Carbohydrate Metabolism

Question 1

essential fructosuria

Answer 1

deficient in fructokinase (fructose –> fructose-1-phosphate)…. fructose appears in urine (benign)

Question 2

hereditary fructose intolerance

Answer 2

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

Question 3

galactosemia

Answer 3

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

Question 4

Von Gierke’s

Answer 4

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

Question 5

McCardles

Answer 5

Glycogen Storage Disorder (V)

muscle glycogen phosphorylase deficiency
painful muscle cramps on exercise
myoglobin and CK in blood

Question 6

Pompoes

Answer 6

Glycogen Storage Disorder (II)

lysosomal acid alpha-glucosidase deficiency
affects muscle and heart
usually HF in infancy causes death

Question 7

Hemolytic Crisis

Answer 7

oxidants cause lipid oxidation and membrane disruption

G-6-PD deficiecy results in accelerated membrane damage

Question 8

what is happening between meals or overnight?

Answer 8

Gluconeogenesis (by using fuel from breakdown of FFAs, etc)

Glycogenolysis (glycogen –> glc)

and

Ketogenesis!

Question 9

First pass: Gluconeogenesis

Answer 9

Pyruvate –> oxaloacetate
enzyme = pyruvate carboxylase
allosteric activator = acetyl-coa

oxaloacetate –> PEP
enzyme= PEP carboxypeptidase

activators: glucagon, cortisol
inhibitors: insulin

Question 10

Second pass: Gluconeogenesis

Answer 10

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

Question 11

Thirst pass: Gluconeogenesis

Answer 11

G-6-P –> Glucose
enzyme: G-6-Phosphatase

activators: glucagon
inhibitors: insulin, glucose, decreased chlorogenic acid

Question 12

Does fat breakdown in adipose tissue stimulate gluconeogenesis? High levels Leptin?

Answer 12

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

Question 13

enzymes of fructose metabolism

Answer 13

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)

Question 14

Enzymes of Galactose metabolism

Answer 14

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!

Question 15

PPP

Answer 15

G6P –> [G6P DH] –> 6PGL –> 6PG –> [6 phosphogluconate Dehydrogenase] –> RIBULOSE 5 PHOSPHATE, NADH

Question 16

Why PPP?

Answer 16

when decreased NADPH and ribose
provides metabolites for other biosynthetic purposes

similar to glycolysis– generates sugar (parallel pathway)

Question 17

fructose biosynthesis (glucose –> fructose)

Answer 17

Polyol Pathway

glucose 
ALDOSE REDUCTASE
sorbitol
SORBITOL DH
fructose

Question 18

Glycogen Synthase

High levels of what activate glycogen synthase?

Answer 18

glc-1-phosphate –> Glycogen

Glycogen is synthesized when blood glucose levels are high

High levels of glucose-6-phosphate activate glycogen synthase

Question 19

Glycogen Phosphorylase

Answer 19

glycogen –> glc-1-phosphate

When blood glucose is low, glycogen is reconverted to glucose in the liver.

stimulated by: AMP
inhibited by: glucose, ATP

Question 20

Epi & NE effects on glycogen phosphorylase

Answer 20

it PHOSPHORYLATE it

= glycogen breakdown! Results in more sugar to be available to body

Question 21

Insulin effects on glycogen phosphorylase

Answer 21

it DEPHOSPHORYLATES it

inhibits breakdown of glycogen and sugar stays in the storage form :)

Question 22

EPI & NE effects on glycogen synthase

Answer 22

it PHOSPHORYLATES it

inhibits glycogen synthase and sugar stays in free form in body (not storage)

Question 23

Insulin effects on glycogen synthase

Answer 23

it DEPHOSPHORYLATES it

this ACTIVATES it and glycogen synthesis happens so we get more storage form of sugar

Question 24

what ingredients do you need to make glucose?

Answer 24

lactate, amino acids, glycerol

Question 25

cori cycle

Answer 25

lactate formed in muscle shuttled to liver, built into glucose, and put back into blood to be taken up to muscle

Question 26

alanine cycle

Answer 26

alanine formed in musscle, shuttle dbacto liver, built into glucose and put back into blood to be taken up by muscle