Galactose + fructose metabolism Flashcards
sucrose
glucose + fructose
2 pathways fructose can take
Mainly metabolised in liver
liver: fructokinase—aldolase B
extrahepatic tissues_ Hexokinse—glycolysis pathway
what property does hexokinase have
its not just specific to glucose works on fructose too
how are fructose 6 phosphate and fructose 1 phosphat produced
liver _ fructose 1 p produced
extrahepatic - fructose 6 phosphat
job of aldolase B
in the liver
converts fructose 1 p into GAP and DHAPN
clinical cases for fructose
due to a deficiency of fructokinase. you get an accumulation of fructose in blood (4x5) release in urine -MELITURIA (sugar in urine)
howver is metabolised normally in the muscles where there is no defect .
deficiency of aldolase B in liver :
a build up of fructose 1 p which has an inhibitory effect on fructokinase leading to fructosuria
vomit - after ingesting sucrose
hyperphosphatemia- phosphate pook gets less so cant make atp- liver damage
inhibition of gluconeogenesis and glycogenolysis - which leads to hypoglcyemia
treatment- avoid sucrose
how is fructose absorbed
by glut 5 faciliated diffusion
how is galactose absorbed
S GLUT - secondary active transport (the same as glucose)
which 2 monosacchardes are epimers
glucose and galactose
how is lactose broken down
galactosidase
metabolism of galactose
like fructose its mainly in the liver but can be in extrahepatic tissues too
liver :
galactokinans forms galactose 1 phopshate
how does glucose 1 phosphate become glucose 6 p
phosphoglucomutase
clinical cases with galactose
galactokinase deficiency
causes elevation of galactose in blood - galactosemia and urine galactosuria.
galctosemia can be caused by a defect of 3 enzymes
- galactokinase
- GALT
- UDP galactose 4 epimerase
when too much galactose it gets reduced in the eye by enzyme aldose reductase to form galacttitiol - cataracts
classical_
deficiency of GALT
build up of galactose 1 p
high level inhibits galactokinase and glucose metabolism
symptoms increase eye presure brain damage short rbc survival + hemolysis hypoglycemia
non classical galactosemia and classical
classical - deficincy of GALT - galactose 1 phosphate uridyl transferase
leloir pathway
galactose
STRUCTURE OF glycolgen
linear part _ a1/4 glycosidic bond
branched - 1,6 glycoside bond
majority is a- 1/4
glycogen has a protein called glycogenin
glycogenolysis
3 enzymes involved
-glycogen phosphorylase- only breaks a 1/4 glycosidic bonds and stops 4 residues away from a 1/6 glycosidic bond
-glycogen debranching enzyme- remodel is a bifunctional enzyme that contains 2 different catalytic sites catalysing 2 different reactions
consists of glucan transferase-
amylo a 1/6 glucosidase- breaks 1-6 bond
-phosphoglucomutase
- release glucose 1 p
- restructure the glycogen molecule (so you can release more glucose 1 p)
- convert 1 to 6
glucose 6 phosphatase
found only in gluconeogenesis organs so liver, kidney sI
what is the fat of glucose 6 phosphate
- glycoloysis- muscles
- PPP
- gluconeogenenesis in liver
when we break down glycogen what are the proportions of glucose 1 p and actual glucose
only 10 % is actual glucose
90% is glucose 1 phosphate
glycogenosis
glucose —–glucose 6 p—–glucose 1 p—-glycogen
- hexokinase
- phopshoglucomutase
- glycogenn synthase
glycogen synthase
uses UDP glucose as a substrate releasing UDP in the process
can’t begin from scratch needs a primer of more than 4 glucose monomers long
also just like glycogen phosphorolase it can only add 1-4 bonds
how do we form udp glucose to form glycogen
glucose 1 p + UTP——udp glucose pyrophosphorylase—-UDP glucose
enzymes involved in glycogen synthesis
- glycogen synthase
2. glycogen branching enzyme
