celule:
transportorii din familia GLUT
GLUT-1eritrocit i creier
GLUT-2ficat, celulele pancreatice
GLUT-4esut adipos i muscular
(dependeni de insulin)
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GLICOLIZAcele dou faze
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Cele dou fazeale glicolizei
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Formarea glucozo-6-P i metabolismul su ulterior
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GLICOLIZAetapa consumatoare de energie
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GLICOLIZAetapa generatoare de energie
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Glicoliza aerob / anaerob i reoxidarea diferit a NADH
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Rezultatele glicolizei aerobe
Ecuaie global:glucoz + 2NAD++ 2ADP + 2Pi
2 piruvat + 2NADH + 2H++ 2ATP + 2H2O
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Glicoliza anaerob i reacia lactat dehidrogenazei
Ecuaie global:
glucoz + 2ADP + 2Pi
2 lactat + 2ATP + 2H2O
Importana reaciei LDH:
Glicoliza poate funciona i poategenera ATP n condiii anaerobe
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Glicolizaimportan particular pentruesuturile gluco-dependente
Creierconsum energetic substanial satisfcut n cea mai mare parte pe seamaglucozei (NU poate degrada acizi grai)
Eritrocitnu are mitocondrii nu poate degrada alte surse de energie (carenecesit desfurarea fosforilrii oxidative)
Muchi scheletic n activitate susinutnecesar energetic disproporionat fa deaportul de oxigen mare parte din ATP este obinut prin glicoliza anaerob
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Alte roluri ale glicolizei
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Reglarea glicolizei
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Reglarea PFK-1 de ctre F-2,6-P2
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Reglarea piruvat kinazei
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METABOLISMUL PIRUVATULUI
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Ci de metabolizare a piruvatului
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Decarboxilarea oxidativ a piruvatului
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Complexul piruvat dehidrogenazei (PDH)
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Componena complexului PDH
Enzima Coenzime necesare Vitaminele din care provin
Piruvat dehidrogenaza (E1) tiamin pirofosfat tiamina (vitamina B1)
Dihidrolipoil transacetilaza (E2) acid lipoic acid lipoic
coenzima A acid pantotenic
Dihidrolipoil dehidrogenaza (E3) FAD riboflavina (vitamina B2)
NAD+ nicotinamida (vitamina PP)
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TPP (tiamin pirofosfat)
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Acidul lipoic
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Coenzima A
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NAD+ FAD
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Mecanismul decarboxilriioxidative a piruvatului
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Reglarea activitii complexului PDH (PDC)
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Bibliografie
David L. Nelson, Michael M. Cox. Lehninger Principles of Biochemistry.5thedition, 2008.
Colleen Smith, Allan D. Marks, Michael Lieberman. MarksBasic Medical Biochemistry: A ClinicalApproach.2ndedition, 2004.
Robert K Murray, Darryl K. Granner, Peter A. Mayes, Victor W. Rodwell. Harpers IllustratedBiochemistry.27th edition, 2006.
Pamela C. Champe, Richard A Harvey, Denise R. Ferrier. Lippincotts Illustrated Reviews Biochemistry. 4thedition, 2007.
Reginald H. Garrett, Charles M. Grisham. Biochemistry.2ndedition, 1999.
Mary K. Campbell, Shawn O. Farrell. Biochemistry.6thedition, 2007.