anabolic reactions

steps which are different in gluconeogenesis compared to glycolysis

• pyruvate carboxylase converts pyruvate into oxaloactetae

• phosphoenolpyruvate carboxykinase converts oxaloacetate into phosphoenolpyruvate

• fructose 1,6 bisphosphatase is used instead and requires ATP

• glucose 6 phosphatase instead - removes phosphate group

does glycolysis generate more energy than is required for gluconeogenesis

yes

pyruvate carboxylase

• converts pyruvate into oxaloacetate using CO2 and ATP

• requires biotin

• allosterically activated by actetylcoa

• tetramer w 4 subunits each

biotin

• covalently attached to pyruvate carboxylase

• through lys side chain

• carrier of actviated carbon dioxide - carboxybiotin

where is glycogen stored

• cytosolic granules in the liver

• muscle cells in vertebrates

glycogenin

• protein at centre of glycogen

• acts as a primer for glycogen synthesis

glycogenolysis

• cleavage of α-1,4 glycosidic bonds

  • catalysed by glycogen phosphorylase

• glycose 1 phosphate → glucose 6 phosphate

  • catalysed by phosphoglucomutase

when does glycogen phosphorylase stop?

glycogen phosphorylase stops at 4 residues from branch point

function of transferase

shifts three glucoses from one branch to another

function of glycogen-debranching enzyme a -1,6-glucosidase

removes branched glucose and leaves elongated unbranched chain

udp glucose

• generated from glucose 1 phosphate and UTP

• for glycogen synthesis

• catalysed by UDP glucose phosphorylase

polymerisation of glucose

• glycogen synthase needs at least 4 glucoses

• glycogenin initiates polymerisation

linear growth

• major regulatory step in glycogen synthesis

• transfer of glucose to growing chain

branching in glycogen formation

• one 1,4 bond is broken and transferred to form 1,6 linkage

• different enzyme introduced branching

• inc glycogen solubility, rate of synthesis and rate of degradation

glucokinase

liver enzyme that catalyzes the phosphorylation of glucose to glucose-6- phosphate

affinity of glucokinase compared to hexokinase

• much lower

• Km is 50 fold higher

GLUT2

• pancreatic beta cells and liver

• transports glucose when blood conc is high

GLUT4

• found in muscle and fat cells

• stimulated by insulin binding to insulin receptor

• recruits vesicles of GLUT4

GLUT1

• in nearly all mammalian cells

• 12 membrane alpha helices

  • six form channel

  • n and c termini are on cytoplasmic side of membrane

which glutamate receptors are maintained at a constant rate

GLUT1,3

Fructose 2,6-bisphosphate (F2,6P)

• Potent allosteric activator of phosphofructokinase-1 (PFK-1), the key regulatory enzyme of glycolysis.

• Potent allosteric inhibitor of fructose 1,6-bisphosphatase, a key regulatory enzyme of gluconeogenesis.

how is F2,6P synthesised

• phosphorylation of single serine residue of fructose 6 phosphate

• catalysed by phosphofructokinase 2

what happens to PFK2 levels and F2,6BP with low blood glucose

• glucagon rises

• inc phosphorylation of PFK2

• inc of FBPase2

• levels of F2,6BP decrease

what happens to PFK2 levels and F2,6BP with high blood glucose

• glucagon falls

• insulin rises

• inc PFK2

• FBPase2 dephosphorylated

• levels of F2,6BP inc

co-ordinated control of PFK2 and fructose 2,6-bisphosphate

found on the same protein