Carbohydrate Metabolism Flashcards
essential fructosuria
deficient in fructokinase (fructose –> fructose-1-phosphate)…. fructose appears in urine (benign)
hereditary fructose intolerance
deficient in aldolase B (F-1-P –> DHAP & glyceraldehyde).
leads to decreased gluconeogenesis and decreased glycogen breakdown.
leads to changes in glucose levels (hypoglycemia), results in poor feeding, FTT, hepatic and renal insufficiency, death
asymptomatic unless diet includes fructose or sucrose
galactosemia
AR inheritance
deficiency in galactos-1-phophate uridyl-transferase (GALT)
cannot convert galactose–> glucose
AST and ALT elevated in newborns
mental deficiency and cirrhosis of liver.
clinical presentation = CATARACTS (galcitol accumulation in lens of eyes)
all newborns screened
Von Gierke’s
Glycogen Storage Disorder (types 1a and 1b)
Endoplasmic reticulum, G-6-P (Ia) or glucose transport (1b) deficiency (liver cannot convert G-6-P to glucose)
fasting hypoglycemia, lactic acedemia, hyperuricemia and ketoacidosis
treatment = steady carbs from diet
McCardles
Glycogen Storage Disorder (V)
muscle glycogen phosphorylase deficiency
painful muscle cramps on exercise
myoglobin and CK in blood
Pompoes
Glycogen Storage Disorder (II)
lysosomal acid alpha-glucosidase deficiency
affects muscle and heart
usually HF in infancy causes death
Hemolytic Crisis
oxidants cause lipid oxidation and membrane disruption
G-6-PD deficiecy results in accelerated membrane damage
what is happening between meals or overnight?
Gluconeogenesis (by using fuel from breakdown of FFAs, etc)
Glycogenolysis (glycogen –> glc)
and
Ketogenesis!
First pass: Gluconeogenesis
Pyruvate –> oxaloacetate
enzyme = pyruvate carboxylase
allosteric activator = acetyl-coa
oxaloacetate –> PEP
enzyme= PEP carboxypeptidase
activators: glucagon, cortisol
inhibitors: insulin
Second pass: Gluconeogenesis
F-1,6-BP –> F-6-P
Enzyme: F-1,6-BPase
allosteric activator: Citrate
activators: glucagon, EPI and NE, ATP
inhibitors: F-2,6-BP, insulin
Thirst pass: Gluconeogenesis
G-6-P –> Glucose
enzyme: G-6-Phosphatase
activators: glucagon
inhibitors: insulin, glucose, decreased chlorogenic acid
Does fat breakdown in adipose tissue stimulate gluconeogenesis? High levels Leptin?
YES! FFAs oxidized in liver (b-ox) provides energy and glycerol for gluconegeneiss
FFAs also raised by increased lipase and adipokines. High leptin, low appetite aka between meals– do gluconeogenesis
enzymes of fructose metabolism
FRUCTOKINASE (fructose –> fructose-1-phosphate)
x essential fructoseria
ALDOLASE B (fructose-1-phosphate --> glyceraldehyde and DHAP-dihydroxycetone phosphate) x hereditary fructose intolerance
TRIOKINASE (Glyceraldehyde –> G-3-P)
Enzymes of Galactose metabolism
Galactokinase (galactose–> galactose-1-phosphate)
GALT (galactose-1-phosphate uridyl-transferase)
(Galactose-1-phosphate –> glucose-1-phosphate)
x galactosemia – can’t convert galactose to glucose!
PPP
G6P –> [G6P DH] –> 6PGL –> 6PG –> [6 phosphogluconate Dehydrogenase] –> RIBULOSE 5 PHOSPHATE, NADH
Why PPP?
when decreased NADPH and ribose
provides metabolites for other biosynthetic purposes
similar to glycolysis– generates sugar (parallel pathway)
fructose biosynthesis (glucose –> fructose)
Polyol Pathway
glucose ALDOSE REDUCTASE sorbitol SORBITOL DH fructose
Glycogen Synthase
High levels of what activate glycogen synthase?
glc-1-phosphate –> Glycogen
Glycogen is synthesized when blood glucose levels are high
High levels of glucose-6-phosphate activate glycogen synthase
Glycogen Phosphorylase
glycogen –> glc-1-phosphate
When blood glucose is low, glycogen is reconverted to glucose in the liver.
stimulated by: AMP
inhibited by: glucose, ATP
Epi & NE effects on glycogen phosphorylase
it PHOSPHORYLATE it
= glycogen breakdown! Results in more sugar to be available to body
Insulin effects on glycogen phosphorylase
it DEPHOSPHORYLATES it
inhibits breakdown of glycogen and sugar stays in the storage form :)
EPI & NE effects on glycogen synthase
it PHOSPHORYLATES it
inhibits glycogen synthase and sugar stays in free form in body (not storage)
Insulin effects on glycogen synthase
it DEPHOSPHORYLATES it
this ACTIVATES it and glycogen synthesis happens so we get more storage form of sugar
what ingredients do you need to make glucose?
lactate, amino acids, glycerol
