Glicólise

Glicólise

(Parte 1 de 4)

Resumo do Capítulo 2 do Marks - Produção de ATP a Partir de Glicose: Glicólise

I. Glicólise:

A. Generalidades: 1.Glicose: pode produzir ATP com ou sem O2 2.Produz piruvato, que pode ser oxidado a CO2 no Ciclo de Krebbs e produzir ATP na fosforilação oxidativa (cadeia respiratória) 3.Glicose é armazenada nas células como glicogênio 4.Glicólise também produz precursores para biossíntese, como o piruvato, precurssor de ácidos graxos

B.Reações da Glicólise: 1. Fase preparatória: a)Conversão de glicose a glicose-6-fosfato

(1)Inicia-se com a transferência de um fosfato de ATP para a glicose, formando glicose-6-fosfato, que não passa pela membrana plasmática --> reação local e irreversível (2)Glicose-6-Fosfato só é produzida a partir da glicose (3) Enzimas: (a)Glicoquinase: só existe no fígado. Km muito alto (b)Hexoquinase: outros tecidos. Km mais baixo (4)SALDO ATP: -1 b)Conversão de glicose-6-fosfato em triose-fosfato (1)Isomerização de glicose-6-Fosfato em frutose-6-fosfato, que é fosforilada e quebrada em triose-fosfato

Fig. 2.3.Phases of the glycolytic pathway.

twice by ATP and cleaved into two triose phosp diture in the beginning of the preparative phase pump,”because this initial utilization of 2 mol in the production of 4 moles of ATP/mole o phase.

In the ATP-generating phase,glyceraldehyde oxidized by NAD!and phosphorylated using energy phosphate bond generated in this step is transferred remaining phosphate is also rearranged to form bond that is transferred to ADP. Because there formed,the yield from the ATP-generating phase is a net yield of 2 moles of ATP,2 moles of NADH, mole of glucose.

1.CONVERSION OF GLUCOSE TO GLUCOSE

Glucose metabolism begins with transfer of a form glucose-6-P (Fig. 2.4). Phosphorylation of within the cell because glucose-6-P cannot be transported membrane. The phosphorylation reaction is irre tions because the reaction has a high negative however,commit glucose to glycolysis.

Glucose-6-P is a branchpoint in carbohydrate almost every pathway that uses glucose,including pathway,and glycogen synthesis. From the opposite generated from other pathways of carbohydrate sis (breakdown of glycogen),the pentose phosphate (the synthesis of glucose from non-carbohydrate

Hexokinases,the enzymes that catalyze the family of tissue-specific isoenzymes that differ isoenzyme found in liver and $cells of the pancreas other hexokinases and is called glucokinase. In is bound to porins in the outer mitochondrial membrane channels; see Chapter 21),which gives these enzymes sized ATP as it exits the mitochondria.

2.CONVERSION OF GLUCOSE-6-P TO THE

In the remainder of the preparative phase of glycolysis, to fructose 6-phosphate (fructose-6-P),again cleaved into two 3-carbon fragments (Fig 2.5). a keto group next to carbon 3,is essential for the between carbons 3 and 4.

The next step of glycolysis,phosphorylation bisphosphate (fructose-1,6-bisP) by phosphofructokinase-1 considered the first committed step of the pathw ATP and is thermodynamically and kinetically irre ocably commits glucose to the glycolytic pathw cells,and its regulation controls the entry of glucose nase,it exists as tissue-specific isoenzymes whose ations in the role of glycolysis in different tissues.

Fructose-1,6-bisP is cleaved into two phosphorylated (triose phosphates) by aldolase (see Fig. 2.5). (DHAP) is isomerized to glyceraldehyde 3-phosphate is a triose phosphate. Thus,for every mole of glucose of glyceraldehyde-3-P continue through the pathw

402SECTION FOUR / FUEL OXIDATION AND THE GENERATION OF ATP

2 NADH 2 ATP 2 ATP

Glucose

Fructose 1,6–bisphosphate 2 Triose phosphates

2 Pyruvate

Preparative phase

Phase I:

ATP–generating phase hexokinaseglucokinase (liver) ATP

Glucose

CH2OH

Pentose phosphate pathway

Otherpathways Glycogensynthesis Glycolysis

CH2OPO3

Fig. 2.4.Glucose 6-phosphate metabolism.

Hexokinases, other kinases, and many other enzymes that catalyze reactions involving the hydrolysis of ATP require Mg2!. The Mg2!forms a complex with the phosphate groups of ATP. Kinases also require K!.

(2)Ação da fosfo-glicoseisomerase : 403CHAPTER 2 / GENERATION OF ATP FROM GLUCOSE:GLYCOLYSIS

CH2OH

CH2OPO3

Glucose 6–phosphate hexokinase (glucokinase in liver) phosphoglucose isomerase

phosphoglycero–mutase enolasepyruvate kinase aldolase triose phosphate isomerase glyceraldehyde 3–phosphate dehydrogenase phosphoglycerate kinase

CH2OH Portion isomerized from aldehyde to keto sugar

Aldol cleavage

High energy acyl-phosphate

High energy enolic phosphate

CH2OPO3

CO CH2OPO3

Fructose 1,6–bisphosphate

CH2OPO3

Glyceraldehyde 3–phosphate

CH2OPO3

CH2OPO3

CH2OH

OPO3

CH2

(Parte 1 de 4)

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