1.4.2 Carbohydrate Metabolism Flashcards
What can be the symptoms of galactosemia?
Failure of neonates to thrive - vomiting and diarrhea result from ingestion of milk
Can also develop blindness - due to precipitation of byproduct in the lens
What is lactose intolerance
Phosphoenolpyruvate carboxykinase, and its role in gluconeogenesis, is inhibited by?
ADP
Why is gluconeogenesis important?
Because hours after a meal the blood glucose levels in a person will return to a fasting state, and there needs to be a means of getting glucose to the brain
Draw an overview map of metabolism
What reactions occur in the mitochondria matrix?
Citric acid cycle
Oxidative phosphorylation
Beta-oxidation
How is glucose an example of a futile cycle?
Glucose enters a cell and is phosphorylated by hexokinase. The phosphorylation leads to the inability of glucose-6-p molecule to exit the cell. The enzyme G-6-Pase can then dephosphorylate the molecule and it just goes around and around and around
UDP-galactose-4-epimerase deficiency can result in?
Similar to the transferase deficiency - treatment is restrict dietary galactose
What is heriditary fructose intolerance?
Lack of aldolase B - severe hypoglycemia
Liver failure can result - treat with avoiding fructose
What are the components of sucrose?
1-2 linkage between glucose and fructose
What is the first reaction in the formation of glucose from lactate?
Lactate to pyruvate
Formation of NADH
Under anaerobic conditions pyruvate is converted into?
Lactate
What are the 3 principle forms of sugar transport?
Facilitated diffusion
Hormone sensitive transporters
Na coupled transport
What is this an image of?
β-D-Fructose
Can G-6-P inhibit both glucokinase and hexokinase?
No
It can inhibit hexokinase but not glucokinase
Fructose-1,6-Bisphosphatase, and its role in gluconeogenesis, is stimulated and inhibited by?
Stim - Citrate
Inhibited - F-2,6-BP, AMP, ADP
How will F-2,6-BP affect gluconeogenesis?
It will inhibit gluconeogenesis
Inhibits the reaction of F-1,6-BP to F-6-P
What are the 3 components of the pyruvate dehydrogenase complex?
E1 - decarboxylase
E2 - dihydrolipoyl transacetylase
E3 - dihydrolipoyl dehydrogenase
What is essential fructosuria?
Lack of fructokinase
Describe the process of galactose metabolism?
F-1,6-BP can also act as an allosteric regulator, how?
F-1,6-BP can also “feed forward” in the reaction to stimulate the conversion of phosphoenolpyruvate to pyruvate.
The GLUT-4 transporter is sensitive to what? What tissues is it found in?
Sensitive to - insulin
Found - muscle, heart, and adipose tissue
What will inhibit the reaction of phosphoenolpyruvate to pyruvate?
ATP and alanine
Insulin will inhibit
gluconeogenesis
Galactosemia is caused by a lack of one of which two enzymes?
galactose-1-phosphate uridyl transferase
or
galactokinase
How do the Km of hexokinase and glucokinase compare?
Hexokinase - low Km
Glucokinase - high Km
Hexokinase is found in the muscle while glucokinase is found?
In the liver
Fructose-1,6-BPase deficiency is what?
Severely inhibited gluconeogenesis and severe hypoglycemia. May be lethal in newborn
What is the beginning reaction of the pentose phosphate pathway?
Glucose 6-p to 6-phosphogluconolactone
What is the principle control step in glycolysis?
Phosphofructokinase
Conversion of F-6-P to F-1,6-BP
Glucokinase is insulin independent or dependent?
Dependent
What reactions occur in the cytosol?
Glycolysis
Pentose phosphate pathway
Fatty acid synthesis
Purine biosynthesis
What are the components of lactose?
1-4 linkage between galactose and glucose
The pyruvate dehydrogenase reaction is what type of reaction?
Irreversible
What are some inhibitors of the PFK reaction? Why?
ATP
Citrate
H+ ions
These are indications that the cellular levels of energy are high
What are the controlling mechanisms of glycogen metabolism? (formation)
Hormonal control
Primarily when levels are normal
Pyruvate carboxylase, used in gluconeogenesis, is stimulated by what? Inhibited by what?
Stimulated by Acetyl CoA
Inhibited by ADP
What is produced in the pentose phoshate pathway? (2)
NADPH
Ribose-5-phosphate
What is this an image of?
alpha-D-galactose
Describe the process of maltose formation
A hemiacetal group on one carbon ring interacts with an alcohol group on another ring to produce a glycosidic bond. (loss of water also occurs)
Cortisol will stimulate?
Gluconeogenesis
Phosphofructokinase has a second reaction that produces what? And what is the role of that product?
Produces F-2,6-BP which acts as a potent stimulator for the forward glycolysis reaction
Since the reaction to convert pyruvate to phosphoenolpyruvate is not allowed, how does the cell get past this to generate glucose for gluconeogenesis?
Conversion of pyruvate to oxaloacetate
Oxaloacetate to phosphoenolpyruvate
What is this an image of?
alpha-D-glucose
What are the controlling mechanisms of glycogen metabolism? (breakdown)
Epinephrine and glucagon
Produce cAMP which will activate a kinase which will stimulate glycogen breakdown
What is the reaction carried out by the pyruvate dehydrogenase complex?
Pyruvate to acetyl CoA and production of NADH and CO2
What are the 5 cofactors os the Pyruvate dehydrogenase complex?
NADH
Thiamin pyrophosphate
lipoic acid
FAD
CoASH
Pyruvate to oxloacetate requires what cofactor?
biotin
What is the principle transporter in the liver?
GLUT 2
